Battery Wire Imbalance

Mar 30, 2013
70
Hunter 356 Georgian Bay
Last season I installed 4 new Trojan T105 6v/225amp batteries in the configuration shown in the attachment. At the end of the season the hydrometer reading on the cell at the positive end of the No.1 battery was below all other cells. It's been suggested that voltage drop is the issue and I should move the Neg. bus-bar to 3ft from bank B and this would balance the voltage drop.
Can anyone tell me if 1. Does moving the neg. terminal make sense and 2. If I simply lengthen the positive and negative cables on bank A to both 6ft to match the cables on bank B would this solve the imbalance or is something else at work.
 

Attachments

May 24, 2004
7,129
CC 30 South Florida
It seems to me that your battery in position #1 has a weak cell. If it were due to voltage drop because of its position in the array I would have expected similar low readings from the adjacent cells in that battery. I would switch the position of that battery with one of the others known to be good and later retest.
 
Jan 12, 2011
930
Hunter 410 full time cruiser
For the normal currents though battery cables the extra length of cable hardy ((basically none) means anything for voltage drop. Add if voltage drop was the problem battery #2 should be about the same as #1. I think the problem is just battery 1 itself.

Fully charge and equalize them and then see how they compare.
 
Aug 15, 2013
193
Hunter 35.5 Legend 003 San Carlos, Sonora, Mexico
Separate the battery banks and then fully Charge & Equalize each battery bank individually. You need a Smart Charger, like a 3-4 stage charger to really equalize the cells (requires a period of overcharging - or out gassing). Be sure to refill with distilled water after the charge. The different lengths of battery cable will only hurt you under high current conditions when the voltage drop will be significant. If you don't have high current loads (such as a DC-AC inverter) on the house bank it shouldn't be a huge deal. When charging at the final voltage limits the current will be low and the voltage drop minimal and the batteries should become fully charged. I would suggest making the wires the same size and the same length for long term use because the difference will be one bank is discharged deeper than the other.

The bad cell is a bad cell, it has nothing to do with your voltage drop or wire lengths. Hopefully Equalizing will resolve it.
 
Sep 15, 2009
6,243
S2 9.2a Fairhope Al
I might add that if you need long cables check the recomended size for what you are doing and go 1 or 2 sizes bigger that will help some with the high load problem...

regards

woody
 
Apr 4, 2013
11
Hunter 420 passage Turkey
Move the earth to battery 4 and that will balance the loads and the charging better. High current charging will cause imbalance problems too. Check the 6ft cables are as large as you can afford!!!!

Equalize the batteries if you can't get them to a guaranteed 100% each month. That means 24 hours on shorepower first and then follow manufacturers instructions on equalizing.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
This is the wiring Sailinglegend is referring to...



or



or




And from Trojan themselves:


The above is exactly how Trojan, Lifeline etc. suggest they be wired....


Beyond that I suspect your cell drift, at this age, is perhaps due to an out of balance cell, contaminated cell, or just a bad cell.

Before I ever put any 6V bank into service I wire them in parallel and charge them to 7.4V. This is the equivalent of 14.8V if they were a 12V bank. This forces all the cells to become in-balance so when wired in series they all reach "full" at the same time. With flooded batteries simply pushing all the cells to 15.5V, as a 12V bank, before installation, can achieve similar results but unfortunately this is rarely done.

After attaining 7.4V I then push the cells, in parallel, to 7.75V or the equivalent of an equalization voltage and let it run for at least 30 minutes or until the current stops dropping.

I call this an in-service or wake up conditioning charge. It makes all batteries as equal as they can be before being put into service, in a series or series/parallel situation. If your charging voltage never gets to a good gassing voltage of 14.6V - 14.8V, at the battery terminals, then it is possible one cell is hitting gassing levels before all the others due to minor cell imbalance..
 
Mar 30, 2013
70
Hunter 356 Georgian Bay
Wire Imbalance - I think I get it

Thank you guys for the great information, information I wish I had when I set the system up initially. I don't think the cell is bad because the hydrometer reading I took at the end of the season after charging the system for over 48 hours and resting it for 4hrs with no load was 1.248 (which is 85% of fully charged) but compared to all others at 1280-1300 I felt something was wrong.
Last season we did give the batteries a good work out cruising for several weeks with the reefer going 24/7. The charging system is a Balmar 110 alternator with external regulator and all the cables are 1/0. We consumed about 125 amps per day and more when sailing but we never allowed the total draw to go below 50% of the rated capacity of the batteries before recharging, of course it never got back up to 100% while we were away.

I will defenatly will separate the banks and charge them up to 7.4 volts and equalize them individually as suggested, then link the 4 together as shown. From what I'm understanding here each battery must experience the same total length of cabling and number of connections in it's round trip circuit.
My only issue is that the two banks are separated one in the aft cabin the other in the lazaret along with the pos-bus, neg-bus, regulator, temp sensors, Victron shunt, Duo-charge for start-bat, I/O switch, main fuse and more, so moving the neg-bus to the aft cabin becomes complicated.
I'm am considering moving all batteries to the lazaret, I located them to the aft cabin to move some weighted towards the center rather than have 600 pounds of batteries on the outer port side. However it might improve my port tack performance. Further comments much appreciated.