Lithium-ion 12v Battery Replacement

[ME_Andy]

I do not understand why you guys are spending ~$150 on supercapacitors when you can get a LiFePO4 with 500 CCA for $215.

[Ecky]

Originally Posted by ME_Andy

I do not understand why you guys are spending ~$150 on supercapacitors when you can get a LiFePO4 with 500 CCA for $215.

Because we get -40 degree weather here and the first time I crank with the battery and then recharge in those conditions, it’s toast.

Edit: If anything, I could have used a much smaller and cheaper LiFePO4 and just relied on the capacitors.

[ME_Andy]

Oh, that's a good reason.

[Ecky]

Update: Went to start my car this morning after having it sit for 3 days, and it was completely dead. Will need to troubleshoot. Temperature outside was around 10F, voltage at battery and caps both was ~5v. Unsure if I have a parasitic draw or if the cold has just destroyed the lithium battery, even with a resistor reducing current.

[teoman]

Is the battery dead?

I am thinking of a usb powerbank with a small boost converter. It will take some time, but it will get tje caps up to voltage to be able to start the car.

[Ecky]

Originally Posted by teoman

Is the battery dead?

I am thinking of a usb powerbank with a small boost converter. It will take some time, but it will get tje caps up to voltage to be able to start the car.

I was able to jump the car and by the time I got to work (~20 minutes) the trickle charging through the 0.3ohm resistor filled the lithium battery up to 12v. It's very early to say for sure but I'm leaning toward "don't buy this if your car ever sits below freezing" with regards to the lithium. The caps I'd still heartily recommend. Maybe even some smaller ones if you plan to use a very small conventional lead acid in parallel.

[Stubby79]

Originally Posted by Ecky

The caps I'd still heartily recommend. Maybe even some smaller ones if you plan to use a very small conventional lead acid in parallel.

Garden tractor battery or one of the high output SLA's from a jumper pack come to mind.

Any reasonable option(s) to keep the li-ion warm or warm them up before use?

[Ecky]

Originally Posted by Stubby79

Garden tractor battery or one of the high output SLA's from a jumper pack come to mind.

Any reasonable option(s) to keep the li-ion warm or warm them up before use?

Keep the car plugged in overnight, or get a much larger battery, a heating element and go out to the car an hour or two before you leave (ever) and start warming it. I'm not sure if it's really even safe to freeze them at all. Maybe take the battery inside every time you park? A big enough battery to always have a heating element running?

[hayden55]

Originally Posted by Stubby79

Any reasonable option(s) to keep the li-ion warm or warm them up before use?

Yes.

Here is an interesting video on supercaps:

https://www.youtube.com/watch?v=cq3ihYJ4rbE

Personally the super cap idea is really cool though. If you could wire the super cap starting battery in parallel with the li-ion high capacity accessory battery and have a switch to hot swap them you would be golden.
Now you guys just need to do some hands on testing.
I recommend a radiant heating loop wrap on the battery, a small water tank with a heating coil, or maybe even 3m Novec if you're feeling appropriate, and in the summer you could just reverse the goal and take energy out. You would just need a bms to start. Arduino with enough inputs could probably cover it.

[Ecky]

Originally Posted by hayden55

Yes.

Here is an interesting video on supercaps:

Personally the super cap idea is really cool though. If you could wire the super cap starting battery in parallel with the li-ion high capacity accessory battery and have a switch to hot swap them you would be golden.
Now you guys just need to do some hands on testing.
I recommend a radiant heating loop wrap on the battery, a small water tank with a heating coil, or maybe even 3m Novec if you're feeling appropriate, and in the summer you could just reverse the goal and take energy out. You would just need a bms to start. Arduino with enough inputs could probably cover it.

If the goal is weight savings, I don't think a lithium is going to achieve it in cold climates.