12 volt systems

Hey folks, I couldn't see a 12 volt forum here, so I'll risk the wrath of my fellow members and post away. I'm stuck with a 12v system in an RV and I was wondering if anyone out there could point out any pitfalls or issues I could fall into using 18650 cells. Any info on your experiences would be invaluable.

Many thanks
Tony.

Pitfalls: 12v is suited to a 9.5-15v range typical of lead acid batteries.

18650 lithium configs for this voltage range are 3s or 4s which equates to either too high or too low.

3s would be a nominal voltage of 9-12.6 which is usually too low for most charge controller cutoffs on the high end, especially if you only want to charge to about 4-4.1v per cell

4s would be a nominal voltage of 12-16.8 which is fine, but with most inverters and charge controllers topping out at around 15v, you wont get the maximum capacity of the cells, and the low voltage disconnect of most inverters will drain the cells way too low to around 2v per cell.

I run a 4s setup with the voltage range set for 12.5-16v as my inverter works at up to 16v, but i dont get the full capacity of the cells. I do however get better than lead acid performance as the higher nominal voltage means less amperage under typical 12v loads.

The long and short is your going to need semi specialised 12v charge controller and inverter setups. In the very least you will need gear that allows you to tweak the voltage cutoffs into the safe range for either the 3s or 4s range when working @ 12v

kind regards

3.2V LiFePO4 (Lithium Iron Phosphate) chemistry is more suitable for 12V systems, as 4x 3.2V = 12.8V, charge voltage is 14.4V.
However 18650 cells that do exist in this chemistry are rare enough you'll end up having to buy new ones most likely.

Another option is to have a 24V battery/inverter, and a buck converter to lower it to 12V for stuff like lighting.

Thanks for your input guys. I prefer li-Ion as opposed to LiFePO4 because of the greater power density. Guess I've got some decisions to make.