Thread: Please help me answer 500w motor question

Originally Posted by kindraii

I am trying to research on how to overload a motor.

I have a 120Watt 110 volt fan motor.

The problem is that i can stop it with 1 finger(the rotor)

i know that if i put more volts it will spin faster.

the question is how can i make it more powerful for short periods of time.

i dont know if the questions below make any sense but from research i got even more questions so here they are:

1. I have a 12Volt battery(car size) and 500Watt converter. so basically it converts 12volt to 120volt and its rated 500watt - so it runs home electronics

but my fan is 120Watt. is there any way to make my fan motor produce 500watt(for short time(5-10 seconds), i dont care if it explodes or burns or other thing happens to it) ppl told me something about resistance. but im thinking i have a 500watt ebike motor, and its powerful, very powerful.

so 120watt motor should be at least 1/5times as powerful, but its less powerful than 36v Dewalt screwdriver

Basically my question is

what tools do i need to use to make my motor much more powerful. i just ask this question to expand my knowledge so i can swap a small motor in my kid vehicle back from the day and make it little drag racer. im very good at mechanics and construction, but my physics and electricity needs your help. gas engine will not fit good and its loud

many thanks , sorry for bad english

1. More volts won't make it spin faster, in fact it may spin slower.
2. In a nearly frictionless system, Acceleration is ((torque)/(Moment of Inertia)
3. Torque is equal to current times a constant of the motor
4. Torque decreases as the motor goes faster.
5. If you get 500 W out then you will need something like 500/.8 = 625 Watts in to cover losses.
6. 625 W / 12 Volts = 52 Amps.
7. Are you sure the battery can supply that much?
8. The fan motor is a load. It takes a generator to produce power. Whatever you do you cannot make the fan motor draw 500 W.
9. For 120 W out you need 120/.8 = 150 watts in
10. 150 Watts in / 12 V = 12.5 Amps.
11. Can the battery supply 12.5 Amps?

You need another motor. Get one that's rated for your application. A fan motory won't do it.

I suspect you are working with a standard 120 volt AC shaded pole fan motor. Your pretty much out of luck with one of those. By design they have very poor starting torque.
A standard issue AC motor will deliver 4 -6 times its rated torque during start up (while drawing about 10x its rated amps though) and can hold about 2 - 3 times its rated load capacity (while drawing about 3 -4x its rated amps) for very short durations.

Neither will do you any good on a DC powered system. I would suggest finding a low voltage high torque DC motor. If its a short run high output you need, an old riding lawn mower starter will knock out loads of power for a short burst! Or even a small car starter motor would work too! Stop by the local scrap yard and see if they will let you have a few for by the pound pricing!
If you came by my place wanting to do some thing like that I would probably give you one as long as you brought the dragster by so I could see it go!

Just look around for devices that run on low DC voltages and have motors in them. Automotive applications have loads of small high powered DC motors. Seat controls, window control motors, ABS brake actuator motors. Things like that all have short burst at high power capacities. The old DC generators from old cars and tractors can knock out a fair amount of power as motors too!