Hi, I have a system that is off grid and currently with being no sun the genset has to be started to charge the batteries. Once the soc on the VRM get to around 80-85% the input current drops off and basically the batteries take a very small input current and stop charging? Does anyone know why this could be? Tia
How do you measure your SOC? BMS ?
Yes through the built in bms of the batteries through the VRM.
A few more details such as type of battery, size of battery bank and what amps you are charging at is required aswell.
They are li gen battery banks x2. 600ah each 53.2v
What settings is your alternator charging with … Perhaps the charging voltage is simply too low?
I have assumed the generator is producing ac and charging through an inverter/charger or charger that is set to a high enough voltage.
They could be close to full but the SOC is out of sync because it has not been fully charged for a while and needs the last bit of charging before reporting 100%. Some BMSs stop increasing the SOC during the final low current charging/ balancing stage and at the end of this SOC will jump to 100%.
Alternatively, they could have a poorly balanced cell that is higher than the others causing the BMS to stop charging early and go to balancing only.
In both cases, looking at the voltages will tell you if the pack is balanced or not and when charging is stopped if the battery is really at 100% or not.
So the generater is 15kva and when the battery soc is low it puts in the limited current set by a digital control but once the batteries get up to around 80% charge, the current drops off.
They haven’t seen a full recharge or soc for a good few weeks now. The bms of the batteries I haven’t got much available data for besides min/max cell voltage.
In this state of charging as they are doing so now. How long would you think they will take a small charge current for until they jumped to 100%?
The inverter is under external control from the BMS, so the BMS is restricting the current.
On the GX device, go into the Device list and click on the BMS or Battery, I can not remember exactly where and you should find a screen with the CVL and CCL, charge voltage limit and charge current limit which the BMS is setting.
If the SOC is accurate and this is a balancing issue this will take several hours, if the SOC is out of sync then it could be an hour or so for final charge. Hard to tell. It is worth giving them a full charge from time to time to keep them in balance.
20A is all the batteries want to eat at the moment.
As the CVL is 56.0V (3.5V for 16 cells) but the batteries are only at 53.1V (3.3V per cell for 16 cells) I am going to guess that the cells are out of balance and very slowly charging now to bring the packs into balance. Do you have cell info reported to the GX or available from the batteries by Bluetooth.
The max and min cell voltage difference throughout the graph have a difference of 0.2v so correct me if I’m wrong but wouldn’t you say they are pretty balanced?
The batteries that are installed are nice looking and very well performing piece of kit however the manufacturer haven’t given many insights to parameters or assistance regarding them or maintaining. They have remote access themselves and are pretty much in control of them but as the end user it’s not easy to have a good understanding. I appreciate your time and feedback
I was wrong, battery is well balanced 0.02V difference. I can not explain why the battery is limiting the current at the voltage it is reaching. It is definitely battery led, the Victron kit is following.
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Now the generator has been stopped already the CCL has increased to over 35A. The victron equipment seems to be doing what’s it’s controlled to do but seems to be some form of bms setting restricting. I will try to get hold of the battery manufacturers again on Monday to see if they can shed some light on it, and I will let you know what the outcome is. Thankyou for your time
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