Battery Configuration Question.

Les49 · October 2016

For the sake of space and convenience I have configured my 24v battery bank as shown below, Basically two 24v four battery banks tied together in parallel in the center instead of the ends. As it is, the two banks are 460ah. All new or less than two month old batteries.
Hopefully you can see the connections well enough to criticize my configuration or approve as you see it. My question is.......when taking individual battery voltage readings, I'm getting 6.7v consistently from all the batteries except for the upper right battery of the left bank of 4. It is reading 7.3 to 7.5v each time I check it. Can anyone see any reason for this as it is configured?
The Charge controller, inverter and desulfate positive connections are all on the upper left positive terminal of the right bank and the negatives of the same are on the lower right battery of the left bank including an earth ground wire.
Please let me know if this could be configured more efficiently, and if you see a cause for the one high voltage reading.
Thanks, Les

Image: https://us.v-cdn.net/6024911/uploads/editor/yu/0n2s1j77pqp7.jpg

BB. · October 2016

Have you measured the specific gravity with a good quality hydrometer? Are all of the batteries the same temeperature (hopefully cool/cold to the touch)?

If you see high specific gravity on all cells in the "different" battery, you can clip a 12 volt bulb (like a brake light or even head light) across the high voltage battery and discharge it while the bank is being charged (sort of the "counter method" of charging the weak batteries with their own charger).

Assuming these are flooded cell, you can simple "equalize" other other batteries and "over charge/gas" the fully charged battery. While equalizing a battery bank (basically controlled over charging of high SG cells to bring low SG cells to 100% full too) is standard practice for lead acid--But something to only do when needed (or once per month for an hour/bring up weak cells). Too much gassing is hard on cells, and can overheat the battery bank (you should be seeing around 2.5% or so charging current while equalizing--Even 2.5% rate of charge can overheat a bank after some numbers of hours--Such as with a genset).

Did the batteries start out all at the same voltage and this guy went different. Or has been high since new (battery was charged to a higher state of charge than the rest of the bank)?

-Bill

BB. · October 2016

I will also add a couple other comments.

For any wire that leaves the battery bank (perhaps the desulfator wiring), the positive lead should have its own fuse, near to the battery bank--You do not want short circuit current through any positive lead without a fuse/breaker.

Alligator clips are not good for high current or continuous use... They do not make very good connections.

-Bill

Les49 · October 2016

Thanks Bill, yes they are flooded batteries and the one in question is new as of last week as are the three others in the left bank. When all 4 of the left bank were installed last Weds. They were all equal voltage at 6.3v. It was only after the initial charge that the (off) battery had charged up to and maintained 7+ volts.

I have not taken a gravity reading on them yet, but will do that this evening after charging slows for the day. I probably should also check individual cell voltages at the same time.

So you did not see a possible cause for this in the actual configuration of the wiring?

I haven't equalize the bank yet either as they are so new........although the new bank was boiling pretty good on the initial charge before it went into absorbing, (charged this bank by itself to bring it up equal with the older bank (6 weeks older).

Les

BB. · October 2016

Looks OK.

Where is the solar charge controller connected? Normally, it should be connected to the +/- common/bus points on the battery bank. ( guess that is the two heavy cables going to the upper left)?

I don't see anything that should cause this issue--Other than these are two different sets of batteries paralleled together--But it should be working.

Sometimes cycling the battery bank is needed over a few weeks/months to bring cells back into balance.

-Bill

Les49 · October 2016

It's working fine, with a good steady 27.3v going to the inverters, but I just noticed that a second battery in the right bank is reading a little over 7v now too so it shouldn't be a problem. (Readings are taken in "Float Status").

Yes, the #2 gauge wire running up from the lower right bat (left bank) and the upper left bat. (right bank) are coming from the controller.

Les49 · October 2016

Just noticed your other post...........The alligator clips are from the desulfator and I have 250amp breakers between the batteries and the inverters. Also have 30 amp inline fuses from the solar strings to the combiner and 80 amp breaker from the combiner to the controller and a disconnect between the controller and batteries.

Les

BB. · October 2016

Safety wise, you need a couple amp fuse/breaker back to the desulfator too... To prevent lighting up those wires too in the event of a short or failed shorted D.S..

Assume any device or wire run can fail shorted. The fuse/breaker/Over Current Protective Device (OCPD--or whatever abbreviation you like) is there to save the wiring from starting a fire (OCPDs are not to there protect the device itself from self damage).

-Billl

westbranch · October 2016

You should be measuring the Voltage ~ 3hrs after all charging has ceased. and there should also be no loads on at the time, better still, to get an accurate reading of the true ''At Rest Voltage'' remove all the loads for the 3 hr period too...,

Les49 · October 2016

Bill I do have the inline fuse and wire all ready............just haven't wired it in yet as I'm moving the desulfator back and forth to my wife's car battery. At that point we'll be rid of the alligator clips as well and have terminal rings on the wire. The car battery has top posts so the clips come in handy on them.
Les

BB. · October 2016

No problem Les.

Always trying to make sure everyone keeps safe.

-Bill

Battery Configuration Question.

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