charger question - bypassing batteries

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charger question - bypassing batteries

Ben Jarrett


Hey everyone,

I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
shipped in 3 separate boxes.  Now that I've had a decent number of
charging cycles, I noticed that one of the batches finishes charging
before the rest.  Also, my elcon is supposed to go to yellow when I reach
80% soc and I haven't seen that yet (mini bms shuts charger off because
of a cell limit).

I'd like to charge up the pack and wait for the mini bms to turn off the charger.
I'd then like to bypass the early achiever cells (about 10 cells) and do another
charger cycle.

Will my charger be ok with this?  I know it won't give me quite the right
ending curve... I would just charge until I get more cells to a higher voltage.
I wasn't sure if a lower pack voltage seen by the charger would be a bad thing.

thanks,
b-en

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Re: charger question - bypassing batteries

corbin dunn
Hi Ben,
A better thing to do is to individually charge the low cells. When I got my TS cells, a few were low and took quite a bit of extra charging (at low amps) to get them up to the same as the others.

I got a cheap ~3.6v Lithium charger. If you need help finding one, let me know and I can dig up the model I bought.

corbin

On Jun 15, 2012, at 9:11 PM, Ben Jarrett <[hidden email]> wrote:

>
>
> Hey everyone,
>
> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
> shipped in 3 separate boxes.  Now that I've had a decent number of
> charging cycles, I noticed that one of the batches finishes charging
> before the rest.  Also, my elcon is supposed to go to yellow when I reach
> 80% soc and I haven't seen that yet (mini bms shuts charger off because
> of a cell limit).
>
> I'd like to charge up the pack and wait for the mini bms to turn off the charger.
> I'd then like to bypass the early achiever cells (about 10 cells) and do another
> charger cycle.
>
> Will my charger be ok with this?  I know it won't give me quite the right
> ending curve... I would just charge until I get more cells to a higher voltage.
> I wasn't sure if a lower pack voltage seen by the charger would be a bad thing.
>
> thanks,
> b-en
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
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Re: charger question - bypassing batteries

corbin dunn
Actually, I found the one I bought from batteryspace.com:


Smart Charger (6.0A) for 3.2V (1cells) LiFePO4 Battery Pack, 100-240VAC, CE listed
CH-LFP3.2V6A 1 $25.95 $25.95

corbin



On Jun 15, 2012, at 9:27 PM, corbin dunn <[hidden email]> wrote:

> Hi Ben,
> A better thing to do is to individually charge the low cells. When I got my TS cells, a few were low and took quite a bit of extra charging (at low amps) to get them up to the same as the others.
>
> I got a cheap ~3.6v Lithium charger. If you need help finding one, let me know and I can dig up the model I bought.
>
> corbin
>
> On Jun 15, 2012, at 9:11 PM, Ben Jarrett <[hidden email]> wrote:
>
>>
>>
>> Hey everyone,
>>
>> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
>> shipped in 3 separate boxes.  Now that I've had a decent number of
>> charging cycles, I noticed that one of the batches finishes charging
>> before the rest.  Also, my elcon is supposed to go to yellow when I reach
>> 80% soc and I haven't seen that yet (mini bms shuts charger off because
>> of a cell limit).
>>
>> I'd like to charge up the pack and wait for the mini bms to turn off the charger.
>> I'd then like to bypass the early achiever cells (about 10 cells) and do another
>> charger cycle.
>>
>> Will my charger be ok with this?  I know it won't give me quite the right
>> ending curve... I would just charge until I get more cells to a higher voltage.
>> I wasn't sure if a lower pack voltage seen by the charger would be a bad thing.
>>
>> thanks,
>> b-en
>>
>> _______________________________________________
>> | 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.
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>

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Re: charger question - bypassing batteries

Willie2
In reply to this post by Ben Jarrett
On Fri, Jun 15, 2012 at 11:11:11PM -0500, Ben Jarrett wrote:

>
>
> Hey everyone,
>
> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
> shipped in 3 separate boxes.  Now that I've had a decent number of
> charging cycles, I noticed that one of the batches finishes charging
> before the rest.  Also, my elcon is supposed to go to yellow when I reach
> 80% soc and I haven't seen that yet (mini bms shuts charger off because
> of a cell limit).

Did you do the initial "top balance".  If not, you should.  It is
likely that cells within your three groups are also not balanced.
As you probably know, you are not balanced until all BMS cell modules
have their red LEDs on.

As Corbin says, you can get an individual cell charger to bring up
cells one at a time.  You can also use one or several power supplies
that have max voltage set appropriately.

I have a "balancing charger" which is four 45v power supplies in
series.  The power supplies put out less current than the BMS cell
modules can by-pass; that is due to a Lee Hart inspired light bulb
arrangement.  After a charge with a regular charger, I hook up the
balancing charger for hours and let it bring up the low cells.  The
balancing charger is hooked up the same way as a regular charger; that
is, the BMS controls the ac input.

It is unlikely that your Elcon charger can detect 80% SOC on a lithium
pack.  That is probably there due to the charger's lead applications.  
I did find a TC/Elcon charger that just happened to do the right thing
for my particular pack for my BMS thresholds.  For 48 cells with low
high voltage cutoff modules, the charger will taper down to less than
an amp as it nears it's maximum voltage (185v for my charger).  That
allows cell modules to by-pass for a long period of time.  I would say
that generally a charger is not likely to be so well matched to your
pack.  "Charger Profile" is an almost meaningless term when the pack is
lithium.  

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  87 days 23 hours 10 minutes

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Re: charger question - bypassing batteries

Cruisin
Change the algorithm in the charger to the next higher voltage and recharge letting the BMS control the charger. The charger is shutting off too soon.
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Re: charger question - bypassing batteries

corbin dunn
In reply to this post by Willie2
Willie's solution is good too, provided you have a charger setup that way.

Another alternative is to connect all the cells in parallel; this makes the total Ah rating be the additive some of each individual cells Ah rating, and the voltage is equal to a single cell's voltage. However, I choose not to do this approach for several reasons:
1. I would have to rewire my pack (even temporarily using low-current capable wires), which would have been a pain.
2. It would still take a while to get all the cells equalized, since one has to put in a bunch of amp-hours for the entire pack in order to reach full charge.

The nice thing about using a small 3.2v LifePo4 charger on single cells is that the charger is essentially a single-cell BMS, and you shouldn't be able to overcharge that single cell with it (I say shouldn't, because who knows what crazy things could happen).

corbin


On Jun 16, 2012, at 2:29 AM, Willie McKemie wrote:

> On Fri, Jun 15, 2012 at 11:11:11PM -0500, Ben Jarrett wrote:
>>
>>
>> Hey everyone,
>>
>> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
>> shipped in 3 separate boxes.  Now that I've had a decent number of
>> charging cycles, I noticed that one of the batches finishes charging
>> before the rest.  Also, my elcon is supposed to go to yellow when I reach
>> 80% soc and I haven't seen that yet (mini bms shuts charger off because
>> of a cell limit).
>
> Did you do the initial "top balance".  If not, you should.  It is
> likely that cells within your three groups are also not balanced.
> As you probably know, you are not balanced until all BMS cell modules
> have their red LEDs on.
>
> As Corbin says, you can get an individual cell charger to bring up
> cells one at a time.  You can also use one or several power supplies
> that have max voltage set appropriately.
>
> I have a "balancing charger" which is four 45v power supplies in
> series.  The power supplies put out less current than the BMS cell
> modules can by-pass; that is due to a Lee Hart inspired light bulb
> arrangement.  After a charge with a regular charger, I hook up the
> balancing charger for hours and let it bring up the low cells.  The
> balancing charger is hooked up the same way as a regular charger; that
> is, the BMS controls the ac input.
>
> It is unlikely that your Elcon charger can detect 80% SOC on a lithium
> pack.  That is probably there due to the charger's lead applications.  
> I did find a TC/Elcon charger that just happened to do the right thing
> for my particular pack for my BMS thresholds.  For 48 cells with low
> high voltage cutoff modules, the charger will taper down to less than
> an amp as it nears it's maximum voltage (185v for my charger).  That
> allows cell modules to by-pass for a long period of time.  I would say
> that generally a charger is not likely to be so well matched to your
> pack.  "Charger Profile" is an almost meaningless term when the pack is
> lithium.  
>
> --
> Willie, ONWARD!  Through the fog!
> http://counter.li.org Linux registered user #228836 since 1995
> Debian3.1/GNU/Linux system uptime  87 days 23 hours 10 minutes
>
> _______________________________________________
> | Moratorium on drag racing discussion is in effect.
> | Please take those discussions elsewhere.  Thanks.
> |
> | REPLYING: address your message to [hidden email] only.
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Re: charger question - bypassing batteries

Mike Nickerson
I am using a Sky Charger that I bought from Xheli through Amazon.  It looks
like it isn't through Amazon any more but can be obtained from xheli.com
directly.

http://www.xheli.com/skychb6durcc.html?gclid=CPWVkZec07ACFaYaQgodw1c14g

This charger supports lead-acid, LiFePO4, NiCd, NiMH.  It is intended for RC
models, but works really well to charge 1-6 cells on our cars.  It has an
output of up to 5A or 50W.  Costs about $55.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of corbin dunn
> Sent: Saturday, June 16, 2012 10:18 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] charger question - bypassing batteries
>
> Willie's solution is good too, provided you have a charger setup that way.
>
> Another alternative is to connect all the cells in parallel; this makes
the total
> Ah rating be the additive some of each individual cells Ah rating, and the
> voltage is equal to a single cell's voltage. However, I choose not to do
this
> approach for several reasons:
> 1. I would have to rewire my pack (even temporarily using low-current
> capable wires), which would have been a pain.
> 2. It would still take a while to get all the cells equalized, since one
has to put
> in a bunch of amp-hours for the entire pack in order to reach full charge.
>
> The nice thing about using a small 3.2v LifePo4 charger on single cells is
that
> the charger is essentially a single-cell BMS, and you shouldn't be able to
> overcharge that single cell with it (I say shouldn't, because who knows
what

> crazy things could happen).
>
> corbin
>
>
> On Jun 16, 2012, at 2:29 AM, Willie McKemie wrote:
>
> > On Fri, Jun 15, 2012 at 11:11:11PM -0500, Ben Jarrett wrote:
> >>
> >>
> >> Hey everyone,
> >>
> >> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms.  My Calbs
> >> shipped in 3 separate boxes.  Now that I've had a decent number of
> >> charging cycles, I noticed that one of the batches finishes charging
> >> before the rest.  Also, my elcon is supposed to go to yellow when I
> >> reach 80% soc and I haven't seen that yet (mini bms shuts charger off
> >> because of a cell limit).
> >
> > Did you do the initial "top balance".  If not, you should.  It is
> > likely that cells within your three groups are also not balanced.
> > As you probably know, you are not balanced until all BMS cell modules
> > have their red LEDs on.
> >
> > As Corbin says, you can get an individual cell charger to bring up
> > cells one at a time.  You can also use one or several power supplies
> > that have max voltage set appropriately.
> >
> > I have a "balancing charger" which is four 45v power supplies in
> > series.  The power supplies put out less current than the BMS cell
> > modules can by-pass; that is due to a Lee Hart inspired light bulb
> > arrangement.  After a charge with a regular charger, I hook up the
> > balancing charger for hours and let it bring up the low cells.  The
> > balancing charger is hooked up the same way as a regular charger; that
> > is, the BMS controls the ac input.
> >
> > It is unlikely that your Elcon charger can detect 80% SOC on a lithium
> > pack.  That is probably there due to the charger's lead applications.
> > I did find a TC/Elcon charger that just happened to do the right thing
> > for my particular pack for my BMS thresholds.  For 48 cells with low
> > high voltage cutoff modules, the charger will taper down to less than
> > an amp as it nears it's maximum voltage (185v for my charger).  That
> > allows cell modules to by-pass for a long period of time.  I would say
> > that generally a charger is not likely to be so well matched to your
> > pack.  "Charger Profile" is an almost meaningless term when the pack
> > is lithium.
> >
> > --
> > Willie, ONWARD!  Through the fog!
> > http://counter.li.org Linux registered user #228836 since 1995
> > Debian3.1/GNU/Linux system uptime  87 days 23 hours 10 minutes
> >
> > _______________________________________________
> > | 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
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>
>
> _______________________________________________
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> |
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Re: charger question - bypassing batteries

Mike Nickerson
I forgot to mention in the last post:  One of the things I really like about
the Sky Charger is the information display.  As it's charging, it shows how
many amps it's charging at and how many Ah (milli Ah actually) it has put
into the cells.  This lets you know exactly how far from balanced your cells
really are.  When I first used the charger, I had some cells that were 20%
low!

Also, even if you charge 5 or 6 cells in a string (helps speed things up),
it charges at a low enough current that your MiniBMS shunts can probably
keep up.  For the first balancing charge, though, I did one cell at a time.
I think I would recommend doing that.  Once things are closer into balance,
you can charge several cells at a time.  

My experience with the Elcon charger on my pack is that it won't go into its
finishing stage (LED turns yellow), until 1/2 to 2/3 of the cells are
starting to shunt.   I found that I needed to go through the cycle of
charging lower cells with the Sky Charger a couple of times before the
charger could completely finish the charge cycle.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Mike Nickerson
> Sent: Saturday, June 16, 2012 10:55 AM
> To: 'Electric Vehicle Discussion List'
> Subject: Re: [EVDL] charger question - bypassing batteries
>
> I am using a Sky Charger that I bought from Xheli through Amazon.  It
looks
> like it isn't through Amazon any more but can be obtained from xheli.com
> directly.
>
> http://www.xheli.com/skychb6durcc.html?gclid=CPWVkZec07ACFaYaQgodw
> 1c14g
>
> This charger supports lead-acid, LiFePO4, NiCd, NiMH.  It is intended for
RC
> models, but works really well to charge 1-6 cells on our cars.  It has an
output
> of up to 5A or 50W.  Costs about $55.
>
> Mike
>

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Re: charger question - bypassing batteries

Lee Hart
In reply to this post by Ben Jarrett
Ben Jarrett wrote:
> I have 50 Calb cells, 2 kW Elcon charger, and a mini bms...
> I noticed that one of the batches finishes charging
> before the rest. Also, my elcon is supposed to go to yellow when I reach
> 80% soc and I haven't seen that yet (mini bms shuts charger off because
> of a cell limit).

As others have said, it sounds like your cells are unbalanced, and the
charger and BMS are not correcting the problem.

What should be happening is that the BMS warns the charger when the
first cell reaches its maximum voltage limit. The charger should then
cut back to a low current, so it won't overpower the shunt regulators in
the mini-BMS. Then when the charger detects that all cells are full, it
shuts off.

Instead, it sounds like your charger shuts off as soon as the BMS
detects a high cell. By shutting off at this point, the unbalance is
detected, but not corrected.

Your best bet is probably to get a single-cell charger for your cells,
and use it to individually charge each cell until it is full (top balance).

Then, modify the charger or BMS so it continues to charge at low current
when the first cells start to bypass. I'm not familiar with your
charger, but it might be as simple as having a timer delay the turn-off
for an hour or two to give the shunt regulators in the BMS time to do
their job.

--
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

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Re: charger question - bypassing batteries

Lee Hart
In reply to this post by corbin dunn
On 6/15/2012 11:27 PM, corbin dunn wrote:
> Hi Ben,
> A better thing to do is to individually charge the low cells. When I got my TS cells, a few were low and took quite a bit of extra charging (at low amps) to get them up to the same as the others.
>
> I got a cheap ~3.6v Lithium charger. If you need help finding one, let me know and I can dig up the model I bought.

I use a generic 5v 30amp power supply for this purpose. I added a big
diode on a heatsink in series with the output; that knocked the output
down to about 4.4v. I then turned down the voltage adjustment trimpot to
get the voltage I wanted (3.6v to 4v for LiFePO4 cells).

--
First they ignore you; then they mock you; then they fight you; then you
win.
        -- Mahatma Gandhi
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

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Re: charger question - bypassing batteries

Mike Nickerson
In reply to this post by Lee Hart
Hi Lee,

I have similar cells, BMS and charger to Ben's.  The system is not as
intelligent as you describe.  The charger decides on its own (from the
current charging voltage and its built-in program) when to switch to lower
current.  It won't do that unless the cells are pretty well matched.  The
BMS doesn't have any communication with the charger about cells at the
shunting level.

Again, as the first cell reaches its overvoltage limit, the BMS doesn't
inform the charger, but instead cuts power to the charger through an AC
relay.  

The MiniBMS system and Elcon charger combination will work fine once the
cells are balanced.  However, in my experience, they are not sufficient to
bring the system into balance if it is very far off.  The charger is simply
charging with too much current still if the cells are significantly out of
balance.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Lee Hart
> Sent: Saturday, June 16, 2012 6:48 PM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] charger question - bypassing batteries
>
> Ben Jarrett wrote:
> > I have 50 Calb cells, 2 kW Elcon charger, and a mini bms...
> > I noticed that one of the batches finishes charging before the rest.
> > Also, my elcon is supposed to go to yellow when I reach 80% soc and I
> > haven't seen that yet (mini bms shuts charger off because of a cell
> > limit).
>
> As others have said, it sounds like your cells are unbalanced, and the
charger
> and BMS are not correcting the problem.
>
> What should be happening is that the BMS warns the charger when the first
> cell reaches its maximum voltage limit. The charger should then cut back
to a
> low current, so it won't overpower the shunt regulators in the mini-BMS.
> Then when the charger detects that all cells are full, it shuts off.
>
> Instead, it sounds like your charger shuts off as soon as the BMS detects
a
> high cell. By shutting off at this point, the unbalance is detected, but
not
> corrected.
>
> Your best bet is probably to get a single-cell charger for your cells, and
use it
> to individually charge each cell until it is full (top balance).
>
> Then, modify the charger or BMS so it continues to charge at low current
> when the first cells start to bypass. I'm not familiar with your charger,
but it
> might be as simple as having a timer delay the turn-off for an hour or two
to

> give the shunt regulators in the BMS time to do their job.
>
> --
> 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
>
> _______________________________________________
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> | Please take those discussions elsewhere.  Thanks.
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Re: charger question - bypassing batteries

Willie2
On Sat, Jun 16, 2012 at 07:18:51PM -0600, Mike Nickerson wrote:
> Hi Lee,
>
> I have similar cells, BMS and charger to Ben's.  The system is not as
> intelligent as you describe.  The charger decides on its own (from the
> current charging voltage and its built-in program) when to switch to lower
> current.  It won't do that unless the cells are pretty well matched.  The
> BMS doesn't have any communication with the charger about cells at the
> shunting level.

I too use a BMS controlled ac relay to cut my charger.  That seems
simplest, safest and works with any charger or combination of
chargers.

However, I think the Elcon/TC charger has some other cut-back
capabilities though I haven't explored them.  There is a CAN bus
option, but I don't know what that does.  Then there is the little
signal connection.  I just have my signal wires shorted together but I
think they can be used with the BMS to cut back the charging rate.  
Sorry, but I know little more than the presence of those two things.

--
Willie, ONWARD!  Through the fog!
http://counter.li.org Linux registered user #228836 since 1995
Debian3.1/GNU/Linux system uptime  88 days 15 hours 34 minutes

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Re: charger question - bypassing batteries

Lee Hart
In reply to this post by Mike Nickerson
On 6/16/2012 8:18 PM, Mike Nickerson wrote:
> I have similar cells, BMS and charger to Ben's.  The system is not as
> intelligent as you describe.  The charger decides on its own (from the
> current charging voltage and its built-in program) when to switch to lower
> current.  It won't do that unless the cells are pretty well matched.  The
> BMS doesn't have any communication with the charger about cells at the
> shunting level.

Hmm... that's a problem. Do you know what its charging algorithm is? My
thought would be to wire in a voltmeter and ammeter, and *watch* what
the charger actually does. I often find that what the manufacturer
claims does not agree with what it *actually* does!

Until that data is available, let's assume it has the simplest algorithm
that would barely work:

a. Charge at maximum current until it reaches V volts.
b. Charge at constant V volts until the current falls to I amps.
c. Shut off.

This works if the cells are all very well matched and top-balanced. At
full charge, the charger assumes that (for example) V = 365v means you
have 100 cells at 3.65v each.

But if the cells are mismatched, some cells will go overvoltage while
others are still undervoltage. The total may be 365v; but individual
cells might range from 3.3v to 4.3v. 3.3v is nowhere near full, and 4.3v
is well into overcharge!

You can add a BMS that shunts some low current around any cell that goes
over some "full" voltage (say, 3.65v). Let's say it can shunt 1 amp. But
if the charger sees less than 365v for the pack as a whole, it can still
be pumping out more current (say, 2 amps). It just overpowers the shunt
regulator; 1 amp goes through the shunt regulator and 1 amp through the
cell, so it *still* overcharges and overvoltages the cell.

This is why you need some way to insure that the charger is at a low
current when the regulators start to bypass. The charger should have an
algorithm that automatically cuts back to a low current well before it
reaches its voltage limit. Or, you need to add some other method to
limit charging current when any shunt regulator is on. Then when *all*
cells have reached their voltage limit, you can shut off the charger.

If your charger has no such means to limit its current, you can add a
relay that switches a resistor in series to limit the current. When the
first BMS regulator turns on, it turns this relay off. The resistor is
chosen to limit the current to whatever the regulators can safely
bypass. (A light bulb works well as a resistor, because they naturally
act as current limiters).

If the charger doesn't already have a shut-off timer, you should add one
of these as well. The simplest type is a 0-12 hour mechanical timer
(Intermatic etc.). It fits in a normal electrical switch box, and has a
knob that you twist to set the maximum time. It has 240vac 20amp
contacts that automatically shut off the AC input to the charger at the
end of the time.

> The MiniBMS system and Elcon charger combination will work fine once the
> cells are balanced.

If the cells are balanced, the BMS shouldn't be doing anything.

If the cells aren't balanced, isn't the BMS supposed to balance them? If
it doesn't work when they are unbalanced, what is the purpose of this BMS?

--
*BE* the change that you wish to see in the world.
        -- Mahatma Gandhi
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

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Re: charger question - bypassing batteries

Ben Jarrett



So in my case, all 50 of my Calb 130 Ah cells started at 3.2 volts.  The charger was
setup by the factory for my pack (supposedly).  It has a sticker on the side saying
it's for 180V max LiFePo4 pack.  So I charge my pack and here's what happens:

* After charging for a few hours on 120V (about 7 amps into the pack), I have some
  cells that start reaching 3.5 Volts.
* At this point, the mini bms starts shunting these cells.  I'm still getting
  around 7amps into the pack.
* If one of these cells hits 3.6 Volts, the mini bms shuts off the charger
  (that's what's happening now).
* For me, I have 10 cells that are shunting when the mini-bms turns off the charger.
* Most of the other cells are at 3.4V (for Lithium, it's hard to know what the SOC
  is from the voltage, but they should be pretty well charged).

So what I'd like to do is:
* Charge my pack until the mini bms shuts off the charger.
* Bypass the 10 early cells (I have a 2 gage bypass cable for emergencies)
* Start the charger again
* Allow the mini bms to shut off the charger
* See if I'm top balanced yet.

Can I damage anything if I hook up my Elcon 2kW charger (that's been "programmed"
for 50 cells) to 40 cells and let it charge?   This is one question I still don't have
an answer for.  Maybe someone out there knows.

I still could get a single cell charger to finish things off, but I'm looking for
a good way to get closer.

thanks!
-ben


On Jun 17, 2012, at 11:28 AM, Lee Hart wrote:

> On 6/16/2012 8:18 PM, Mike Nickerson wrote:
>> I have similar cells, BMS and charger to Ben's.  The system is not as
>> intelligent as you describe.  The charger decides on its own (from the
>> current charging voltage and its built-in program) when to switch to lower
>> current.  It won't do that unless the cells are pretty well matched.  The
>> BMS doesn't have any communication with the charger about cells at the
>> shunting level.
>
> Hmm... that's a problem. Do you know what its charging algorithm is? My
> thought would be to wire in a voltmeter and ammeter, and *watch* what
> the charger actually does. I often find that what the manufacturer
> claims does not agree with what it *actually* does!
>
> Until that data is available, let's assume it has the simplest algorithm
> that would barely work:
>
> a. Charge at maximum current until it reaches V volts.
> b. Charge at constant V volts until the current falls to I amps.
> c. Shut off.
>
> This works if the cells are all very well matched and top-balanced. At
> full charge, the charger assumes that (for example) V = 365v means you
> have 100 cells at 3.65v each.
>
> But if the cells are mismatched, some cells will go overvoltage while
> others are still undervoltage. The total may be 365v; but individual
> cells might range from 3.3v to 4.3v. 3.3v is nowhere near full, and 4.3v
> is well into overcharge!
>
> You can add a BMS that shunts some low current around any cell that goes
> over some "full" voltage (say, 3.65v). Let's say it can shunt 1 amp. But
> if the charger sees less than 365v for the pack as a whole, it can still
> be pumping out more current (say, 2 amps). It just overpowers the shunt
> regulator; 1 amp goes through the shunt regulator and 1 amp through the
> cell, so it *still* overcharges and overvoltages the cell.
>
> This is why you need some way to insure that the charger is at a low
> current when the regulators start to bypass. The charger should have an
> algorithm that automatically cuts back to a low current well before it
> reaches its voltage limit. Or, you need to add some other method to
> limit charging current when any shunt regulator is on. Then when *all*
> cells have reached their voltage limit, you can shut off the charger.
>
> If your charger has no such means to limit its current, you can add a
> relay that switches a resistor in series to limit the current. When the
> first BMS regulator turns on, it turns this relay off. The resistor is
> chosen to limit the current to whatever the regulators can safely
> bypass. (A light bulb works well as a resistor, because they naturally
> act as current limiters).
>
> If the charger doesn't already have a shut-off timer, you should add one
> of these as well. The simplest type is a 0-12 hour mechanical timer
> (Intermatic etc.). It fits in a normal electrical switch box, and has a
> knob that you twist to set the maximum time. It has 240vac 20amp
> contacts that automatically shut off the AC input to the charger at the
> end of the time.
>
>> The MiniBMS system and Elcon charger combination will work fine once the
>> cells are balanced.
>
> If the cells are balanced, the BMS shouldn't be doing anything.
>
> If the cells aren't balanced, isn't the BMS supposed to balance them? If
> it doesn't work when they are unbalanced, what is the purpose of this BMS?
>
> --
> *BE* the change that you wish to see in the world.
> -- Mahatma Gandhi
> --
> 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
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Re: charger question - bypassing batteries

David Nelson-5
You could just wait a few minutes and restart the charger. It should run
for a little bit and then get shut off by the BMS again. Each time the low
cells are getting closer to full. If they really are at 3.4v when the
charger it cut off then they aren't too far behind.

You might just want to put a resistor across the few high cells and then
run the charger again. That would likely be cheaper and you know your
charger won't mind.

On Sunday, June 17, 2012, Ben Jarrett wrote:

>
>
>
> So in my case, all 50 of my Calb 130 Ah cells started at 3.2 volts.  The
> charger was
> setup by the factory for my pack (supposedly).  It has a sticker on the
> side saying
> it's for 180V max LiFePo4 pack.  So I charge my pack and here's what
> happens:
>
> * After charging for a few hours on 120V (about 7 amps into the pack), I
> have some
>  cells that start reaching 3.5 Volts.
> * At this point, the mini bms starts shunting these cells.  I'm still
> getting
>  around 7amps into the pack.
> * If one of these cells hits 3.6 Volts, the mini bms shuts off the charger
>  (that's what's happening now).
> * For me, I have 10 cells that are shunting when the mini-bms turns off
> the charger.
> * Most of the other cells are at 3.4V (for Lithium, it's hard to know what
> the SOC
>  is from the voltage, but they should be pretty well charged).
>
> So what I'd like to do is:
> * Charge my pack until the mini bms shuts off the charger.
> * Bypass the 10 early cells (I have a 2 gage bypass cable for emergencies)
> * Start the charger again
> * Allow the mini bms to shut off the charger
> * See if I'm top balanced yet.
>
> Can I damage anything if I hook up my Elcon 2kW charger (that's been
> "programmed"
> for 50 cells) to 40 cells and let it charge?   This is one question I
> still don't have
> an answer for.  Maybe someone out there knows.
>
> I still could get a single cell charger to finish things off, but I'm
> looking for
> a good way to get closer.
>
> thanks!
> -ben
>
>
> On Jun 17, 2012, at 11:28 AM, Lee Hart wrote:
>
> > On 6/16/2012 8:18 PM, Mike Nickerson wrote:
> >> I have similar cells, BMS and charger to Ben's.  The system is not as
> >> intelligent as you describe.  The charger decides on its own (from the
> >> current charging voltage and its built-in program) when to switch to
> lower
> >> current.  It won't do that unless the cells are pretty well matched.
>  The
> >> BMS doesn't have any communication with the charger about cells at the
> >> shunting level.
> >
> > Hmm... that's a problem. Do you know what its charging algorithm is? My
> > thought would be to wire in a voltmeter and ammeter, and *watch* what
> > the charger actually does. I often find that what the manufacturer
> > claims does not agree with what it *actually* does!
> >
> > Until that data is available, let's assume it has the simplest algorithm
> > that would barely work:
> >
> > a. Charge at maximum current until it reaches V volts.
> > b. Charge at constant V volts until the current falls to I amps.
> > c. Shut off.
> >
> > This works if the cells are all very well matched and top-balanced. At
> > full charge, the charger assumes that (for example) V = 365v means you
> > have 100 cells at 3.65v each.
> >
> > But if the cells are mismatched, some cells will go overvoltage while
> > others are still undervoltage. The total may be 365v; but individual
> > cells might range from 3.3v to 4.3v. 3.3v is nowhere near full, and 4.3v
> > is well into overcharge!
> >
> > You can add a BMS that shunts some low current around any cell that goes
> > over some "full" voltage (say, 3.65v). Let's say it can shunt 1 amp. But
> > if the charger sees less than 365v for the pack as a whole, it can still
> > be pumping out more current (say, 2 amps). It just overpowers the shunt
> > regulator; 1 amp goes through the shunt regulator and 1 amp through the
> > cell, so it *still* overcharges and overvoltages the cell.
> >
> > This is why you need some way to insure that the charger is at a low
> > current when the regulators start to bypass. The charger should have an
> > algorithm that automatically cuts back to a low current well before it
> > reaches its voltage limit. Or, you need to add some other method to
> > limit charging current when any shunt regulator is on. Then when *all*
> > cells have reached their voltage limit, you can shut off the charger.
> >
> > If your charger has no such means to limit its current, you can add a
> > relay that switches a resistor in series to limit the current. When the
> > first BMS regulator turns on, it turns this relay off. The resistor is
> > chosen to limit the current to whatever the regulators can safely
> > bypass. (A light bulb works well as a resistor, because they naturally
> > act as current limiters).
> >
> > If the charger doesn't already have a shut-off timer, you should add one
> > of these as well. The simplest type is a 0-12 hour mechanical timer
> > (Intermatic etc.). It fits in a normal electrical switch box, and has a
> > knob that you twist to set the maximum time. It has 240vac 20amp
> > contacts that automatically shut off the AC input to the charger at the
> > end of the time.
> >
> >> The MiniBMS system and Elcon charger combination will work fine once the
> >> cells are balanced.
> >
> > If the cells are balanced, the BMS shouldn't be doing anything.
> >
> > If the cells aren't balanced, isn't the BMS supposed to balance them? If
> > it doesn't work when they are unbalanced, what is the purpose of this
> BMS?
> >
> > --
> > *BE* the change that you wish to see in the world.
> >       -- Mahatma Gandhi
> > --
> > 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<http://lists.sjsu.edu/mailman/listinfo/ev>



--
David D. Nelson
http://evalbum.com/1328
http://2003gizmo.blogspot.com
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Re: charger question - bypassing batteries

Cor van de Water
In reply to this post by Cruisin
If the charger never reaches its 80% indication
because one of the cells gets too high and the
BMS shuts the charger off, then I would expect that
it will help to set the charger voltage *lower* until
it is the *charger* that shuts off the charging, not
the emergency shutoff from the BMS because a cell goes
over limit.
In fact, with the charger at (much) lower voltage
you would allow any high cells to be shunted for a
while by the BMS so all high cells are pushed to lower SoC
until the point that you might be able to turn the
charger up a little when after a long period of shunting
all cells stop shunting because the total pack voltage
is divided more equally and all cells stay below the
shunting voltage. If that happens then you can turn the
charger up just a tad until you reach the point that
the lowest cell is almost shunting while all other cells
are barely shunting. That gives the lowest voltage and
the lowest waste of energy while making sure that all
of your pack will get balanced if you charge long enough.
It has the risk of over-charging cells at too low current
so it is wise to not charge to this point very often,
only when you absolutely need the max energy from your pack
(very long trip) or an occasional balance charge, once
a month or so. At all other charges you might want to
shut off the charger when it reaches 80% SoC or so to
get the longest life from your pack.

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 Cruisin
Sent: Saturday, June 16, 2012 5:45 AM
To: [hidden email]
Subject: Re: [EVDL] charger question - bypassing batteries

Change the algorithm in the charger to the next higher voltage and
recharge letting the BMS control the charger. The charger is shutting
off too soon.

--
View this message in context:
http://electric-vehicle-discussion-list.413529.n4.nabble.com/charger-que
stion-bypassing-batteries-tp4655708p4655722.html
Sent from the Electric Vehicle Discussion List mailing list archive at
Nabble.com.

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Re: charger question - bypassing batteries

Lee Hart
In reply to this post by Ben Jarrett
Ben Jarrett wrote:
> So in my case, all 50 of my Calb 130 Ah cells started at 3.2 volts.

That means they were initially somewhere between 20% and 80% state of
charge.

> The charger was setup by the factory for my pack (supposedly)...
> for 180V max LiFePo4 pack.

With 50 cells, that's 3.6v per cell; a reasonable "full" end point.

> * After charging for a few hours... some cells reach 3.5 Volts.
> * At this point, the mini bms starts shunting these cells.\
>   I'm still getting around 7amps into the pack.

It is desirable for the charger to cut back its current. But it sounds
like it just stays at 7 amps. The mini-BMS can't bypass 7 amps, so it
can't stop these cells from continuing to charge. Very little balancing
is going on.

> * If one of these cells hits 3.6 Volts, the mini bms shuts off the
>   charger (that's what's happening now).

It's basically saying "I can't slow down the charger or stop these cells
from overcharging, so I'll shut the charger down completely. It saves
your batteries; but does little or no balancing.

> * I have 10 cells that are shunting when the mini-bms turns off the charger.
> So what I'd like to do is:
> * Charge my pack until the mini bms shuts off the charger.
> * Bypass the 10 early cells (I have a 2 gauge bypass cable for emergencies)
> * Start the charger again
> * Allow the mini bms to shut off the charger
> * See if I'm top balanced yet.

This would be a tedious and error-prone way to do it. It would be easy
to make a mistake and leave it on too long. 180v across 40 cells is 4.5v
each, which would murder them!

You have a BMS; you just need to get things set up so it actually works.
Find some way to get the charging current down low enough so the
mini-BMS can bypass it to stop the "full" cells from charging any more.
The low cells can then continue charging for long enough to bring them
into balance.

For example, stick an ordinary 120v 100 watt tungsten light bulb in
series with the charger output. It will limit the current to under 1
amp. Then the BMS can run for long enough to finish charging the low
cells, without overcharging the high cells and having to shut down the
charger too early.

> Can I damage anything if I hook up my Elcon 2kW charger (that's been "programmed"
> for 50 cells) to 40 cells and let it charge?

The charger won't be hurt; it will current limit at its maximum charging
current (7 amps). However, it will still be trying to drive the pack up
to 180v. The voltage will keep rising until it does! That would destroy
your CALB cells.

If you left the BMS connected, it would still shut off the charger when
any cell reached 3.6v. But you'd still be getting no balancing action,
so you haven't corrected the problem.

Here's an analogy. Suppose you're trying to fill gallon milk jugs with a
garden hose. The goal is to exactly fill each one; not leave it 80%
full, or overfill it so you flood the floor.

You can't do this by running the hose at full blast, and then suddenly
shutting it off completely. As the water nears the top, the bubbling and
swirling water will foam out the top and make a mess. Or, if you shut
off before any water foams out the top, then when the air bubbles out,
you're left with a jug only perhaps 80-90% full.

You need *slow down* the hose to a trickle as it nears full. Then you
can see where you are, and stop when you *just* reach full. That way,
you can precisely fill each jug to the same level.

--
First they ignore you; then they mock you; then they fight you; then you
win.
        -- Mahatma Gandhi
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net

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Re: charger question - bypassing batteries

Mike Beem
When I set up my 40 CALB 100Ah cells with miniBMS, it took me almost 2
weeks of charging to get the whole pack to the point that all cells were
above 3.5 v (all red LED's lit) at the same time. I used a variety of
chargers from an adjustable power supply (one that Dimitri recommended)
which can charge individual cells, or small groups of cells, a 12v charger,
and a 24v charger for groups of cells. I would use a 12v DC 50 watt bulb
and a 12v load tester to drain the first ones to light up while charging.
Once they all reached that point, I haven't had to do anything.  I just
periodically check end of charge to make sure that they still all light up
before one hits the shut off point. It has been a little over 6 months, and
I haven't seen any real variation yet; cells are all within 0.01 of each
other.
Michael B

On Mon, Jun 18, 2012 at 12:30 PM, Lee Hart <[hidden email]> wrote:

> Ben Jarrett wrote:
> > So in my case, all 50 of my Calb 130 Ah cells started at 3.2 volts.
>
> That means they were initially somewhere between 20% and 80% state of
> charge.
>
> > The charger was setup by the factory for my pack (supposedly)...
> > for 180V max LiFePo4 pack.
>
> With 50 cells, that's 3.6v per cell; a reasonable "full" end point.
>
>
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Re: charger question - bypassing batteries

corbin dunn
In reply to this post by Ben Jarrett

On Jun 17, 2012, at 9:55 AM, Ben Jarrett <[hidden email]> wrote:

>
> So what I'd like to do is:
> * Charge my pack until the mini bms shuts off the charger.
> * Bypass the 10 early cells (I have a 2 gage bypass cable for emergencies)
> * Start the charger again
> * Allow the mini bms to shut off the charger
> * See if I'm top balanced yet.

You don't really want to do that...you would have to have a different charger to charge 40 cells vs 50 cells (or to reprogram the charger's max voltage - which I don't think you can do to yours, but you can on a Manzanita Micro PFC charger).

Just charge all the other cells that are low. Or, manually "shunt off" current on the high cells to get them lower. However, I haven't done the second option, so I'm not sure what the best way to do it is (maybe a light bulb).

corbin

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Re: charger question - bypassing batteries

Mike Nickerson
In reply to this post by Lee Hart
Hi Lee,

I agree that the MiniBMS isn't the most efficient (and can't do a very
effective job of balancing a pack that isn't balanced), but it can do a good
job of keeping a pack balanced.  It also does a reasonable job of protecting
the pack until you get it balanced.

The issue preventing the MiniBMS from cutting back the charger is that the
main control board doesn't know about that situation.  As far as I can tell,
the only communication between the cell monitors and the main control board
is the current loop daisy-chained between all the cells.  When a cell
monitor sees that its cell is outside specs (high or low), it cuts that
current loop and informs the control board.  However, there is no
communication when a cell monitor starts to shunt.

Once the pack is balanced and the charger sees the pack voltage that causes
it to taper back on the current, things work much better.  You may have
10-15 minutes time for the shunts to do their job and keep things balanced.
It took me a couple of tries to get the pack balanced enough for this to
happen.  Once the pack was balanced enough that the charger terminated the
charge, I have seen it stay that way for several months.

When I took my pack apart last winter, it got out of balance again.  That's
because the cells on the ends no longer have their BMS firmly attached and
they end up with a higher state of charge if the BMS isn't connected for a
while.  However, a couple of passes with my small charger and I had the pack
back in balance.  It has stayed in balance again.

Mike

> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]] On
> Behalf Of Lee Hart
> Sent: Sunday, June 17, 2012 10:28 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] charger question - bypassing batteries
>
> On 6/16/2012 8:18 PM, Mike Nickerson wrote:
> > I have similar cells, BMS and charger to Ben's.  The system is not as
> > intelligent as you describe.  The charger decides on its own (from the
> > current charging voltage and its built-in program) when to switch to
> > lower current.  It won't do that unless the cells are pretty well
> > matched.  The BMS doesn't have any communication with the charger
> > about cells at the shunting level.
>
> Hmm... that's a problem. Do you know what its charging algorithm is? My
> thought would be to wire in a voltmeter and ammeter, and *watch* what
> the charger actually does. I often find that what the manufacturer claims
> does not agree with what it *actually* does!
>
> Until that data is available, let's assume it has the simplest algorithm
that
> would barely work:
>
> a. Charge at maximum current until it reaches V volts.
> b. Charge at constant V volts until the current falls to I amps.
> c. Shut off.
>
> This works if the cells are all very well matched and top-balanced. At
full
> charge, the charger assumes that (for example) V = 365v means you have 100
> cells at 3.65v each.
>
> But if the cells are mismatched, some cells will go overvoltage while
others
> are still undervoltage. The total may be 365v; but individual cells might
> range from 3.3v to 4.3v. 3.3v is nowhere near full, and 4.3v is well into
> overcharge!
>
> You can add a BMS that shunts some low current around any cell that goes
> over some "full" voltage (say, 3.65v). Let's say it can shunt 1 amp. But
if the
> charger sees less than 365v for the pack as a whole, it can still be
pumping
> out more current (say, 2 amps). It just overpowers the shunt regulator; 1
> amp goes through the shunt regulator and 1 amp through the cell, so it
> *still* overcharges and overvoltages the cell.
>
> This is why you need some way to insure that the charger is at a low
current
> when the regulators start to bypass. The charger should have an algorithm
> that automatically cuts back to a low current well before it reaches its
> voltage limit. Or, you need to add some other method to limit charging
> current when any shunt regulator is on. Then when *all* cells have reached
> their voltage limit, you can shut off the charger.
>
> If your charger has no such means to limit its current, you can add a
relay
> that switches a resistor in series to limit the current. When the first
BMS
> regulator turns on, it turns this relay off. The resistor is chosen to
limit the
> current to whatever the regulators can safely bypass. (A light bulb works
> well as a resistor, because they naturally act as current limiters).
>
> If the charger doesn't already have a shut-off timer, you should add one
of
> these as well. The simplest type is a 0-12 hour mechanical timer
(Intermatic
> etc.). It fits in a normal electrical switch box, and has a knob that you
twist to
> set the maximum time. It has 240vac 20amp contacts that automatically shut
> off the AC input to the charger at the end of the time.
>
> > The MiniBMS system and Elcon charger combination will work fine once
> > the cells are balanced.
>
> If the cells are balanced, the BMS shouldn't be doing anything.
>
> If the cells aren't balanced, isn't the BMS supposed to balance them? If
it

> doesn't work when they are unbalanced, what is the purpose of this BMS?
>
> --
> *BE* the change that you wish to see in the world.
> -- Mahatma Gandhi
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart at earthlink.net
>
> _______________________________________________
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