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Old 06-24-2022, 09:27 PM   #1
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Voltage

Is it normal for a monitor panel to read a lower voltage that the batteries while charging? The monitor panel says 13.2v at float, and a multimeter at the battery terminals reads 13.7v. The chassis batteries also read 12.7 at monitor panel and 13.1v with multimeter.
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Old 06-24-2022, 09:40 PM   #2
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You may want to try another multimeter to confirm the accuracy of your current meter. Your measurements show a .4-.5V drop between the battery and the monitor panel. That may not be unusual if the batteries are at the rear and the monitor is at the front. Is there a way to recalibrate the monitor to match the readings from the multimeter?
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Old 06-24-2022, 09:48 PM   #3
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Keep in mind you can have some voltage drop in the wiring between the batteries and the monitor panel. Ours also tends to read a bit lower.
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Old 06-24-2022, 09:58 PM   #4
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You may want to try another multimeter to confirm the accuracy of your current meter. Your measurements show a .4-.5V drop between the battery and the monitor panel. That may not be unusual if the batteries are at the rear and the monitor is at the front. Is there a way to recalibrate the monitor to match the readings from the multimeter?
I don’t believe there is a way to recalibrate the panel. I don’t have another multimeter either. I’m just worried that the inverter charger is going based off of the monitors voltage and is overcharging the batteries.
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Old 06-25-2022, 09:47 AM   #5
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Look up the voltage drop per ft on the internet. Remember dc is measured coming and going for wire length. You can easily have 60 to 70 ft of wire length in a big coach.
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Old 06-25-2022, 10:39 AM   #6
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I donít believe there is a way to recalibrate the panel. I donít have another multimeter either. Iím just worried that the inverter charger is going based off of the monitors voltage and is overcharging the batteries.
Iíd image that your inverter/charger is sensing voltage via a shorter length of 2/0 or 4/0 wire that connects the charger to the batteries. I use a Victron 712 battery monitor that allows me to view house and chassis battery voltage on a phone. Displayed voltages are within a few hundredths of a volt, as compared to the measurements taken with a fairly high end multimeter.
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Old 06-25-2022, 12:10 PM   #7
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Regardless of the difference in readings I recently looked at my house batteries meter, it showed 12.1 volts. My volt/ohm meter read 12.3v. I had accidentally tripped the circuit breaker for the onboard charger. Back on, all was well.
But if I hadn't installed a seperate house battery volt meter I would have dead batteries in no time, reducing their life. Money well spent, < $10.
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Old 06-25-2022, 12:48 PM   #8
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Personally I wouldn't worry about it. The minuscule difference is due to cable length. Now you have a good reference as to what your actual battery voltage is while under charge. I have a battery voltage l.e.d. indicator plugged into the 12v socket next to the dinette. From that I can tell if there is anything to really worry about. Also if you have a battery status light(s) on the monitor panel you can calibrate it to your gauge or v.o.m. measurements.
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Old 06-25-2022, 01:10 PM   #9
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Personally I wouldn't worry about it.

Sorry, I disagree.


13.2 to 13.7 is a HUGE difference. If that .5 VDC difference is maintained lower in the SOC range, it can be very misleading. 12.2 VDC actual voltage (50% discharged) would read 11.7 VDC!!!


Start by cleaning all connections between house bank and meter-- both positive and negative sides.


If delta is over about .2 VDC, I would run dedicated wires to the meter to give you accurate readings.
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Old 06-25-2022, 07:21 PM   #10
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" 12.2 VDC actual voltage (50% discharged) would read 11.7 VDC!!!"




- By that point you'd be involved in more than looking at voltages- there would be signs of it elsewhere in the rv. Remember I said references to battery voltage were a distance from the battery bank.
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Old 06-25-2022, 08:37 PM   #11
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I would take my multimeter and see what reading you get at the panel to verify if there is actually a drop in voltage or if the panel is just not accurate.
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Old 06-26-2022, 03:09 AM   #12
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I would take my multimeter and see what reading you get at the panel to verify if there is actually a drop in voltage or if the panel is just not accurate.

Yep, that takes all the guesswork out.
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Old 06-26-2022, 07:21 AM   #13
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Why not take a couple readings from battery when panel says fully charged and when the inverter is charging at 90 - 95%

Also if possible try to measure at the inverter when it is charging.

Goal being to see what the charger is actually doing based on the settings.
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Old 06-26-2022, 09:57 AM   #14
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The voltage drop across a wire is proportional to the current. So assuming it's a voltage drop issue, try reducing your 12v load and you should see the difference go down.
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