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Old 11-18-2011, 12:22 PM   #15
JohnnieB
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Join Date: Jun 2011
Location: West Virginia
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Default Re: 84 Marathon resistor cart project

I took a look at your spreadsheet.

Probably the best indicators are the 11/13 entry (12 hr charge - 5 hr rest) along with the 11/14 entry showing self discharge rates since batteries had not been used or charged for about 30 hrs.

Here's what it tells me.

1 & 6 = Full charge - Okay, but Self discharge rate seems a bit high. Need to be load tested.
2 & 4 = 80% & 90% Charge respectfully - might improve, but probably needs to be replaced.
3 & 5 = 50% & 60% respectfully - Needs to be replaced.

IIRC: You've got a manual charger with a timer. What I would do, is put the batteries on charge and leave them on charge until the highest individual 6V battery voltage reached 7.3 - 7.4V. That would correspond to the pack voltage of 44V - 46V that an automatic charger shuts off at.

If you have a 12V car battery charger, you could also charge them in the closer matched pairs (1&6 - 2&4 - 3&5) until they reached 14.6V - 15.3V.
Then charge the daylights out them with your 36V charger.

FWIW:
My 2008 PDS cart came with six T-105 batteries, all date coded 11/09 (L9 stamped into Negative terminal) and the electrolyte was above plates in all cells.
The pack would only charge to 85%, and the extreme voltage spread between batteries was about 0.1V. (at least a 12 hr rest)
After some fun and games, the pack now charges to 95% and the extreme voltage spread is only 0.04V. (at least a 12 hr rest)

What I did was basically, charge the daylights out of them. I put them on charge every night whether or not I had used the cart.
Some times I would restart the charger two or three times in one day even though the cart never moved an inch.
Granted, I used up some Discharge/Recharge cycles, but I ended up with a more useable battery pack, which was my goal.

My plan is to replace the pack next spring and re-purpose the old one for task lighting during power outages. (Series charge and parallel feed to 12V bulbs via 10 ga twisted pairs.)
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