Upgrading 24V setup - BMS/heat pad questions

Hello Everybody,

I'm upgrading my current setup which was had 2x 80aH AGM (in 24V setup) batteries in my remote off-grid summer house in northren Poland and have some questions.


My currect setup:
- Panels: 4x 285W in 2S2P configuration
- SCC: EPEVER MPPT TRIRON 4210N 40A
- 24/7/365 Load: Security Alarm system that uses around 200mA at 12VDC (using a 24V->12V stepdown)
- Only during April-Sept: 1300W Inverter (2000W peak, with slow start mode and remote trigger) to power: 450W Pump, Small Fridge, small 20W circulation pump, 250W Garden pump, coffee ginder etc.
After puting it all into a energy audit calc I got around ~2kWh per day

Im currently getting quotes from Alibaba for 8x 272 Lishen LiFePo4 batteries.
The best offer I got is from Amy from Shenzhen Luyuan (Product price + freight = $70*8 + $243 =$803).
The batteries will have little visual flaws, but I was assured that the IR, and capacity will match and be up to spec (hope so ).

Questions:
1. Choosing a BMS
The undervoltage will be controlled primarily by the inverter protection (22V) during high power usage, but the alarm will be connected directly to the BMS.
I would need a BMS that restarts automatically when the batteries reach the reconnect threshold (and ofc does not disconnect the charge circut when undervoltage triggers).
The max charge current is 40a, and the max continuous discharge current is 55A (peak at 80A).
I do plan to use a Arduino to remotely control the garden pump, and connect to the RS485 of the EPever. So a BMS with some connectable interface would be great to monitor the cells as well.
Based on what I read on the forum a good match for my needs is the: JBD 8S LiFePo4 100A UART model from Aliexpress https://www.aliexpress.com/item/4000828229543.html
- Is my pick suitable?
- Are there any better options that are ~$100 and match my needs?

2. Do I need heat pads?
We do have cold winters here and below zero temps are common (average temp -5 degC). The SCC does have a temp probe and according to what I've read should not charge below the set temp.
Powering only the alarm the batteries should last ~80-100 days without charge.
- If I provide very good isolation and air-tight packaging will the heat from batteries and electronics (BMS, 24V->12V converter) powering only the alarm (200mA) keep the batteries above ambient temperature (e.g. 5 degrees)?
- Does anyone know if the EPEVER performs a trickle charge if temp is below zero or is the charging disabled completly?
- Should I look into creating a automated setup with heating pads? I do have some aH to spare with the alarm as the only load during winter.

3. Please let me know if I'm missing someting or calculating it wrong.

Any advice would be most appreciated.

Should I split my questions and move them to a more appropriate subforum?

BMS, you can order from,
also distributed by Overkill,
This BMS seems to meet your requirements.
I think you will need heat pads but will need care with the control system to ensure the pack is not drained to BMS disharge cutoff. Perhaps an auxiliary AGM battery could be linked into the control electronics.
The spec on my lithium batteries allows low current charging down to -9C of 0.1 capacity, 0C to 5C, 0.3 capacity. Some chargers from Votronics have a reduce charge below 0C but I dont think the EPever has this facility.

Mike

Thanks Mike for the links and comments.
I would gladly buy from Overkill (has very good reviews here), but shipping from USA to Europe will probably cost almost as much as the BMS.

Isn't the BMS you linked from LLT the same as in the link I provided? Or is my some clone?

Good idea with the aux AGM, I could use my old batteries with some simple control circuit.

Banszi said:

BMS you linked from LLT the same as in the link I provided? Or is my some clone?

Click to expand...

I think its the same, I used the link I provided, hopefully from the manufacturer direct. All the information suggests its the BMS as retailed by Overkill. I am also based in Europe, and as much as I would like to buy from Overkill ( he has great support for his product), shipping and tax make buying from the USA too expensive.

Mike

This BMS does seem to fit my needs.
I would like to connect it to an Arduino. Has anyone tried this?
Is there any RS485 documentation for the Overkill/JBD BMS? Registers, Baud etc?

Small update on the 272aH batteries: Amy from Shenzhen Luyuan told me they are out of stock, but luckly found another supplier with a slighlty better overall price.