Yet another solution: what about adding 3 more MP II so there will be 6 in total. BUT - the additional three to be switched off for most of the time and only used when i’m doing some power hungry things in my workshop. The question here is: how Victron system will handle powering those additional three MP II’s (one per phase)? I can only switch them on one by one - will the sync to the already running MP II’s? It is only about powering them on and waiting for them to check the voltages, phases and then they will connect seamlessly?
Hello Bogi, interesting project!
Yes, you can use 6 instead of 3 MP, but keep in mind that this needs to re-configure your system for usage of 6 (3x2 in parallel mode) to work properly. From that on, turning off three of them (or even one) to save standby energy would cause the whole system to shut down. So all of the 6 MP have to be switched on, allways.
Since as you wrote you do NOT need that much power 99% of the time to run all your house without the workshop, it would not be cost effective to have more than 3 MP. The system design as a whole should match the requirements for the most frequent use case. So my suggestion is to use the smaller setup and staying off-grid for most of the time and only going on-grid when running your workshop. The grid can handle load jumps easily, while your system provides enough power for the more even distribution while loads running continuously.
Yes, it’s right that the reaction of the MP system to load jumps causes short term spikes in grid feed-in, but same applies for power regulation of any inverter. So having big load jumps without grid tie may and will cause heavy voltage spikes or drops which may damage other connected stuff over time. So being on-grid for this will do the trick though. The little feed-in spikes will not do any trouble since in most cases especially without bi-directional grid meter (like apparently in your case with feed-in being not allowed) no one will notice them at all!
That being said, I recomend using DC connection for all of your additional PV modules, since this is in your use case more effectiv most of the time.
Hope it helps!
1 Like
Hi Boggi,
I see something that looks like Slovakian language there on the sheet. So just wanted to tell you, if you’re not happy with the battery setup you’re testing now, check out Akumulátor LiFePO4 48V/280Ah - 14,3 kWh - VERTICAL - bílá | E-pohon - elektrokola a sety na přestavbu pro všechny . It’s great value and I’m sure they ship to Slovakia. The quality seems to be top-notch, made in Europe, near Brno in CZ. I’ve been to their place - it’s legit producer and they sell it mostly via their own web. They make sure to buy A-grade cells directly from EVE and quality checked JKBMSses and workmanship is great too. They support Victron products, in fact recommend. I’m super happy with the battery (have it for about a year) and it’s even cheaper now.
The way I see it, it’s very difficult to justify messing with old batteries with prices of safe LiFePo4 ready-to-roll batteries like that.
Anyhow, good luck with your DIY effort!
Thanks guys. Not Slovakian but i live 30 km from Slovakian border:) I’m very happy with my setup, learning curve is very interesting.
Guys, is it true that Victron went cheap on 4k5 and 6k5 models and used aluminium wires in the transformer! I’ve checked and compared MP II 48/5000 and MP II 48/6k5 units - they weight the same 29 kg while the latter one is slightly bigger enclosure. WTF?!
I do not know if it’s true, but for bigger chokes and transformers it is perfectly normal to use Al for the wiring in the coils. Primarily to save on weight.
Professionally I work with VFD’s up to the Megawatt range. These all have aluminium windings. Only thing to take into account is the corrosion on account of the dissimilar metals when connected to copper busbars. But that can easily be mitigated with special grease or CupAl washers.
It is pretty away from “perfect”. I think it was primarily to safe… money. We need details - what is the change is cross sectional area between 5000 and 6k5. Cheap materials are cheaper for a reason. Look at the power tools. They went from full copper windings to CCA and bye bye reliability. Overheating issues became something normal - easy fix: decrease duty ratings:D
Just sold my 3 x MP II 48/5000. Will need more power. Gents, is it better to go with 3 x 6k5 model or 3 x 48/8000?
8000 can still be more loaded, yes, it is more expensive, but maybe better suited for highly unbalanced application? I need off-grid operation but will have to keep AC_IN connected to back up in case of heavy surges. Hopefully no issues with configuration to have zero feed-in. I read that in ESS mode Multipluses passing AC_IN through and kicking in as inverters when grid goes off. Can they be in inverter mode all the time and have AC_IN connected at the same time?
Hello Bogi!
Since it’s not that big of a deal moneywise compared to the 6k5… go for the 8000! Or consider the 10k or 15k…
Projects allways tend to become big and bigger as soon as you learn more and embrace the benefits of the victron ecosystem. You won’t change your gear every now and then, so do it once, and do it right! ;O)
All the best!
1 Like
Thank you Thomas for your input. It is in general in line with my thoughts. There will be 6 batteries attached to the system, 16 x 324Ah cells each. Ca 100 kWh in total. I heard somewhere that Smart Shunt is not recommended in bigger systems (is 100 kWh already big enough?) - BMSes data is used. Currently, in my experimental installation, i have 500 A shunt from Victron but with 3 x 8000 it can easily be saturated. If not then still it is just an additional power loss element. Looks like i’m gonna sell it once confirmed JKBMS is working fine with Victron and energy in the cells is measured in correct way.
Hey Bogi!
I use 9 DIY modules of 16x315Ah (145kWh in total) with JK-BMS PB1A16S10P on 3x MP II 48/5000. From my experience I highly recomend using a Smart Shunt (for me 500A does the job, for you 1000A would be the better option). The JK in general are fine, connection to the Cerbo via Battery-CAN was plug&play after setting the right protocol. But the current measurement of the JK is not good enough. For calibration only one single point of current value can be used, which would be nice if the measurement unit would work linear - but it doesn’t! Within only a few days the SOC values of all the JK drift appart (slightly against each other and in high rates against the Smart Shunt) and the reported overall value is complete useless garbage. Since the SOC is core parameter for the whole system management, this does not work out without precise measurement.
Hope it helps!
1 Like
Thank you, Thomas, for your input. As i already have S/Shunt 500A i’ll stay with it until i face the saturation on it when drawing anough power from batteries. Then will consider going for 1000 A. I saw some posts people were complaining about JKs interfacing with Victron - to be more precise: daisy chained JK BMSes were not able to exchange all the required data with Victron ecosystem properly. So you say you have no issues? JK v19?
Yeah, SOC driffting is so annoying. Seems like there is no good solution for it so far:/
Hey Bogi,
last issue first… what’s actually drifting is not the SOC itself but its reading by the inaccurate measurement and calculation within the BMS (well, hopefully the calculation per se is not faulty, but the measurement is non-linear so the calculation gets the wrong data in the first place). Calibrating at a top current of lets say 80A leads to correct results near arround that current but inaccurate readings at much lower draws, what leads to increasing deviation between calculated and actual amount of charge. For me using the SmartShunt sufficiently solves this. JK is v15.41.
Yea, the interfacing between JK and Victron may or may not be kind of an issue, but it highly depends on what you expect. The daisy chaining of a bunch of BMSes via Battery CAN afaik was never meant to transmit all of the data the BMS provide. And the JK provide a lot of’em! In order for the system to work properly only a few of them are really needed or used, and just these data are all available in the Victron system. Even DVCC works technicaly fine, as long as the SOC deviation does not play out to much. Since the reported overall value is the mean value of all single BMSes, deviation between them does not affect. When top charging with ballancing is reached every now and then, the SOC are sync’ed and reset.
I do not use DVCC, it’s more the like plug&play thing where the battery tells the system how to behave. Not mine… I coded my own dynamic ESS in NodeRed so the system is in control of everything. DVCC would go against that.
For more data being available a connection via USB-to-RS485 adaptor is an option, but needs more software tweaking in the GX device. Without further programming on your own terms, these additional data to be seen in the Victron system is impossible and more like nice to have and play around. Usefull? Nope. At least not for now. For me it is much more convenient to connect the JK App that way to my batteries and see all of the provided parameter and data perfectly sorted. Better than this would not be possible within the Victron system.