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

[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.

[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).

[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.

[MecaNaught]

Originally Posted by Mk.32

snip

I really appreciate the time and effort you put into that reply, it gives some very good insight into and otherwise mysterious world of batteries.

Are there any batteries you would recommend for offseason use where the Amp-hour rule doesn't apply? Just a higher Ah battery of the same type or is there anything better?

[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.

[adciv]

That would seem to imply misuse then (under the way we typically call it at work). In your opinion, would you say the brownout protection on the roborio is helping to prevent battery death? I know we're replacing once it starts to trigger.

[Al Skierkiewicz]

If one reads the data sheet linked above, the max shutdown current is 36 amps. Most motors draw more than that all on their own. Please remember that the current AGM battery is regularly sourcing more than 500 amps in our service.

[AdamHeard]

Originally Posted by Al Skierkiewicz

If one reads the data sheet linked above, the max shutdown current is 36 amps. Most motors draw more than that all on their own. Please remember that the current AGM battery is regularly sourcing more than 500 amps in our service.

While true for that specific pack, there are many LiFePO4 cells that can safety source such currents when assembled into the AH size we would run.

[kiettyyyy]

Originally Posted by AdamHeard

While true for that specific pack, there are many LiFePO4 cells that can safety source such currents when assembled into the AH size we would run.

Exactly. I've worked with LiFePO4 cells all the time when I worked in the plug-in hybrid automotive industry. These cells are intrinsically safer than other lithium chemistries.

I built multiple 40AH packs using CALB, Thundersky and some large cylindrical cells for demo robots. They work fine provided you have a BMS to monitor the cells and protect them from over charging and discharging.

[Chadfrom308]

Eh, just use a high- C rated RC car battery. 10AH would be fine. Make sure to use the hardshell.

My RC car pulls 200 or 300 amps on acceleration and they do fine. MaxAmps makes great ones but they are expensive. Charge them at 20amps if you want, they will do fine.

Make sure they have the hard case. Put a Lipo low voltage sensor on it, they are typically $5.

Never had a lipo explode or puff up. Just be cautious because they have the ability to.

Have fun

[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.

[Al Skierkiewicz]

So we can talk apples to apples, the Tesla battery is also 375 volts.