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Old 05-11-2020, 10:34 PM   #1
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Default Voltage question

Checking voltage of my lithium batteries today and voltage read 13.16v on meter on the wall and checked voltage at a couple 12v sockets and read 13.25v
wondering anyone would venture to say which is correct.

Joe
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Old 05-11-2020, 11:09 PM   #2
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That's a good bit of discrepancy. I've been pretty lucky in that several "cheap" 12v socket voltage meters show with a tenth or two of the tank-level/voltage display, my milti-meter, and my battery monitor reads.

So it depends on which readout you consider reliable, or if you can get your hands a third volt meter.
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Old 05-12-2020, 02:31 PM   #3
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Do you have a digital multimeter that can test a few 9V batteries from Dollarama? This is what the battery looks like:


My Dawson meter is pretty accurate. It might be 1mV (0.001V) high in the 10V range.

I just tested 3 of the above noted 9V batteries, all with a date code of 01-2025 on the bottom of the battery & all purchased today. I suggest getting three of them.

battery A: 9.689V
battery B: 9.693V
battery C: 9.681V

So 9.687V average.
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Old 05-12-2020, 11:16 PM   #4
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Quote:
Originally Posted by markopolo View Post
Do you have a digital multimeter that can test a few 9V batteries from Dollarama? This is what the battery looks like:

My Dawson meter is pretty accurate. It might be 1mV (0.001V) high in the 10V range.

I just tested 3 of the above noted 9V batteries, all with a date code of 01-2025 on the bottom of the battery & all purchased today. I suggest getting three of them.

battery A: 9.689V
battery B: 9.693V
battery C: 9.681V

So 9.687V average.
I hadn't thought of using batteries as a control group instead of using more meters.
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Old 05-12-2020, 11:45 PM   #5
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Quote:
Originally Posted by mira1 View Post
Checking voltage of my lithium batteries today and voltage read 13.16v on meter on the wall and checked voltage at a couple 12v sockets and read 13.25v
wondering anyone would venture to say which is correct.

Joe
You said one of those voltage readings was from "meter on the wall". Does that mean you used a different meter to check voltage at sockets? If so then I don't think those are unusual voltage variations.
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Old 05-13-2020, 09:15 AM   #6
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The battery capacity between the voltages Joe posted (13.16V & 13.25V) could be 140 amp hours on his 400Ah LFP setup. I used battery voltage info that Winston posted about his prismatic cells to calculate that. It's approximately 100Ah capacity between those voltages if using data from my cylindrical cells.

You can see why more accurate voltage readings are needed with lithium batteries.

A Voltage Reference is needed if wondering about the accuracy of voltage measuring equipment.

The Dollarama 9V cells could be used as a somewhat accurate voltage reference if Joe is able to find them with the same date code that I posted. I measured them at room temperature 22C / 72F. The batteries are $2.50 each and there are lots of Dollarama stores in New Brunswick so they're both inexpensive and easy to find.

There's a good chance that additional meters will also be inaccurate so the better option IMO is to figure out just how inaccurate the existing meters are and that's why you need a voltage reference.
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Old 05-17-2020, 04:07 PM   #7
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I suspect the difference is due to the voltage drop across the different cables from the source to the measurement points (meter on the wall and the sockets). "Perfectly accurate" meters will give different readings if the actual voltages are different. Different gauge cables of different lengths will result in slightly different voltages. In other words, both readings could be "correct", i.e., correct to within the tolerances of the voltage meter.
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Old 05-17-2020, 04:41 PM   #8
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Quote:
Originally Posted by sneval View Post
I suspect the difference is due to the voltage drop across the different cables

agreed


BTW the "free" multimeters at harbor freight are worth every penny


I have fluke meters and the HF are close through out the ranges when tested


I test rv park power before plugging in ( found a few miswires) and trouble shoot the dc systems


...one of these is velcroed to my house battery and permanently wired ( w fuse) for quick easy checks on my battery health, charging systems and solar panel


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Old 05-17-2020, 04:53 PM   #9
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agreed


BTW the "free" multimeters at harbor freight are worth every penny
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Old 05-18-2020, 11:45 AM   #10
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noise reduction capacitors

https://www.rvtravel.com/rv-electric...ectrical-leak/
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