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Old 05-29-2017, 03:16 PM   #1
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Which voltage display to believe?

My (2017 AI GT) house batteries are mostly charged at present and I see three voltage displays:

Magnum: 12.7v
Main control panel (rocker switch to Batt. Aux.): 13.08
Solar controller: 12.7v.

Which one is more reliable?

Also, my understanding is that 12.2v represents about 50% discharge (per the Lifeline battery user manual). Does that sound right?
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Old 05-29-2017, 03:25 PM   #2
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Hi

Unfortunately, none of them are as accurate as a ~$20 multimeter with the probes right on the battery terminals. If you don't have one already, they are a handy item to have.

If your system is under load (battery is charging or discharging), the drop in the wiring will throw things off. It also will have a bit of an impact on the battery voltage. The best way to measure voltage to get capacity remaining is with the battery not doing anything for about a half hour. There are a few minor things (temperature, battery age, ...) that impact the capacity as guessed from the voltage. Google is your friend for digging up this sort of information.

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Old 05-29-2017, 03:44 PM   #3
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I would take the 12.7 as the more accurate reading. 12.2 is approximately 50% SOC. Although to get a perfectly accurate reading the batteries have to be sitting idle for a for several hours with no in or out current. When I go to the trailer the first thing I do is take a reading from the batteries with a multimeter. That will be the most accurate reading I can get.
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Old 05-29-2017, 04:32 PM   #4
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All other things being equal, I'd trust the Magnum's reading the most if I had no evidence from direct testing (using a multimeter, as described above, though I'd recommend better than a $20 one. My Fluke cost a bit more than that, but that was 15 yrs ago and it may outlast me.)

The SeeLevel in our Flying Cloud consistently reads about 0.1v lower than the multimeter on the batteries. That was an issue of some concern for me until I put the Fluke on the battery terminals.
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Old 05-29-2017, 07:35 PM   #5
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Thanks to above, but I'm guessing it's easier to get access to the battery terminals in a trailer than in the Interstate. Not sure how I could do that without crawling under the van.
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Old 05-30-2017, 06:13 AM   #6
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If you can't hit the battery it's self in the interstate, go to the main fuse panel. Turn everything off and use your multimeter to check the voltage there. Measure between the hot side of an empty fuse holder and chassis. The main reason to go to the battery is that it takes out the issue of wiring issues like loose terminals.

As noted above, you *can* get better multimeters than the $20 big box store versions. Truth be told, I don't own any $20 multimeters. These days they are indeed *far* more accurate than a panel indicator. They also are much more rugged than they once were. Fluke made all of my hand held voltmeters. I run HP's on the bench. If you can afford better, get a Fluke.

A pannel meter may be a 5% sort of gizmo. That's going to be 0.6V at 12V. A 0.1% accuracy would get you to 0.012V. Unless you are doing temperature correction on the reading, that is closer than you need to get.

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Old 05-30-2017, 12:35 PM   #7
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What else does your Magnum say? If you are plugged in at the time of these readings, and it also displays "BatterySave" then that would make sense since Battsave means charging is off, and therefore the charge is likely to be somewhere between 13.1V (Float) and 12.6V (Battsave).
The Atkins (solar) display is inaccurate.

Update: Remember, the Magnum is cycling between its modes, so the battery voltage and the Magnum voltage are likely to be different.
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Old 05-30-2017, 02:38 PM   #8
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The difference is prbobly due wire resistance between the Magnum and your other inficator(s).
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Old 05-30-2017, 03:45 PM   #9
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I was told by the dealer to use the volt readings on the solar.

Never really paid attention because I am either at Full hook up or I have my gens.
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Old 05-30-2017, 07:25 PM   #10
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If the $20 or more for a VOM scares you off, I've found the ones at Harbor Freight for free to $7 (same meter) are more than accurate enough for RV use.
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Old 05-30-2017, 09:09 PM   #11
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Quote:
Originally Posted by cazual6 View Post
I was told by the dealer to use the volt readings on the solar.
I'd recommend you don't go back to that dealer. The least accurate of the 3 readings will come from the Atkinson "Sun Explorer" panel, which gets its info from the Atkinson solar charge controller. The charge controller output is connected to a terminal on the positive bus and a random ground, which on my coach was the ground point on the BIM. Not exactly the best way to see what's going on with the batteries......
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Old 05-30-2017, 09:26 PM   #12
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Quote:
Originally Posted by FlyFishinRVr View Post
I'd recommend you don't go back to that dealer. The least accurate of the 3 readings will come from the Atkinson "Sun Explorer" panel, which gets its info from the Atkinson solar charge controller. The charge controller output is connected to a terminal on the positive bus and a random ground, which on my coach was the ground point on the BIM. Not exactly the best way to see what's going on with the batteries......
I'd point out that "cazual 6" has a Flying Cloud (at least according to profile), not a Sprinter, so it may not be the same controller.
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Old 05-30-2017, 11:28 PM   #13
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Originally Posted by DKB_SATX View Post
I'd point out that "cazual 6" has a Flying Cloud (at least according to profile), not a Sprinter, so it may not be the same controller.
Ah, missed that. Good catch. Not sure why someone that doesn't have an Interstate would chime in on an Interstate electrical thread, but my comment re. how the solar controller is monitoring the battery voltage is still valid for the OP (i.e. don't believe it).
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Old 05-31-2017, 01:31 AM   #14
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Ah, missed that. Good catch. Not sure why someone that doesn't have an Interstate would chime in on an Interstate electrical thread, but my comment re. how the solar controller is monitoring the battery voltage is still valid for the OP (i.e. don't believe it).
People read the Portal page and see posts and threads, and may not realize which subforum a thread is in. It's often unintentional. And until you get to something like the behavior of specific solar controller, electrons are electrons.
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