question

pilotchuckles avatar image

Multiplus II charger voltage inaccurate

I just installed a MP2 in my RV. The charger is set up according to the setting recommended by the battery manufacture: Absorption 14.4V and Float of 13.8. Most of the time the MP shows appropriate DC voltage in this range but only produces around 13.1 to 13.5 V verified by a multi meter. This low voltage allows the battery to discharge even while plugged into shore power. If I change a setting by even .01 V on the MP, it quickly displaces it current produced voltage and then jumps back up the appropriate charge voltage and charges the battery. This however only stays this way for a short time and then the voltage being produced drops back down in the 13.2-13.5 range while the display still shows a voltage in the 13.9-14.2 range. I have updated the firmware, but that did not seem to make a difference. Both picture were taken at the same time. Any suggestions? 2021-10-24-22-23-17-000.png2021-10-24-22-23-06-000.png

MultiPlus Quattro Inverter Chargerbattery chargingvoltage
1635466724906.png (153.9 KiB)
1635466791463.png (122.6 KiB)
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3 Answers
Paul B avatar image
Paul B answered ·

the first picture I think is from a BMV unit The secound is from your inverter charger , these are two separate units, if the voltage is not the same then you have a voltage drop between the Inv/Charger to the battery.

also you may have a cerbo or venus device and this sets what unit is to control the charging settings, ie the battery monitor that is to be used


the multi will only show the Voltage at its terminal and the amps charge or the amps used BY THE MULTI

the BMV bat monitor show the net usage going into or out of the battery.

use a mutil meter and check the voltage AT the inverter termials and then check it also at the battery terminals both should read the same.

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pilotchuckles avatar image
pilotchuckles answered ·

I used a multimeter and the voltage coming out of the MP does not match what the display shows. The output is constantly .5 +/- .1 volts less than what the display is showing. This has been verified at multiple voltage settings.

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It would help if you posted the MP settings.

Here are my charger settings. settings.png

settings.png (60.2 KiB)
kevgermany avatar image
kevgermany answered ·

Shouldn't be, but did you check for cable resistance/drop?

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Yes, the voltage coming out of the box matches the battery voltage and is not the same as the voltage the MP states it is creating. If I change a setting the voltage display corrects itself and matches the actual produced voltage and charges the battery. This works works until it goes into float mode and then the disagreement starts again.