battery charge voltage

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battery charge voltage

jonglauser
Over the Holiday I tried to run an equalize charge on my 96V lead
pack. I have an attached garage at ~50 deg. I set the battery current
to 5A and the voltage to 120V (I think. The knob is not graduated in
voltage. It's a Russco charger). It started up at 5A and the voltage
slowly rose. After all day charging it was still doing 5A and 111V. I
thought maybe my pack was lower SOC than I though and left it going
(there was no sulfer smell)

After 24 hours it was still at 5A 111V. Still no smell, and I couldnt
hear bubbling, though I didnt listen very closely.

I cant seem to get the pack up to the same charge voltage I used to.
Even if I raise the current to 10 battery amps I only ever see the
pack go to 113V or so on my emeter and a cheap handheld meter.

Does this indicate a bad cell or two?

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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Re: battery charge voltage

Roland Wiench
Hello Jon,

Before doing a equalizing charge, you must first charge the battery at the
normal charge rate at the C/10 rate which is the ampere-hour rating of the
battery divided by 10.

The normal charge rate in some batteries range from 7.2 to 7.4 volts for a 6
volt or 14.4 to 14.8 for 12 volts per battery at 80F.  A battery at 50F
needs to have it voltage increase 0.028 per cell per every 10 degrees drop
below 80 F.

So your 96 volt pack has 32 cells.  Then 0.028 volts x 32 equals a 0.896
volt increase per every 10 degrees drop below 80F.  At 50F, you have three
10 degrees drop, so 0.896 x 3 = 2.679 volt increase.

Lets say you normal charge for your batteries 118.4V at 80F, then at 50F,
you add 2.679 volts for a 121.079 volt charge.

A equalization charge for a 96 volt pack is 7.8 volts per 6 volts or 15.6
volts per 12 volt for a total pack charge voltage of 124.8 volts at 80F.

At 50F you add 2.579V to 124.8V for a equalization charge of 127.379 volts.

If a battery is deeply discharge at a low temperature, then the 5 amp charge
will take for ever to rise the voltage.  One time, I try to charge a 300 AH
2700 lb pack at 5 amps at a temperature of 60F and 8 your later, it may have
risen a bit.

To do a equalization charge, first charge the batteries up using the correct
C/10 rate to the maximum normal charge voltage which will be about 90 to 95%
State of Charge.  Then reduce the ampere if the charge has not done so after
it reaches the maximum temperature corrected voltage.

Next increase the voltage to the correct equalization charge voltage which
is temperature corrected using the above formula.

Now if you have done all of the above, and the pack voltage is low, than
take a voltage reading of each battery and a electrolyte reading of each
cell.   A very low electrolyte reading in one cell as compare to the others,
either means the cell has minutes shorts and the charge voltage has been
shunting that one cell.

Or this could be cause by the electrolyte being diluted by over watering
which is a normal happening.  If these batteries were true traction
batteries, you could also read the voltage of each cell because of the
expose links between cells.

Now if the voltage is reading normal in that one cell, but the electrolyte
is low, then it's a diluted electrolyte which can be chemical balance. If
the voltage reads low, then either A high resistance cell cause by a
sulfated cell or minute shorts between the plates.

You could take the EV to a battery shop, which they may have several types
of battery capacity test equipment.  I have a load tester that is design for
deep cycle batteries that puts on a 75 amp load.  You then calculated the
amount of time it drops in voltage in reference to the Reserve Minutes at 75
amps that is listed for that battery.

Roland




----- Original Message -----
From: "Jon Glauser" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Monday, January 04, 2010 11:04 AM
Subject: [EVDL] battery charge voltage


> Over the Holiday I tried to run an equalize charge on my 96V lead
> pack. I have an attached garage at ~50 deg. I set the battery current
> to 5A and the voltage to 120V (I think. The knob is not graduated in
> voltage. It's a Russco charger). It started up at 5A and the voltage
> slowly rose. After all day charging it was still doing 5A and 111V. I
> thought maybe my pack was lower SOC than I though and left it going
> (there was no sulfer smell)
>
> After 24 hours it was still at 5A 111V. Still no smell, and I couldnt
> hear bubbling, though I didnt listen very closely.
>
> I cant seem to get the pack up to the same charge voltage I used to.
> Even if I raise the current to 10 battery amps I only ever see the
> pack go to 113V or so on my emeter and a cheap handheld meter.
>
> Does this indicate a bad cell or two?
>
> -Jon Glauser
> http://jonglauser.blogspot.com
> http://www.evalbum.com/555
>
> _______________________________________________
> General support: http://evdl.org/help/
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Re: battery charge voltage

Chuck Hursch-2
In reply to this post by jonglauser
I'd have to wonder if the RUSSCO is really putting any significant
current into your pack.  I presume you're reading the current meter on
the charger.  Can you verify with a clip-on ammeter or
shunt/voltage-drop whether you're actually getting any current?

Jon Glauser wrote:

> Over the Holiday I tried to run an equalize charge on my 96V lead
> pack. I have an attached garage at ~50 deg. I set the battery current
> to 5A and the voltage to 120V (I think. The knob is not graduated in
> voltage. It's a Russco charger). It started up at 5A and the voltage
> slowly rose. After all day charging it was still doing 5A and 111V. I
> thought maybe my pack was lower SOC than I though and left it going
> (there was no sulfer smell)
>
> After 24 hours it was still at 5A 111V. Still no smell, and I couldnt
> hear bubbling, though I didnt listen very closely.
>
> I cant seem to get the pack up to the same charge voltage I used to.
> Even if I raise the current to 10 battery amps I only ever see the
> pack go to 113V or so on my emeter and a cheap handheld meter.
>
> Does this indicate a bad cell or two?
>
> -Jon Glauser
> http://jonglauser.blogspot.com
> http://www.evalbum.com/555
>
> _______________________________________________
> General support: http://evdl.org/help/
> Unsubscribe: http://www.evdl.org/help/index.html#usub
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archive / Forum: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>


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Re: battery charge voltage

jonglauser
On Mon, Jan 4, 2010 at 2:21 PM, Chuck Hursch <[hidden email]> wrote:
> I'd have to wonder if the RUSSCO is really putting any significant
> current into your pack.  I presume you're reading the current meter on
> the charger.  Can you verify with a clip-on ammeter or
> shunt/voltage-drop whether you're actually getting any current?

Both the Russco meter and my e-meter read the same for 5A and 10A

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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Re: battery charge voltage

Cor van de Water
When the voltage is not rising for hours then they should be "full".
What is the Ah capacity?
Your 5A charger may be much below the C/10 that results in the
charge voltages that Roland mentions.
Older batteries and low current chargers have caused
"forever charging" events in the past, where a charger
failed to reach a set point for going from bulk to finish
charging.
Unless your batteries were severely under-charged, stuffing
120Ah into them will likely bring them up to full and the
best way to check is either to listen very closely and/or
in silent area, if you have a stethoscope you can put the
receiver against the (flat) side of the battery case so you
can clearly hear the bubbling.
If you have no stethoscope, you may even be able to use a
flexible hose to "hear" near the battery, especially near
the fill caps (where the gasses can escape) and hold the other
side of the hose near your ear.

To check for bad cells, you simply take a voltmeter to the pack
while charging and measure each of the batteries. If one is
2.3V lower than the others, one cell is shorted.
(The Russco is not isolated, I think so be careful when
measuring - AC grid power is present in addition to DC)
111V / 48 cells = 2.31V per cell.
If you feel your battery cases, do they feel warm?
Heat production in a battery is a sure sign of a
full battery which is turning charge energy into heat
because it cannot be used to charge the cells any further.
Also, heating causes the battery voltage to drop.

When I used a 2A charger to slowly charge my 110Ah pack
(I quickly added a second unit to go to 4A) the voltage
would actually hit the maximum 390V (15V per battery)
but soon after that drop to 380V (14.6V per battery)
due to the batteries warming up when they got full.

Regards,

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 Jon Glauser
Sent: Tuesday, January 05, 2010 4:00 AM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] battery charge voltage

On Mon, Jan 4, 2010 at 2:21 PM, Chuck Hursch <[hidden email]> wrote:
> I'd have to wonder if the RUSSCO is really putting any significant
> current into your pack.  I presume you're reading the current meter on

> the charger.  Can you verify with a clip-on ammeter or
> shunt/voltage-drop whether you're actually getting any current?

Both the Russco meter and my e-meter read the same for 5A and 10A

-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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Re: battery charge voltage

jonglauser
Thanks to everyones suggestions. Last night I logged to my emeter and
setup the charger to run full current.

I hit a peak voltage of 114.5V and a peak current of 15.6A

The current started out high and linearly reduced for almost 2 hours.
Then it hit a knee at about 13A and parabolicly dropped to about 10A
over the next hour. At about the same knee the voltage leveled off
after raising linearly at 113.6V, then slowly raised to its peak of
114.6 over the next hour. This looks great, and I think I need to
adjust my charger voltage down to 114V to get this beautiful charge
profile. After this, the current then rose parabolicly to 14A and
slowly rose thereafter while the voltage fell back down to about 110V.

Total time to reach charge was about 3.5 hours (I usually pull out 3-4 kWh)

My only concern is the low voltage. I dont have a thermometer, but I
dont think my pack was at 80F by this time.
I have the file available (10MB) if anyone really wants it.

I had measured the individual batteries under charge previously. I
might have a bad cell, but I dont have the numbers in front of me.
If I have a bad cell, would it be best to replace the battery or try
to live with it until it goes really bad?


-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555



On Tue, Jan 5, 2010 at 7:41 AM, Cor van de Water <[hidden email]> wrote:

> When the voltage is not rising for hours then they should be "full".
> What is the Ah capacity?
> Your 5A charger may be much below the C/10 that results in the
> charge voltages that Roland mentions.
> Older batteries and low current chargers have caused
> "forever charging" events in the past, where a charger
> failed to reach a set point for going from bulk to finish
> charging.
> Unless your batteries were severely under-charged, stuffing
> 120Ah into them will likely bring them up to full and the
> best way to check is either to listen very closely and/or
> in silent area, if you have a stethoscope you can put the
> receiver against the (flat) side of the battery case so you
> can clearly hear the bubbling.
> If you have no stethoscope, you may even be able to use a
> flexible hose to "hear" near the battery, especially near
> the fill caps (where the gasses can escape) and hold the other
> side of the hose near your ear.
>
> To check for bad cells, you simply take a voltmeter to the pack
> while charging and measure each of the batteries. If one is
> 2.3V lower than the others, one cell is shorted.
> (The Russco is not isolated, I think so be careful when
> measuring - AC grid power is present in addition to DC)
> 111V / 48 cells = 2.31V per cell.
> If you feel your battery cases, do they feel warm?
> Heat production in a battery is a sure sign of a
> full battery which is turning charge energy into heat
> because it cannot be used to charge the cells any further.
> Also, heating causes the battery voltage to drop.
>
> When I used a 2A charger to slowly charge my 110Ah pack
> (I quickly added a second unit to go to 4A) the voltage
> would actually hit the maximum 390V (15V per battery)
> but soon after that drop to 380V (14.6V per battery)
> due to the batteries warming up when they got full.
>
> Regards,
>
> 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 Jon Glauser
> Sent: Tuesday, January 05, 2010 4:00 AM
> To: Electric Vehicle Discussion List
> Subject: Re: [EVDL] battery charge voltage
>
> On Mon, Jan 4, 2010 at 2:21 PM, Chuck Hursch <[hidden email]> wrote:
>> I'd have to wonder if the RUSSCO is really putting any significant
>> current into your pack.  I presume you're reading the current meter on
>
>> the charger.  Can you verify with a clip-on ammeter or
>> shunt/voltage-drop whether you're actually getting any current?
>
> Both the Russco meter and my e-meter read the same for 5A and 10A
>
> -Jon Glauser
> http://jonglauser.blogspot.com
> http://www.evalbum.com/555
>
> _______________________________________________
> General support: http://evdl.org/help/
> Unsubscribe: http://www.evdl.org/help/index.html#usub
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> http://lists.sjsu.edu/mailman/listinfo/ev
>
>
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>

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Re: battery charge voltage

EVDL Administrator
On 5 Jan 2010 at 10:13, Jon Glauser wrote:

> Last night I logged to my emeter and
> setup the charger to run full current.
>
> I hit a peak voltage of 114.5V and a peak current of 15.6A
>
> The current started out high and linearly reduced for almost 2 hours.
> Then it hit a knee at about 13A and parabolicly dropped to about 10A
> over the next hour. At about the same knee the voltage leveled off
> after raising linearly at 113.6V, then slowly raised to its peak of
> 114.6 over the next hour. This looks great, and I think I need to
> adjust my charger voltage down to 114V to get this beautiful charge
> profile. After this, the current then rose parabolicly to 14A and
> slowly rose thereafter while the voltage fell back down to about 110V.

Maybe I'm missing something but this charge profile doesn't sound so
beautiful to me.  It sounds like you have a simple taper charger, a more or
less voltage-regulated power supply with its current mainly limited by the
resistance of its wiring.  I would have thought that a Russco would be more
controlled than this.  Perhaps I'm misunderstanding what you wrote.

I don't like that last sentence at all.  It suggests that you're driving the
battery toward or into thermal runaway.  A finish current of over 14 amps is
WAY too high, unless your battery capacity is in the range of 700 amp hours.

If you're using flooded batteries, you're not charging them to

My first inclination is to say that the last sentence above is troubling -
at first glance it seems as if you may be driving the battery into thermal
runaway, with the current rising as the voltage falls.  But the first part
sounds like you're not reaching a high enough voltage, and your charger is
limiting voltage too early.  

If you're charging a 96v pack of flooded batteries, the voltage should rise
to 115.2v to 118.4v, then level off as current begins to fall.  When current
falls to C/50 (the battery's amp hour capacity expressed in amps, divided by
50) with the voltage still stable, the charge is essentially complete.  For
a 220ah battery this is 5.5 amps.  You might then have an equalization phase
(not on every cycle) where you hold the current at 5.5 amps or perhaps less
for a couple of hours, or until the voltage stops rising, or until the
voltage hits 120 (15vpc).

Note that these voltage should be compensated for INTERNAL battery
temperature, if it's not at about 20 deg C.  Reduce voltage 0.003 volts per
cell (0.144v for your 96v battery) for each degree C above 20 deg C, and
vice versa for each degree below 20 deg C.

Also, old batteries usually can't achieve as high a voltage as they could
when new.  This is a normal part of the aging process.  My voltage isn't as
high as it was when I was 25, either.  ;-)

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: battery charge voltage

EVDL Administrator
Oops, ack, sorry, I accidentally hit the send button before I finished
rewriting that post to fix my first impressions.  Let's belay those first
three paragraphs and try this again.

=====

> Last night I logged to my emeter and setup the charger to run full
> current.
>
> I hit a peak voltage of 114.5V and a peak current of 15.6A
>
> The current started out high and linearly reduced for almost 2 hours.
> Then it hit a knee at about 13A and parabolicly dropped to about 10A
> over the next hour. At about the same knee the voltage leveled off
> after raising linearly at 113.6V, then slowly raised to its peak of
> 114.6 over the next hour. This looks great, and I think I need to
> adjust my charger voltage down to 114V to get this beautiful charge
> profile. After this, the current then rose parabolicly to 14A and
> slowly rose thereafter while the voltage fell back down to about 110V.

My first inclination is to say that the last sentence above is troubling -
at first glance it seems as if you may be driving the battery into thermal
runaway, with the current rising as the voltage falls.  But the first part
sounds like you're not reaching a high enough voltage, and your charger is
limiting voltage too early.  

If you're charging a 96v pack of flooded batteries, the voltage should rise
to 115.2v to 118.4v, then level off as current begins to fall.  When current
falls to C/50 (the battery's amp hour capacity expressed in amps, divided by
50) with the voltage still stable, the charge is essentially complete.  For
a 220ah battery this is 5.5 amps.  You might then have an equalization phase
(not on every cycle) where you hold the current at 5.5 amps or perhaps less
for a couple of hours, or until the voltage stops rising, or until the
voltage hits 120 (15vpc).  

Note that these voltage should be compensated for INTERNAL battery
temperature, if it's not at about 20 deg C.  Reduce voltage 0.003 volts per
cell (0.144v for your 96v battery) for each degree C above 20 deg C, and
vice versa for each degree below 20 deg C.  

Also, old batteries usually can't achieve as high a voltage as they could
when new.  This is a normal part of the aging process.  My voltage isn't as
high as it was when I was 25, either.  ;-)  

David Roden - Akron, Ohio, USA
EVDL Administrator

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Re: battery charge voltage

jonglauser
In reply to this post by EVDL Administrator
Thanks for responding David. I was hoping someone would speak up.
You're right, it's not charging correctly. I dont know why however and
have been seeking advise. My guess is a bad battery/cell. Aside from
buying a paktraker I'm having a hard time finding which one is bad. I
have a suspicion though, based on historical statistical data of
battery voltages after a drive. I have 2 that are usually a bit lower
voltage than the rest. Not a lot, but consistent. They pack is 14
months old, used 5-6 days/week, average 13 miles/day. (I just realized
my EValbum mileage is wrong)

I'm not sure how old my Russco charger is, but I suspect quite old. I
bought it with the car, both used. It could be the charger but I dont
have the money to randomly guess at what to fix/replace. If it's a
battery, I am in the prorated warranty period and can get a
replacement.

I know what the charge profile SHOULD do, but when it doesnt I get lost.

I have a graph from 24 Oct 08, the month I bought the pack:
http://picasaweb.google.com/lh/photo/iTk1apLY-Bt243uXnq7LmA?feat=directlink


my run last night:
http://picasaweb.google.com/lh/photo/4yQlHPprMVe9g-lTfI-mxg?feat=directlink
http://picasaweb.google.com/lh/photo/ldXjBxfY3MKZyqSgVCNNxw?feat=directlink



-Jon Glauser
http://jonglauser.blogspot.com
http://www.evalbum.com/555

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