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.
Terminators are installed on both ends, even the connection works with terminator on one end (BMS.Can). Interesting thing is that the more power consumption is, the more common are data transmission errors.
Below are screenshots of battery sets from 2 sites. First site has average consumption 3.5kW, and second has 1.7kW. You will see that there are spikes in SoC (which indicates error in data transmission - in that moment battery voltage, current and temperature are also affected) on first site. Second site rarely has spikes (there aren’t shown on screenshot), but power consumption is half comparing with first site.
First thought about spikes/fake data is that batteries are unbalanced, so we charged them to 100% and that gave us better results - less or no errors in next few days. Cables from DC bus to the batteries are the same length, batteries are never discharge below 25%.
BSL batteries don’t have this problem and balancing is well done.
Awesome. Always good practice anyway for the beginning.
Yeah agreed.Possibly that disconnects due to balance issues causing spikes on disconnect and reconnect.
Happens on some batteries where their synchronisation or full charge detection is a bit off. BSL does a weird thing when if you are charhing hard , then diwconnect all charge sources wil also trigger a false 100% on some firmware.
Good to know, i have seen charging issues with daisy chained bigger banks. Also causes disconnects and random shut downs as one or twobattery get unhappy.
I tried that too, and the system behaves a little better, but still not stable as it should be. There is no set current values on which genset operates completely stable. Site equipment has power factor 1, as MultiPlus II has with disabled weak AC input. If we turn off DC charging on MultiPlus II, Genset is working perfect. When DC charging is turned on, then genset goes crazy and of course power factor. The worst situation is when only DC charging form MultiPlus II is enabled.
We changed generator, AVR, but nothing helped. From the readings, we didn’t see any overload on genset if we talk about apparent power. Maximum recorded load from genset is about 10kVA. If only DC charging is turned on (no AC output), MultiPlus II consumes about 6.5-7kW, and that is almost the half of genset available power, so the genset shouldn’t have struggle with delivering that power, even with power factor 0.9 - which is the lowest recorded in unstable operation of genset only with DC charging.
This week, we had operation of switching gensets on two sites. On first one genset work unstable, on second one works great. Guess what… Genset from first site works perfectly on second site - back to square one.
Yet, we don’t have any assumption what causes this issue. At least, we are now 100% sure that batteries, genset and MultiPlus II aren’t cause of this problem. Also, we tried with different lengths of AC cable from genset to the MultiPlus II - it’s the same.
We noticed that genset works a little bit better when it’s warmed up and thats all.
Edit: forgot about questions
All of batteries (5 pcs) are connected parallel to the DC bus, with the same length of cables.
I tried, but it didn’t really helped. Instability is still present but to a lesser extent.
BMS.Can is terminated.
Felicity Solar has charge/discharge limits 400/400A, and BSL batteries 800/1000A.
Of course, we have tested this when SoC was between 40% and 70% and temperature above 15C, to exclude possible limitation in charge.
Yeah, here is mine experience about SoC of BSL.
Charging to 80% goes as it should be. From 80-90% current drops and it takes some time to reach 90%. After 90% to about 93% charging is much slower, and finally when reaches 93%, it goes instantly to 100%.
On the other side, if batteries are constantly charged from 25% to 60% for some period (about 5-7 days) - which is our case, because genset primary charge batteries (in that SoC range) due to lack of the sun in those winter days. Voltage of batteries drops below 50V on SoC 30-35% and the genset must be started to charge batteries to 100% do compensate this unbalance. In real case, SoC is below 20% if voltage is below 50V.
BSL BMS isn’t that accurate with SoC, but it does decent job of balancing cells and at least doesn’t have problems which Felicity Solar has.
The genset is planned to be permanently on site. Because of test, we have to move one genset to another site, to exclude potential problem with genset. Also, all of other equipment is permanently on site.
Then take a look at the charging current control wizard.
You could install a temperature switch on the genset and keep the charging current lower when the engine is cold.
When the engine has reached operating temperature, the charging current is regulated to maximum.
A simple switching contact via a thermal switch with a capillary sensor is sufficient.
If the whole thing is to remain mobile … a simple time relay could be connected to the AC in, which then simply switches over after a time x and the charging current increases.
Yes, we considered that because something is better than nothing. Pre warm can be set in Cerbo GX, which will help. It takes 5 minutes for engine to get a little bit more stable - in our case.
