Why Can't DC Motors be Labeled the Same as AC Motors?

Because a DC permanent magnet motor's output is limited by the lower of being able to cool itself or being able to sustain the current passing through it. AC motors just stall when overloaded. DC permanent magnet motors just carry on turning until something breaks/cooks/burns out.

Exactly. I have come across that many times. Then you call the MFT with the need for a motor and even after supplying an equipment mn/ sn they would look.at the motor with that look of i-dun-o.

Exactly. I have come across that many times. Then you call the MFT with the need for a motor and even after supplying an equipment mn/ sn they would look.at the motor with that look of i-dun-o.

Motors CAN be labeled the same way. Still, it does not mean the same thing.

An inductive AC motor does not run synchronously, as the slip allows an interaction between rotor and stator. when the load gets too high, the motor stalls, and remain there, usually intact.

A synchronous motor does not slip, only gets phase delayed by load, until stall.

A DC motor covers a wide rpm range, and provides widely different power to the load. High rpm / low power is no problem. Low rpm / high power might readily burn out the motor. Hence recommended rpm/power data is important. Additionally, synchronicity has no meaning here.

Thanks for the answers, not exactly what I wanted to hear, but I understand.

I have been trying to devise a low voltage, high torque, beach and woods wheelchair with limited resources.

I guess I will have to satisfy myself with whatever I can scavenge, to make this gadget.

Thanks again for the information.

Beach and woods?....have you ever seen this.?

Not exactly electric but it might provide some inspiration.

Okay, maybe not.

Yep, gear motor is the way to go, with mountain bike style wheels. It may slow you down, but gets thru.

Friend,

Have you considered a DC motor running a small hydraulic pump. The hydraulic system can then be designed so it cannot overload the motor, and you might be able to put in some form of speed control on the motor, to only run fast enough to maintain pressure. The hydraulics could then go to the wheels with variable torque hydraulic motors--high speed at low torque ranging to low speed at high torque, all depending on the conditions you are experiencing. This would probably allow you to even do some form of crawling over obstacles (of appropriate size). Another possibility is to run the battery ouput through a switch mode type of voltage increasing power supply to get a higher DC output and then run this into a variable frequency drive to an AC motor. Many of the drive manufacturers make drives that have no AC input end--designed to run off a DC input instead. Perhaps if you were to contact them they may help you with selecting an off-the-shelf model or doing a custom one for you at very low cost. Going with a VFD will give you somewhat easier control of the motor speed (in my opinion).

Keep on puttering with this progect! --JMM

If you look at wheelchair forums you will find that there have been many designs made to suit your needs. Also look at this thread on CR4. "Looking for High amp, low insertion force DC power connector." Also www.tadwa.org.au website. You will see that they have wheels for manual chairs that work in soft sand. Only for manuals as they have to be put on at the beach and because a stainless steel manual chair is available. With the cost of power chairs being the same as a small car i can only guess how much one that was waterproof to mil specs would cost. Don't forget the batteries. Even leakproof batteries breath, so once immersed in cold water they will suck in sea water thus altering their chemistry.

When I have searched most DC motor manufacturers sites they spec things that only electrical emgineers are familiar with. Very few have anything describing actual power output.

One of the answers spoke to OEM items and that of course does answer why when looking at 24vdc motors are sort of mysterious. The motors used in power wheel chairs are big secrets. I have no intention to submerge parts of the chair or even intentionally get it very near the water just on the beachs.

Most of the motors I can identify by output wattage are far less than 1/2 hp 2-300 watts, where 5-600 output watts would be more desirable. The torque is variable by manufacturers but relatively low.

Low RPM motors with a higher torque rating in the 1/2hp+ 5-600 watts range would be preferable. If I could get the right combination of motor and controllers then LiFepPO4 batteries would be the desired method to get power to it. But properly identifying the motor capabilities is the big deal.

I only know enough to be dangerous, (to myself) not quite smart enough to make sense of the way all manufacturers label their DC motors.

Thanks for the input.

I say again, check out wheelchair forums. Many new wheelchairs have 1Kw motors. Many new motors are 4 pole for greater torque. The motor/controller combination gives long battery life and high power when required. I suggest you go to a wheelchair repair facility and see if they will donate used and surplus motor/trans units to you. We throw many in the bin so i guess you would be able to get them over there.

Jim

I have not had good luck dealing with wheelchair repair shops. They are an independent lot. Most do not approve of tinkerers or at least hold them in low regard

And I also do belong to several wheelchair forums. The majority are spokespeople for manufacturers. I was searching for some fresh ideas. Thanks all.

One approach might be to use a regular wheelchair gearmotor with an add-on two-speed transmission having, say, 1:1 and 1:2 ratios. Another possibility would be a snowmobile type of drive system. Whatever you do is apt to need some customizing, though. Maybe such an arrangement already exists?