2P4S or 4S2P and why?

[bigroadadventure]

I think it’s the disconnect part that is discouraging me. My inverters can pull 200A at 24v - I don’t trust a $50 BMS in the middle of that flow for the long haul. And interfacing an actuator has challenges also (like inrush current welding it shut).

 

[CheezWiz]

I think it’s the disconnect part that is discouraging me. My inverters can pull 200A at 24v - I don’t trust a $50 BMS in the middle of that flow for the long haul. And interfacing an actuator has challenges also (like inrush current welding it shut).

The arcing part should be pretty easy to deal with. https://www.industrologic.com/mechrela.htm

 

[electric]

If you are making a single battery pack, always do P first then S. You will never find commercial application that does the opposite, for many good reasons. Any argument against is just silly, bunch of "what if's" which never actually happen in real life.

 

[electric]

The arcing part should be pretty easy to deal with. https://www.industrologic.com/mechrela.htm

Actually this is one of the hardest parts in BMS design. Most killed BMS's are dead because of either capacitive inrush (on connect) or inductive kickback ( on disconnect ). Usually 12V smaller inverters don't need a pre-charge, but 24V and above is strongly recommended or even a must have, especially on 48V or higher.
That article you linked is not good for capacitive inrush, you actually need a dedicated relay+resistor for precharge and a way to control it.
The way Will does it in videos is not the best because manual precharge is quickly absorbed by inverter's logic circuits, but it's better than nothing.

 

[electric]

I think it’s the disconnect part that is discouraging me. My inverters can pull 200A at 24v - I don’t trust a $50 BMS in the middle of that flow for the long haul. And interfacing an actuator has challenges also (like inrush current welding it shut).

this is a very smart concern. Never trust Chinese BMS Amps rating, divide it by 2-3 for real rating and watch for it's temp rise under load. Keep battery/inverter cables short and close to each other to minimize inductive kickback.

 

[Keith_PDX]

I personally think REC BMS has the best pre-charge unit. At first glance it looks like it could be used independently of their BMS.

REC ACCESSORIES – REC BMS

www.rec-bms.com

 

[mrevesz]

I would just go 2P4S with a single BMS and call it perfect.

 

[wkstewart]

I realize this thread is not new but Will did a good video on configuring a 2P4S configuration and hooking up the BMS in this video. I built a 12V LiFePO4 battery using 8 cells, 3.2V each, with a single 4S BMS. Seems to work great.

How to Build LARGE LifePO4 Solar Batteries w/ Raw Cells and a BMS