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Todd Wallace avatar image
Todd Wallace asked

MPPT 100/30 not fully charging 12v AGM according to BMV-712 monitor

Hey, so i've been running a BMV-712 battery monitor for awhile now and recently upgraded my solar charge controller to a victron mppt 100/30. everything is running the latest firmware. according to the app, it spent 1 hour in absoprtion and reached float, but the battery monitor says i am short -6 amphours into my 100Ah AGM battery. what am I doing wrong? I know its possible to link the two devices but havent done that yet. will that help? exactly how will the MPPT knowing the actual SOC affect the different charging stages of the solar charge controller? also the voltage measurement on the mppt seems higher than the voltage reported by the monitor. actual battery voltage measured with a multimeter shows the monitor is correct, and the mppt higher by maybe 0.2 to 0.3 volts. thanks

MPPT ControllersBMV Battery Monitor
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Trevin Corkery avatar image Trevin Corkery commented ·

I am not sure if this will help, but if both devices are "Smart" do you have the "VE.Smart Networking" setup? This would allow the BMV and MPPT to share such as battery voltage, temperature, etc and probably allow for a better charge.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi Todd,

The missing Ah is explained in the manual for the BMV-712, so have another read of that. It's in section 3.3.

If you have a SmartSolar MPPT, or a new Bluetooth dongle you can create a VE.Smart Network with the BMV-712 so that they share the battery voltage. Otherwise the BMV will have the more accurate voltage reading.

The State of charge will have no effect on the MPPT's charge decisions. It will make those based on time, current absorbed and the voltage reading available to it.

The State of Charge is for you to help with the management of your system.

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Todd Wallace avatar image Todd Wallace commented ·

Thank you for responding so quickly. Yeah, I understand about the peukert exponent and charge efficiency. I used the datasheet for my AGM battery to setup those values correctly. The thing is, my previous charge controller (not victron) was within 1 or 2 Ah of 0 with the appropriate settings from my battery info. The previous controller would stay in absorption longer given the same starting voltage etc. I know the tail current for the MPPT 100/30 is fixed at 2A and cant be changed unfortunately. I think the issue might be that my system is small and sometimes the loads are small (maybe just 1A), plus in New England we have intermittent cloud cover where the panels are sufficient to reach absoprtion but not enough provide over 2A. In regards to the voltage, I will defintely setup the VE. Smart Network, but im a little concerned about the difference in voltage readings. The MPPT is currently reporting 13.4 volts out to the battery whereas the monitor is saying 12.77v. thats a huge difference. is that normal? just want to make sure i dont have a problem with my controller.

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