Batteries not charging equally?

ILFE

This morning I was looking at the system. It was very early, but I noticed the charger was already fluctuating between 11.5 and 12.0 amperes going into the batteries. So, I decided to clamp the meter on each leg just to see how close they were. (Each battery is wired equidistant from the ProStar 30m controller. The system is 12vdc and each battery is 12 volts.)

The meter readings for each battery were as follows (as close as I can remember, as I didn't write them down): 3.2, 3.4, 4.7, 1.3

So, is this normal as far as charging goes? Or, is this where someone is going to tell me I need a high dollar MPPT controller that will sort this out for me? (Supposedly, I have an MPPT controller coming fairly soon, from Midnite.)

Blackcherry04

Re: Batteries not charging equally?

It's because no two batteries have the exact internal resistance, they never accept current and charge or discharge at the same rate on a common buss. Your job is to supply the a equal chance by the way you set up the connections and let them do their thing. If you find them to be different in their SG level that you can correct. I like to shuffle mine around on the buss once a year, that sometimes will make a difference.

ILFE

Re: Batteries not charging equally?

Blackcherry04 wrote: »

It's because no two batteries have the exact internal resistance, they never accept current and charge or discharge at the same rate on a common buss. Your job is to supply the a equal chance by the way you set up the connections and let them do their thing. If you find them to be different in their SG level that you can correct. I like to shuffle mine around on the buss once a year, that sometimes will make a difference.

Thanks, Blackcherry.

At the moment, all four batteries are attached to bus bars. I just received an order I have been waiting on from the states. It included four marine rated battery positive and negative junction posts. I want to remove the battery cables from the buss bars and mount them all on the 3/8" studs.

Blackcherry04 wrote: »

If you find them to be different in their SG level that you can correct.

I will check the specific gravity when I go back out there. How may I correct it, if there is much difference in the SG?

And, if you don't mind, how far apart on the SG would one consider that they need correcting?

Blackcherry04

Re: Batteries not charging equally?

ILFE wrote: »

Thanks, Blackcherry.

I will check the specific gravity when I go back out there. How may I correct it, if there is much difference in the SG?

And, if you don't mind, how far apart on the SG would one consider that they need correcting?

You correct it with a Equalization charge ( fast ) or by raising the Absorb voltage and time ( slow ). I don't know your batteries, but if the are filled with 1.265 and they are say 1.230, thats low, ideally they should be within ( .020 to .030 of each other ) if you have only one battery ( or cell ) that different from the others, it's best to pull it and work on it alone, rather than subject them all to a EQ. The Idea is to balance them the best you can internally, It still doesn't fix it all , it's the nature of the lead acid beast.

ILFE

Re: Batteries not charging equally?

Okay. I will try to get back out there in the next day or two and check the specific gravity.

Thanks again. I appreciate the replies.

vtmaps

Re: Batteries not charging equally?

ILFE wrote: »

The meter readings for each battery were as follows (as close as I can remember, as I didn't write them down): 3.2, 3.4, 4.7, 1.3

You have four parallel batteries... that is trouble. The basic problem is that parallel batteries are unstable.
Short discussion here: http://forum.solar-electric.com/showthread.php?14674

What you must do now is charge the under performing battery by itself. If you try to equalize all four batteries you will cook three of them and the weak battery will not get charged.

When you charge the weak battery, do a long absorption charge before you do an equalization charge.

--vtMaps

Blackcherry04

Re: Batteries not charging equally?

The meter readings for each battery were as follows (as close as I can remember, as I didn't write them down): 3.2, 3.4, 4.7, 1.3

All we know is snapshot in time, without watching the whole charge cycle and and seeing the amperage rate per battery overtime. Once the battery with the High acceptance rate fills it will change for the lagging battery. Series batteries have the same issues , you just don't see it.

ILFE

Re: Batteries not charging equally?

vtmaps wrote: »

You have four parallel batteries... that is trouble. The basic problem is that parallel batteries are unstable.
Short discussion here: http://forum.solar-electric.com/showthread.php?14674

What you must do now is charge the under performing battery by itself. If you try to equalize all four batteries you will cook three of them and the weak battery will not get charged.

When you charge the weak battery, do a long absorption charge before you do an equalization charge.

--vtMaps

How can I force a ProStar 30m to make any length of time absorption charge? Everything it does, as far as I know, will be automatic, no? When I read advice like this concerning other controllers, I figure since they are higher end MPPT controllers, they have user controlled settings on them?

ILFE

Re: Batteries not charging equally?

Blackcherry04 wrote: »

All we know is snapshot in time, without watching the whole charge cycle and and seeing the amperage rate per battery overtime. Once the battery with the High acceptance rate fills it will change for the lagging battery. Series batteries have the same issues , you just don't see it.

I figured as much. I thought of changing the system voltage to 24 volts after I add more panels to the array. However, I want to keep the system voltage at 12 volts for lighting, appliances and my 12 volt input inverter. Of course, I know what some of you more knowledgable folks say about too many battery strings as well.

Blackcherry04

Re: Batteries not charging equally?

ILFE wrote: »

I figured as much. I thought of changing the system voltage to 24 volts after I add more panels to the array. However, I want to keep the system voltage at 12 volts for lighting, appliances and my 12 volt input inverter. Of course, I know what some of you more knowledgable folks say about too many battery strings as well.

It's just hard to say if there is a issue or not. If the 1.3 amp battery was the low resistance battery, it may have already filled and the high amperage battery may be the lagger. I'd watch it and see how they equal out at the end of the charge cycle.

I can't see your buss, I'd shuffle the batteries location and see if it makes a difference. The First battery (ies ) on the positive end will always take the largest beating during the discharge cycle in parallel, so the recharge cycle can be more lopsided.
.

ILFE

Re: Batteries not charging equally?

I will make it a point to go back in the next day or so and check them again, as I will have more time. Hopefully they will be closer. I guess the SG check will tell the story, though. I will post my findings after checking the batteries.