# Voltage durring charging



## frodus (Apr 12, 2008)

Your pack is what we call "out of balance".... i.e. the cells all have different State of charges, hence showing different charge voltages.

How long has it been since you individually charged each battery?

Stop immediately, get a 12V charger and individually charge each battery until full. Don't bulk charge again until this is done.

Did you parallel the batteries first? or parallel the two strings of 12? You should parallel the pack at the 12V battery level, so 2 in parallel and then 12 of those in series.

Are the batteries all the same kind? age? model?


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## J-Ro (Aug 9, 2012)

I individually charged each battery before hooking them all together a few weeks ago.

The age and health of each battery does vary a bit becasue i got them on the cheap 2nd hand but they were all pretty lightly used.

Ive driven the vehicle around on a few test drives and have recharged them with the 144v charger probably 5 times since the indivdual charging.

I have paralleled the 2 strings of 12 rather than parralleled pairs and series them together. These seemed like the easiest solution. Is it not a good way to go? Is this method more of a problem during discharge or charge? If charging I have a pretty easy method of removing each half of the pack from the system.



frodus said:


> Your pack is what we call "out of balance".... i.e. the cells all have different State of charges, hence showing different charge voltages.
> 
> How long has it been since you individually charged each battery?
> 
> ...


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## frodus (Apr 12, 2008)

Parallel sets stay more balanced, it's usually a better idea to parallel first, then series.

If they're all about the same age, then something may be wrong... are any damaged? Any way you could go to an auto store and have them test each battery to see if any are bad?

If you JUST charged them all, they shouldn't go out of balance after 5 charge/discharges.

Did you tap off of either pack at all?


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## J-Ro (Aug 9, 2012)

When I picked up all the batteries I used a battery tester on them all and they all tested good at that time (which was 5 month ago now).

I could run the tester across them again and see what they say.

Now that I have the charger unplugged I'm showing about 13.10 volts per battery (the ones I can easily reach anyways) without much variance.

I'll have to think about how I can reconnect the batteries to get the parrallel action first but it sounds like you dont think this is the immediate issue?


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## J-Ro (Aug 9, 2012)

I took the truck for a drive to pull a bunch of current out of the batteries to do a bit of a load test of sorts.

Immediatly after pulling 72 aH out of the pack (theres 230aH in total) I measured the voltages of each battery:

String 1:
(Most Negative) 10.17, 12.33, 12.40, 12.32, 12.13, 12.32, 12.24, 12.15, 12.40, 12.40, 12.34, 12.41 (Most Positive)

String 2:
(Most Negative) 12.06, 12.14, 12.20, 12.19, 12.19, 12.14, 12.11, 12.20, 12.13, 12.03, 12.13, 12.18 (Most Positive)

Now I'm not sure this actually tells me anything does it? If i am unsure of the battery balance (although in theory they should have been good). Should I do individual battery charges and then do a similar test?

If i trust the charge was balanced then i guess this shows me that most neg in string one is shot and there are several batts in string #1 that are more healthy than the rest. 

Would everyone agree with this? Thanks!


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## major (Apr 4, 2008)

J-Ro said:


> I took the truck for a drive to pull a bunch of current out of the batteries to do a bit of a load test of sorts.
> 
> Immediatly after pulling 72 aH out of the pack (theres 230aH in total) I measured the voltages of each battery:
> 
> ...


When you run two series strings in parallel you don't know if the current shares equally between the two, both in charge and discharge. So the bad battery (#1) in string 1 could have caused string 2 to contribute higher current under load and therefore deliver more Ah during your test run. In other words, discharging more than string 1 resulting in higher battery voltages.

Take a look at this thread: http://www.diyelectriccar.com/forums/showthread.php?t=78826 You can see the variation in battery capacity. Also notice the actual charge (Ah) available from the load test.


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## J-Ro (Aug 9, 2012)

OK great info there!

So would you guys recommend that i replace the ~10v battery with another (I have a spare of the same relative age/health as the rest), individual charge them all back to full and do a similar driving road test and recheck their voltages?

I'm also gathering that reconfiguring my pack to a series of 12 parallel pairs would be the smartest bet correct?

For selecting pairs should I run an actual load test on all the batteries and then pick similar health batteries as pairs?

Thanks for the help!


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## Sunking (Aug 10, 2009)

You just discovered the huge flaw of parallel batteries and extremely critical with any lead acid batteries. Lead Acid batteries should never be connected in parallel. If you need 200 AH, then buy 200 AH cells and connect all in series. 

Even worse is AGM batteries as most cannot have an EQ charge applied to them. Those that can be EQ require careful temperature monitoring during the process.


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## kennybobby (Aug 10, 2012)

Maybe you can just leave your 2 series strings in place and use them one at a time instead of trying to go parallel--switch over to the second series string when the first runs low.


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## EVfun (Mar 14, 2010)

Looks pretty simple. You have a dud in string 1 and string 2 is doing most of the work when driving so it is at a lower state of charge. That said, the rest of you batteries look pretty good. 

It is difficult to charge series strings of sealed lead acid batteries without damaging them. Individual shunt regulators used to be commonly seen in packs. You will have to finish charge slowly to keep from damaging some over time.


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## J-Ro (Aug 9, 2012)

I really like the idea of running half the pack to work and the other half of the pack on the drive home...then maybe I could alternate every other day since its about 31 amp hours to work and 41 amp hours coming home.

If i were buying brand new batteries I'd definately follow the advice of buying batteries of the proper AH rating however I am able to pick up lightly used batteries from my work for $5 to $9 a peice so I'm really just looking for the best way to utilize the resource I've got.

If charging series sealed batteries is difficult, what should I do to reduce the risk? commonly check that the individual battery voltages are similar during charge? or ?

Thanks!


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## J-Ro (Aug 9, 2012)

so i disconnected the 2 packs and began to charge string 2 by itself...the string with apparently all good batteries.

Several times i checked the voltages of all 12 batteries and they were all within about 0.15v of each other as the voltage rose. The last i checked was when they were hovering at 14.0v

The charger has now transitioned over to constant voltage I guess its called now that 175v has been reached. I measure a current of about 3 amps flowing into the batteries and the individual batt voltages have spread apart.

They are now:
(Most Negative) 15.21, 15.42, 13.96, 14.32, 14.05, 14.53, 15.65, 14.10, 15.11, 14.34, 15.16, 13.89 (Most Positive)

Why would they all be so similar up until the current is dropped down? Is this nessicarily bad considering the current is so low? Recall these are AGM batteries.


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## Sunking (Aug 10, 2009)

J-Ro said:


> If i were buying brand new batteries I'd definately follow the advice of buying batteries of the proper AH rating however I am able to pick up lightly used batteries from my work for $5 to $9 a peice so I'm really just looking for the best way to utilize the resource I've got.


OK this raises a Red Flag for me. Do you know the manufacture and model number? I suspect what you are getting is SLI batteries aka Start/Cranking batteries which is really a poor candidate for EV's



J-Ro said:


> If charging series sealed batteries is difficult, what should I do to reduce the risk?


With AGM you should be using temperature compensation type of charger. It changes the voltage set points according to the pilot cell temp. The colder the battery is, the higher the voltage set point. The biggest danger charging AGM is Thermal Run Away.


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## J-Ro (Aug 9, 2012)

Hi Sunking - These are AGM batteries intended for deep cycle use, its the application these particular batteries are produced for. I get them cheap because I work at an automotive OEM and we recycle the batteries after very little use on them...every test is with a new battery.

The batteries are manufactured by East Penn, not sure the exact model number of them.

The charger I am using is made by quick charge. it does not have a temperature input but i am using the AGM charge profile that is pre-programmed into the unit.


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## J-Ro (Aug 9, 2012)

****This was in response to a deleted post incase its confusing to read this post****

*NOT* automotive starting batteries....they are AGM Deep cycle batteries whose designed intent is to be discharged fairly low & recharged once per day in their OEM application.

I understand that lead acid is a bad technology for EVs in comparison to others but ive only got $200 invested in this battery pack. So if it performs only marginaly I consider that a win.

Since I am not an electrical engineer I am trying to learn about the charge cycle I am observing and be sure I am doing what is least detrimental to the life of the batteries...even though I got them cheap I dont want to be dumb about my setup and not care if i damage batteries.

So far i have determined 1) I had a bad battery...probably 1 bad cell. This battery has been replaced 2) I dont want parallel strings...I plan to run half the pack each half of my daily trip and during charing

What else can I learn from the information I have provided? Thanks for everyones help on this...I'm learning!


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## quickcharge (Aug 15, 2009)

That's why I deleted it, because I re-read posts.


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## kennybobby (Aug 10, 2012)

*You have probably overcharged them...*



J-Ro said:


> ....
> The charger has now transitioned over to constant voltage I guess its called now that *175v* has been reached.
> 
> They are now:
> ...


AGM's are not like flooded cells and are more sensitive to overcharging and the heat of same. They don't have provision for the out-gassing that occurs above 14.4 volts. Why did you set the voltage so high, 175/12 = 14.58. From your spread with cells above 14.4 it is likely they are damaged from overcharging. You will be able to tell if you put a load on them and the voltage collapses and they have no guts left.


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## quickcharge (Aug 15, 2009)

No, that little difference is not going to ruin your batteries. Many AGM's spec 14.7. In any case there's a window to operate in. The problem is the inherent nature of lead acids to become imbalanced in a series string, the charger has no control over it. Temp comp won't help imbalance either, unless you want to monitor each battery, even then, voltage can exceed spec. without generating much heat.


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## PStechPaul (May 1, 2012)

You can get greater effective total A-h if you run from all the batteries at once rather than 1/2 the pack at a time. For instance, if your batteries are 100 Ah and you pull 50 A (0.5C), with a Peukert of 1.222, you will get effectively 60 Ah, or 1.2 hours total. If you draw 100 A (1.0C) from each string separately, you will get 51 Ah effective capacity, or 0.514 hours from each string, and 1.03 hours total. So you lose about 20% of your range, and also probably shorten the life of the batteries.

If you can connect all the batteries in series, for 288V, the total pack draw will be reduced, and the current obviously will be the same for each battery. If the controller can handle the higher voltage, it would just run at a lower PWM to provide the same motor current, and you would have the availability of twice the previous voltage for very short bursts of torque and acceleration.

Also, the 288V would be enough for a VF controller and a three phase 230 VAC motor, if you would like to try that option. You could even use the VFD into a three phase diode bridge and adjust the output for 100 VAC or 144 VDC, essentially as a DC-DC converter.


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## J-Ro (Aug 9, 2012)

KennyBobby -- The manufacturer calls for 14.75v per battery at the rough ambients that I am charging at & higher voltages at lower temps.

Paul - Thanks for putting some math into the 2 seperate packs vs 1 pack idea. I was thinking I would likely hurt my range a bit but wasnt thinking that 20% would be in the realm of possibility -- Yikes! My controller cant handly any more voltage so the giant string isnt really an option since I dont want to buy another controller or other equipment.

Would running both packs durring discharge and then charging each hald individually be a good alternative to not hurting my range by doing a complete split up of the packs?

Finally -- I have some embarrasing news to report. My test drive this morning on half packs caused some of the plastic caps on my battery interlink bars to melt. I suppose I noticed it this time because the current was much higher per battery link with only half the pack being used...well guess what. the nuts on the battery terminals close to the melted plastic...not very tight at all...i think my 3 year old must have tighened those  I torqed down all the nuts really well and started a charge on the half pack that rested on the drive home and i dont have the variance in individual battery voltage anymore, they are all within 0.1v


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## EVfun (Mar 14, 2010)

The numbers for that 1 string don't seem so out of line for a non-identical pack. Lead batteries do not all have the same charge efficiency and will scatter at the end. I'd recommend taking the peak voltage down or adding battery regulators. Slowing down the end of charge often helps too. There will be scatter. If you can keep them under 15.3 I wouldn't panic. You should try to keep them under 15.0 except during periodic low current equalization charges. You will slowly use up water you can't replace, but lead dies even faster if you chronically under-charge it.


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## Electric Forklift Guy (Dec 13, 2012)

You will constantly have trouble with this set-up because you are running lead acids in parallel and its very difficult to equalize AGM's in any situation.

You can get NEW 200AH , 6v flooded deep cycles ( 2200 series )for about 100 dollars each

This would eliminate the need for paralleling two strings and you can easily equalize a flooded cell 

If you can fit 24 of these in your vehicle and sell the AGM's you have for a decent price you can recover most of the cost.


If you're determined to stick with the AGM's , the best solution is to charge the the two strings separately and use them in parallel

But you'll have to watch them like a hawk since one shorted cell ( like the first battery on string 1) can cause the others to gas while charging which will ruin them after only a few charges.


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