999zip999 said:
So can we see the brand the manufacturer of the name of the Lifepo4 you're going to use
I haven't got to even considering that part yet. The SLA needs replacing again -- they seem to last about 5 years -- and is going to cost around £12.
I wondered whether I could replace it with some form of Li pack, and looking around LiFePO4 seems to be the closest chemistry to being "fit & forget".
I'd very much have liked to convert it such that is can be used with the existing wall mount and wall-wart and in the same way -- use it and drop it back into the holster and it'll be charged for next time.
I don't want to have to half disassemble the thing, transfer the cells/pack to a different charger unit, monitor them closely for an hour just-in-case, reassemble. I'll throw it away and buy a new one (or just buy another SLA) rather than have that faff.
The SLA is 48 x 70 x 110, so I'd need to fit 4 x 3.2 /3.8 LiFePO4 cells, or 3 x 3.7/4.2 LiCo cells into that space along with any BMS etc.
I naively hoped that the existing SLA charging board internal to the unit might work, or be adapted to work directly with the pack I make, thus avoiding the need to purchase a separate unit. The wall wart is spec'd at 15V@200mA, is full-wave rectified and smoothed. The charge/ready cycle appears to be controlled by 12V zener diodes. Our habit is to switch the wall-wart off once the green ready LED shows -- my wife is very dilligent about such things.
My thought was that if I replaced the 12V zeners with 14.4v ones, that would give me close enough to the 3.8V/15.2V max for the LiFePO4 and undercharge would be good for longevity. Provided we religiously turned it off once green shows, we would avoid any trickle charging.
4S LiFePO4 balance boards are common and cheap, which should take care of balancing for such a low demand (~100-120W) pack.
The whole idea has taken on a life of its own as I've spent an inordinate amount time trying to model and understand the exist circuit board, just cos its interesting.