Dual volt meters for dual 12V batteries - Page 1
Forum section: electronics / projects

author: adauphin
author_rank: Unknown
timestamp: May 09, 2016, 05:34:32 pm
content: I would like to use a voltmeter to monitor the batts in my kids ride on toy. The two 12V batteries are wired in series for 24V so is it possible to achieve this without one battery influencing the readings of another?

author: mikerj
author_rank: Super Contributor
timestamp: May 09, 2016, 05:41:16 pm
content: Not quite sure what you are asking here since you say "dual voltmeters" in the title, but then mention "a voltmeter" in your post.If you connect a single voltmeter across the two batteries, the voltage is the sum of the two battery voltages, so the reading will be influenced by both batteries. If you use two voltmeters and connect each one across a battery, the readings will be independent of each other.

author: hammy
author_rank: Unknown
timestamp: May 09, 2016, 05:45:10 pm
content: Quote from: mikerj on May 09, 2016, 05:41:16 pm... or one voltmeter connected with a switch to read one battery or the other.

author: adauphin
author_rank: Unknown
timestamp: May 09, 2016, 06:12:50 pm
content: The vehicle uses two 12V batteries, I want to install a dual voltmeter setup, two different displays to monitor each battery independently but at the same time. I can ask the kids to bring it in for a recharge when one of the batteries reach a certain voltage threshold...ie, maybe 11.9V.Easier to let them monitor the voltage simultaneously than toggle back and forth. I wasn't sure that if I installed a voltmeter across one battery if the other would somehow influence the reading.

author: Delta
author_rank: Super Contributor
timestamp: May 09, 2016, 06:19:18 pm
content: Quote from: adauphin on May 09, 2016, 05:34:32 pmSo when you say that, you actually mean "I would like to use two voltmeters"?A separate voltmeter across each battery will work fine, they won't affect each other in any way.EDIT: Affect, not effect. Call myself a grammar pedant...

author: adauphin
author_rank: Unknown
timestamp: May 09, 2016, 06:44:19 pm
content: Quote from: Delta on May 09, 2016, 06:19:18 pmOk, yes....I didn't meant to word it in a singular fashion....my mistake. Yes, two voltmeters, one for each battery.Thanks, I will go forward with this then.....thanks.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 09, 2016, 06:46:05 pm
content: On the other hand, monitoring the whole 24V pack once is (almost) as good as monitoring the 12V blocks separately, and it would be much easier to look at a single reading and bring it back to charging when it drops below about 23V.Having two meters, one for each battery, doesn't give much benefit.

author: adauphin
author_rank: Unknown
timestamp: May 09, 2016, 07:34:47 pm
content: Quote from: Siwastaja on May 09, 2016, 06:46:05 pmI was thinking that, and while the batteries get charged right away on a good charger, both are within about 1-3% of each other at time of charge. However I was thinking on the possibility of one battery getting much lower than normal and while they would still operate I could save it from too deep of a discharge.I could be overthinking this...but as a big DIY person watching both batteries is the safest bet.I could add a low voltage alarm set for less than 23V as well I suppose.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 09, 2016, 07:55:20 pm
content: Yes, overdischarging a single cell is a real issue with lead-acid batteries, too.The more there are cells in series, the worse it gets, but 12s (i.e., 24V) is not that much worse than 6s (i.e., 12V) already is. (What I'm trying to say is that it can happen even within the 12V battery!)I'd prefer simplicity and ease-of-use in this case because it's known to increase robustness.

author: Delta
author_rank: Super Contributor
timestamp: May 09, 2016, 08:51:29 pm
content: Pah, don't listen to him! The more gauges and meters the better!

author: hammy
author_rank: Unknown
timestamp: May 09, 2016, 08:53:25 pm
content: Quote from: Delta on May 09, 2016, 08:51:29 pmEspecially for the kids who drive this car/toy/thing/whatever ... :-)