DC versus AC for Solar PV

classic Classic list List threaded Threaded
18 messages Options
Reply | Threaded
Open this post in threaded view
|

DC versus AC for Solar PV

Larry Gales
I know that many EV users consider charging their cars from a solar PV
system on the roof of their house. I believe that almost all current
systems convert the DC solar PV power to AC with an inverter, which,
while it is about 95% efficient, is the only solar PV component that
is prone to maintenance and replacement.


What would be the advantages of using solar PV in a pure DC system,
where all the appliances in the house use DC power and the EV is charged
using DC power?  What sort of DC-to-DC converter is needed, and
is it more efficient, less expensive, and/or less maintenance prone than
with an AC inverters?

Thanks,

--
Larry Gales
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120602/4e897c4d/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Cor van de Water
Larry,
At low power levels the DC route is much more efficient
than the detour via AC.
For example, I have a 12V battery that feeds an internet
modem with WiFi radio, an internet telephone and a
conference phone - all directly connected at 12V DC.
Total power draw at 1 Amp is 12 Watts. The 42 Ah battery
will last almost 2 days if power disappears.
The normal way of powering these 3 devices was originally
with AC adapters. Maybe the AC power draw was not so much
higher - maybe only 15 Watts AC, but to get this small
amount of AC, an inverter may have a 50% or less efficiency.
So, it draws more than 30 Watts from the battery, so the
same battery now lasts less than 16 hours, possibly *much* less.

On the other hand, if the power draw is high then the
problem with running 12V is that current is high and the
resistance of the lines causes a large power drop.
This can cause the DC case to become less efficient than
AC conversion, due to the higher voltage and consequently
lower current.

Of course, if you match the PV panels to your EV pack so
they can charge without any conversion, then you can make
it reach the highest efficiency by avoiding the detour
via AC, but your EV must allow direct DC input and be
able to interrupt that current safely when charging
completes (this can be as simple as a low resistance
FET transistor, controlled by the BMS).

Hope this clarifies,

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     XoIP: +31877841130
Tel: +1 408 383 7626        Tel: +91 (040)23117400 x203

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Larry Gales
Sent: Saturday, June 02, 2012 2:16 PM
To: SEVA; Electric Vehicle Discussion List
Subject: [EVDL] DC versus AC for Solar PV

I know that many EV users consider charging their cars from a solar PV
system on the roof of their house. I believe that almost all current
systems convert the DC solar PV power to AC with an inverter, which,
while it is about 95% efficient, is the only solar PV component that is
prone to maintenance and replacement.


What would be the advantages of using solar PV in a pure DC system,
where all the appliances in the house use DC power and the EV is charged
using DC power?  What sort of DC-to-DC converter is needed, and is it
more efficient, less expensive, and/or less maintenance prone than with
an AC inverters?

Thanks,

--
Larry Gales
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://lists.sjsu.edu/mailman/private/ev/attachments/20120602/4e897c4d/a
ttachment.html
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

brucedp5
This post was updated on .
I do not have personal practical experience myself, but can
confirm what Cor posted about using a pure DC system at low
current load levels.

In the late 1990's after my retrofit to add lots of goodies
to my S-10 Blazer EV (like a mod to the battery racks to
be able to also handle the taller T-145 batteries), when I
changed out my T145 pack because it no longer had the
range I needed to do the occasional long runs to prove it
could be done, there were still a couple 'good-enough'
batteries amongst the 22 T145 battery pack that still had
some serviceable life left in them.

At the time, my co-worker at the Sunnyvale hp site, had a
small rustic cabin on his very remote N. Cal. property he
had bagged in a land auction years before (from some goofy-
fool who the Feds busted for growing dope).

I gave him two of my tired (for my purposes) T145's, and
he took them up to his cabin to use with his cheap little
PV system (the PV panel was so low an amperage, he did not
have a charge controller on it).

He used it not with an inverter, but purely for late night
DC bulb lighting. No refrigerator load or anything like
that, everything else was low-tech (the guy was a
survivalist Y2k nut).

Those old T145s worked fine for him for several years. Not
complaining, he did mention that the DC system voltage
would sag if the lights were left on all night (an issue
with a DC system design, not the batteries).

So, even with a low current draw, expect the same voltage
and current drooping when the SOC capacity goes lower than
50%. I would notice the same effect when I drove my Blazer
EV that had a DC design: as the SOC reduced, so did the
pack voltage and thus driving performance (that's only
normal).


{brucedp.150m.com}



-
On Sat, Jun 2, 2012, at 10:59 PM, Cor van de Water wrote:
> Larry,
> At low power levels the DC route is much more efficient
> than the detour via AC.
-

--
http://www.fastmail.fm - Email service worth paying for. Try it for free

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to ev@lists.sjsu.edu only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Zeke Yewdall
In reply to this post by Cor van de Water
I'd agree with Cor -- at low power levels -- 50 watts or less, go straight
DC.  But at higher power levels, it can often be easier to do AC.

Inverters are around 97% efficient for the best grid-tie only ones now --
part of this is that they are using high voltage (200 to 500 volts DC)
instead of 12 to 48 volts DC.  And, a 10 to 15 year warrantee is standard.
They aren't expected to go out every 2 or 3 years like back in the 80's.
I've been doing a lot of system maintenance recently, and it's actually
more common for me to find problems with the solar panels than the
inverters (mostly damage from squirrels, and raccoons, though actual solar
panel failures are becoming more common as the panels are made cheaper and
cheaper).  There are certain brands of inverters that I do find failed all
of the time, but the better brands are very rare to have issues.

If you've got a DC battery based system (non EV) then you have a 48 volt
battery bank (or 24 or 12, but those are fairly rare any more).  The big
electronic component is the charge controller, which has all of the maximum
power point tracking equipment in it, rather than having it in the inverter
like with a grid-tie only system.  That takes the voltage of the solar
panels (from 60 to 200 volts DC) and converts it down to the battery
voltage of 48VDC nominal (44 volts to 60 volts operating).  They are
upwards of 97 to 98% efficient usually, and in my experience are fairly
trouble free... at least as good as the good inverters.  Then... of course,
if you have loads that are not 48 volts DC (which is most often the case)
you have a separate inverter which takes the battery voltage and converts
to 120/240vac at around 92 to 95% efficiency depending on the model and
manufacturer.

The issue with doing PV direct at high voltage directly into the EV is
handling the charge control and maximum power point tracking.  The voltage
of a PV array varies about 20% from summer to winter because of the
temperature of the panels... and this is in addition to the battery voltage
varying between a discharged and full pack.  So, if you design the PV array
to be slightly higher than the full pack voltage, in the summertime with a
hot array... it will end up being at least 25% to 30% higher than the pack
starting (discharged) voltage in the wintertime with a cold array.  You
just lose that extra potential voltage by hooking the array to the lower
voltage pack.  Almost all battery based PV systems use a DC-DC converter in
the charge controller, and maximum power point tracking algorithms to allow
the PV array to operate at it's best voltage, then convert that down to the
battery voltage at ~97% efficiency, instead of just losing that 20+% in
some times of the year.  The 2 or 3% loss is better than having a voltage
mismatch loss which varies from a few percent at the best case to 25 to 30%
at worst case, during the year..... though it does introduce more expensive
electronics in there.   The widespread use of MPPT charge controllers is
only in the last 5 to 10 years, as DC-DC converters became cheap and
reliable enough. The issue with doing this for an EV bank is that the
highest voltage equipment that I commonly use is for a 60 volt nominal
battery bank.  I guess if you reconfigured your EV bank into 48VDC pieces
for solar charging, then back to the higher voltage (96, 144) for EV use,
you could use existing MPPT charge controllers.

The other problem with doing DC direct is that, at least for me, my car is
sitting at my house most of the night, but tends to be out doing errands
and such during the day, when the sun it out.  Running that sunshine into
the grid is a more efficient (since I get 100% efficient net metering -
-something you never get with a real world battery) way to store it than
doing stationary batteries then dumping back into the EV batteries.

Z




On Sat, Jun 2, 2012 at 11:59 PM, Cor van de Water <[hidden email]> wrote:

> Larry,
> At low power levels the DC route is much more efficient
> than the detour via AC.
> For example, I have a 12V battery that feeds an internet
> modem with WiFi radio, an internet telephone and a
> conference phone - all directly connected at 12V DC.
> Total power draw at 1 Amp is 12 Watts. The 42 Ah battery
> will last almost 2 days if power disappears.
> The normal way of powering these 3 devices was originally
> with AC adapters. Maybe the AC power draw was not so much
> higher - maybe only 15 Watts AC, but to get this small
> amount of AC, an inverter may have a 50% or less efficiency.
> So, it draws more than 30 Watts from the battery, so the
> same battery now lasts less than 16 hours, possibly *much* less.
>
> On the other hand, if the power draw is high then the
> problem with running 12V is that current is high and the
> resistance of the lines causes a large power drop.
> This can cause the DC case to become less efficient than
> AC conversion, due to the higher voltage and consequently
> lower current.
>
> Of course, if you match the PV panels to your EV pack so
> they can charge without any conversion, then you can make
> it reach the highest efficiency by avoiding the detour
> via AC, but your EV must allow direct DC input and be
> able to interrupt that current safely when charging
> completes (this can be as simple as a low resistance
> FET transistor, controlled by the BMS).
>
> Hope this clarifies,
>
> Cor van de Water
> Chief Scientist
> Proxim Wireless Corporation http://www.proxim.com
> Email: [hidden email]    Private: http://www.cvandewater.com
> Skype: cor_van_de_water     XoIP: +31877841130
> Tel: +1 408 383 7626        Tel: +91 (040)23117400 x203
>
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Larry Gales
> Sent: Saturday, June 02, 2012 2:16 PM
> To: SEVA; Electric Vehicle Discussion List
> Subject: [EVDL] DC versus AC for Solar PV
>
> I know that many EV users consider charging their cars from a solar PV
> system on the roof of their house. I believe that almost all current
> systems convert the DC solar PV power to AC with an inverter, which,
> while it is about 95% efficient, is the only solar PV component that is
> prone to maintenance and replacement.
>
>
> What would be the advantages of using solar PV in a pure DC system,
> where all the appliances in the house use DC power and the EV is charged
> using DC power?  What sort of DC-to-DC converter is needed, and is it
> more efficient, less expensive, and/or less maintenance prone than with
> an AC inverters?
>
> Thanks,
>
> --
> Larry Gales
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL:
> http://lists.sjsu.edu/mailman/private/ev/attachments/20120602/4e897c4d/a
> ttachment.html
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120603/dc2bb5bd/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Lee Hart
In reply to this post by Larry Gales
On 6/2/2012 4:15 PM, Larry Gales wrote:
> I believe that almost all current systems convert the DC solar PV power
> to AC with an inverter, which, while it is about 95% efficient, is the
> only solar PV component that is prone to maintenance and replacement.

Most PV rebate programs require that you use them to generate AC power.
The utilities want you generate AC, and not have any direct DC loads or
batteries.

Inverter peak efficiency can be 95%; but the part-load efficiency is
lower. Since your light levels are rarely at peak, the inverter rarely
operates at peak efficiency.

> What would be the advantages of using solar PV in a pure DC system,
> where all the appliances in the house use DC power and the EV is charged
> using DC power?

It could be more efficient. It would be easier to have backup DC power
with batteries when the grid is down (and could use your EV's batteries).

> What sort of DC-to-DC converter is needed

Depending on how you set it up, you may not need a DC/DC converter. The
traditional method is to have a 12v system; all PV panels, lights,
motors, batteries, and other loads are 12v. It's very simple and
straightforward, but if you need significant amounts of power, the low
voltage requires large wires.

There are also 24v, 36v, and 48v versions of this. The wiring is
smaller, but it is harder to find lights, motors, and other devices for
these voltages.

100 years ago, homes were routinely wired for 120v DC. All the same
lights, switches, motors, etc. used back then could be used today;
however, they are now antiques. Many modern 120vac devices still work on
DC; but many WILL NOT! You'd have to know what you're doing to find ones
that are OK on DC.

The biggest problem with a 120vdc system is that most modern switches
are AC ONLY! They will fail almost immediately if used to switch 120vdc.

Systems with no DC/DC converter work the best when you have a small
number of loads, and can easily match the voltages of the PV panels and
loads to each other. For example, if your EV has a 96v pack (an odd
voltage), you could use four standard 24v PV panels to produce 96v for
charging the EV and nothing else. That would be a simple efficient
system. Then use an inverter or DC/DC to convert that 96v to whatever
other loads you wanted to operate.

You can add DC/DC converters so that the PV panels, batteries, and
various loads can be different voltages. A good DC/DC is more efficient
than an inverter, but not by much. If you're clever, the motor
controller in your EV can be used as a big DC/DC converter.

Given all this, it is easy to see why most people use an inverter. It is
the simplest solution, even if it isn't the cheapest, most efficient, or
most reliable. All your existing 120vac devices and wiring can be used
as-is.

> is it more efficient, less expensive, and/or less maintenance prone than
> with an AC inverters?

Don't forget that another perfectly workable solution for changing
voltages and DC/AC conversion is a motor-generator set. While bigger,
heavier, and less efficient; they can also be simpler, cheaper,
extremely reliable, and long-lived.
--
Ingenuity gets you through times of no money better than money
will get you through times of no ingenuity. -- Terry Pratchett
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Larry Gales
Thanks for all this useful information.  I was thinking in terms of a
wholly off-the-grid situation in which all electrical appliances are
located around a small central core, as opposed to being distributed
throughout the house.

I was thinking of this as something we might need to do  in the future if
our economic system starts to become unstable and costly and people are
forced to rely more on their own resources.

-- Larry Gales

On Sun, Jun 3, 2012 at 10:16 AM, Lee Hart <[hidden email]> wrote:

> On 6/2/2012 4:15 PM, Larry Gales wrote:
> > I believe that almost all current systems convert the DC solar PV power
> > to AC with an inverter, which, while it is about 95% efficient, is the
> > only solar PV component that is prone to maintenance and replacement.
>
> Most PV rebate programs require that you use them to generate AC power.
> The utilities want you generate AC, and not have any direct DC loads or
> batteries.
>
> Inverter peak efficiency can be 95%; but the part-load efficiency is
> lower. Since your light levels are rarely at peak, the inverter rarely
> operates at peak efficiency.
>
> > What would be the advantages of using solar PV in a pure DC system,
> > where all the appliances in the house use DC power and the EV is charged
> > using DC power?
>
> It could be more efficient. It would be easier to have backup DC power
> with batteries when the grid is down (and could use your EV's batteries).
>
> > What sort of DC-to-DC converter is needed
>
> Depending on how you set it up, you may not need a DC/DC converter. The
> traditional method is to have a 12v system; all PV panels, lights,
> motors, batteries, and other loads are 12v. It's very simple and
> straightforward, but if you need significant amounts of power, the low
> voltage requires large wires.
>
> There are also 24v, 36v, and 48v versions of this. The wiring is
> smaller, but it is harder to find lights, motors, and other devices for
> these voltages.
>
> 100 years ago, homes were routinely wired for 120v DC. All the same
> lights, switches, motors, etc. used back then could be used today;
> however, they are now antiques. Many modern 120vac devices still work on
> DC; but many WILL NOT! You'd have to know what you're doing to find ones
> that are OK on DC.
>
> The biggest problem with a 120vdc system is that most modern switches
> are AC ONLY! They will fail almost immediately if used to switch 120vdc.
>
> Systems with no DC/DC converter work the best when you have a small
> number of loads, and can easily match the voltages of the PV panels and
> loads to each other. For example, if your EV has a 96v pack (an odd
> voltage), you could use four standard 24v PV panels to produce 96v for
> charging the EV and nothing else. That would be a simple efficient
> system. Then use an inverter or DC/DC to convert that 96v to whatever
> other loads you wanted to operate.
>
> You can add DC/DC converters so that the PV panels, batteries, and
> various loads can be different voltages. A good DC/DC is more efficient
> than an inverter, but not by much. If you're clever, the motor
> controller in your EV can be used as a big DC/DC converter.
>
> Given all this, it is easy to see why most people use an inverter. It is
> the simplest solution, even if it isn't the cheapest, most efficient, or
> most reliable. All your existing 120vac devices and wiring can be used
> as-is.
>
> > is it more efficient, less expensive, and/or less maintenance prone than
> > with an AC inverters?
>
> Don't forget that another perfectly workable solution for changing
> voltages and DC/AC conversion is a motor-generator set. While bigger,
> heavier, and less efficient; they can also be simpler, cheaper,
> extremely reliable, and long-lived.
> --
> Ingenuity gets you through times of no money better than money
> will get you through times of no ingenuity. -- Terry Pratchett
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>



--
Larry Gales
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120603/6a1c7238/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

gtyler54
In reply to this post by Lee Hart
We once lived in a rural community in South Africa that had no electricity
supply. At that time power electronics was new, FET's had just come on the
market, and we did not have inverters like you do today, an inverter used
SCR's normally and ran at the output frequency, so had big transformers. I
had been designing small Dc-Dc converters for running alarm enunciators at
refineries in my previous job using bipolar power transistors, so I built
one like that to run some of our appliances like a TV, an Apple 2 computer,
a hair dryer incandescent lights etc.  
        The problem was the mains supply in that part of the world was 220
AC, and to run things that were designed for 220 ac with a peak of 320V,
220V dc was too low, but for a light bulb it needed to be 220DC. I managed
to compromise on 260V that everything seemed to be ok with. As Lee says, you
could not switch anything off, but you could have the switch off and turn it
on, so to switch anything off I turned off the dc-dc convertor.
        The dc-dc was cheap to make, just 2 MJ4502 transistors which I found
could run well at high frequency, switching off in 200ns, at least 10 times
less that any other one and ran at up to 30A. it was a self oscillating
circuit, and was very efficient, ran cool even at 500W output.
        It was possible to use switches if a snubber (capacitor with a
series resistor) was fitted across the contacts, even at 260V DC. If a DC
bus was used now, switches would be electronic with build in circuit beaker
action for overload.

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Lee Hart
Sent: Monday, 4 June 2012 5:17 a.m.
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] DC versus AC for Solar PV

On 6/2/2012 4:15 PM, Larry Gales wrote:
> I believe that almost all current systems convert the DC solar PV power
> to AC with an inverter, which, while it is about 95% efficient, is the
> only solar PV component that is prone to maintenance and replacement.

Most PV rebate programs require that you use them to generate AC power.
The utilities want you generate AC, and not have any direct DC loads or
batteries.

Inverter peak efficiency can be 95%; but the part-load efficiency is
lower. Since your light levels are rarely at peak, the inverter rarely
operates at peak efficiency.

> What would be the advantages of using solar PV in a pure DC system,
> where all the appliances in the house use DC power and the EV is charged
> using DC power?

It could be more efficient. It would be easier to have backup DC power
with batteries when the grid is down (and could use your EV's batteries).

> What sort of DC-to-DC converter is needed

Depending on how you set it up, you may not need a DC/DC converter. The
traditional method is to have a 12v system; all PV panels, lights,
motors, batteries, and other loads are 12v. It's very simple and
straightforward, but if you need significant amounts of power, the low
voltage requires large wires.

There are also 24v, 36v, and 48v versions of this. The wiring is
smaller, but it is harder to find lights, motors, and other devices for
these voltages.

100 years ago, homes were routinely wired for 120v DC. All the same
lights, switches, motors, etc. used back then could be used today;
however, they are now antiques. Many modern 120vac devices still work on
DC; but many WILL NOT! You'd have to know what you're doing to find ones
that are OK on DC.......

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Robert MacDowell-2
In reply to this post by Lee Hart
On Sun, Jun 3, 2012 at 10:16 AM, Lee Hart <[hidden email]> wrote:

> On 6/2/2012 4:15 PM, Larry Gales wrote:
> > I believe that almost all current systems convert the DC solar PV power
> > to AC with an inverter, which, while it is about 95% efficient, is the
> > only solar PV component that is prone to maintenance and replacement.
>
> Most PV rebate programs require that you use them to generate AC power.
> The utilities want you generate AC, and not have any direct DC loads or
> batteries.



And even more than that, solar is by nature a "peaking unit" which means
you are selling the grid 25 cent peaker power.  You charge your EV at night
on 5 cent midnight power.

That arbitrage works naturally in your favor if you can angle yourself so
you're the guy getting the benefit.  Obviously a lot of other slick
operators are after that same benefit, hence, the contracts.


>
> > What would be the advantages of using solar PV in a pure DC system,
> > where all the appliances in the house use DC power and the EV is charged
> > using DC power?
>
> It could be more efficient. It would be easier to have backup DC power
> with batteries when the grid is down (and could use your EV's batteries).
>
>
The only gotcha is transmission losses.  This one guy bought a 500W
windmill, wound to make three-phase AC rectified to 12 VDC.  Spent a
fortune running 6ga. wire to the battery bank 300 feet away.  Didn't
understand why only 50 watts was showing up at his battery bank.

Other than that, I'm not a big fan of higher voltage DC because its
switchgear need to be specially built to handle the continuous arcing that
is present with DC.  For instance I had a DC fuse, the thing is the size of
a briefcase.  The bulk of it was arc chutes.  Behind the fuse is a coil of
2-3 turns in series with the fuse.  The collapsing of that magnetic field
yanks the arc up and out the arc chute.   Even the small switches have a
definitive "Snap!" feature that yanks the contact points apart violently,
no matter how slow you throw the switch.  This type of arc-snuffing feature
just doesn't exist in ordinary AC switches and breakers and fuses, as those
self-snuff.

Robert
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120603/03bf8ea5/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

martinwinlow

On 4 Jun 2012, at 02:34, Robert MacDowell wrote:

> On Sun, Jun 3, 2012 at 10:16 AM, Lee Hart <[hidden email]> wrote:
>
>> On 6/2/2012 4:15 PM, Larry Gales wrote:
>>> I believe that almost all current systems convert the DC solar PV power
>>> to AC with an inverter, which, while it is about 95% efficient, is the
>>> only solar PV component that is prone to maintenance and replacement.
>>
>> Most PV rebate programs require that you use them to generate AC power.
>> The utilities want you generate AC, and not have any direct DC loads or
>> batteries.
>
>
>
> And even more than that, solar is by nature a "peaking unit" which means
> you are selling the grid 25 cent peaker power.  You charge your EV at night
> on 5 cent midnight power.
>
> That arbitrage works naturally in your favor if you can angle yourself so
> you're the guy getting the benefit.  Obviously a lot of other slick
> operators are after that same benefit, hence, the contracts.
>
>
>>

Interestingly, (and slightly OT) a good friend informed me yesterday that his 4kW solar array has netted him £600 (nearly $US1k) income in the 3 months it has been installed at his Pa's house on the south coast of England.  Thanks to the UK G-ment's Feed In Tarrif, he gets the income and can use the electricity too.  Now all I've got to do is to convince him that he really should do that 2008 Mazda RX8 (with the blown Wankel engine that no-one wants to touch) EV conversion!

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120604/77e4ef07/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Peri Hartman
That's a pretty impressive return on investment.  What does that come to in
terms of kwh?  I would guess somewhere around 0.03 pence or about $.05?
Which 3 months of the year was that - hopefully a good representation of
typically cloudy dreary weather?

Peri

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf
Of Martin WINLOW
Sent: 04 June, 2012 1:39 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] DC versus AC for Solar PV


On 4 Jun 2012, at 02:34, Robert MacDowell wrote:

> On Sun, Jun 3, 2012 at 10:16 AM, Lee Hart <[hidden email]> wrote:
>
>> On 6/2/2012 4:15 PM, Larry Gales wrote:
>>> I believe that almost all current systems convert the DC solar PV
>>> power to AC with an inverter, which, while it is about 95%
>>> efficient, is the only solar PV component that is prone to maintenance
and replacement.

>>
>> Most PV rebate programs require that you use them to generate AC power.
>> The utilities want you generate AC, and not have any direct DC loads
>> or batteries.
>
>
>
> And even more than that, solar is by nature a "peaking unit" which
> means you are selling the grid 25 cent peaker power.  You charge your
> EV at night on 5 cent midnight power.
>
> That arbitrage works naturally in your favor if you can angle yourself
> so you're the guy getting the benefit.  Obviously a lot of other slick
> operators are after that same benefit, hence, the contracts.
>
>
>>

Interestingly, (and slightly OT) a good friend informed me yesterday that
his 4kW solar array has netted him £600 (nearly $US1k) income in the 3
months it has been installed at his Pa's house on the south coast of
England.  Thanks to the UK G-ment's Feed In Tarrif, he gets the income and
can use the electricity too.  Now all I've got to do is to convince him that
he really should do that 2008 Mazda RX8 (with the blown Wankel engine that
no-one wants to touch) EV conversion!

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk

-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://lists.sjsu.edu/mailman/private/ev/attachments/20120604/77e4ef07/attac
hment.html
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev




_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Lee Hart
In reply to this post by Robert MacDowell-2
On 6/3/2012 8:34 PM, Robert MacDowell wrote:
> And even more than that, solar is by nature a "peaking unit" which means
> you are selling the grid 25 cent peaker power.  You charge your EV at night
> on 5 cent midnight power.
>
> That arbitrage works naturally in your favor if you can angle yourself so
> you're the guy getting the benefit.

I.e. it benefits the utilities.

And, we had to fight the utilities even to get net metering. When they
had their way, they set up rates that were even more one-sided!

>>> What would be the advantages of using solar PV in a pure DC system,

> The only gotcha is transmission losses.  This one guy bought a 500W
> windmill, wound to make three-phase AC rectified to 12 VDC.  Spent a
> fortune running 6ga. wire to the battery bank 300 feet away.  Didn't
> understand why only 50 watts was showing up at his battery bank.

Hmm... 500w / 12v = 42 amps. #6 wire resistance is 0.3951 ohms per
1000'. 600' of #6 would be 600/1000 x 0.3951 = 0.237 ohms. At 42 amps,
the voltage drop would be 42a x 0.237ohm = 9.95 volts. No wonder he got
so little out of it!

He needed a much thicker wire to carry that much current that far. I
agree that copper is an overly expensive way to do it. Aluminum would be
cheaper. If he's the scrounger type, at 12v he could even use old water
pipe or scrap metal -- anything with enough cross sectional area.

Another alternative: Alternators naturally produce AC. So get some 12v
to 240vac transformers. Use three at the alternator to step the 12vac up
to 240vac (three because it's 3-phase), and three at the other end to
step it back down to 12v. Put the rectifiers at the far end, instead of
in the alternator. The transformers will be around 95% efficient, so a
pair of them still gives you 90% of the power. And the losses in that
300' run of #6 wire vanish into insignificance.

> Other than that, I'm not a big fan of higher voltage DC because its
> switchgear need to be specially built to handle the continuous arcing that
> is present with DC.

Very true! Novices underestimate the arcing potential of DC circuits.

> For instance I had a DC fuse, the thing is the size of
> a briefcase.

Wow; that must have been quite the fuse! What voltage and current rating?

The DC rated fuses we use in EVs (rated at a few hundred volts and a few
hundred amps DC) are still only about an inch diameter and a few inches
long. They are typically a thick fiberglass tube, filled with sand, with
a silver fuse link, and strong cast metal endcaps. They have interrupt
ratings of 10,000 amps or more.

> Even the small switches have a definitive "Snap!" feature that
> yanks  the contact points apart violently, no matter how slow you
> throw the switch.  This type of arc-snuffing feature just doesn't
> exist in ordinary AC switches and breakers and fuses

Exactly. 50-year-old home light switches were designed for AC or DC, and
had this feature. They made a loud "clack" when switched. If you look
inside, the mechanism provided a huge air gap between the open contacts
(like 2 gaps of 1/4" each), and the time to open and close did not
depend on how slowly you moved the lever. Such switches work fine today
for switching things in an EV.

Modern DC-rated fuses, circuit breakers, contactors, and switches do
exist. But you won't find them at the local hardware store any more!
--
Humanity is acquiring all the right technology for all the wrong reasons.
        -- R. Buckminster Fuller
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Cor van de Water
It is all about system design.
Had he anticipated that his battery was 100 meters (or more)
away from the wind generator then he would have chosen to have the
motor wound (or even found a real cheap standard moter) at 240V AC
and simply transported that with run-of-the-mill 14 or 12 gauge
wire to the battery bank, then step that voltage down near the
battery bank to get the high-current low-voltage - presumably
he had this bank close to his loads in the home...

If he already had this wind generator then he can either tranport
it at higher voltage (like the unitilities do) or move the
battery to the generator to feed the full 500W into the battery
and presumably he creates 120V AC from that battery to feed
his house, which would then need a 300ft run, but again that is
much easier than trying to transport 12V DC.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     XoIP: +31877841130
Tel: +1 408 383 7626        Tel: +91 (040)23117400 x203

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Lee Hart
Sent: Monday, June 04, 2012 9:38 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] DC versus AC for Solar PV

On 6/3/2012 8:34 PM, Robert MacDowell wrote:
> And even more than that, solar is by nature a "peaking unit" which
> means you are selling the grid 25 cent peaker power.  You charge your
> EV at night on 5 cent midnight power.
>
> That arbitrage works naturally in your favor if you can angle yourself

> so you're the guy getting the benefit.

I.e. it benefits the utilities.

And, we had to fight the utilities even to get net metering. When they
had their way, they set up rates that were even more one-sided!

>>> What would be the advantages of using solar PV in a pure DC system,

> The only gotcha is transmission losses.  This one guy bought a 500W
> windmill, wound to make three-phase AC rectified to 12 VDC.  Spent a
> fortune running 6ga. wire to the battery bank 300 feet away.  Didn't
> understand why only 50 watts was showing up at his battery bank.

Hmm... 500w / 12v = 42 amps. #6 wire resistance is 0.3951 ohms per
1000'. 600' of #6 would be 600/1000 x 0.3951 = 0.237 ohms. At 42 amps,
the voltage drop would be 42a x 0.237ohm = 9.95 volts. No wonder he got
so little out of it!

He needed a much thicker wire to carry that much current that far. I
agree that copper is an overly expensive way to do it. Aluminum would be
cheaper. If he's the scrounger type, at 12v he could even use old water
pipe or scrap metal -- anything with enough cross sectional area.

Another alternative: Alternators naturally produce AC. So get some 12v
to 240vac transformers. Use three at the alternator to step the 12vac up
to 240vac (three because it's 3-phase), and three at the other end to
step it back down to 12v. Put the rectifiers at the far end, instead of
in the alternator. The transformers will be around 95% efficient, so a
pair of them still gives you 90% of the power. And the losses in that
300' run of #6 wire vanish into insignificance.

> Other than that, I'm not a big fan of higher voltage DC because its
> switchgear need to be specially built to handle the continuous arcing
> that is present with DC.

Very true! Novices underestimate the arcing potential of DC circuits.

> For instance I had a DC fuse, the thing is the size of a briefcase.

Wow; that must have been quite the fuse! What voltage and current
rating?

The DC rated fuses we use in EVs (rated at a few hundred volts and a few
hundred amps DC) are still only about an inch diameter and a few inches
long. They are typically a thick fiberglass tube, filled with sand, with
a silver fuse link, and strong cast metal endcaps. They have interrupt
ratings of 10,000 amps or more.

> Even the small switches have a definitive "Snap!" feature that yanks  
> the contact points apart violently, no matter how slow you throw the
> switch.  This type of arc-snuffing feature just doesn't exist in
> ordinary AC switches and breakers and fuses

Exactly. 50-year-old home light switches were designed for AC or DC, and
had this feature. They made a loud "clack" when switched. If you look
inside, the mechanism provided a huge air gap between the open contacts
(like 2 gaps of 1/4" each), and the time to open and close did not
depend on how slowly you moved the lever. Such switches work fine today
for switching things in an EV.

Modern DC-rated fuses, circuit breakers, contactors, and switches do
exist. But you won't find them at the local hardware store any more!
--
Humanity is acquiring all the right technology for all the wrong
reasons.
        -- R. Buckminster Fuller
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

martinwinlow
In reply to this post by Peri Hartman
Peri,

It's actually only about 1400 kWh and is not very typical as we had an unusually sunny spring this year. This was from mid Feb to date. The reason the income is so high is due to the Feed In Tarrif that we have in the UK (and in other parts of Europe... and elsewhere?) to encourage people and businesses to buy into micro-generation - solar, wind and hydro being the most common.  This is all part of the UK's commitment to reduce carbon emmisions and increase the proportion of renewable energy generation.

The deal is that for retro-fitted, residential arrays you get 43p for every solar kWh generated.  Then you get another 3 pence or so from your electricity supplier if you are generating more than you are using - and you save whatever the cost of the electricity that you would otherwise be taking off the grid at the going rate - around 13p/kWh during the day here at the moment - a bit more if you have a split tariff ('Economy 7' as we call it over here, tho there are more complex tariffs available as well).  And all this guaranteed (by the G-ment) for 25 years and index linked (to inflation).

Unfortunately, the scheme was rather more successful than the G-ment thought it would be and they have being trying to reign in cost of it all - and have been taken to court over this already.  It is coming down to about 21p/kWh soon and I expect it will go altogether next year, if not sooner.

Interestingly, the price of solar has fallen dramatically on the back of the FIT scheme here in the UK.  I have been interested in PV all my life and have kept in touch with prices for yonks.  PV modules have dropped to half the price they were 2 years ago and are still going down.  So although the FIT is nice (3 times better return on investment than the best bank rate at the moment) the traditional payback time of 20-25 years has fallen down to about half that without the FIT and  about 3-4 years with it.

Regards, Martin Winlow
Herts, UK
http://www.evalbum.com/2092
www.winlow.co.uk


On 4 Jun 2012, at 15:48, Peri Hartman wrote:

> That's a pretty impressive return on investment.  What does that come to in
> terms of kwh?  I would guess somewhere around 0.03 pence or about $.05?
> Which 3 months of the year was that - hopefully a good representation of
> typically cloudy dreary weather?
>
> Peri
>
>
> Interestingly, (and slightly OT) a good friend informed me yesterday that
> his 4kW solar array has netted him £600 (nearly $US1k) income in the 3
> months it has been installed at his Pa's house on the south coast of
> England.  Thanks to the UK G-ment's Feed In Tarrif, he gets the income and
> can use the electricity too.  Now all I've got to do is to convince him that
> he really should do that 2008 Mazda RX8 (with the blown Wankel engine that
> no-one wants to touch) EV conversion!
>
> Regards, Martin Winlow
> Herts, UK
> http://www.evalbum.com/2092
> www.winlow.co.uk
>
>



-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120605/fdd7df9a/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Robert MacDowell-2
In reply to this post by Lee Hart
On Mon, Jun 4, 2012 at 9:38 AM, Lee Hart <[hidden email]> wrote:

> On 6/3/2012 8:34 PM, Robert MacDowell wrote:
> > And even more than that, solar is by nature a "peaking unit" which means
> > you are selling the grid 25 cent peaker power.  You charge your EV at
> night
> > on 5 cent midnight power.
> >
> > That arbitrage works naturally in your favor if you can angle yourself so
> > you're the guy getting the benefit.
>
> I.e. it benefits the utilities.
>
> And, we had to fight the utilities even to get net metering. When they
> had their way, they set up rates that were even more one-sided!
>
> >>> What would be the advantages of using solar PV in a pure DC system,
>
> > The only gotcha is transmission losses.  This one guy bought a 500W
> > windmill, wound to make three-phase AC rectified to 12 VDC.  Spent a
> > fortune running 6ga. wire to the battery bank 300 feet away.
>

He needed a much thicker wire to carry that much current that far. I
> agree that copper is an overly expensive way to do it. Aluminum would be
> cheaper. If he's the scrounger type, at 12v he could even use old water
> pipe or scrap metal -- anything with enough cross sectional area.


Yeah, electric railroads use the steel rails for the current return.  It's
not a material you would select for conductivity, but there's so much of it
that it beats the copper/bronze trolley wire (and aluminum feeder) by a
wide margin.



> Another alternative: Alternators naturally produce AC. So get some 12v
> to 240vac transformers. ... Put the rectifiers at the far end...
>


Yeah, exactly...  or wind the alternator head for that voltage in the first
place and then transform down to what you want at the other end. The only
problem is the frequency is somewhat variable, so it's difficult to size
the transformer ideally.



> > For instance I had a DC fuse, the thing is the size of
> > a briefcase.
>
>
> Wow; that must have been quite the fuse! What voltage and current rating?
>


1500V at 400A.   The fuse proper (the replaceable unit) is just a 1" wide
ribbon of copper with a hole drilled in it, the remaining material defining
the ampacity.   All the rest is dedicated to the magnetic blowout and arc
chute.



> The DC rated fuses we use in EVs (rated at a few hundred volts and a few
> hundred amps DC) are still only about an inch diameter and a few inches
> long. They are typically a thick fiberglass tube, filled with sand, with
> a silver fuse link, and strong cast metal endcaps. They have interrupt
> ratings of 10,000 amps or more.
>


So, same ampacity as the interurban coach but with a worse case maximum
rating.  (neither the substation nor the trolley wire would be capable of
delivering 10,000 amps.)

I wonder why the fuses got so much smaller and why it was no longer
necessary to have arc chutes or blowouts.



> Modern DC-rated fuses, circuit breakers, contactors, and switches do
> exist. But you won't find them at the local hardware store any more!
>


I'd love to know where to get them.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120605/ccfd6f70/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Morgan LaMoore
On Tue, Jun 5, 2012 at 3:33 PM, Robert MacDowell <[hidden email]> wrote:
> ...
> So, same ampacity as the interurban coach but with a worse case maximum
> rating.  (neither the substation nor the trolley wire would be capable of
> delivering 10,000 amps.)
>
> I wonder why the fuses got so much smaller and why it was no longer
> necessary to have arc chutes or blowouts.
> ...

I would guess it's the difference between 1500VDC and 400-600VDC.

A sand-filled cylinder that can quench an arc at 400-600VDC may fail
or explode at 1500VDC. All of the arc's energy is absorbed by the fuse
as heat. If that's too much energy, the fuse may rupture and let the
arc spread to nearby metal. Instead using air and magnetic blow-outs
with arc chutes should avoid that.

-Morgan LaMoore

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Cor van de Water
In reply to this post by Robert MacDowell-2
Lee wrote:
> Modern DC-rated fuses, circuit breakers, contactors, and switches do
> exist. But you won't find them at the local hardware store any more!
>
Robert MacDowell answered:
>I'd love to know where to get them.

I guess in old (unrenovated) houses and possibly in stores
that get the results from "deconstruction" of old buildings.
But my guess is that normally the ripped out wiring and
installations go to the landfill, so you better be there
before something is torn down.
You could check real estate ads for fixer uppers and other
real estate that is sold for the acreage, not for the
"tear-down" that is on the lot, walk through it and check if
it still has the old DC switches, then ask if you could contact
the buyer (or return after 1-2 weeks) to check if they indeed
are tearing everything down/out and salvage what you need.

Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     XoIP: +31877841130
Tel: +1 408 383 7626        Tel: +91 (040)23117400 x203

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Lee Hart
In reply to this post by Robert MacDowell-2
>> Modern DC-rated fuses, circuit breakers, contactors, and switches do
>> exist. But you won't find them at the local hardware store any more!

Robert MacDowell wrote:
> I'd love to know where to get them.

I collect them when the opportunity arises, and have perhaps a dozen of
them. They can still be found with a little scrounging. Grandpa's garage
or basement probably have some. Architectural supply companies (that
sell parts salvaged from old buildings) have them. They also show up at
garage sales and estate sales. Some old hardware stores and electrical
supply houses still have some in dusty boxes somewhere.

--
Humanity is acquiring all the right technology for all the wrong reasons.
        -- R. Buckminster Fuller
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
Reply | Threaded
Open this post in threaded view
|

Re: DC versus AC for Solar PV

Zeke Yewdall
They aren't necessarily cheap, but if you need new DC rated circuit
breakers, check out Midnite solar... they make a wide variety of 125VDC,
150VDC, and 300VDC rated circuit breakers, from 3 amps up to 250 amps, with
proper boxes for them all too.

Z

On Tue, Jun 5, 2012 at 6:46 PM, Lee Hart <[hidden email]> wrote:

> >> Modern DC-rated fuses, circuit breakers, contactors, and switches do
> >> exist. But you won't find them at the local hardware store any more!
>
> Robert MacDowell wrote:
> > I'd love to know where to get them.
>
> I collect them when the opportunity arises, and have perhaps a dozen of
> them. They can still be found with a little scrounging. Grandpa's garage
> or basement probably have some. Architectural supply companies (that
> sell parts salvaged from old buildings) have them. They also show up at
> garage sales and estate sales. Some old hardware stores and electrical
> supply houses still have some in dusty boxes somewhere.
>
> --
> Humanity is acquiring all the right technology for all the wrong reasons.
>        -- R. Buckminster Fuller
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.sjsu.edu/mailman/private/ev/attachments/20120606/e06bd8eb/attachment.html 
_______________________________________________
| Moratorium on drag racing discussion is in effect.
| Please take those discussions elsewhere.  Thanks.
|
| REPLYING: address your message to [hidden email] only.
| Multiple-address or CCed messages may be rejected.
| UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
| OTHER HELP: http://evdl.org/help/
| CONFIGURE: http://lists.sjsu.edu/mailman/listinfo/ev