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

[adciv]

To play the other side....

Between not just longer charge life, but longer cycle life, it can be cheaper to use a lithium over the legal SLABs. Yes they can cost several times more, but you aren't cycling your legal batteries as much and so they last longer. I remember one team saying they did so much off season stuff they used up 10 batteries a year. I'm not going to debate if that's due to misuse or what. Regardless, their life span is also longer and can result in long term savings to a team.

At work, we expect a SLAB to last 2 years if not heavily cycled. In FRC I have found we will get 3 or 4 seasons. At work, we expect a lithium to last 5 to 10. Even with the increased up front costs, this can yield substantial savings in the long run.

[asid61]

115 recycled batteries perhaps every 3-4 years. Our "competition" batteries were at most a year old and we bought 2 batteries a year, so typically we would have 4 batteries for a competition. Batteries up to 2 years older than that (depending on how well they held a charge) would be used for testing at home, prototyping, and occasionally outreach. So for a LiFePO4 to make sense, we would need them to last around 4x as long due to the cost, which is 8 years of competition and 16 years of casual use.
Given the discharge rating on the LiFePO4 batteries, I'm not sure it would give you that much increased lifespan. Are there ones rated for higher discharge rates that aren't too expensive? I would be interested in these for extended outreach mainly.

[Mk.32]

Originally Posted by asid61

115 recycled batteries perhaps every 3-4 years. Our "competition" batteries were at most a year old and we bought 2 batteries a year, so typically we would have 4 batteries for a competition. Batteries up to 2 years older than that (depending on how well they held a charge) would be used for testing at home, prototyping, and occasionally outreach. So for a LiFePO4 to make sense, we would need them to last around 4x as long due to the cost, which is 8 years of competition and 16 years of casual use.
Given the discharge rating on the LiFePO4 batteries, I'm not sure it would give you that much increased lifespan. Are there ones rated for higher discharge rates that aren't too expensive? I would be interested in these for extended outreach mainly.

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.

[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.

[Mk.32]

Originally Posted by AdamHeard

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.

All the downsides apply to LIFEPO4 as much as any other lithium battery, the LiFepo4 stuff is probably safer when it goes off compared to a LiPo but it's still a pretty big hazard...

I'm all game for getting LiFepo4 packs but I don't think it's gonna happen anytime soon.

[AdamHeard]

Originally Posted by Mk.32

All the downsides apply to LIFEPO4 as much as any other lithium battery, the LiFepo4 stuff is probably safer when it goes off compared to a LiPo but it's still a pretty big hazard...

I'm all game for getting LiFepo4 packs but I don't think it's gonna happen anytime soon.

Do some research and over-current and puncture test for LiFePO4, they don't trivially throw smoke/flames like other lithium chemistries.

They are completely uncomparable to "LiPo" cells.

[Mk.32]

Originally Posted by AdamHeard

Do some research and over-current and puncture test for LiFePO4, they don't trivially throw smoke/flames like other lithium chemistries.

They are completely uncomparable to "LiPo" cells.

I have personally poked holes in most of them....

A123s are fairly safe, some other Lifepo4's are not as much but when they vent they vent. https://www.youtube.com/watch?v=EMARDvMz62A

The pouch types LiFepo4s also vent pretty energetically, that was what a kid at a local robot event had go off in his bit and he got a face full of lithium smoke (And this was like a tiny 2AH 12v pack).

Sure LiFepo4 it's much safer then LiPo but I still wouldn't trust high school kids with them.

[asid61]

Originally Posted by Mk.32

I have personally poked holes in most of them....

A123s are fairly safe, some other Lifepo4's are not as much but when they vent they vent. https://www.youtube.com/watch?v=EMARDvMz62A

The pouch types LiFepo4s also vent pretty energetically, that was what a kid at a local robot event had go off in his bit and he got a face full of lithium smoke (And this was like a tiny 2AH 12v pack).

Sure LiFepo4 it's much safer then LiPo but I still wouldn't trust high school kids with them.

That just looks like a bit of toxic smoke... compared to the fiery conflagrations of LiPO I think LiFePO4 is still way safer.
Especially in the SLA "packaging" like in the OP's link, I would find it hard pressed to kill one.

[Mk.32]

Originally Posted by asid61

That just looks like a bit of toxic smoke... compared to the fiery conflagrations of LiPO I think LiFePO4 is still way safer.
Especially in the SLA "packaging" like in the OP's link, I would find it hard pressed to kill one.

The types of battery OP linked has internal protections and a fuse (in this case a 25amp internal one) that keeps it pretty safe.

Like i said LiFepo4 is safer then LiPo but I still wouldn't trust high school kids with ones without a built in BMS/etc. And I don't now of any pre-made packs 12v 10-15ah that can handle the 200amp burst current FRC demands for a reasonable price.

The A123 packs I've put together/the ones you generally find in battlebots (like tombstone) are just raw cells wired together connected to whatever. Would not trust students with these.

[MecaNaught]

Wow, this thread got a lot more attention than I thought it would. Thank you all for your replies.

The biggest reason I see here that it wouldn't work is the 20A max output.

I do know that lithium batteries of all types are more hazardous due to their ability to rupture and spill out toxic fumes. However, lipo4 (supposedly) is a much safer chemistry. Combine that with good physical and circuit protections, I think these batteries would be usable for teams that know what they are.

The main reasons I wanted to use this battery was for better consistency with charges, lifetime, consistent output over the duration of the output, and it'd be a nice piece. I see now though that there is atleast one major drawback that prevents them from being used in FRC bots.

Someday I hope there are better batteries FRC can recommend, because we go through a lot of lead acid batteries every year, and it seems to be quite hit or miss if they'l keep their charge over time. One of our big things in competition is making sure the battery we put on our robot has the highest charge, because many shooting/throwing mechanisms will change depending upon the charge of a battery.

[Al Skierkiewicz]

Originally Posted by Mk.32

And I don't now of any pre-made packs 12v 10-15ah that can handle the 200amp burst current FRC demands for a reasonable price.

Teams regularly exceed 500 amps on the current battery.

[FrankJ]

Not that this has anything to do with FRC bots, but I wonder what is the current draw on a Tesla car in "Ludicrous Speed" speed mode.

[Chris_Ely]

Originally Posted by FrankJ

Not that this has anything to do with FRC bots, but I wonder what is the current draw on a Tesla car in "Ludicrous Speed" speed mode.

According to Wired, 1,500 Amps.

[AdamHeard]

Originally Posted by Mk.32

I have personally poked holes in most of them....

A123s are fairly safe, some other Lifepo4's are not as much but when they vent they vent. https://www.youtube.com/watch?v=EMARDvMz62A

The pouch types LiFepo4s also vent pretty energetically, that was what a kid at a local robot event had go off in his bit and he got a face full of lithium smoke (And this was like a tiny 2AH 12v pack).

Sure LiFepo4 it's much safer then LiPo but I still wouldn't trust high school kids with them.

You do realize SLA will also potentially energetically vent when punctured?

Few battery chemistries will let you store significant energy and be happy when you dead short them internally (and SLA isn't one of them).

[Tom Line]

Originally Posted by adciv

To play the other side....

Between not just longer charge life, but longer cycle life, it can be cheaper to use a lithium over the legal SLABs. Yes they can cost several times more, but you aren't cycling your legal batteries as much and so they last longer. I remember one team saying they did so much off season stuff they used up 10 batteries a year. I'm not going to debate if that's due to misuse or what. Regardless, their life span is also longer and can result in long term savings to a team.

At work, we expect a SLAB to last 2 years if not heavily cycled. In FRC I have found we will get 3 or 4 seasons. At work, we expect a lithium to last 5 to 10. Even with the increased up front costs, this can yield substantial savings in the long run.

10 batteries isn't outlandish. We usually lose 4 or 5 a year, and I can remember a couple years ago when we did a lot worse. Some of the team were hot-cycling batteries to complete discharge at a week long fair demonstration without realizing what would happen. We lost around 10 that year.