Can "Round" LifePo4 Cell Be Used To Make Wheelchair Battery?

[The Mighty Volt]

Hi all,

I was thinking of importing some cells, welding them up into packs and pitching them at various markets, such as electric bike, electric wheelchair, etc.

One thing I noticed was that there is no Value Added Tax payable on "Wheelchair and Hearing Aid" batteries, where I live.

Thus, I was wondering if an electric wheelchair battery pack had any technical differences which would mark it out as being substantially, either chemically or physically, from other electric propulsion batteries.

Many thanks.

 

[amberwolf]

Since many, perhaps most, of the wheelchairs/powerchairs I've ever seen appear to use the batteries as ballast weight, using the significantly lighter lithium stuff instead of lead might not work as well for those chairs.

Typically they use lead-acid, almost always gel, often in the U1 size (around 31Ah). 24V is typical, very occasinally 36V. Usually two batteries, sometimes four.

Cellman's flat cells would probably work very well for the application, for anything that doesn't need the ballast for keeping the chair upright/balanced. Of course, in those situations other weight could be added to do that job.

Other cells that are high-C-rate and high-capacity that require zero care by the user would also work.

The catch is that zero-care problem. They would *have* to have a BMS on them that is bombproof, because most of the people using these things rely on them, basing their entire lives around them working properly, but they do not typically know to do more than just plug it in and go. Nor do they want to care, either. Just like we don't, with ebikes and other EVs, but at least we can get technical enough to deal with it when it doesn't work. Often enough, they're not going to be able to, and would have to call service techs.

If a BMS failure caused a fire especially during use, serious injury or death could occur. Same could happen during charging (and would be more likely) but at least the chair would be unoccupied. You would definitely want the highest quality cells and BMS you could possibly get for this application to minimize these risks, even though they are very very low with LiFePO4 anyway.

 

[The Mighty Volt]

Since many, perhaps most, of the wheelchairs/powerchairs I've ever seen appear to use the batteries as ballast weight, using the significantly lighter lithium stuff instead of lead might not work as well for those chairs.

Typically they use lead-acid, almost always gel, often in the U1 size (around 31Ah). 24V is typical, very occasinally 36V. Usually two batteries, sometimes four.

Cellman's flat cells would probably work very well for the application, for anything that doesn't need the ballast for keeping the chair upright/balanced. Of course, in those situations other weight could be added to do that job.

Other cells that are high-C-rate and high-capacity that require zero care by the user would also work.

The catch is that zero-care problem. They would *have* to have a BMS on them that is bombproof, because most of the people using these things rely on them, basing their entire lives around them working properly, but they do not typically know to do more than just plug it in and go. Nor do they want to care, either. Just like we don't, with ebikes and other EVs, but at least we can get technical enough to deal with it when it doesn't work. Often enough, they're not going to be able to, and would have to call service techs.

If a BMS failure caused a fire especially during use, serious injury or death could occur. Same could happen during charging (and would be more likely) but at least the chair would be unoccupied. You would definitely want the highest quality cells and BMS you could possibly get for this application to minimize these risks, even though they are very very low with LiFePO4 anyway.

Yes, point taken,....I guess the overriding fact is that the person is in a wheelchair.... for a reason and are not likely to be able to deal with an emergency. Good point.

I just had a sample leave China marked as "Wheelchair Battery Sample"....maybe it will avoid VAT, but we will wait and see. The reason I ask is that if I import it at Wheelchair Compatible I must also SELL IT as Wheelchair Compatible. So that's why I needed to ask.

Thanks Amberwolf!

 

[mettleramiel]

There is a chair out there that uses Lithium, here's a link http://shoprider.com/category/power-chairs/shoprider-smartie_UL8W.php it's an indoor, short range chair only

Many wheelchairs nowadays don't use the weight of the batteries for balance, it's very common now to have chairs with 6 wheels and rather hefty suspension to keep it upright. My job is the repair wheelchairs, they are very hard to tip nowadays with or without batteries even when they are top heavy.

I agree with the last poster, reliability and safety are paramount with this stuff, but a bigger factor is price. With a mid-range chair costing $2500-$3000 for the base then adding the seating and any tilt system if necessary, it's quite common for a new powerchair to cost $5000-$10000. Lithium batteries would just add more to that.

One final thought is that they just aren't really needed. Most chairs don't go faster than 5mph so they get an average range of 20-30miles. That's usually plenty of range for these people who make an effort to live close to all amenities. Plus, if you've ever riden a powerchair on the sidewalk, you'll quickly see that all those cracks in the sidewalk really shake you up. You get pretty sore rather quickly. Mobility scooters would benefit much more since they go a bit faster and people often complain or range or the low speed (about 6-8mph), but again, those sidewalks can be hell.

 

[BMI]

The vast majority of electric wheelchair and mobility scooter LiFePO4 batteries are made up from "round" (cylindrical) cells.

We are in the final stages of development of a very high quality dedicated medical/hospital application battery.
The battery will be available in 12V 10Ah and 12V 15Ah versions. Two packs will be used in series for 24V wheelchair applications. The batteries will have a fast recharge time of around 20 minutes.
For low discharge application powering medical equipment the battery is fitted with a medical grade Lemo socket rated at 10A while for high power applications (such as mobility scooters and the like) direct connection to the battery terminals will be used. The BMS via battery terminal connection will be provided with resettable over current cut off of 70A. Individual cell monitoring will be provided with LVC protection.
Version 1 will be the basic battery but version 2 will have a 5 segment LED "battery fuel gauge" built into the battery to let the user know when their battery is getting low and requires a recharge.

The taxes and charges applicable to the different battery types varies from country to country depending on the government and their policies.
For example here in Australia all lead acid batteries imported attract 5% customs duty. LiFePO4 batteries on the other hand are totally exempt from customs duty since they are deemed to be "environmentally friendly".

 

[gilnet]

There is a chair on the market that has them.amberwolf has some of their nick batt pks.they fit on the wheel.they replaced the nicks with lith.either 6 or 9ah.He should know the ones I am talking about.I just can't recall name right now.pretty sure they are cylindrical because the nicks are.(Am sneaking this in hospital so...gotta go!))

 

[amberwolf]

The E-Motion ones? Like the pics in one of my build threads of those blue round NiMH packs?