Hello, I have a system consisting of a Multiplus II 48/5000/70-50 inverter, a 250/100 MPPT and another 150/100, a Color Control GX and two Pylontech US5000 batteries. The issue is that, for the past few days, it has started exporting to the grid before the battery reaches 95%, as it used to do until now.
I’ve noticed that the battery’s BMS says 60%, while the Multiplus shows a reading of 95%, switches to absorption and exports to the grid. This happens when it reads 51.90 volts.
You should never see 2V difference between MP2 and battery.
Please check and clean all DC contacts.
In addition you could add a V-sense line.
This is an around direct connection from MP2 to battery plus to measure voltage not via the main DC cables. This will compensate the difference.
But you need to find the root cause, e.g. loose contact as this a safety / fire risk.
If you have an IR/remote temperature measurement drive or IR camera, charge/discharge to grid (ESS grid set point) or use other ways to generate load on DC cables and battery. Then measure temperature on all contacts with the remote temperature measurement device.
Well, I think you’re right, as I found this while investigating. The middle cable is burnt, and it’s the negative one that goes to the battery. I’m going to replace it with a new one. Thanks for your help
Please substitute the DC bus bar by a Victron Lynx Distributor with fuses sized for your cables.
With some additional hardware and some free software, you get alarms in Venus OS und VRM if a fuse is blown.
See my system thread linked in my profile, which includes all items needed.
Attention!
Before connecting both batteries to same DC. Us bar they need to have same voltage.
Charge m/discharge alone to appr 60% SOC and check voltage. If voltage is around 0.1-0.2V same, you can connect both batteries while switch off.
If you have higher difference you batteries can supply up to 2000 Amps! So the step to check voltage is very important.
After having connected power again your system, charge to 100% SOC and keep it a few hours.
This will give the batteries that was not charge the last weeks time to top balance.
