Use of Lithium Iron Phosphate (LiFePO4) batteries in place of Lead Acid for FRC robot

[AdamHeard]

Originally Posted by Mk.32

LiFEPO4 and Lithium Ion 18650 cells and such are not generally rated with large output capacity with some exceptions. One being the A123 26550 cell with an insane 70amp output. (i'm building a pack with a bunch of these). Most of the no-name chinese cells are not rated even close for output, and the ones that claim to do so are usually lying outright.

For demos and whatever, if you can obtain such a battery rated to handle the current draw, and know the correct procedures for handling it, go right ahead it's a great solution. But realize one accident and your robot will literally burn to the ground.

I haven't done the math factoring life span of SLA vs Lithium (A123s are 1000+ cycles). But it can be argued both ways. Just from all the various battery tech I have seen I don't think there's anything suitable for wide spread FRC use yet. (As much as I would love an LiPo pack on the robot).

But the answer the question the OP posted, the LiFEPO4 battery he linked to is way under-rated and not designed for an application such as running a FIRST robot, even a demo bot. (It's probably for elec wheelchairs or something).

Also I seen this used interchangeably before, Lithium Iron Phosphate (LiFEPO4), Lithium Manganese Oxide (LMO), Lithium Nickel Manganese Cobalt Oxide (NMC), are all different chemistrys of "Li-ion". Lithium Polyers are a subset of Li-ion batteries that use a a polymer additive to allow them to be created in different shapes but are effective the same as li-ion. All of these different batteries have very different specs in terms of power density, max output, and abuse tolerance.

Pretty much every downside you listed is of other lithium chemistries, not LiFePO4. LiFePO4 is as safe, if not safer, than SLA batteries.

If teams were to make their own packs by purchasing cells, yes they would be absurdly priced...

However, if someone were to make a battery for FRC in the quantities required they could make one that would be 10-12 Ah, source the required current, and be around $200.

Each LiFePO4 battery would then be equivalent to 2-3 FRC style SLA batteries, and last a good deal longer as they aren't nearly as affected by the deep discharge.