I am trying to power a 72 V, 3000 W motor. The ESC is nominal voltage: 72 V.
Under voltage: 42 V
Rated current: 50 A
Rated power: 3000 W
I know I need a 72 V battery, I'm just trying to figure which 30 A, 40 A, 50 A battery will work. Will a 72 V, 30 A LiFePo4 battery work? Am I even in the right realm of batteries? Need it to have a decent amount of distance like a power wheel chair.

Please help as I am stuck in the middle of project.

  • \$\begingroup\$ Power output capability and capacity are two different things. The batteries will have to be able to handle 3000W (approximately 40A at 72V). The runtime depends on the capacity of the battery. (I.e. 80Ah for 2 hours at full power) \$\endgroup\$ Apr 9 at 21:06
  • \$\begingroup\$ Where did the figure of 3000 W come from? I'm on my third electric bike and all three have used 250 W motors. 3000 W seems way too much. \$\endgroup\$
    – Transistor
    Apr 9 at 21:09
  • \$\begingroup\$ The bldc 72v 3000 w brushless motor amd esc from kunray on amazon \$\endgroup\$
    – user337136
    Apr 9 at 21:11
  • 2
    \$\begingroup\$ Have you done your power requirement calculations for the kart? You need to work out worst case power requirement - typically this will be accelerating the mass of the kart and driver when accelerating from rest on the worst-case hill start. That will determine the motor and peak battery current. Then you need to work out average motor current and required range to figure out the battery capacity. Do that before chosing a motor and battery. \$\endgroup\$
    – Transistor
    Apr 9 at 21:37
  • 2
    \$\begingroup\$ No, you've avoided wasting money. You're attempting an engineering project (with several major safety concerns including vehicle safety and fire). You either need to study a bit to learn enough to design the system or copy the specification of an existing design - motor size, gearing and battery size. \$\endgroup\$
    – Transistor
    Apr 9 at 21:41

1 Answer 1


Based on what you're saying about your plan, with the volts and amps and component parts and stuff, you seem to be looking at a particular approach. This approach requires cultivation of a great deal of technical skill. There are no shortcuts here. At least, on that path. However, I would point out two things:

  • due to the way the government subsidizes power chairs, there are a whole lot of slightly broken power chairs and scooters out there on the used market.
  • for complicated reasons many power-chair users are morbidly obese, and many scooters and powr chairs are built with that in mind. That means for you, plenty of margin for enhancements.

Option: K.I.S.S. Do the least possible to adapt an existing product.

As an example for how simple this could be, think of a scooter modified to make space for 4 extra battery packs. The battery cable (battery to scooter controls) is lengthened so it can be plugged into to any of the packs easily. When the scooter starts limping, stop and move the plug, and off you go. As a bonus, when you get home, you can charge all batteries in parallel using multiple chargers.

This requires no electrical skill at all, simply the fabrication skills to lay out and mount the batteries and wireway (so the cord isn't a snag nuisance and isn't at risk of damage).

The next level of sophistication could be finding an existing scooter/chair that is not dependent on a particular battery chemistry. Now for instance a lead-acid battery pack could be swapped for lithium of about the same battery voltage. But remember what I said about technical skill: lithium as a technology is full of pitfalls. Well-made consumer products shield us from these pitfalls, but if you are stacking battery modules off a Nissan Leaf or spot-welding 18650's and assembling a pack, then YOU become responsible for balancer, BMS and safe charger. So you'll really need to be hitting the books at that point.

Of course the impulse will be to "get it to functioning and declare victory" but that's how you get a battery fire.

With a custom battery, one thing you might also do is put the charger on the scooter. In other words, it's exactly like an EV, where the charger is on board the car. And that in turn might enable you to recharge "on the road" - either off a 120V socket, or guess what? The world is quickly filling up with J1772 charge ports that will let you Supercharge (by scooter standards, anyway).

Heavily modding a mobility scooter is a significant leap in skill level.

There are a couple of huge skill barriers here:

First, mechanical fabrication - you'll need to own a home metal shop. Take a look at the Wintergatan Marble Machine video series for a good sense of that kind of fabrication requires - Martin is conspicuously lacking in basic stuff like mill and lathe, but makes a lot of CAD drawings and has machinists fabricate parts. That guy has a significant budget, though.

Next is electrical chops. You don't even know what a "motor controller" is, you just think you hook battery to motor and then ??? happens. So that tells me you have some huge skill levels to climb in the area of electric vehicle design. But this is a fantastic time to be climbing that hill... since EVs have finally arrived, and everybody's making EVs of every size. So get involved on EV builder forums and ask for advice on learning tools.

Hard mode: scratch building a vehicle

In such an effort, the electric powertrain is the smallest part of the job. The hard part is building the rest of the machine! There's a case to be made for doing that, despite the difficulty, because the way the government subsidizes power chairs and scooters, an awful lot of them aren't very durable. They're designed for puttering around the senior home, not long-haul adventures in the naked city.

To skill up in this area, I would be looking at the ATV community.

And better still, disability law does not allow businesses to discriminate - they can't legally say you're not allowed in the shop because your mobility scooter is custom instead of a name brand.

That said, you need to meet them halfway. The thing you build needs to look like a mobility scooter. For instance if you take a Harley motorcycle and pull the gas engine off it and gear it for 4 MPH, the grocery store is not going to let you drive around the aisles in a Harley, and the cops will back them up on that 100%. Same thing if it looks like an off-road ATV.

A scratch build could be absolutely epic, though. It could use a module out of a Tesla Model S battery, giving it over 5 kilowatt-hours of range for about 60 pounds. That takes a Tesla 20 miles at 70 MPH, I can't imagine how far it'd take a scooter, probably more, maybe 60 miles? lol. And if you add the water cooling, you absolutely can charge that thing at the same speed as a Tesla Supercharger (it's 1/16 of a pack that can charge at 150kW, so figure 8000 watts). And like I say, that's available at level 2 public AC EV charge stations. (the green ones on plugshare.com).

That charge speed is just bonkers, and you wouldn't really build it to charge THAT fast because it would be too costly for the limited usefulness it would have. I just mention it to show the upper limit of what is possible.

  • \$\begingroup\$ Thanks. My ultimate goal is to take a power wheels truck and use it to get around my town. Not really trying to go fast. Just want distance. And with the power wheel being able to hold my weight I figured it could be my base. Create a small frame to marry the axle components to it and that's all. Maybe some lights to be seen. Just wanna be able to go to store without bothering my neighbor for a ride or trying to make the 30 minute walk, which would probably be about 10 min if I could walk properly. I really appreciate the break down and explanation. Never even knew about leaf batteries. \$\endgroup\$
    – user337136
    Apr 11 at 15:29
  • \$\begingroup\$ @Go yeah, Leaf batteries are awesome. However they are 7.6 volts - it'll probably still work without further modifications to the vehicle, since lead acid batteries run a little high themselves. Might go 10% faster, I wouldn't go faster than that on a sidewalk or you'll get reported. However charging would be another matter. You would have to get a) balancer, b) BMS and c) charger correct, or you could have a battery fire. But lots of products/help is out there to do that. \$\endgroup\$ Apr 11 at 19:18
  • \$\begingroup\$ Well the battery I was looking at has the BMS built in and comes with a charger. I was just wondering which one would be a good fit. 72v no matter what. But what ah.... do I go 20, 30, 40, 50? Not sure which one to purchase. Im not running the stock motors either. Those are trashed. I bought the 72v 3000w go kart motor. \$\endgroup\$
    – user337136
    Apr 12 at 20:06
  • \$\begingroup\$ @Gogogadget Since you don't yet have the necessary skills to design the thing, you are buying things far too soon. Send them back while you still can. "I bought before I thought" IS NOT a position you want to be in because of the fallacy of sunk costs (the brain-virus that says "Surely there must be a way to salvage those past bad decisions" no, there's really not.) Seriously. You've been warned. There's a valuable lesson here. Try to learn it earlier than Martin did. Martin scratch built that machine in the background, and knows when to quit. \$\endgroup\$ Apr 12 at 20:29
  • \$\begingroup\$ Ok. I don't see what that has to do with my project. I'm trying to create a simple project. I only need a recommendation of which battery I could go with. You are making this way more than it is. I appreciate your input but it's not helping me. Thank you. \$\endgroup\$
    – user337136
    Apr 13 at 14:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.