Voltage deviations Hawker PzB 150

[stajo]

Hi, I'm testing some (12) truck cells that came from some 3-wheel post office vehicle. At first I let them stand a few days and adjust to room temperature, they was stored in a cold storage with temporary charging for a good while before. Then I tested with some charging, first a few hours of modest 2,3ish per cell 27,5 total then when current when towards zero I followed up with around 2,35. Current never over 5-6 A. One of the cells, no 8 went up a little higher in voltage then the others to 2,39 and another one, no 9 followed on 2,37 and the rest around 2,34-35. After a few hours I took it down to float on 2,26-2,27 to float for a few days. In float they were fairly alike, 2,267 (no 2)-2,287 (no 12) between lowest ang highest.

Then I first filled up with distilled water to good levels let them stand and self discharge for a week or so and monitored that. They kept very close within a 10th of a volt. After that I thought I would try to put a little balance charge on them again and to my surprice no 8 goes up way higher then the others, over 2,6V while the others stay on 2,3-2,4. Quicky stopped charging, cranked the voltage down a bit, started again and no 8 went off. Tried one last time with very very low charging voltage, around 2,2 where they rested after charging. Again no 8 went sky high. There is now hardly any current at all, around 0,1 A.

Posting an excel chart over voltages over time. What is the state of no 8?

[Sunking]

So what is the problem other than you have a weak/bad cell?

[stajo]

I was wondering in what way it is weak and if I can do anything about it. I guess it is not sulfatet, that would make it harder to take charge right? Shall I do a discharge test and measure over time?

[bcroe]

A quick load test may reveal that 8 is done, can't maintain voltage under load. Bruce Roe

[Sunking]

I was wondering in what way it is weak and if I can do anything about it. I guess it is not sulfatet, that would make it harder to take charge right? Shall I do a discharge test and measure over time?

It is a dead give away you have a sulfated cell and there is no way to reverse it. As Bruce indicated you can find the bad cell(s) or battery with a load test. Apply a good heavy load and a weak cell, cells, or battery will crash. The issue is with sulfated cells is RESISTANCE to current. The internal resistance shoots up, and is the cause of 95% of all battery failures. There are two classic signs which are blatantly obvious when tested.

1. When you put the battery on a charger, it charges way to fast. Your charger is being fooled into thinking the battery is fully charged. What is happening when you run a charge current through the high resistance causes the voltage to rise to fast and fools the charger.

2. The Load Test fails for the same reason, when you demand current, the bad cell(s) resistance cause the voltage to collapse.

Sorry to say but there is no way to fix that as it happens to all batteries. Only thing you can try is a long and proper EQ charge. If that does not work you are SOL. To perform a proper EQ make sure you have the electrolyt at the proper level, perform a normal full charge cycle, then EQ for 12 to 24 hours until specific gravity and voltage equalizes. If you have a bad cell, that cell voltage will shoot up and specific gravity will not come up. If that happens you have a brand new boat anchor.