equalising Powersonics

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equalising Powersonics

drowe67
Hello List,

I have a 2 month old pack of 8 Powersonic PG12V103 110AH AGMs.  Recently
I discovered two of them were completely discharged at about 50% of the
range they had when first installed.

Something similar happened to my last battery pack, so by an expensive
process of elimination (!) I suspect it is my chargers.  I have simple
dual stage chargers (one per battery) that start out at about 12A, then
the current ramps down until they hit 14.7V, at which stage the charger
switches to float.  These chargers do not do equalisation.

So I think my problem may be that the internal cells of the batteries
have become unbalanced.

I am in the process of buying an EV charger with equalisation.

Is there a way to recover the capacity of the poorly performing
batteries?  Since it has only been two months I am hoping sulphation
hasn't completely set it.  I currently have 1A (C/100) passing through
the whole string via a simple manual bad-boy charger (variac, bride,
fuse, ammeter) in an attempt to gently charge any partially charged
cells.

BTW I now have 8000 km total on my EV and my wife and I love it.  We
hardly every use the ICE.  Just need to sort out these battery problems.

Thank you,

David

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Re: equalising Powersonics

drowe67
Hi,

Could some one pls suggest a way to equalise batteries that have cells
way out of balance?

Thank you,

David

On Mon, 2009-09-21 at 09:37 +0930, David Rowe wrote:

> Hello List,
>
> I have a 2 month old pack of 8 Powersonic PG12V103 110AH AGMs.  Recently
> I discovered two of them were completely discharged at about 50% of the
> range they had when first installed.
>
> Something similar happened to my last battery pack, so by an expensive
> process of elimination (!) I suspect it is my chargers.  I have simple
> dual stage chargers (one per battery) that start out at about 12A, then
> the current ramps down until they hit 14.7V, at which stage the charger
> switches to float.  These chargers do not do equalisation.
>
> So I think my problem may be that the internal cells of the batteries
> have become unbalanced.
>
> I am in the process of buying an EV charger with equalisation.
>
> Is there a way to recover the capacity of the poorly performing
> batteries?  Since it has only been two months I am hoping sulphation
> hasn't completely set it.  I currently have 1A (C/100) passing through
> the whole string via a simple manual bad-boy charger (variac, bride,
> fuse, ammeter) in an attempt to gently charge any partially charged
> cells.
>
> BTW I now have 8000 km total on my EV and my wife and I love it.  We
> hardly every use the ICE.  Just need to sort out these battery problems.
>
> Thank you,
>
> David
>
> _______________________________________________
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> Usage guidelines: http://evdl.org/help/index.html#conv
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> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev

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Re: equalising Powersonics

Roger Stockton
David Rowe wrote:

> Could some one pls suggest a way to equalise batteries that
> have cells way out of balance?

I've had good luck using a power supply to float the individual batteries at a constant voltage for extended periods.

Use a diode between the power supply and the battery to protect the power supply from damage that might result if the battery tries to discharge into it.

I would set the power supply to something like 14.7-15V (for a 12V battery) and leave the battery on charge for at least a couple of days.  A dumb 12V automotive charger may work for this if you don't have an adjustable power supply to use; just be sure to check the voltage periodically to make sure the charger doesn't take the battery over 15V.

Don't try to equalise them by charging in series as even 1A is enough to vent the full batteries (that is, you will "equalise" them by hammering the good ones down at the same time as you bring the weak ones up ;^).

Hope this helps,

Roger.

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Re: equalising Powersonics

drowe67
Hi Roger,

Thank you for your reply.

> I would set the power supply to something like 14.7-15V (for a 12V
>  battery) and leave the battery on charge for at least a couple of
>  days.  A dumb 12V automotive charger may work for this if you don't
>  have an adjustable power supply to use; just be sure to check the
>  voltage periodically to make sure the charger doesn't take the battery
>  over 15V.

Yes I have a lab type power supply that has adjustable voltage and
current limiting.  

However I was wondering about 15V max.  If one cell in an unbalanced
battery is say at 75% charge, it may require 25AH to fully charge it.
At 15V the current of a full but unbalanced battery might be quite low,
like 250mA.  Does this mean it may take 25/0.25 = 100 hours to equalise
the battery?  I guess this is OK, no harm in leaving the battery for 4
days or so.

> Don't try to equalise them by charging in series as even 1A is enough
> to vent the full batteries (that is, you will "equalise" them by
> hammering the good ones down at the same time as you bring the weak
> ones up ;^).

Thanks for the tip - so far I have just run the 1A for a few hours after
each charge to perform a 2-4% of C manual equalisation, which I
understand is what a proper EV charger does.

Thanks again for your help

Cheers,

David


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Re: equalising Powersonics

Cor van de Water
Typically an AGM type battery should be able to take a
few percent of its capacity as equalization charge, I have
heard 3% before so that would mean that over-charging a
100+Ah AGM at 1A should be no big deal.
Note that during continuous over-charge the battery will
get warm and the charging *voltage* will drop.
I saw my AGMs first go to 15V but as I continued
equalization, the voltage came down to about 14.6V per battery
simply from the temp increase.

Success,

Cor van de Water
Director HW & Systems Architecture Group Proxim Wireless
Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: +1 408 383 7626        VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of David Rowe
Sent: Tuesday, September 22, 2009 4:55 AM
To: Roger Stockton; 'Electric Vehicle Discussion List'
Subject: Re: [EVDL] equalising Powersonics

Hi Roger,

Thank you for your reply.

> I would set the power supply to something like 14.7-15V (for a 12V
>  battery) and leave the battery on charge for at least a couple of  
> days.  A dumb 12V automotive charger may work for this if you don't  
> have an adjustable power supply to use; just be sure to check the  
> voltage periodically to make sure the charger doesn't take the battery

> over 15V.

Yes I have a lab type power supply that has adjustable voltage and
current limiting.  

However I was wondering about 15V max.  If one cell in an unbalanced
battery is say at 75% charge, it may require 25AH to fully charge it.
At 15V the current of a full but unbalanced battery might be quite low,
like 250mA.  Does this mean it may take 25/0.25 = 100 hours to equalise
the battery?  I guess this is OK, no harm in leaving the battery for 4
days or so.

> Don't try to equalise them by charging in series as even 1A is enough
> to vent the full batteries (that is, you will "equalise" them by
> hammering the good ones down at the same time as you bring the weak
> ones up ;^).

Thanks for the tip - so far I have just run the 1A for a few hours after
each charge to perform a 2-4% of C manual equalisation, which I
understand is what a proper EV charger does.

Thanks again for your help

Cheers,

David


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Re: equalising Powersonics

Lee Hart
In reply to this post by drowe67
Roger Stockton wrote:
>> I would set the power supply to something like 14.7-15V (for a 12V
>>  battery) and leave the battery on charge for at least a couple of
>>  days.  A dumb 12V automotive charger may work for this if you don't
>>  have an adjustable power supply to use; just be sure to check the
>>  voltage periodically to make sure the charger doesn't take the battery
>>  over 15V.

This works well on a battery that isn't too far out of balance, or
hasn't been discharged too deeply.

If the battery has been sitting idle a long time (many months), or has
been very deeply discharged (so its no-load voltage is under 12v), then
sterner measures may be needed. In this case, you need to connect a
higher voltage supply, but limit the current to a very low level
(something that the AGM or gel battery can stand on a continuous basis).

I use a 24v supply with a light bulb in series to limit the current. The
bulb should be chosen to limit the current to less than 1% of the
battery's amphour capacity (i.e. 1 amp max for a 100ah battery).

On a battery that has one or more very dead cells, the voltage initially
goes up quite high, over the 15v you might expect. But the current is
very low; a fraction of an amp. The current is so low in fact, that the
battery is hardly charging at all. The higher-than-normal voltage is
needed to get at least some current to flow, to start the charging process.

Over a period of hours (or even days in severe cases), you should see
the current slowly rise, and the voltage come down. Once the voltage
goes under the usual max limit of 15v for a 12v battery, then you can
disconnect this "recovery" charger, and finish charging with a normal
battery charger as Roger outlined.

David Rowe wrote:
> However I was wondering about 15V max.  If one cell in an unbalanced
> battery is say at 75% charge, it may require 25AH to fully charge it.
> At 15V the current of a full but unbalanced battery might be quite low,
> like 250mA.  Does this mean it may take 25/0.25 = 100 hours to equalise
> the battery?

Yes; it can take days! There is no way to recharge the low cell except
by overcharging the full cells in series. So, you need to limit the
current so you don't damage the full cells.

Most AGMs and gels can tolerate a continuous charging current of about
0.5% to 1% of their rated amphour capacity for a few days. Yes, you are
damaging the good cells by slowly overcharging them to death. But you
have no choice -- you can't get at the individual cells to charge only
the weak one. This is a "necessary evil" to bring the weak cell up to
capacity. The battery is only as strong as its weakest link.

>> Don't try to equalise them by charging in series as even 1A is enough
>> to vent the full batteries (that is, you will "equalise" them by
>> hammering the good ones down at the same time as you bring the weak
>> ones up ;^).

Exactly right. When you have more than one battery, you do *not* want to
deliberately beat up the good ones up to charge the weaker ones.

> Thanks for the tip - so far I have just run the 1A for a few hours after
> each charge to perform a 2-4% of C manual equalisation, which I
> understand is what a proper EV charger does.

That's about right for a normal equalization. But it may not be enough
if your batteries are really far out of balance.

As an extreme example, Optima recommends a 16-hour charge at 4 amps to
force-equalize their AGM battery. That's 16h x 4a = 64ah into a 55ah
battery -- roughly a 20% overcharge! The battery gets hot, and vents.
But it does get equalized, no matter how far off it was!

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: equalising Powersonics - update

drowe67
Hello Roger, Cor, and Lee,

Thank you for your suggestions on helping me bring my low capacity
batteries up to spec.

Using your ideas I have been attempting equalise one of my 100AH
Powersonic batteries.  I applied 250mA for 3.75 days (22AH total), the
battery voltage was about 15.4V.  The battery stayed at room temperature
and if I put my ear on the battery I could (just) hear some quiet
bubbling.  For comparison the 13.8V float current is about 100mA.

I measured the battery capacity using a constant 40A, discharging it
down to 11V.  Before equalising it was 48AH, after equalising it was
53AH, and improvement of 5AH.  An identical battery measured 67AH when
tested new at the same 40AH current down to the same 11V.

So I have had some improvement!  I am wondering though why a 22AH charge
only delivers an extra 5AH?  Could be damage to the battery, or perhaps
the equalisation process isn't 100% efficient.  I may try another few
days of equalisation at similar currents and see if I can recover any
more capacity.

Thanks again for your help,

David


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Re: equalising Powersonics - update

Lee Hart
David Rowe wrote:
> Using your ideas I have been attempting equalise one of my 100AH
> Powersonic batteries. I applied 250mA for 3.75 days (22AH total)...
> Before equalising it was 48AH, after equalising it was 53AH, an
> improvement of 5AH. An identical battery measured 67AH when
> tested new at the same 40AH current down to the same 11V.
> So I have had some improvement!

Good. Not much, but something.

> I am wondering though why a 22AH charge only delivers an extra 5AH?

Because most of the excess energy was going into gassing and heating. If
the battery's seals are good, the gas should have just pressurized the
case, and the gas would recombine back into water (and the battery would
heat up a bit).

> Could be damage to the battery, or perhaps the equalisation process
> isn't 100% efficient.

Equalization is by nature inefficient. If the battery were fully
equalized, then doing an equalization anyway is 0% efficient (*all* the
excess energy goes away as gassing or heating).

> I may try another few days of equalisation at similar currents

I wouldn't. If that's all the improvement you got, then the battery is
now probably as equalized as it's going to get.

Suppose a battery has a cell that is 10ah lower than the rest. You
equalize, putting in 5ah extra; you get 4ah back. You equalize again,
putting in another 5ah, and again get 4ah back. But now, you've correct
the original 10ah deficit -- if you put equalize a third time with
another 5ah excess, you only get 2ah more back (because now all cells
are equal). Equalize a 4th time, and you get no improvement at all.
--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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KillaCycle and ElectroCat both set NEDRA records!

Bill Dube
In reply to this post by drowe67
        Excuse the crappy hand-held video. I think others got much better footage.

Both the KillaCycle and the ElectroCat managed to set new NEDRA
records this afternoon at Bandimere Speedway. The KillaCycle, ridden
by Scotty Pollacheck managed to bump up the record up for _all_ EVs
in the 1/4 mile to 7.864 @ 169 MPH.

Eva Hakansson on her ElectroCat, 100% street-legal in both the USA
and Sweden, set the open NEDRA record for a 48 volt street-legal
motorcycle; 13.249 @ 52.97 MPH.  (She selected the 1/8th mile record,
even though her 1/4 mile time was also new record.)

        I was, in my own inept fashion, filming the KillaCycle, but you can
see Eva here and there in a few frames, setting her record.

        http://www.youtube.com/watch?v=akximCGuLm8

Bandimere is, by far, the absolute best track in the world to set
records with electric-powered vehicles. Fantastic traction. 20% less
air to push out of the way. Very EV-friendly owners, the Bandimere
family. Plenty of grid power available.

Bill Dube' and Eva Hakansson

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Re: equalising Powersonics - update

drowe67
In reply to this post by Lee Hart
> > I may try another few days of equalisation at similar currents
>
> I wouldn't. If that's all the improvement you got, then the battery is
> now probably as equalized as it's going to get.

This was good advice, but I was curious.  So I just tried another
equalisation - 500mA for 10 hours, battery voltage less than 15.5V (an
extra 5AH).  When tested again the capacity was 51AH, a little less than
53A after the initial equalisation test.  This could be measurement
noise, or further battery damage, but clearly there was no significant
improvement of capacity from the second equalisation attempt - as you
predicted Lee!

Here is a plot of the battery discharge before (red) and after (green)
the equalisation exercise (constant 40A load):

http://rowetel.com/images/ev_ps6_equal.png

A small improvement.  Knowing the discharge curve is helpful - tells me
not to drive with this battery beneath 12V

Here is a plot of an identical battery when new (red), plotted with the
current #6 battery (green).

http://rowetel.com/images/ev_ps6_ps1.png

The new battery had a shallower discharge curve but went for 100
minutes.  I noticed the same thing on my previous battery pack, the
curve got steeper as the batteries aged. When new they had most of their
capacity between 12 and 11V, when old they stayed above 12V until then
dropped like a rock.

So my theory is (i) through lack of equalisation a cell in battery #6
became unbalanced; (ii) we then drove thru a point where the cell became
reversed, damaging the cell and leading to reduced capacity.

There is also another battery will low capacity - I will test that next
and perhaps one of the good ones to get a feel for the rest of the pack.

Hopefully a proper EV charger that does equalisation on each charge will
help maintain the remaining batteries.  In my application we charge
twice a day (average of about 25% DoD on each charge).  Perhaps the
large number of charge cycles is worse for equalisation.

I use separate chargers as I though they would be better for AGMs,
however my chargers don't do equalisation.  The new charger I have
ordered is a single (series string) charger that does do equalisation.

Thanks to all for your help and comments.

Cheers,

David


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Re: KillaCycle and ElectroCat both set NEDRA records!

lawlessind
In reply to this post by Bill Dube
Congratulations Eva, Scotty, and Bill!  I hope we can race together
sometime in the near future.

Shawn Lawless


-----Original Message-----
From: Bill Dube <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Sun, Sep 27, 2009 8:46 pm
Subject: [EVDL] KillaCycle and ElectroCat both set NEDRA records!



     Excuse the crappy hand-held video. I think others got much better
footage.

Both the KillaCycle and the ElectroCat managed to set new NEDRA
records this afternoon at Bandimere Speedway. The KillaCycle, ridden
by Scotty Pollacheck managed to bump up the record up for _all_ EVs
in the 1/4 mile to 7.864 @ 169 MPH.

Eva Hakansson on her ElectroCat, 100% street-legal in both the USA
and Sweden, set the open NEDRA record for a 48 volt street-legal
motorcycle; 13.249 @ 52.97 MPH.  (She selected the 1/8th mile record,
even though her 1/4 mile time was also new record.)

    I was, in my own inept fashion, filming the KillaCycle, but you can
see Eva here and there in a few frames, setting her record.

    http://www.youtube.com/watch?v=akximCGuLm8

Bandimere is, by far, the absolute best track in the world to set
records with electric-powered vehicles. Fantastic traction. 20% less
air to push out of the way. Very EV-friendly owners, the Bandimere
family. Plenty of grid power available.

Bill Dube' and Eva Hakansson

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Re: KillaCycle and ElectroCat both set NEDRA records!

KilowattA798
In reply to this post by Bill Dube
In a message dated 9/27/2009 6:02:18 PM US Mountain Standard Time,
[hidden email] writes:

> Subj: [EVDL] KillaCycle and ElectroCat both set NEDRA records!
> Date:9/27/2009 6:02:18 PM US Mountain Standard Time
> From:[hidden email]
> Reply-to:[hidden email]
> To:[hidden email]
> Received from Internet:
>
>
>
>     Excuse the crappy hand-held video. I think others got much better
> footage.
>
> Both the KillaCycle and the ElectroCat managed to set new NEDRA
> records this afternoon at Bandimere Speedway. The KillaCycle, ridden
> by Scotty Pollacheck managed to bump up the record up for _all_ EVs
> in the 1/4 mile to 7.864 @ 169 MPH.
>
> Eva Hakansson on her ElectroCat, 100% street-legal in both the USA
> and Sweden, set the open NEDRA record for a 48 volt street-legal
> motorcycle; 13.249 @ 52.97 MPH.  (She selected the 1/8th mile record,
> even though her 1/4 mile time was also new record.)
>
>     I was, in my own inept fashion, filming the KillaCycle, but you can
> see Eva here and there in a few frames, setting her record.
>
>     http://www.youtube.com/watch?v=akximCGuLm8
>
> Bandimere is, by far, the absolute best track in the world to set
> records with electric-powered vehicles. Fantastic traction. 20% less
> air to push out of the way. Very EV-friendly owners, the Bandimere
> family. Plenty of grid power available.
>
> Bill Dube' and Eva Hakansson
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
Good job Bill and Eva.How many other EVs showed? Any more records? How many
folks in the stands?
Dennis Berube
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Re: KillaCycle and ElectroCat both set NEDRA records!

Bill Dube
A few other EVs showed up to display, but only the ElectroCat and the
KillaCycle elected to race. About 30 folks came out specifically to
see the electrics race. A local TV news channel covered the
ElectroCat in a parade the day before, and we got a bit of print and
web coverage at the NEDRA event.

         The main event at the track was a local level bracket race,
so the stands were pretty much empty. Plenty of competitors of
course, (probably 200) but bracket racing is all about the enjoyment
of the competitors and not so much a spectator sport. Kind of like
league bowling.

         The KillaCycle posted the very best ET of the event, by the
way. Not even the big-block dragsters were quicker. That is always
fun when it happens. :-)

>Good job Bill and Eva.How many other EVs showed? Any more records? How many
>folks in the stands?
>Dennis Berube

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lead acid battery capacity and recovery

drowe67
In reply to this post by drowe67
Hello List,

Say I have a C=100Ah lead-acid battery that I discharge at C/2=50A.  The
battery hits 10.8V after 1 hr and I stop the test.  This, I understand,
pulls about half of the batteries energy out of it, so the SoC would be
50%.

If I leave that battery for 24 hours then start discharging again, will
I be able to continue to discharge at 50A for some period of time?

Thanks,

David


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Re: lead acid battery capacity and recovery

Roland Wiench



----- Original Message -----
From: "David Rowe" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Tuesday, September 29, 2009 1:49 AM
Subject: [EVDL] lead acid battery capacity and recovery


> Hello List,
>
> Say I have a C=100Ah lead-acid battery that I discharge at C/2=50A.  The
> battery hits 10.8V after 1 hr and I stop the test.  This, I understand,
> pulls about half of the batteries energy out of it, so the SoC would be
> 50%.
>
> If I leave that battery for 24 hours then start discharging again, will
> I be able to continue to discharge at 50A for some period of time?
>
> Thanks,
>
> David
>
Hello David,

The 10.8 volts would be the sag voltage at load.  After you let the
batteries rest for a while, a 50% SOC voltage would be actually 12.10 volts.

If you could read the capacity of the a new battery after each cycle, you
will see the capacity start to increase for the first 50 to 100 charge and
discharge cycles depending on the depth of each discharge.

During these first cycles, the surface of the plates open up more passages
which increases the plate area, thus more capacity.

After this initial break in, where the battery capacity does not increase
any more.  During this first initial phase, I will charge the battery every
time even if I only took out only 2 AH, so as to prevent any salvation of
the plates.

My new US 6 volt 251 AH batteries started out at 950 amps and now has
increase to about 975 amps capacity. Like my last set of batteries that
lasted 8 years and 7 months, they reach as high as 1047 ampere.

Then after that, the capacity drop to about 600 amps which is about a
average of 400 amps for the eight years or 50 amps a year. This is about 1
amp a week or about 0.1 to 0.2 amp a day.

So after each discharge cycle, you will have to increase the charging time
about 10% longer to get to 100% SOC during the initial break in phase  plus
a micro second longer each time to get to 100% SOC as they age.

If you have instrumentation to see exactly what the capacity of the battery
is, then you can get close to where the 100% State of Charge will equal the
1.277 specific gravity which equals the maximum ampere rating of the battery
which equals the rated ampere-hour.

I adjust the Charge Efficiency Factor (CEF) in my Electronic Recording
Indicators Readout Instrumentation or E-Meter to a value of 90% to
compensate for the inefficiency of the charger and the AC input circuits
during the first 2 or 3 years.  Then after that I increase the CEF.

Roland


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Re: lead acid battery capacity and recovery

Lee Hart
In reply to this post by drowe67
David Rowe wrote:
> Hello List,
>
> Say I have a C=100Ah lead-acid battery that I discharge at C/2=50A.  The
> battery hits 10.8V after 1 hr and I stop the test.  This, I understand,
> pulls about half of the batteries energy out of it, so the SoC would be
> 50%.
>
> If I leave that battery for 24 hours then start discharging again, will
> I be able to continue to discharge at 50A for some period of time?

Yes. Depending on the battery, it might give you 50a for another 30
minutes before it reaches 10.8v.

If you stop, and let it rest another 24 hours, you'll get 50a for
another 15 minutes.

If you continue, you'll eventually get the full 100ah out of it (or even
a little more, since the average current is so low -- it's like
discharging it at the 200-hour rate).

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Re: lead acid battery capacity and recovery

jyanof
Extending this thread to include cycle life...

USbattery has this chart for cycle life vs. DOD (which I understand should
be interpreted as a general trend and may not represent EV use).
http://www.usbattery.com/usb_images/cycle_life.xls.pdf

It also has this chart for Minutes of Capacity vs. Discharge Rate.
http://www.usbattery.com/usb_images/USB%20Capacity%20Chart.pdf

Hypothetical Situation and questions.

A US2200 is discharged at 100A for 80 mins (It's entire capacity according
to the chart)  This is 133 Ah.

Are the following correct?

1.  To calculate SOC: compare to the 20hr rating of 232 Ah, 1 - 133/232 =
42.5% SOC

1a.  The SG of the cells will reflect the 42.5% SOC.

2.  In the cycle life chart, DOD on the x-axis would be 100 - 42.5 = 57.5%.


If you were wondering, I ask this because I initially interpreted the DOD in
the cycle-life chart as the percentage of capacity used at the given
discharge rate (despite the clear labeling of the x-axis).  In the situation
above, this would equate to 100% DOD instead of 57.5%.  Having read this
thread, I believe I was mistaken...

Thanks!
Joe



On Tue, Sep 29, 2009 at 8:37 AM, Lee Hart <[hidden email]> wrote:

> David Rowe wrote:
> > Hello List,
> >
> > Say I have a C=100Ah lead-acid battery that I discharge at C/2=50A.  The
> > battery hits 10.8V after 1 hr and I stop the test.  This, I understand,
> > pulls about half of the batteries energy out of it, so the SoC would be
> > 50%.
> >
> > If I leave that battery for 24 hours then start discharging again, will
> > I be able to continue to discharge at 50A for some period of time?
>
> Yes. Depending on the battery, it might give you 50a for another 30
> minutes before it reaches 10.8v.
>
> If you stop, and let it rest another 24 hours, you'll get 50a for
> another 15 minutes.
>
> If you continue, you'll eventually get the full 100ah out of it (or even
> a little more, since the average current is so low -- it's like
> discharging it at the 200-hour rate).
>
> --
> Lee A. Hart             | Ring the bells that still can ring
> 814 8th Ave N           | Forget the perfect offering
> Sartell MN 56377        | There is a crack in everything
> leeahart earthlink.net  | That's how the light gets in -- Leonard Cohen
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>
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