LiFePo4's as a lightweight car battery replacement?

[Racebrewer]

Hi Guys,

Serious but slightly off-track (actually on racetrack) question.

Over at the RX8 Forum there is a guy who used 4 LiFePo4's to make a lightweight car battery as weight is critical for racing.

Here is the link:

http://www.rx8club.com/showthread.php?t=215618

Noting that they are LiFePo rather than LiPo's is this a good idea or a bad idea? Porsche now offers a lightweight racing battery for $1,700 if you were wondering how serious this.

Thanks for the input,

John

John

[Illum]

Well, for starting applications I see no reason why it wouldn't work, its the charging part that makes me wonder. Electrical noise in automotive circuits can be pretty hectic at times. Pulses, oscillations, and the occiasional surge from a dump load can't be good for a sensitive circuit set to charge lithiums....course for racing they would have done away with the many conveniences of a modern user-level automobile, but for most it would be difficult to justify the returns given that price tag.

[Shadowww]

Noting that they are LiFePo rather than LiPo's is this a good idea or a bad idea?

They are LiFePO4, and the "PO" (phosphate) in name of LiFePO4 has nothing to do with "Po" (polymer) in LiPo.
It's a very good idea to use LiFePO4's, because
1. 4 of them provide very similar voltages to lead-acid (4*3.2 = 12.8V nominal, 4*3.6 = 14.4V fully charged, 4*2.5 = 10V empty)
2. They are very safe, compared to LiPo's - they don't vent with flame, they don't puff, they don't many things
3. They last very, very long life (10+ years / 2000+ cycles)
4. Extreme temperatures don't affect them very much, they work well even in extreme cold / extreme heat

[georges80]

and already used on motorbikes:

http://www.shoraipower.com/

cheers,
george.

[FlatlandBusa]

Like georges80 said, they have been used with success in motorcycles for a while now.

I see no reason why a larger one would not work or two smaller ones in parallel.

1300cc+ 13.5-1 compression busa motors are started with them with them.

http://www.fullspectrumpower.com/

http://antigravitybatteries.com/

[nullmodem]

The Shorai's are really light...saw them first hand at the motorcycle show. However, you cannot connect a standard charger or battery tender to it, and to really do it justice, you have to get their specialized charger.

Which makes me think, if there is no charging circuit built into the battery, how come they don't suffer the same overcharging issues/problems? An IB rally would really put these to the test!

[georges80]

In the case of the Shorai, they can be charged at a max of 3.7V per cell, so 14.8V max. So, a nominal 14.4V stock alternator setup would not be overcharging the cells and would be doing a reasonable job of topping them up to full capacity.

In terms of a battery tender, the need for something lifepo4 specific would be to ensure the batteries are charged correctly and then terminate at the right point and then kept in maintenance.

cheers,
george.

[nullmodem]

That makes sense. I was thinking about the length of time the battery is charged...since the bike has no CC/CV type charge controller.

[walterr839]

The special Shorai battery tender for the Shorai batteries uses a balancing circuit that a a normal tender does not have.
I have been using one on a high compression Ducati for the past year with good success.

[CKOD]

That makes sense. I was thinking about the length of time the battery is charged...since the bike has no CC/CV type charge controller.

On an automotive battery youre not charging it from dead after using it for starting And lead acid has the same CC/CV requrement (actually, worse if you want to get into the details of it) for a float charge 14.5v max and ideally lower, ~14.0V while running would be better.

Ive used a 4S4P pack of OlevinPower 26650 cells (china made A123 brand cells, iirc, like legit licensed stuff, not just generic LiFePO4 cells) to start a jeep cherokee V8 with the FLA battery disconnected. It was a bit weaker then the normal battery, but It was on the end of ~6' of 4 AWG wire, and the pack is light enough you can lift it with a pinky finger.

With an addition of a balancing circuit to keep the cells equalized, they would definitely be a suitable replacement, the only problem is standby capacity. My 9.2AH pack could start the vehicle just fine, but leave the headlights on, and its dead in an hour or less. So that standby capacity will be $$$ to get.