Lithium-ion 12v Battery Replacement

[Ecky]

Originally Posted by hayden55

I was going to say just use a Lead acid battery for the winter... But then I saw you lived in Oregon and thats like 10 months out of the year lol

Depends where in Oregon. West half and the winters are milder than yours.

[redpoint5]

Freezing temps are only 3 months of the year (in the valley), with generally cool temps about 5 months. Right now is absolutely perfect, sunny and 73 degrees. Still shorts and tee shirt weather.

The other thing I've been meaning to test is lithium vs Pb charging efficiency. Lead acid is extremely poor at accepting a charge when it's near full, which is exactly how they are utilized in vehicles. That, on top of alternators being something like only 50% or less efficient, and we might have a significant amount of fuel consumption merely keeping it topped off. Lithium batteries do not suffer the same horrible drop in charge efficiency.

I think I'll do several tests draining each battery 5%, then measuring how much energy it takes to bring them back to full.

[hayden55]

Originally Posted by redpoint5

Freezing temps are only 3 months of the year (in the valley), with generally cool temps about 5 months. Right now is absolutely perfect, sunny and 73 degrees. Still shorts and tee shirt weather.

Ooof I think the joke must be on me then. I haven't seen a day below satans oven (unless its raining) in I don't know when. It was 105 on the heat index yesterday here where I'm at in the dirty south.

[hayden55]

I just stuck a clamp on my 30hp outboard boat motor and only saw 7.0A max. Stuck it on the Prius.... 1.6A when it flicked on but after that i never even saw it go past 1.0A. Maybe this would be a fun project for the Prius instead? Seems like all of the low voltage stuff doesn't use anything power wise.

[teoman]

1.5A seems a bit low. Check with the headlights on. If it doesnt jump up another 4+ amps then your measurementa may be incorrect.

[RedDevil]

Head- tail- and instrument lighting will take 120 to 150 Watt in most cars, so that should cause a jump of 10 to 12 Ampere.

[teoman]

Redpoint5, with your setup and a fully charged lithium pack (or while actively charging it), do you observe a drop in fuel consumption?

[teoman]

Getting ready to invest in this. The idea is to make kind of a hybrid for the electricity usage.

The idea is is to put a big lithium battery pack in the car to be able to run the car for 3 hours plus regenerative braking.

I found a very good deal on some 3.7v 43Ah lithium cells. But i must act fast.

I was thinking baybe 3S configuration that i will convert to 15V amd send to a capacitor array, and then directly connect it to the alternator for charging (assuming they can take all the alternator current).

A 4s configuration might be ok connected directly. But voltage may be too high to be fully charged. On the plus side if they are connected directly then i do not have to worry about the pack running dead as the alternator will kick in and not let the pack drop too low. Tje alternator signal would have to be tricked a little bit to get 16V output on regenerative braking to get some benefit.


Then there is the multiple in series configurations. 5s 6s ... 10s. Tjese would be used with a stepdown voltage regulator to constantly keep the capacitors at 16v.

[teoman]

The cells operate at 3.73v

Charhing is constant current 41A up to 4.15v and then cutoff at 2.5A.

Discharge is up to 41A down to 3V.

Now if i go with the 3S and 3P that means that they will be at 11.1v and at 3P they can accept a current of 123A. If i were to connect it directly to the car while braking (bypassing the boost converter and the caps) the alernator would see 11.1 V and try to raise it to 14.4V ish. Not sure if that would make the alternator give its max amps or if it the voltage difference would be insufficient.

[redpoint5]

Originally Posted by teoman

Redpoint5, with your setup and a fully charged lithium pack (or while actively charging it), do you observe a drop in fuel consumption?

I only have a LiFePO4 in my Prius currently, and don't observe any difference in fuel economy, though I wasn't carefully tracking it.

I haven't tried the lithium swap in the Acura yet, but it's on my list of things to do. My expectation is 5% increase in fuel economy when the alternator is "virtually" disabled, and close to normal fuel economy when in normal alternator mode.