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Voltage increase when load applied

Jhig

New Member
Joined
Jan 23, 2023
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Salt Lake City
Hi all,

Saw something strange today and was wondering if anyone has any insight. I have a renogy 100ah lithium battery and was measuring the voltage with my multimeter at 12.5v with no loads applied. However, when I turned on my lights which are hooked up to the battery, the voltage of the battery would jump to 13v. Any ideas why this would happen? Is this something to be concerned about?

Thanks!
 
Battery voltage was 12.5v with no loads and then jumps to 13v
I dunno, sounds odd, maybe the BMS is going to sleep with a tiny voltage leak. Then on BMS awakening, the true voltage is measured?
Is there a bluetooth app that you can watch the BMS with?

I wouldn't read too much into this but keep this possibility in mind if you are judging Soc based on voltage (i do this). I suspect that once you got to 13V, turning the lights off did not cause the voltage to go back to 12.5V. It would be interesting (or frustrating?) watching to see if you can detect how much time of inactivity it takes for this to happen (and we're reaching at the BMS sleep idea already!).

Is there a particular reason your battery voltage is so low?
 
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I dunno, sounds odd, maybe the BMS is going to sleep with a tiny voltage leak. Then on BMS awakening, the true voltage is measured?
Is there a bluetooth app that you can watch the BMS with?

I wouldn't read too much into this but keep this possibility in mind if you are judging Soc based on voltage (i do this). I suspect that once you got to 13V, turning the lights off did not cause the voltage to go back to 12.5V. It would be interesting (or frustrating?) watching to see if you can detect how much time of inactivity it takes for this to happen (and we're reaching at the BMS sleep idea already!).

Is there a particular reason your battery voltage is so low?
I don’t think the Bluetooth app will allow me to monitor the BMS.

You are correct, when I turn the lights off the voltage stays at 13v for a while. I’ll try to see how long until it drops back down.

And I’m not sure why my voltage of my battery is so low. The “smart” battery tells me I have 80% SOC, which makes no sense for that voltage. I may have to ask renogy about this.
 
How is the battery telling you the SOC?
What charger(s) do you have and how are their charging parameters set?
It’s one of the smart renogy batteries so it has a RS485 port that I can connect a BT-2 module to see the SOC.

I have the renogy wanderer li 30a charge controller and a single 100w solar panel. It’s just set to the out of the box lithium setting, but am going to try to reduce the boost charging voltage and time. I’m having issues with that as well so maybe these two things are related. Here’s the other issue I’ve been running into:


Thanks everyone!
 
Here’s the other issue I’ve been running into:
Thanks, that helps quite a bit.

I'd follow sunshine_eggo's suggestions until your charge cycle completes charging without the BMS cutting off (thats bad when that happens, the worst thing is solar may still power your wanderer and spike the voltage to array voltage). Completing a charge cycle or two should help it get a more accurate SoC calculation.

Do you think this threads topic is related to the battery error code issue? Does one happen after the other or some kind of pattern? Probably not but i look for patterns in everything.
 
Thanks, that helps quite a bit.

I'd follow sunshine_eggo's suggestions until your charge cycle completes charging without the BMS cutting off (thats bad when that happens, the worst thing is solar may still power your wanderer and spike the voltage to array voltage). Completing a charge cycle or two should help it get a more accurate SoC calculation.

Do you think this threads topic is related to the battery error code issue? Does one happen after the other or some kind of pattern? Probably not but i look for patterns in everything.
I’m not sure, I just noticed yesterday when I was using my multimeter to try and trouble shoot the battery error code issue. I have an AC to DC charger that I am going to try out tomorrow to charge the battery fully and see if the voltage still drops after being idle for a few minutes. I’ll also try lowering the voltage of my charge controller and see if that makes a difference. I’ll report back.
 
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