Author Topic: Unstable SLA Voltage or Faulty DMM  (Read 291 times)

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Offline metrologist

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Unstable SLA Voltage or Faulty DMM
« on: June 13, 2018, 02:50:45 am »
I have 3 SLA batteries that probably came out of UPS. Last year I had them connected to a solar panel for most of the summer to try and revive them - I think one or two were still OK volts when I got them, and one was down to 10.5. I let them sit on the shelf over winter and measured the voltages this morning. All three were bouncing around between 12.5V and 14V. That has to be a faulty DMM, right? It's the free harbor freight model.
 

Offline thm_w

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Re: Unstable SLA Voltage or Faulty DMM
« Reply #1 on: June 13, 2018, 07:12:01 am »
Your name is metrologist and you don't have a suitable DMM to measure with?  :P

You could try placing a small load on it and see if it will stabilize on a number.
I've seen odd voltages with SLA, but should never bounce with a static load afaik. So most likely meter is not reliable.
 

Offline metrologist

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Re: Unstable SLA Voltage or Faulty DMM
« Reply #2 on: June 13, 2018, 07:51:25 am »
Well, I was out in the garage on my way to out to work. I'll verify again, but just the very idea that it could be the battery was a bit perplexing, and all three? I'd never seen that, and if it is the meter, that might be something of interest.

BTW, I have kind of a split personality. Sometimes I go by Metrolojest.  :-DD
 

Offline metrologist

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Re: Unstable SLA Voltage or Faulty DMM
« Reply #3 on: June 13, 2018, 09:13:55 am »
Well, when I got home I measured again. stable 12.48, 12.46, and 12.25, just toggle the last digit ever so often. I had a second cheapo meter that verified within 20mV.  :-//
 

Offline Gyro

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Re: Unstable SLA Voltage or Faulty DMM
« Reply #4 on: June 14, 2018, 04:13:26 am »
It sounds as if you need to clean and/or check for continuity of your test leads (check they don't go o/c with a little tension on them). Either that or plug them in fully!  ;)
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline metrologist

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Re: Unstable SLA Voltage or Faulty DMM
« Reply #5 on: June 14, 2018, 05:09:29 am »
Might also be a weak DMM battery. Those leads though... I just wanted a sanity check that SLA batteries could not exhibit that phenomena, or it would be extremely rare. I guess anything could be happening with aged batteries.
 


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