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Ok that's the same relays I bought, so there might not be a thousand alternatives. About doubling up relay setups in parallel I would be cautious, if the circuit needs to be opened while pulling a high current there could be strange effects if both relays don't open exactly at the same moment...

Ok I see that your friend has designed some serious setup here. He uses a relay as the way the BMS cuts current through the battery. However there are no separate circuits for charging and discharging (hard to do because the Multiplus does both on one bus. So if the BMS wants to forbid discharge...

Heavy draw of the battery in the cold doesn't seem to be a concern for their health, actually I think it's better, the natural aging of the battery is slowed down in the cold. Discharging it will even have the benefit of warming them up a bit via Joule effect. However, you loose (temporarily)...

How do two batteries in parallel become unbalanced? I thought that could not happen because they both experience the same voltage anyway and that balance is all about voltage differences between components. I agree with one BMS needed instead of two.

It seems all right, but you can add as many wires and connections in your diagram, in the end what will matter is how you setup your system (voltage, amps, temps limits etc...) in regard to your connections. And the choices you will have to make for that depend on your priorities for this system...

Alright, then you can think about a tunable heat exchanger that could be setup across the insulated box wall: for instance an aluminium radiator with a fan attached. When the fan doesn't blow the heat flow from the box is not so fast (thermal resistance increased), but when it blows on the...

Yes exactly, that's the beauty of it :) If you take a simple case where both resistors are the same, then P = R*I^2 if you only put one resistor, and P = (R*(I/2)^2)+(R*(I/2)^2) = (R*I^2) / 2. That's actually also how you can prove too that 2 resistors in parallel that have the same resistance...

Very good question, I also tinkered a bit to find a good solution to easily charge the battery, especially when setting It up and doing the initial balance by charging all cells up to 3.65V in parallel. Indeed the voltage of my inverter/charger cannot be set so low. In the end I went for a...

@Steve_S can you confirm that the SoC that is displayed by the Chargery BMS is computed from the voltage of the battery and not from Coulomb counting with the shunt? That is the impression I got when I tested it and if it's the case it seems pretty useless (because of the super flat voltage...

Ok that's a good start already! I would be curious to know what the first calculator is, could you share the link? I have a hard time to understand the table it generated. "Kw" seems to be an energy unit but that's not how one would correctly write it: kW is a power unit, while kWh is an energy...

Also about the PV panels you should maybe check 300W panels (24V panels), I've seen some at around the same price of the 100W panels (12V panels I guess) that you're mentioning. So even a 9 kWp PV setup should be pretty cheap compared to the battery, around 3-5 k€ I guess.

Always nice if this can help you and others as well :) In your case I would say that the simplest and most effective for you would be the REC BMS, because it seems you will just have to plug in the CAN connector and wire everything to the battery and you will be all set. The Victron equipment...

About the Chargery BMS, it's stated in the data sheet that it features over temperature protection and differential temperature protection (between both temp probes I guess, but we don't know what this protection cuts: charge and/or discharge?). But what about low temperature protection, to...

Personnaly I would try to keep the BMS as the last resort fail safe, meaning it should only disconnect the battery from the system if all other regulations did not work properly. I would do that because I suspect that an MPPT-SCC would not be very happy from a sudden electric surge coming from...

Sure, I understand that the signals that the Chargery BMS outputs are made for Normally Open relays. It seems to me that this specific Smart Dual Relays was actually designed to be a drop-in replacement of such relays. They are not plain latching relays, but a driver circuit is interfaced...

I've just written a thread (there: Online tools to size (autonomous) PV setup) trying to compile the tools I came across during my research about autonomous PV systems. There may be some other tools you can use to help sizing your setup, hope this can help.

Do you have a better idea idea of your daily/monthly/annual electricity consumption, and does it vary seasonally? It should be easier then to size the PV+battery system you would need. Also do you intend to go completely off-grid or will you still have access to an electricity provider for bad...

Thanks @nosys70 for these explanations! A link to a nice thread about this question that I just went through quickly: https://diysolarforum.com/threads/incrementally-adding-dc-batteries.186/ I understand better now why putting two batteries in parallel can have issues. Indeed paralleling two...

Maybe a super simple solution to this cold problem for people using NO relays controlled by their BMS (typically Chargery): just put the relays inside the insulated box containing your cells, this way the "wasted" energy used to keep the coils powered will be used to heat up the cells. Maybe...

Let's hope it's just a balancing issue! Because yes the cells may have arrived at the same voltage, but because they are sent with around 50% SOC (which is good) they are in the flat part of the Voltage v. Amphours curve. So it could be that the first cell was actually at 45% SOC while the...

I found out latching relays with driver circuit (or just driver circuit) that do just that in this post https://diysolarforum.com/threads/chargery-bms-now-with-low-temp-cutoff.3153/post-30137 if you're interested. I guess I'll go with that for my setup, at least for the discharge relay (for...