under-load voltage abnormally low (1.61v per cell)

[sportcoupe]

Well almost 24 hours after the charger shut off on it's own (after watering the batteries) I show a voltage of 77.6v, normally it was 76.4-76.5 in the weeks before.

Is it possible since the batts were slightly low on water and it stayed in bulk charge for 12+ hours 3 days ago that I overcharged them? I rode the cart a long time to 50% SoC after the bulk charge issue and charged again, this time it did shut off presumably because I added the water.

I am using my Fluke meter so there isn't a misread. Trying to determine if my charger is sick and overcharging the batts.

[sportcoupe]

36 hours off charger and pack is still at 77.5v. I don't think my batts are sick. I have not condemned the charger yet either. I still need to ride it again so I can get another charge cycle in it. Delta Q replied again and insisted I change the charger algorithm to Trojans even though I only was able to ride 5 miles on that profile. With the US Battery algorithm I get in excess of 18 miles range.

[JohnnieB]

Ironically, having the batteries on bulk charge for 12+ hours may have actually helped them.

As I understand it, they were never "Fully" charged prior to you changing the charger to the # 4 algorithm. Therefore the plates were more sulfated than they should have been for their chronological age had they been properly charged from the beginning. The prolonged bulk charge was essentially an extended "Equalization" charge and some of the crystalline Lead Sulfate was broken down in the process and there are now more sulfate ions in the active chemistry.

Being low on water and the prolonged equalization charged may have shortened their lifespan somewhat, but you've regained run-time and performance for the time being.

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I'm not sure where Delta-Q is coming from when they insist you charge US Battery products with a Trojan Battery profile. Granted, algorithm #4 is for US2200 batteries (6V 232AH) while your 8V batteries are only 121AH, but the max output of the charger is 12A, which is within the 10% of AH capacity charge rate recommended by US Battery for their products and the voltage and current trigger points used to charge a 72V pack are the same whether you use 6V, 8V or 12V batteries to build the pack.

Attached is the OCV (Open Circuit Voltage) vs SoC list I got from US Battery showing VPC (Volts per Cell) for their Deep-Cycle Lead-Acid Wet-Cell products. Based on that data, 76.4V-76.5V is 96.4% to 97.4% SoC while 77.6V projects out to 107.5% SoC. Basically, the pack voltage you are now getting is in the range seen for some, but not all, new batteries.

What are the individual battery voltages? Hopefully they are all about the same.

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Personally, I'd continue to use Algorithm#4 and enjoy the better range and performance, while keeping a closer eye on the fluid level.