A FLA to Lithium question for you engineers out there
 

I have been looking at electric wheelchairs for a good six months now. I want\need to replace my 12YO scooter that has provided good service, but I'm looking for "more". I have MS that limits my ability to walk much past 200 yards.

I want a new foldable, lightweight (less than 70-lbs) power wheelchair that I can toss on an airplane, use on trips, etc.

Now, I've come across a few that have great ground clearance (more than 10") and most that have at best, 3". (Unacceptable)

I'm looking at one now that has all the "standard" stuff,....2-250W motors, foldable, etc.

The one that I came across has all the "stuff" but I'm sure the batteries are just like my scooter.....gel-cell. 24V with 10AH....and they state the batteries alone weight 38-lbs. Dead giveaway they are gel-cell. That and the word "lithium" is never mentioned. Rear wheel diameter is 15.5".

I know the larger the drive wheel diameter the less torque the unit will have....so that is somewhat concerning. These "General Specs" of most state it will climb anywhere from 6-degrees to 8-degrees...which ain't that much. OTOH, I'm not looking to 4WD "mud it up" either. I'm looking to get across cobble-stone with not a lot of resistance.

So, I'm thinking ....why not just toss the gel-cel (yeah....warranty be damned) and hook up a 24V higher amp\hr lithium? Less weight...more travel distance. I know that airlines and lithium don't always get along, but I believe if the battery is quickly detachable (at the loading ramp) the battery can be stored in the cabin while the rest is tossed in cargo.

Power is just power.

Any thoughts on this? You can certainly add a "Liability disclaimer" at the end of any post you make. I'm not looking for certanity...I'm looking for ease of use and will it work.

Re: A FLA to Lithium question for you engineers out there
 

Good project! I don’t see a problem at all Dave except for the one you already mentioned, lithium in the cargo hold of planes. You’ll need 8s LiFePO4 or 7S NMC. NMC will be smaller and lighter for the same energy but also more volatile. A smart BMS with a screen that shows SOC will eliminate the need for an extra SOC meter. Screens are readily available for most smart JBD BMS’s.

You could use 18650 cells. You’ll need 28 3Ah ones for a 12Ah pack, or even the larger 21700 cells. 21 4Ah cells are required. But pretty much any NMC or LiFePO4 cells can be used as long as they suit the application.

Cheers
Pat.

Re: A FLA to Lithium question for you engineers out there
 

Thanks Pat. I've got the tiny grey matter thinking. I may be leaning towards a "drop 'n drive" setup such as this https://dakotalithium.com/product/da...ery-twin-pack/. These weigh 30-lbs less than the batteries that come with the unit.

If I series connect these I'll get 24V and 23-A\H out of them. For all the traveling I want to do on this type of "motor transport" I don't need a large amount of AH. My current scooter has two 12V in series with (IIRC) 21AH and I've never been close to running out of juice. (Well...except that time when TSA "forgot" to put my charger back in the seat bag.....and I noticed that on a layover .....my wife called the TSA and they said "You forgot the charger"....I don't recall ever seeing her so angry!!)

Re: A FLA to Lithium question for you engineers out there
 

Ohhhh, what fun is that. :? :mrgreen:

Re: A FLA to Lithium question for you engineers out there
 

I've done a pile of research on a few of these models with rear wheel diameters that go from 15.5" to 22". Both have motors stated to be (2) 250watt motors @24V. From the reviews I've been reading some have stated they struggle to get across a grass lawn. Other's give them glowing reports....but not stating what terrain the chairs are traveling across.

Now I realize there could be an issue with something on the unit such as an overtightened wheel bearing\axle etc., and the user simply is not capable of evaluating the unit for such an event.

I do know that if the motor is 250watts, and it's powered by 24V, that the amps of each motor would roughly be 10. But how that would convert to the torque\speed of a unit using different diameter wheels...I don't know. (Although there may be the term "work" somewhere in such a calculation.)

Weight is also a critical factor as one unit weighs in at 48-lbs with a 22" wheel and the other is 65-lbs with a 15.5" wheel.

Well, I'll continue to research these units until I either rule them out as inadequate, or find one that provides "real" life event usage. 8)

And of course, these lightweight "foldable" units are coming from China and have USA sales forces with limited support. So....there's that!

Re: A FLA to Lithium question for you engineers out there
 

Don’t forget Dave that the performance will increase with lithium due to the reduced voltage sag. But yes, the better it is to begin with, the better it will be after the conversion.

Also consider a 24v battery as used in e-bikes and scooters. Probably more convenient to remove for travelling than 2 12v batteries. The single battery solution being better is also a factor here.

Re: A FLA to Lithium question for you engineers out there
 

Pat, thanks much. I really appreciate your input!:thumbup::thumbup:

Re: A FLA to Lithium question for you engineers out there
 

So....another question.....is there any significant difference between brushed motors vs non-brushed?

I understand the concept and how each works, but is there a significant difference between them?

Re: A FLA to Lithium question for you engineers out there
 

I’m certainly no expert in motors but from my understanding, all things being equal, brushless are more efficient. As a consequence, for the same power input, a brushless motor is more powerful.

Are AC models an option? AC would be even more powerful and efficient.

Re: A FLA to Lithium question for you engineers out there
 

I haven't come across any A\C motors for any type of scooter\wheelchair\hover-board, etc.

I'm searching for a 36V motor and controller as well but that seems to be non-existent. IMHO 36V would be far better than the 24V 250 watt motors that are on the majority of factory units, as well as aftermarket upgrade\replace motors.

I would think if I just hooked up a 36V power source, the little controllers would toast out in short order.