Juraj Nikolov avatar image
Juraj Nikolov asked

Battery combination

I want to ask such a strange question, is it possible to combine Pylontech batteries (4x3.6kWh) and 2xLifePo4 280Ah on a common connector??? .
What I noticed in the documentation is that the pylontech charges the batteries at 3.467V (52V) during absorption and the Float charges at 3.4V (51V).
My point is that I have both types of batteries and I would like to use their capacity. When they are connected in parallel on the bus and the parameters are set in the BMS for 280Ah batteries, it should work safely.
Basically the charging would be controlled by the Pylontech BMS or not controlled by the Pylontech BMS and the Pylon BMS would adjust the charging current and voltage by itself like the other two BMS now, only the toy cables that come with the Pylontech can handle 100A continuously AND the charging from the MPPT must not exceed 100A, so I won't use the potential of the panels :).

So this would be a question of how long it would last and if it could be solved or if two more batteries could be charged, I suppose not, but maybe someone here has already tried it :)
Or I can use SmarShnut and set it to 856Ah, plus Abs.V 52V, Float.V51, Abs.Time 1h ...

Crazy or not??? : )

Thank you for your opinion

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johanndo avatar image johanndo commented ·
The BMV or SmartShunt only measure Amps in and out and Voltage and calculates Ah, W, Wh, it doesn't control charging in any way, it is like a Multimeter. So Absorption Voltage, Absorption Time have no meaning to them
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1 Answer
Alexandra avatar image
Alexandra answered ·

@Juraj Nikolov

TLDR at bottom.

I have a byd and randomo brand mixed system at home for the sake of this exact experiment.

They have exactly the same charge parameters needs/bms capability. (Voltage and amps for each stage) BYD controls the system (needs this as the GX keeps the batteries live), so the charge rate is lower than the two banks can handle max (but this is not an issue.)

They are bus bar connected so separate to each other but adding capacity and fusing etc for safety. Battery cables the same for good current sharing.

No issues so far as the combined setup has the full current needed to supply the system at full capacity and overload.

Both sets charge up and balance. And both sets discharge ok. We have had one battery from the non byd shut down, randomly not even sure why (possible reason was a PV overshoot on a large load disconnect), but after restart had no other issues since Would I do that for a customer no, but for our own interests or experiment, yes.

TLDR if the charge voltages of both are the same you should be fine if on a bus bar.

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Juraj Nikolov avatar image Juraj Nikolov commented ·

So then it should work... Great.

Otherwise, if on JK BMS, I will set the charging voltage for each cell so that it corresponds to the charging voltage of the Pylontechs, and in the DVCC I will limit the charging current to a maximum of 100A, it should work :) .

Otherwise, if I set the Cell-OVPR to 3.5 in JKBMS, which I have, I don't need to change this, next I have a cell-UVP of 2.8 according to the pylon, it should be 2.75, that is also OK

Start balance 3.45V , according to the pylon, it should be 3.467V thas is also OK.

Otherwise, the JKBMS settings what i have are very close to what Pylontech has, so hypothetically it could play togedher.

It's a shame that GX does not support JK BMS via CAN...

Another thing I regret is that it does not support two BMS via RS485, but only one.

Do you happen to know if it is possible to log JK-BMS via RS485 to Grafana and from there forward the logs to VRM? I would like to have information about the state of the battery packs in one place, I don't need GX to control the charging of the battery packs, but the logs from the BMS would be great, at least in the testing state so that people can see what's going on. Probably sould be possible to make some one device with as has the Pylon, they also comunicate via RS485 and then by output via CAN. That will be next advance level :D

And sorry for being annoying, I have one last question.

I'm a bit disillusioned about whether or not to ground DC behind MPPTs (common grounding witch use AC) ??? It seems stupid to me... but to be sure, before I try it, I'll try to ask the more experienced. I am a noobie and I still learn, I am not profesional in this important details. SPD from panels i got grouded at the common ground (with AC that I mean it is OK, if is DC grounded to AC).

I am of the opinion that DC should be separate from AC, I mean by grounding. Otherwise, it is better to use DC - not to ground it as to clamp it to the common ground from AC.

Am I wrong??? I wouldn't like to burn out :D so I'd better check 10 times... :)

Thank you very much for the advice.

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Alexandra avatar image Alexandra ♦ Juraj Nikolov commented ·

@Juraj Nikolov

When you are grounding the case of the mppt you are not grounding any DC. It is there if there is ever a fault that needs to go to ground.

The easiest way to log two different batteries to the vrm is with the either some BMVs or smart shunts

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Juraj Nikolov avatar image Juraj Nikolov Alexandra ♦ commented ·

So if I had... which I didn't have :P but I already have grounded MPPTS bodies :) so DC minus, it's not grounded, I also haven't grounded it yet, so I'm not ground it - never ;)

As for BMV or SmartShunt, but it has no way of knowing the state of the battery cells, the BMS knows it, or what hapenings with the cells, SmartShunt is not smart enough for that :P

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Alexandra avatar image Alexandra ♦ Juraj Nikolov commented ·
@Juraj Nikolov

Yes each BMS controls its own battery, (this is notmal in any system) even with a matched stack bank.

The SOC of each battery to report to the system can be achived with two BMVs to report to the VRM was my point.

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