Are LFP batteries suitable for electric wheelchairs/scooter?

meetyg

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Hi.
I was wondering if LFP batteries are suitable to replace lead-acid (AGM/SLA) batteries in an electric wheelchair/scooter?

Are the rectangular batteries used for solar good for mobile applications or could they be internally damaged by the movement/bumps?

Also, could they be used as a drop-in replacement (assuming similar voltage range) or would they need a special charger?

Also, could they handle the discharge rate? From my understanding 1C is OK, or should it be lower?

I don't have exact specs of the scooter my dad has, but was thinking to replace his current (pretty old) LA batteries with some LFP ones (either ready-made or DIY with BMS of course). The voltage is either 12v or 24v.

I was thinking of LFP (LifePo4) because of their safety and more appropriate voltage range (as far as I understand).
Thanks.
 

gideonzook

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Jun 15, 2021
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we have used rhinovoltz lifepo 4 24 volt 80 amp hour batterys with good success. watch voltage as they will suddenly stop when low
 

DThames

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I built a 24v battery for my father-in-law. I used 3P8S 5000ah 32x650 (24)cells from Battery Hookup. His scooter had 2, 12v sealed lead acid in series. Tested amps were about 20 or less. I used a 30a Daly BMS. I did get a charger more in line with the LFP voltage that I wanted to use. I would expect that if you push the battery to a full 14.4 voltage that it wouldn't take much imbalance to cause a BMS over voltage cell trip, so I went for another charger and only charge to about 3.5v per cell. He is very happy with the battery.
 

meetyg

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I built a 24v battery for my father-in-law. I used 3P8S 5000ah 32x650 (24)cells from Battery Hookup. His scooter had 2, 12v sealed lead acid in series. Tested amps were about 20 or less. I used a 30a Daly BMS. I did get a charger more in line with the LFP voltage that I wanted to use. I would expect that if you push the battery to a full 14.4 voltage that it wouldn't take much imbalance to cause a BMS over voltage cell trip, so I went for another charger and only charge to about 3.5v per cell. He is very happy with the battery.
Nice!
How did you test the amps? Was the motor under load or just free running?
 

DThames

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Nice!
How did you test the amps? Was the motor under load or just free running?
I used a clamp on amp meter and ran it up a little hill that he goes over on his way to the mailbox. I thought that would likely be the typical largest load that he sees.
 

Substrate

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Yes they are! However, the drop-in mentality is a mistake.

If you are serious, then I highly recommend this site:


Here you'll find most of the mistakes that are made, like using a drop-in with a bms that fails when you need it most - like crossing the street or simply trying to make it home 22 miles away. Hence, balance is only achieved during the charge cycle with the charger itself handling charging and balancing chores. Not some add-on bms.

Drop-in's and their bms are not designed for very very high-current wheelchair use, such as "zero degree turns on carpet" and so forth.

In addition, many get ripped off by simply replacing their existing AH capacity with a drop-in of the same size. Not really worth it. And this means customization to a larger capacity to get the most bang for buck.

Note that many chairs with lead-acid batteries are simply treated very badly during charge, and are quite often under-charged and die earlier than expected. If an LFP battery done right is not your thing, then perhaps study the threads about lead-acid charging and care, tailored specifically to chairs and some of their own specific OEM battery-killing connections.
 

meetyg

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Yes they are! However, the drop-in mentality is a mistake.

If you are serious, then I highly recommend this site:


Here you'll find most of the mistakes that are made, like using a drop-in with a bms that fails when you need it most - like crossing the street or simply trying to make it home 22 miles away. Hence, balance is only achieved during the charge cycle with the charger itself handling charging and balancing chores. Not some add-on bms.

Drop-in's and their bms are not designed for very very high-current wheelchair use, such as "zero degree turns on carpet" and so forth.

In addition, many get ripped off by simply replacing their existing AH capacity with a drop-in of the same size. Not really worth it. And this means customization to a larger capacity to get the most bang for buck.

Note that many chairs with lead-acid batteries are simply treated very badly during charge, and are quite often under-charged and die earlier than expected. If an LFP battery done right is not your thing, then perhaps study the threads about lead-acid charging and care, tailored specifically to chairs and some of their own specific OEM battery-killing connections.
Thanks for the info, especially the link to wheelchair forum!

What is you opinion on ready made packs that include a BMS? Do you think those are also not advisable? I have seen some 100Ah packs state that the can handle 100A and 130A burst (30 seconds).
 

DThames

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Thanks for the info, especially the link to wheelchair forum!

What is you opinion on ready made packs that include a BMS? Do you think those are also not advisable? I have seen some 100Ah packs state that the can handle 100A and 130A burst (30 seconds).
Are you referring to a specific "ready made pack"?
 

Substrate

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A motive-power application is far different from our house-power application. Where a single point of failure (bms) is not just an annoyance, but could be life-threatening when you hit the gas, and there's no go.

Also, drop-in cases may make fitment a problem, tempting the user to go smaller than they have the capacity for if they build it themselves.

Like here, it is DIY - either by themselves or by carers with skills to follow the directions of the owner.

To be sure, these people who have been *living* on their creations for far longer than this forum has been around, are smarter than you or I about this application. If a drop-in was the solution, they'd recommend it. But they don't. They wish it were true, but for the most part it isn't.

We can bench-race specifications all day here with speculation, but the ones truly interested will follow those threads in that other forum and LEARN, instead of just opening the wallet.
 

Tecnodave

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LFP batteries are used in many mobile applications sucessfully, For instance BYD (Build your Dreams), China is a major builder of autos, busses, and dock yard trailer tuggers (the ones that move the containers from the ships to the delivery dock) They have hundreds of 40 and 60 foot transit busses serving cities across America and Canada, they are built in Lancaster, California. They are also used in diesel electric hybird city transit busses here in Santa Cruz county, Ca.

Most home built electric cars are using LFP. Its well proven. All the Tesla’s built in China will be LFP, China will not allow cars that burst into flame to be manufactured there, Really irks Elon Musk as he has forever badmouthed LFP.
 

curiouscarbon

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Jun 29, 2020
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LFP is appropriate for mobile scooter 100%

It is very helpful to rigorously establish that your battery meter is an accurate (good) one. To avoid empty tank time.

As people mentioned, if it suddenly stops when you are not expecting it, that can cause quite a potential problem.

If you buy pre-built LFP, then the individual cell voltages may not be available for you to measure.

Basically, a 12V LFP battery will have four LFP cells inside connected in series. Any safe battery will disconnect all of the cells if any of the cells get below X or above Y voltage. X=2.0-3.0V, Y=3.6-3.65V

So there are five important voltage numbers, cell 1, cell 2, cell 3, cell 4, and then the sum total voltage.

If you build your own, then you can see each cell voltage and decide the conditions under which it will execute a safety disconnect of battery, removing traction power.

Either way, be sure to test the safety disconnect mechanism multiple times before going out, unless you’ve got a backup plan. Once you’ve got a good feel for when the disconnect happens vs what the battery meter says (hopefully this stays relatively constant cycle to cycle), then you’re doing well.

Please ask as many questions as you like, traction LFP is really powerful topic and worthy of engineering!

Even Tesla had some problems with LFP state of charge estimation as recently as this last year.

One last thing to mention is to be mindful that any modifications to the mass distribution in the scooter still allow comfortable balance during turns and stuff. Honestly as long as it’s at the bottom where batteries often are it should be fine. Always test before relying on it!
 

Substrate

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Yep. For those actually living / working in wheelchairs, it is best to get *expert* advice from those who have have been dealing with the peculiarities of that application for a very long time, rather than here I'm afraid - be it it old-fashioned lead-acid, or LFP.

Different applications require different solutions - not just looking at specs and winging it, especially if your butt isn't sitting on top of the bank all day - every day - long.
 

meetyg

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Thanks for all the great info.
Seems more complicated (and costly) than I initially thought.
I will look into those wheelchair forums, especially to learn more about converting to Lithium/LFP.
 
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