12v power case

BaconButtie · Dec 21, 2017

Well, finallygot round to it after much searching and reading, time to build a portable 12v power case.
Sourced my cells from eBay, mainly from old laptop battery packs but the cells I chose to use are from old Ebike packs as I managed to source 3 used ones of the same make & model which used identical cells, all PanasonicCGR18650CG cells @ 2200mAh (the silver ones in the photo) I had to re-wrap them as they had been super glued together so the original wrap got destroyed during disassembly.

I have gone for a 4s 20p set up in 4 packs wired in parallel to give a total of 80 cells and around 16v 175000mAh output if my understanding of how parallel / series connections work is right :-/

This is to be housed in a custom made flight case (not yet built this) and run through a DC to DC buck converter to give a stable 12v output then supplying 4 USB charging ports which have built-in12v to 5v converters, 1 x 12v car auxiliarypower socket (lighter socket) to power a removable12v LED light.

Charging & balance ports will be accessiblefrom the outside of the case mounted on a custom IO plate so there is no need to open the case to charge the battery.

So far I think I am OK with the theory of how all this works. The only bit I am stuck on is fusing. Is it 100% essential to have cell level fuses or can I just use 1 fuse on the main live feed or will this only protect the output terminals and not the cells?

If cell level fusing is needed is tinned copper wire sufficient for this and if so what AWG would you recommend, bearing in mind the total Amp draw if all outputs are being used would not exceed 3amps max. (2 x mobile phones, 1 x Bluetoothspeaker, 1 x LED light)

Any suggestions, tips or criticisms are welcome as I am a complete noob at this although I do have a basic understanding of electronics but mainly in domestic power supply.

Oderus420 · Dec 21, 2017

Sounds like a fun project. Keep us posted!

Wattsup · Dec 21, 2017

Hey that's my thread title, get your own

Looking good. Good fun the portable 12 volt builds!

So no inverter with your case?

BaconButtie · Dec 21, 2017

Wattsup said:
Hey that's my thread title, get your own

Looking good. Good fun the portable 12 volt builds!

So no inverter with your case?

LOL, sorry about nicking your thread title, could not think of what else to call it.

no inverter in this build, no real need for one as the case will only be used for phone charging and a LED light but I do have enough cells to build a 120 cell case. So if this one goes to plan and works well then I may do the MK2 with a small inverter. Just trying to keep size and weight to a minimum for portability.

daromer · Dec 23, 2017

Fusing is if you want to. If you have time and can then fuse it. I would go with 36SWG as an example or around 0.2mm2. They will burn at or around 5A.

Why use converter down to 12V? If the 5V outlets have built in there is no need to double convert it. You only loose more power. Just make sure they do work with current voltage.

BaconButtie · Dec 23, 2017

daromer said:
Fusing is if you want to. If you have time and can then fuse it. I would go with 36SWG as an example or around 0.2mm2. They will burn at or around 5A.

Why use converter down to 12V? If the 5V outlets have built in there is no need to double convert it. You only loose more power. Just make sure they do work with current voltage.

Thanks for the reply, I will fuse as there is no rush to have this finished, as for the 5v USB outlets they only work with a 12v input, basicallyan in-carUSB adapter.

daromer · Dec 23, 2017

Yeah but cars can have up to 15V or even more in worst case. Most of them take 16-20V as input.

BaconButtie · Dec 26, 2017

daromer said:
Yeah but cars can have up to 15V or even more in worst case. Most of them take 16-20V as input.

True, I have ordered a few different types / makes so will bench test them and see what they can take. Battery pakis now fully charged and balanced @ 16.2v so if one of the adapters works at 16 volts then i will discard the buck converter.