Lithium-ion 12v Battery Replacement

[Ecky]

I had no luck looking for a passive temperature controller. This looks like the lowest current thermostat I could find:

https://www.amazon.com/GERI-Single-C...erature+switch

<5mw when the relay isn't active.

I'm thinking of pairing it with one or two of these:

https://www.ebay.com/itm/DC12V-5W-6x...688:rk:16:pf:0

And to wrap the whole thing in a thermal blanket of some sort.

Thoughts?

[hayden55]

Originally Posted by Ecky

I had no luck looking for a passive temperature controller. This looks like the lowest current thermostat I could find:

https://www.amazon.com/GERI-Single-C...erature+switch

<5mw when the relay isn't active.

I'm thinking of pairing it with one or two of these:

https://www.ebay.com/itm/DC12V-5W-6x...688:rk:16:pf:0

And to wrap the whole thing in a thermal blanket of some sort.

Thoughts?

Interesting. I would give it a shot. I have a version of what you bought with a thermal probe and a 30A relay to convert my ranger to an electric fan. But its gonna be a while. The transmission religiously fights me from removing it so nothing else will start until i finish. *sighs and laughs a little crazy*

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[Ecky]

I ordered one of those too, just to try. The higher power consumption makes me a bit wary, looks like even without the heater running it could drain my lithium battery from full to empty in around 20 days, or probably realistically drain it in 1.5-2 weeks. I doubt the car will ever sit that long but I may not find it feasible to have the battery self-warm. Guess we'll see. Really it just needs to get me through the weekend and be able to charge back up during my ~20 minute each way commute.

[teoman]

Just paid for the caps. It did cost a bit more than expected.

130 for the caps 40 for shipping and then some random fees to bring the total up to 185 usd.

I should get them next month. (First they fly to Iowa then some one brings them over here)

[hayden55]

I like that everyone is choosing different paths here. I think I may assemble a LG 18650 battery in my Jon boat to test. I only need 7A to run the starter on my 30 horse Yamaha. lol

[Ecky]

Update on my battery + cap combo:

I haven't had any more mornings where the car didn't start, so perhaps I left a light on or didn't close a door completely. Had an experience I'd like to share though.

I had been using a cheap 100A relay from eBay between my DC-DC converter and the caps, to separate the two when parked and cut down on parasitic drain. The build quality was shoddy but it just needed to last long enough for my engine swap. Very occasionally the relay failed to engage and needed to be jarred before it would *click* and the car would start charging.

I left one morning for work when it was around -5F (about a week and a half ago). Around half a mile from my house my rear-view screens began to cut out and I got an EPS light, indicating to me the 12v system wasn't charging. I pulled over in a residential area, tilted the driver seat forward (hoping to get the charging system going again before the engine quit firing) and DISASTER.

The 8 gauge wire going between the capacitors and DC-DC converter was the only line I hadn't placed a fuse or breaker on, in part because it was so short - maybe 24 inches and with the relay in the middle. When I moved the relay to try and get it to engage, the wire leading from the caps came loose and touched... something, I'm not sure what, which was grounded. Instantly the 8 gauge braided copper lit up like a tungsten filament in a light bulb and vaporized. The insulation from the wire burst into flame. I beat out the flames with my bare hands to keep my car from burning to the ground. Here are the largest bits I was able to find of the 8 gauge braided copper:




Moral of the story, shorting out very large capacitors is not remotely like shorting out a large battery. Treat them with respect.

I managed to limp the car back home just using the lithium battery, and called a coworker to pick me up. That evening I added a 100 amp breaker a few inches from the capacitors, and manually turn it off whenever I park the car.

~

To protect my LiFePO4 battery from further damage from the cold I ordered a pair of 5w heating pads. I attached these in parallel to a thermostat, then wrapped the battery in closed-cell foam and duct tape. I planned to have the battery heat itself, but for now I'm just running it from the DC-DC converter when the car is on, and relying on the insulation to keep the battery warmer longer. Fuses on everything, of course.

[Daox]

Wow, that sounds like some fireworks display. I'm glad nothing horrible happened.

[Stubby79]

While that shouldn't surprise me, I hadn't even considered it. Yikes! That's some nutty amperage they can put out!

[hayden55]

Definitely puts into perspective why they put kill plugs on HV batteries. Pull the orange plug out and the wires die.

[serialk11r]

Wow that's crazy...glad it isn't too bad.

Since I moved to the East Coast, I haven't gotten a car yet, but this cold temperature battery thing was on my mind. In NJ/NY we don't have it as bad as Vermont but cranking my rental car at 0F on Monday was pretty unsettling...it sounded like trying to crank the car with a dead battery.

This company builds batteries with heaters in them (heaters activate when the battery is "being charged" but too cold to actually charge), but the cells are not the high current type that you would want for a car starter battery unless you have a really, really tiny engine. I suppose they're a good candidate for pairing with capacitors but that's some extra hassle. https://relionbattery.com/blog/lithi...y-cold-weather

As you can see, the RB-35X is 35Ah but can only charge at 2C (70A) and discharge cutoff is at a pretty weak 160A. On an older car with a 90A alternator and a small 4 cylinder this is probably fine, but anything newer usually comes with a more powerful alternator that could potentially fry the battery.

I think a DIY heater to emulate this on a higher current capable battery could work well. Have a diode preventing current from flowing to the battery, and a relay to short that out at 0C, then have the heater connected to the alternator and have the same relay shut it off simultaneously.