Lead Acid Battery Testing Theory

Question

Lead Acid Battery Testing Theory

hgordon (Chemical)

(OP)

20 Dec 18 22:31

Hi all,

I am in the fire protection business where we use lead acid batteries on constant float charge to start diesel pumps for sprinklers.
Our H&S department is not keen on specific gravity testing.
I am more inclined to say load testing is more beneficial. Keeping in mind our sites are in the 100's and we don't the time or resource to maintain batteries if they are starting to fail.
When our batteries fail it is commonly positive plate corrosion and other affects of this.
This mechanism should not lower the OCV of a battery because the acid concentraion should not be affected by plate corrosion, rather the battery may take longer to charge as there is higher internal resistance.
Sulfation I do not believe is an issue with float charge and this may lower acid concentration as it takes away sulfate from the electrolyte.
So, I think load testing is good that it takes into account both battery voltage and internal resistance/current capacity.
We also ensure we check electrolyte levels as to not lower battery capacity this way.
Is my ideas correct?

itsmoked (Electrical) · Answer 1 · 2018-12-20 23:20:48

I agree with load testing. However.

With a recent vexing problem I had with starting a diesel I have come to the conclusion the ONLY way to reliably test an engine starting system is to test it in situ and ONLY in situ. The actual cables, the terminals, and the physical terminal connection to battery and starter can each cause a complete failure to start. Leaving you with a "the battery was good but so what" result.

Pulling the battery from circuit and testing leaves several failure points untested.

I recommend you use two logging DMMs. Clip one to the starter terminal - the actual Bendix stud and to the starter body. The second meter you stab into the actual battery posts of the battery - NOT the terminal lugs clamped to the battery posts.

Start the recorders and start the engine. Those tests will tell-all. As the battery ages out it will show directly as greater and greater voltage drops. The drop will be mirrored on the starter but slightly greater drops as the current starts to go up to support the motor with the lowering of the voltage. The starter reading will instantly show corrosion or loosening connections.

Check this:

For 33 years this clapped-out idiocy of a cable termination started the diesel. Two weeks ago the tiny 1/8" x 1/8" patch of one side of the 3/0 cable finally blew away deep inside the connector during a hard start cycle. Game over. Battery voltage during a start attempt 12.1V. Voltage on Bendix starter stud 0.51V. This defect would've been seen years ago the test procedure described above.

Keith Cress
kcress - http://www.flaminsystems.com

IRstuff (Aerospace) · Answer 2 · 2018-12-22 18:10:48

I'd almost recommend some sort hybrid approach. We used to have a piece of equipment that was rarely used; nevertheless, the maintenance contract dictated a yearly PM, which included some sort of stress test. Invariably, the stress test would induce latent failures in the machine and it would crash the first time it was used after PM.

In any case, there might need to be multiple starts and/or some load testing afterwards.

TTFN (ta ta for now)
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itsmoked (Electrical) · Answer 3 · 2018-12-22 21:38:16

Except since these things self test themselves weekly or monthly they're getting the repetitive testing you seek anyway. Developing issues will quickly appear if a log is kept.

Keith Cress
kcress - http://www.flaminsystems.com

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