Lithium-ion 12v Battery Replacement

[Ecky]

Well the charge current issue is going to be true of nearly any lithium battery, which is what I was talking about some weeks ago. How does anyone use lithium when it's well below freezing?

[redpoint5]

Originally Posted by Ecky

Well the charge current issue is going to be true of nearly any lithium battery, which is what I was talking about some weeks ago. How does anyone use lithium when it's well below freezing?

Temperature controlled heating elements. Cars such as the Chevy Bolt and Tesla heat the batteries when they drop below a certain temperature. When the car is plugged in, that energy comes from the grid, and when it isn't plugged in, comes from the battery itself.

In fact, one guy stranded himself in his Bolt when he ran the state of charge below the threshold that the car requires to heat the battery, and then attempted to DCFC. The car won't use DCFC power to run the heating element, and the battery was too cold to charge, so it was stuck until he could first plug into an AC outlet to warm the battery, and then into the DCFC to quickly charge.

[Ecky]

I'm going to try it, and just see if I can keep the current really low. It will live inside the cabin which should help a little.

[Daox]

Anyone know how hot is too hot for lithium, or lead for that matter?

[Ecky]

https://www.batteryspace.com/prod-specs/9055.pdf

Looks like 113F charge and 140F discharge for this particular (LiFePO4) battery. My impression is that they perform better the warmer they get (probably to a point), but that colder batteries have longer lifespans so long as they're not charged or discharged at a rate greater than they can handle at that temperature.

[redpoint5]

Batteries are probably happiest around room temperature, which is why I'm a fan of having them live inside the passenger compartment.

One lecture I watched suggested damage most quickly accumulates on Lithium Ion batteries by spending long periods of time charging when they are hot. In fact, the expert said that it would be better to more rapidly charge the battery if it must be charged while hot in the first place. So counter-intuitively, slow charging a hot battery is not good for it.

[Ecky]

Perhaps, but rapidly charging heats a battery further, does it not? So that's a bit of an impossible scenario - do you charge slowly when hot, or quickly but even hotter?

[teoman]

I have also now just launched my own project. (by making the first big purchase).

I got a set of 12 LG 3.7V 43Ah cells. I intend to make a 4P 3S pack out of them. This should be enough to make most of my commutes alternator free. This will give me approx 1.7 kWh of usable power. ( I am also dreaming of doing a altermotor to make it a true hybrid that is also why the pack is oversized).

I intend on going the virtual alternator delete route.
This super capacitor bank will replace the battery. (is this the same one as you have Redpoint?)
https://www.amazon.com/gp/product/B017FZ0M0A/ref=ox_sc_act_title_1?smid=AWGOTVCIAJJAB&psc=1

The capacitor bank will constantly charged up to 14.7V from the lithium battery pack. I want to go to 16V but initial research (which did not come up with much, just one guy having problems with his guage cluster above 14.7V) suggested it may be too much.

The charging will be done by this module
https://www.amazon.com/Solu-Converter-Step-down-Adjustable-Constant/dp/B00VWLT2KU/ref=sr_1_42?ie=UTF8&qid=1542373548&sr=8-42&keywords=step+down+voltage+regulator
or many of them in parallel.

I think that I may have found a good BMS (which would help me see how much juice I have left in my pack)

https://www.youtube.com/watch?v=ClGmMY0kXvQ

https://www.aliexpress.com/item/4S-L...b-ccba32bf91ab

Not fully sire how I will implement regenerative braking. Or if I should go 5s or 6s.

[redpoint5]

Yes, those Maxwell BCAP350s are the same ones I have, though my balance board is simpler, consisting of just a diode and LED across each capacitor.

It should be able to start a 4-cylinder car by itself.

[teoman]

Do you have a link to a bigger one? To start a diese for example.