Gang charging batteries

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pennzy
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Gang charging batteries

I gang charge 10 gel cell 12 volt batteries in parallel . Recently I thought the charger was bad because the batteries were not charging as usual . Then I took out the older batteries and tried again. Seems old or bad batteries affect the charge of the others. Could someone please explain why this is .

WalkIntoTheLight
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Just a guess, but if the old batteries wouldn’t hold as high a voltage as the new batteries, they were probably limiting the necessary voltage (usually around 14.8v during charge, or 13.6v during top-off) required for a full charge. Or perhaps sucking up too much of the current, if something was shorted in them?

Did you measure the voltage being applied to the batteries?

cu42
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What was the current coming out of the charger? I am assuming the older batteries were taking too much current and holding the overall voltage down.

Were the charging leads or any battery terminals warm? This could tell you which ones or if the charger was taking excess current.

Another thing that can cause uneven charging or even damage batteries eventually is connecting the charging leads to one end of the bank then daisy chaining the rest of the batteries to the end. The charge leads should be connected pos on one end and ground on the opposite end to keep resistance and voltage even to each battery.

pennzy
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The charger starts at 4 amps and slowly reduces as the batteries charge. The charge voltage is in the 13.something range. The way I determined which bad batteries to remove was by watching the amp meter on the charger as I removed each battery . The bad ones made the output amperage jump up when in the circuit. When only good ones remained , the current dropped and the voltage of the batteries all were 12.something volts. All the bad batteries were about 9 volts or less .

WalkIntoTheLight
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pennzy wrote:
All the bad batteries were about 9 volts or less .

That’s really low unless you deep-discharged the battery and did not give it any charge after that. Seeing as you were giving them charge, I suspect 1 of the cells in those batteries was shorted out. Nothing you can do except recycle it.

Ronin42
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Maybe I don’t understand the question.

But

When you connect batteries in parallel you are making a (in essence) a single larger battery. If one or more of your (sub batteries) have an issue you just added that issue to you big battery.

The weakest link kind of thing.
or
Only as good as your worst sub battery aka cell.

(“It’s good that most people can’t remember their previous lives. Otherwise
things would be a lot more complicated than they already are.”
Ajaan Lee Dhammadharo)

pennzy
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Is there a way to charge 10 batteries with one charger at the same time where if one is bad, it doesn’t affect the charging of the others I guess is the question . Rather than gang charging, a better term would be fleet charging.

snakebite
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if any parallel battery shorts a cell it drags the rest to its level.
so it was rendering the whole group a 10v battery.

pennzy
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Fusing of each line doesn’t seem to help take the bad battery out of the equation , maybe if the fuse value was lower ? Would a shorted battery trip a fuse?

cu42
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Fusing each line or battery is not a reliable way of figuring out which battery is bad or keeping the bank charging correctly, especially with a low amperage charger. The bad batteries are not necessarily “shorting” so determining a fuse value would be highly variable depending on many factors.

What size are these batteries? Ah rating would help here.

The only good way charge and check batteries is individually. After you have determined which batteries are good vs bad should you try to load or charge them in a bank. If any batteries are questionable, you should unhook them from the bank and charge and test separately then discard if bad or put back into the bank if good.

Bottom line, it is not a good idea nor productive to have bad batteries in any bank.

On another note, bad batteries can also cause a higher than normal load on the charger tricking it into thinking it is still in an active or bulk charging stage and thus maintaining a higher voltage and current output level. This can cause overcharging of the good batteries in the bank and lead to failure of those as well.

Get those bad batteries out of that circuit and only use a quality intelligent or smart style charger. Do not use a simple two stage or worse yet, non regulated or wheeled unit charger or anything with a knob that chooses amp settings.

moderator007
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Some good info already given. The only way I see it working is having enough voltage and current to over come the voltage and current lost in the bad cell. 10 cells in parallel at 4 amps is only 400ma per cell. I have seen lead acid batteries when measured with a DMM read 12.6v and seem perfectly fine until you apply a load to them, they fall flat on their face dead. In lead acid batteries the sulfate crystals form between the plates until they touch. Making a short that only shorts when you ask for lots of current. Not advising anyone to do this but I have directly shorted the battery with a thick cooper wire. This creates like a overload of current jumping across those sulfate crystals that can free the plates. I had it work one time and hasn’t worked on probably 5 other batteries I have tried. Could be that it depends on just how much sulfate has built up.

cu42
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Good info 007.

It does seem like his charger does not have enough power to overcome the bad cells. On the flip side, I would be concerned if he did use more current without closely monitoring the process. Heat could build up even at a few amps per cell depending on conditions.

If the bad batteries are sulfated, they can sometimes be desulfated by a couple of methods. As 007 stated, placing a large load or short on the battery can break loose the crystals. Another way is to use a desulfating charger that can actually slowly break loose the sulfation and bring back the battery to closer to its original state. I have had success using both methods and each has upsides. I like the specialized charger since it seems to have a better end result when it does work and is less risky. Sometimes shorting and hot charging alternately is the way.

The chargers I have used in the past are the Ctek and Noco units and they have brought back dozens of batteries over the years and so has the shorting/hot charging method.

On the batteries falling on their face under load while showing good voltage, I have had that happen many times over the years also. In addition to sulfation, I have seen this as a result of an open circuit in the cell connectors. Some batteries have cheaply pinched or faulty welding at this point at manufacture or as a result of abuse #stopbatteryabuse #batterieshavefeelingstoo #batterylivesmatter. An open cell battery can still show good voltage if the opening is just a hairline and the electrolyte in the gap causes it to show voltage but fail under load. This is not easy to fix and takes much effort to find the open connector.

So I just did it again. Too much info and probably more than anyone cares about.

moderator007
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The simple solution would be to get rid of the older weaker batteries. Not the cheapest solution but probably the least problematic.

cu42
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Ditching the bad cells is definitely the best and safest route unless you have lots of time on your hands and some safety glasses.

I know someone in the industry who can bring back almost any battery from any voltage. He will go round and round with a battery for days doing different steps. We once gave him a handful of batteries we couldn’t revive using all the above methods. He called back a week later with half of them working fine. Two were below 6 volts and heavily sulfated and stratified not showing more than a few amps output at dead short. We couldn’t believe it. Good on him for persistence and know how. He pocketed a few hundred extra dollars selling B stock batteries that week.

pennzy
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The batteries are 7 ah and are normally kept charged from a charge coil under a flywheel on a small engine. Once per year they get gang charged after sitting idle for the winter. The bad batteries were all about 10 years old so they served well. After identifying the bad ones , I try to individually charge them one more time before taking them out of service. The charger is an automatic 4amp auto charger , nothing smart , though it does reduce current as the batteries charge.The charger is on a 12 hour timer.