Questions for my New Solar Shed Project

I’ve started collecting and processing 18650 cells that I will be integrating into a 7S##P battery in my solar shed project that that will be based around a MPP Solar LV2424. Any feedback on my design below would be much appreciated.

I like the idea of building a DIYBMS, but this is not an all in one solution. I do have some outstanding questions regarding this type of solution:

  • From what I can tell I would need to either add some sort of battery disconnect controlled by DIYBMS (shunt trip, contactor, other?) to shut off the battery in case of a problem. What is the best/most efficient way to do this?
  • Do I need to add some sort of disconnect to the solar panels as well? or will the MPP take care of this?
  • Do I really need a shunt to measure battery current? What if I omit this?
  • Are there any thing else I need to consider for integrating a DIYBMS?

Thank you all in advance for any feedback.

If you use the ESP32 CONTROLLER you may switch Relais when a problem appears.
Also a large one which could disconnect the battery.

The MPPT will normally not take care. If you need or not… Up to you.

No. Depending on the inverter this one may also measure current.
If you work completely without current measurement you can’t regulate the charge.
Especially if the BMS detects a high voltage in one cell.

It’s a passive BMS. If a cell gets over voltage energie will be burnt. Not transferred.
If the cells are well balanced it works. If not you are a little in trouble to synchronize.
I have the case because I was to stupid to initialize the cells good enough before using.
It took me 2 weeks to synchronize from 250mv difference to 20mv.

Thanks for the reply, greatly appreciated. I was planning on going with the ESP32 as it offers more.

Hey @TheStealth , I have a very similar setup to yours,
For the 2P 125A DC breaker between the Inverter and the battries I am using a :hager HLF299S breaker

and attached this is a shunt trip to it so the BMS can auto disconnect, this shunt works on a voltage range fron 12v-48v

between the breaker and the battery I have also added a Jean Müller NH-Fuse Switch Disconnector KETO-00 on the positive line, I am using 80A fuses as I have a 14S3P bank made from 18650’s

The reson for the KETO Fuses is that if something really really bad happens the breakers above only have a 10kA Short circuit rating, and anything above that could potental create an internal short and render the breaker useless and still allow current thorugh, where as the NH fuses have 120kA,

For the solar panels I have installed fuse on each of the positive lines of ea array, and have matched the fuse at 100% of the max amp he array could produce. Then I have again added a DC breaker. The Solar fuse are smal 38x10 15A fuse, din rail mounted type.

With regards to the DIYDMS shunt, it’s not nessesery, your inverter will be setup to charge Li-Ion battreis, and the BMS monitors the cells and the pack, so if you over/under charge either of those your rules should trip the shunt trip above.

I am currently using the original Controller and a relay board to apply power to the shunt trip if one of my rules are met.

I hope this info helps

@rolfbartels Thank you so much for the information! I also had the same thoughts of combining fuses and circuit breakers for added protection. Out of curiosity, where did you purchase these components?

@TheStealth I’m in south africa, so got them from local suppliers