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Old 02-11-2019, 06:09 AM   #1
ajk170
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Volt meter installation

Hi All- I have a pretty basic question about the installation of a volt meter- my gut tells me these things need to be wired directly to a battery to monitor it properly but could I remove my USB and 12 volt station that's in my kitchen and wire a new station in that includes a volt meter? My assumption is it will not read correctly due to something that's wired in-between the docking station and the battery. I just don't want to run a dedicated wire and then fish it through a wall. If it needs o be direct, maybe I can make a waterproof thing and wire it to the battery box.

Thanks!
-Andy
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Old 02-11-2019, 07:10 AM   #2
roadglide
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I almost bought a volt meter combo usb and lighter at quartzsite you can order that combo I mentioned. I would pull the lighter plug out and check the voltage with a meter .
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Old 02-11-2019, 07:53 AM   #3
JRTJH
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The problem with any "remotely located" DC voltmeter is DC load. Most USB charger stations are wired off branch circuits from the main battery wiring. Most commonly through the converter/charger DC fuse panel. When using a 14 or 16 ga wire to power a 2 amp circuit, the voltage will drop based on the power consumption at the USB port. Installing a voltmeter at that point will monitor the voltage drop, not the battery voltage. So, essentially, if you install a voltmeter at the terminal end (along with the USB port) then if anything is plugged in along that wiring run, the voltage measured will be that line only, not the true battery power.

If you want to "try it and see", then once you have the voltmeter in hand, pull the USB charger port, use temporary wiring, connect the volt meter, turn it on and read the voltage (should be 12.6 +/- VDC. Then plug in something to the USB port and start charging that item. Monitor the voltage on the meter. My thoughts are it will drop to 11.0 +/- VDC. If so, then it's not reading "true battery voltage" but "voltage drop through a branch line". It will "work OK" wired that way as long as nothing is plugged into that branch line (from the fuse panel) but the way trailers are wired, that may not be the only device on that line, so reading "battery voltage" would be "iffy" .....

The "best method" is to either monitor "true battery voltage" with a dedicated line to the volt meter from the battery terminals, or to monitor "true converter applied voltage" with a volt meter connected to the input terminal on the converter/charger (the big red wire on the power center).....
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Old 02-11-2019, 04:02 PM   #4
roadglide
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I ordered a volt meter that has amps that required 100 amp 75 millamp shunt and decided to wire the meter direct to the batters with out the shunt and 2 extra wires. Looking at my volt meter while using a toaster powered by 3 k inverter will drop from 13.5 to 12 .5 volts it was fun to watch once.
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Old 02-11-2019, 09:22 PM   #5
ajk170
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Thanks guys! looks like I’ll just wire it at the battery - I saw some simple ideas with the battery box that will do what I want.
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