Three weeks after installation of hybrid power plant for mobile operator, we couldn’t solve issue with unstable DC charging of MultiPlus II.
The concept of the system is as follows:
16x PV panels - 460Wp and 8x PV panels - 565Wp
3x SmartSolar MPPT 150/70
1x MultiPlus II 48/10000/140
5x Felicity Solar LPBF48200-M (9,5kWh, 200Ah)
1x GenSet - 13kVA, with ComAp AMF 25 controller
Power consumption of site - 1,5 kW - 2 kW. Power factor is 1.
All of the firmware are on their latest versions for all equipment.
BMS is established, but due to poor implementation of Pylontech BMS which gives us headaches (giving fake readings in short time which causes MultiPlus II to turn off, etc) on 4 more locations too, BMS is turned off. Parameters on MPPT and MultiPlus II are configured manually.
MODBUS is established via ComAp AMF 25 controller and Cerbo GX via 4G router.
DC charging from MPPT controllers work perfectly fine. There are no spikes or drops. Voltages are fine.
And now there show goes… When GenSet is turned on, MultiPlus II switches to bypass mode to power mobile operator and to DC charging with 120A. GetSet works normal for 5-6 seconds and then its RPM start to vary, together with power factor and MultiPlus II DC charging current. Those variations are big enough to cause MultiPlus II to shutdown due to overfrequency protection. That stage of instability continues for next 5-6 seconds and then charging and GenSet are stable for next 5-6 seconds and the process repeats.
What we tried:
Changing MultiPlus II;
Checking cables and connections;
Turning off completely Cerbo GX and communication - leaving GenSet and MultiPlus II independent;
Chaning Generator and AVR on GenSet;
Updating every all of equipment to the latest firmware - even on batteries;
Turning BMS on and off;
Trying to charge batteries one by one, and there is instability on all of them.
Trying to power resistive bank and load GenSet to its maximum, also varying load. Everything is working perfect.
Tried with “Weak AC input” option in VE configure and it works fine, but with charging current of 80A.
Tried with toggle on and off Dynamic current limit and Power assist in VE configure - no luck.
Tried with disabling VSense.
The problem is even worse because we built up hybrid power system on 2 other sites after this one - with identical equipment, except batteries, which are now BSL batteries (10,24kWh, 200Ah, 5 pcs per site). Also I want to double mention that MultiPlus II and GenSet are the same on those 2 new locations and everything is working perfect and stable.
In this equation, only Felicity Solar batteries are suspected, but there is no logical explanation for me how is that possible. I want to double mention that batteries are charging fine with MPPTs, even with 11kWp in some time.
Every advice will be very appreciated, to reduce headaches here
1 system with 9 MP2 15 kva and 40 batteries Weco 4k4 and a genset of 150 kva. Impossible to draw more than 60 kva… And with another genset of 100 kva. Not more than 40 kW…
The genset begins to be unstable and give Big fluctuations of voltage and current.
We don’t understand how to solve that for now… WE followed all the recommandations of Victron. I install for 15 years.
Srđan: I’m not familiar with many Felicity Solar batteries, and their web page looks weird putting “ion” and “LiFePO4” in the same line, which one is it???
Here’s a theory; Are they are 100A BMS or a 25A BMS?
There are some weak BMS that rely on you having X in parallel to keep the individual currents per battery low. If your input current is X, and X/5 is higher than its limit, lets say hitting 26A when the limit is 25A, it could be tripping. Then, the others will now have X/4, which will definitely be too high, and this cascades down the pack in milliseconds, then the current stops (nowhere to go), and they all come back online.
Given your 80A test worked (the “Weak AC input” option), but not the 120A “normal” case, i would try turning off “Weak AC” and setting the battery current limit to 80A - if you are ok there, up that to say 90A, etc until you get the fault, then back off.
We will try to swap genset completely soon (probably next week).
One month after I wrote this post, this problem occurred on another site and now we have 2 unstable sites (of 6 in total) with almost identical equipment except batteries - first site uses Felicity Solar, second site uses BSL battery and length of the cables).
Conclusion is that batteries (BSL batteries and Felicity Solar) aren’t the cause of the issue.
I’ve also tried that, but didn’t work - both for Felicity Solar batteries and BSL batteries.
Felicity solar batteries have poor implementation of BMS (it’s from Pylontech) and we have big headaches with it. It gives wrong information to the MultiPlus II and MPPTs (for example - battery voltage “suddenly” drops to -4104VDC?!, battery temperature goes to 1041C, etc), which caused shutdown of MultiPlus II on 5 minutes (which is unacceptable for mobile operator). Those fake informations are given in few milisecond which cause shutdowns.
To avoid this problem, we had to set DVCC parameters manually.
Firmware of batteries are the latest one, Venus OS too.
BSL batteries are way better than Felicity Solar ones.
Are these batteries on the VE.Can bus? If so, do you have the terminators on both ends? Terminators are often not required, as serial is rock solid. A friend of mine ‘invented’ (joking here, someone is bound to have done this previously) a protocol he called SoWP - Serial over Water Pipe. If you put your serial negative onto an earth probe, and push a hot wire (the positive) into an alkathene (an insulator) water pipe until you get the wire inside the pipe but still sealed, and there is enough salt in the water, you can do the same 100m away and run low baud rate serial through just the conductivity of the water (with the earth as the return).
But … with batteries, at 500kb/s (although this isn’t particularly fast for serial) and lots of sockets and plugs that make up the bus which the signal has to flow along, if the signal gets too distorted by reflections, interference, etc, the terminators help a lot.
A mangled packet or noisy line could give you a number like -4104V - that’s probably just one or two bits being flipped.
