question

Try setting the Absorb Voltage in the Multiplus to a value +0.1 v higher than your MPPT. See if that will temporarily solve the problem. Are you sharing the charging information between the Multiplus and MPPT?

Post an image of your battery and charging parameters.

Looks as if the BMS is shutting down the charge, not the multiplus, as there's a big voltage spike immediately after the shut down point.

Is the solar charger running at the same time as these graphs above? Would help to see the graph from the solar charger at the same time.

What happens when it's just the multiplus charging?

How big is the battery? Max charge current? Solar charger model/output?

hi all,

thanks for your quick replies. Here are the missing information:

• General info: the camper van setup is the following: the lifepo4 battery can be charged either via solar (2*200W) MPPT 100/30, via AC (Multiplus 12/500/20) or via starter battery/alternator +DCDC converter (max. 25A) with LiFePO4 charging characteristics on the road. However only one (or none) of the options is used at the same time.
• Therefore no charging information are shared among the devices.
• The lifepo4 being used has an internal BMS which is accepting charging currents up to 100A (BullTron 12V 150Ah Basic). While charging on the road from DCDC converter the battery is accepting up to 25Amps without any issues.
• The MPPT charger is used with two foldable 200W solar panels which however weren't plugged in when I noticed the suspicious behavior of the Multiplus.
• I am not able to change any parameters of the multiplus (beside these which can be modified via dip switches) because I cannot access it via Bluetooth and I don’t have the VE smart dongle.

I hope these information will help to understand the issue and can lead to any kind of solution.

Thanks a lot

Just a guess. Check the cabling from multiplus to batteries. Switches, fuses, connection tightness. I'm surprised by the low charge rate and cut outs.

Also check multiplus temperature. Is it getting hot/fan coming on?

I have some more information right now. I stopped the charging process yesterday evening since I was not able to exceed 94% SoC.

Over night the soc dropped to 85% due to the running refrigerator and so I turned on the Multi again this morning. Now I can observe the same behaviour as last night but the recorded data is much clearer. First the charging works fine with like max. current and then the system enters the incorrectly behaviour again. See attached screenshots (the last images shows the whole charging process from 85% to 94% SoC)

Hi!

Have exactly the same problem, did you find a solution?

1) I don't have VE configure so I have just put the dip switches to LiFe
2) My 400Ah Battery (LiTime) can be charge to 14.6V according to technical documentation, so the BMS shouldn't be activated, but?
3) No Solar connected

The problem occurrence when reaching about 13,9-14,1 charging volt

I think there could bee a imbalance in the cells in the battery. If you can try observing the cell voltage.

one of the cells could go over max cell voltage and the BMS would shutdown the Charge.

Sounds logic, but it is a completely sealed battery with BMS, so no way to measure cell voltage. What voltage do BMS usually need to balance cells, I'm thinking if I can provide that voltage over some hours...?

This behaviour signals, as has been mentioned, the BMS is cutting charge because one of the cells is going above 3.65v. This happens quickly with lifepo4 because of the knee in the voltage of the charge curve.

I build my batteries out of used lifepo4 cells because it is very cost effective to do so. They are almost always going to be in varied condition and won't be in balance. I have to deal with this all the time.

Charging to 14.4-14.6 is only possible if your cells are perfectly balanced, or you have a cell balancer which is able to keep up with your rate of charge. In a sealed/preassembled battery its hard to know what is going on.

Solution: Set your absorb voltage to 13.8v - extend your absorb time and/or use the tail current to switch to float. You'll still get to ~90%+ the capacity of your battery, you will extend its usable life, and you'll give the internal balance mechanism whatever it might be a bit more headroom to work with to balance your cells.

The ONLY time I charge lifepo4 to 3.65v/cell, is in a disassembled state to top balance them prior to assembly or maintenance.

My experience with bms in dropin batterys, are they have a hard time to keep cell balanced.

Normaly the only solution is to extend absorption time and reduce voltage as @R0bb0 recomend