How many volts can a 110w brush motor handle?

[alpharalpha]

I am thinking of buying a couple of used electric wheelchair tires 110w each, originally because I broke my leg and was getting burned out on pushing the manual around (plus hey electric power is fun, right?) Now I'm getting healed up, riding my e-bike again and walking around better. The seller was out of town until now so I have a chance again to get them, seems like they could be fun. For wheelchair use the 24v is ok, but I'm asking because later on I'd like to build an upright or semi recumbent e-trike and it seems like the standard rear wheels are the same as wheelchair wheels so was wondering if down the road I could use them for that project. Of course I'd rewire it with different controllers etc, but how much voltage can a 110 watt brushed motor handle, could each one take 18 volts, that way I could use my 36 volts of lifepo4 prismatic cells (3.2v x 30ah ea.) I don't care about torque, just wonder what my top speed would be without damaging the motors.

 

[amberwolf]

How many volts can a 110w brush motor handle?

What is the insulation rated for?
What are the brushes rated for?

The answer to those is your limit on voltage.

The question you need to ask is how much *current* it can handle, for how long, and that again you'd have to check with the manufacturer, or test it. The current will be limited by the controller via PWM, just like brushless ones.

Realistically, you can probably double it's power output for at least a short time (minutes) if you give it time to cool off afterward, but it's going to shorten the brush life. For a few seconds, you can probably use many times the rated power, again with shortening of life the more you do that, and the harder you push it.


I put perhaps 10x the rated power into a (stalled) brushed powerchair motor once, for less than a few seconds, during a chain derailment/jam while riding, before it blew up the controller, tore spokes thru the rim, bent the axle, broke the chain, and damaged the chainrings, and you could see the discoloration on the commutator.

Details of that are somewhere on my old http:/electricle.blogspot.com on a post I think called chainrings are all evil or something like that.

 

[alpharalpha]

Ok, no good for e-trike. If the controller/joystick works fine I'll stick with the rated 24v but if they don't and I diy a couple cheapo controllers and some thumb throttles like we discussed before would it be reasonable to expect the 110w motor to handle a 30% increase from 12v to 18v? And not constantly, just occasionally where there might be long stretches to cover?

 

[amberwolf]

I don't think those are wired in series for wheelchair use, so each one gets 24V (peak, PWMd) from it's own section of the controller (independent, for steering), unless they are different from any of the ones I've played with so far.

So if you wire them in series, you'll actuallly be *undervolting* them.

As for current, power, etc., again it isn't directly the voltage that is the issue, it's the current limit of your controller. Like with just about all motors we deal with for vehicles here on ES, the higher the voltage, the higher the speed, and the higher the current the higher the torque.

If you have no current limit on a controller (meaning, you just hook up the batteries directly to the motor whenever you engage the throttle (switch, at that point, as it's no longer variable), then you're usually going to get a lot more than the "rated" power out of the system, if the system normally would have a current limit.

I'm sure the existing system has a current limit, so that if you tried to wheelchair up a steep slope it wouldn't just apply full battery voltage and current capability to the motors, and burn them out from overheating probably pretty quickly.

Any new brushed controller you use for them will also have a current limit (or should, to prevent cooking itself if nothing else). You just need to match that limit with the voltage of the battery you intend to use, to keep the resulting max watt rating within the motor's ability to deal with the heat buildup.

If the manufacturer of the motor doesn't ahve a label on there about the max the motor can do, and no specs are available from them either, you'd have to experiment to find out what that limit is, cuz it depends on how they built it, how it sheds heat, and what the temperature rating for the winding enamel is, brushes, any plastic parts, etc.

For instance, on those pwoerchair mtoros I used, at least one of htem had a plastic brushholder plate, and I warped or even partially melted that when using that smaller motor at higher currents than it was intended for. Probably are still pics and stuff on the blog site, dunno what I owuld have labelled the post, though.

Other mtoors had bakelite or similar hard and heat-tolerant materials for the brushholders, and didn't suffer teh same problem.

Bearings and grease and whatnot are other things that might not be rated for a high temperature.