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Old 12-06-2018, 09:15 AM   #141 (permalink)
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I do not understand why you guys are spending ~$150 on supercapacitors when you can get a LiFePO4 with 500 CCA for $215.

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Old 12-06-2018, 11:45 AM   #142 (permalink)
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Originally Posted by ME_Andy View Post
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.

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Old 12-06-2018, 11:51 AM   #143 (permalink)
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Oh, that's a good reason.
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Old 12-26-2018, 09:43 AM   #144 (permalink)
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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.
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Old 12-27-2018, 07:32 AM   #145 (permalink)
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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.
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Old 12-27-2018, 07:54 AM   #146 (permalink)
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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.
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Old 12-27-2018, 12:07 PM   #147 (permalink)
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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?
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Old 12-27-2018, 12:30 PM   #148 (permalink)
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Quote:
Originally Posted by Stubby79 View Post
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?
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Old 12-27-2018, 12:31 PM   #149 (permalink)
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Quote:
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Any reasonable option(s) to keep the li-ion warm or warm them up before use?
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.
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Old 12-27-2018, 12:42 PM   #150 (permalink)
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Quote:
Originally Posted by hayden55 View Post
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.

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