View Full Version : Use of Lithium Iron Phosphate (LiFePO4) batteries in place of Lead Acid for FRC robot
MecaNaught
28-07-2016, 02:20
In researching a higher Amp hour battery for off season robots, I've
found a LiFePO4 battery that is the exact form and size as the normal 18AH lead acid batteries. However, I am not experienced with the specifications, and I'd rather avoid frying any of our boards. Anyone know if these would be safe replacement? (Only for non competition use of course)
Normal Lead acid:
http://www.power-sonic.com/images/powersonic/sla_batteries/ps_psg_series/12volt/PS-12180_12_Sept_10.pdf
Magical Lithium battery:
http://www.power-sonic.com/images/powersonic/LithiumIron/PSL-12200.pdf
Infact, I'm surprised FRC doesn't use these batteries in competition, but perhaps they're too new.
In researching a higher Amp hour battery for off season robots, I've
found a LiFePO4 battery that is the exact form and size as the normal 18AH lead acid batteries. However, I am not experienced with the specifications, and I'd rather avoid frying any of our boards. Anyone know if these would be safe replacement? (Only for non competition use of course)
Normal Lead acid:
http://www.power-sonic.com/images/powersonic/sla_batteries/ps_psg_series/12volt/PS-12180_12_Sept_10.pdf
Magical Lithium battery:
http://www.power-sonic.com/images/powersonic/LithiumIron/PSL-12200.pdf
Infact, I'm surprised FRC doesn't use these batteries in competition, but perhaps they're too new.
There's a few reasons why first doesn't use Lithium batteries and it really isn't surprising. I work as a engineer in the drone industry so I've gotten pretty comfy with the world of lithium batteries.
First, have you looked at the cost of anything like that?
So lets look at that battery you picked out, most of those types of bricks are made up from round cells welded/soldered together, if you scroll down on the datasheet that pack uses a IFR26650EC cell, and it uses 4 in series 7 in parallel so a total of 28 cells. So that cell being what looks like a no name, and so is the pack I couldn't find a price but you can look at the price of the cell
http://www.batteryspace.com/lifepo4-26650-rechargeable-cell-3-2v-3300-mah-19-8a-rate-10wh---un38-3-passed-ndgr.aspx
That's $7.50 a cell for a no name brand (more for an "brand name") so with 28 cells that brings the cost up to $210 before cost of manufacturing the case and packaging and putting it together/etc. Add all of those you can be looking at $300+ per battery. So if FIRST made us buy these batteries... we'll we would need a lot more fundraising... compared to the cost of $40 each for our SLAs.
Second, the PSL-1220 pack is rated for a MAXIUM discharge of 20amps...... think about that for a second. On you're first robot you should be using at least 4 of the 40amp breakers and probably a few of the 20/30amp breakers. Meaning that you're robot has the potential to draw 200-300amps burst down to 50-100 amps contentiously depending on how you're robot is designed. So this battery would be woefully unable to keep up.
To explain father, I like to generalize that they are two categories of lithium batteries, power types and energy types.
Power batteries are types that can output large number of amps and handle surges of current without damage, but they lack capacity compared to something of the same size and weight as a energy battery. This is what you need to power a robot, or say a gokart, or a tesla, or drone/RC plane/etc.
Energy batteries, are batteries that can pack a lot of capacity into a small size/light weight package but lack the ability to output a large number of amps without permanent damage. These types of batteries are useful for powering things like your laptop, or smart phone or computer packup, etc. Those types of devices do not demand high current nor do they have surges of current. This is what the PSL-1220 is.
Now to supply a first robot's need of power you need obviously more of a power type of battery, something that can handle large current draw without damage. That would be something like this: http://www.a123systems.com/Collateral/Documents/English-US/A123%20Systems%20ANR26650%20Data%20Sheet.pdf
A123 26650 cells are LiFEPO4 power cells, that ONE cell can output 70 amps! But notice how it only holds 2.5AH compared to the 3.3AH of the cells used to build the PSL-1220 battery (which can only deliver a few amps each). A 12v pack built of A123 batteries with the proper hardware would be a GREAT replacement for the first pack, able to deliver crazy amounts of power, be a good deal lighter but it will literally cost hundreds of $$ for each pack at retail pricing. You'll also notice on the data sheet for the SLA battery it's rated for 180amps for a 10sec burst, and because of the SLA chemistry you can safety go over this number for even shorter periods of time.
Thirdly, a few more downsides of Lithium batteries compared to SLA is that Lithium batteries need to have there cell voltages monitored very closely. Use up to much of the battery? permanent damage. Draw to many amps out of the battery? permanent damage. Charge it to much? permanent damage/fire. Charge it to fast? permanent damage/fire. So it's pretty easy to ruin your $$$$ lithium pack (and I've seen high school students abuse the SLAs more then they should). A lot of modern day electronics that use lithium battery packs have a BMS (battery management systems) a bit of electronics and software designed to keep you from doing any of those things to the pack. But for something that can handle the level of power from a FIRST bot it will not be cheap. The SLA batteries we use are very durable, you can kind do whatever you want to do them and they keep ticking and they are designed to be used to start motorcycles so they can handle a large surge of amps and because they are Sealed generally pretty safe. They do degrade kinda quickly usually after 150-300 full cycles (depending) but are so cheap this isn't really much of an issue.
Fourthly the safety aspect...
Now LIFEPO4 is just one type of lithum batteries, it's also probably the safest type of so. But lithium batteries can vent if you short them for to long, overcharge them, puncture them, crush or dent them and etc. What happens when a lithium polymer (a bit more potent the LIFEPO4) battery decides to vent or is helped along the way? https://www.youtube.com/watch?v=1wW_36XIupw (and that's a 4ah 12v battery now imagine what a 20AH going off would look like).
So TDLR: The PSL-12200 is only rated for a 20amp output which is no where near enough to power a first robot, maybe okay for testing of bench top electronics and free spinning a motor. Lithium in general is really expensive compared to SLA and various types of lithium (generally the cheaper ones) can be dangerous and should not be trusted in the hands of high school students...... (I have been at a high school level mini-battlebot event where a student had a lithium battery go off in his face.....).
We are using a LiFePO4 battery on our tee shirt cannon. It is twice the amp hour rating of a FRC battery, but we get about 3 times the run time with it. The robot has a big compressor by FRC terms and a 4 cim drive which probably puts it mid field in FRC terms for power demand. The battery was custom made by one of our sponsors and I don't know the internal details. We have yet to catch it on fire :]
You're not crashing your T-Shirt cannon into other robots at 20ft/s. The cannon is benign in comparison in multiple ways.
I think I know where Mk.32 is coming from as I work in the same industry. These batteries can be hazardous and we put a lot of effort into battery level & system level protections to prevent catastrophic battery failures. I've seen enough damage to robot batteries over the past six seasons that FRC would probably be burning down two building per year if we went with most existing lithium batteries.
You're not crashing your T-Shirt cannon into other robots at 20ft/s. The cannon is benign in comparison in multiple ways.
I think I know where Mk.32 is coming from as I work in the same industry. These batteries can be hazardous and we put a lot of effort into battery level & system level protections to prevent catastrophic battery failures. I've seen enough damage to robot batteries over the past six seasons that FRC would probably be burning down two building per year if we went with most existing lithium batteries.
The OP was asking about demos and not suggesting using it for FRC. There are multiple threads on CD discussing LiPO for FRC. I don't see that happening anytime soon. But then I am not the GDC so that is just an opinion.
The company that made our battery makes custom batteries for the military. They know far more than me about designing a battery. Admittedly we don't slam our cannon into things full speed so it isn't getting the mechanical shocks typical in some games. Electrical loading wise it is in the middle of our last 8 FRC robots.
Can you PM me the name of that company? I'm interested for work.
In testing, we've still damaged batteries. In 2013 our robot lost control and ran into a battery sitting next to the wall and pierced the casing. (no bumper on at the time). There's a lot of ways to damage batteries outside of testing. I've been tempted to get one for demos but I'm still leery.
I know this is not for competition, but just use the standard batteries. Is the convenience of changing your battery slightly less often worth even the slightest increased risk?
I know this is not for competition, but just use the standard batteries. Is the convenience of changing your battery slightly less often worth even the slightest increased risk?
When we were building our tee shirt robot, the original thought was use a deep cycle marine battery. The LiPO battery will last an entire football game. (it is a football game: the robot isn't moving and shooting the entire time). So yes it is worth it. We would go through roughly 3 FRC batteries in the same time frame. We were fortunate at the time to have an expert resource to specify the battery so the risk was mitigated.
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.
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.
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
28-07-2016, 17:02
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.
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
28-07-2016, 17:28
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.
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.
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
28-07-2016, 19:08
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).
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
28-07-2016, 21:10
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
28-07-2016, 21:18
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
28-07-2016, 22:14
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.
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
01-08-2016, 17:15
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
01-08-2016, 17:18
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
01-08-2016, 23:31
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
02-08-2016, 08:49
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
09-08-2016, 10:51
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.
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
09-08-2016, 11:04
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 (https://www.wired.com/2015/07/teslas-new-ludicrous-mode-makes-model-s-supercar/), 1,500 Amps.
Al Skierkiewicz
16-08-2016, 14:01
So we can talk apples to apples, the Tesla battery is also 375 volts.
So we can talk apples to apples, the Tesla battery is also 375 volts.
I guess we will need bigger motor controllers?
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