What is the relationship of amperage and voltage aside from wattage?

Question

I am familiar with the formula for wattage w=va but if a 12v 10 amp motor is run at 24v instead does it still draw 10 amps, or less? Or more?

If the amperage stays the same is the wattage of the motor then increased?

I tracked down a little info since asking that highlights the complexity. Thanks!!

http://www.the12volt.com/ohm/ohmslaw.asp

Is there any property of the motor that can be considered a constant?

I understood about inherent resistance. I also understand potential heat issues but in fact many motors are de-rated so they can handle a wide range of loads.

I am running a 24v rated hub motor at 36 volts with no heat problem or significant extra wear to the brushes. Loads are highly variable depending on load, velocity, and slope but the motor is rated at 240 watts at 24v and that is where I got the 10 amp rating.

I am trying to figure out the acutal ratings for the motor when pushed this way so I can calculate some of the switching requirements.

Actually the motor has been performing great at the increased voltage. It doesn't heat up at all but I can see a potential issue when I push the load limits on steep slopes or heavier riders.

Thanks again for all the help.

Answer 1

You are missing part of the equation. Resistance. W=VI where I=Current. V=IR R=Resistance. R=V/I. I=V/R. This is known as Ohms Law. If you increase the voltage to 24V you will probably burn out the motor since the resistance of the circuit has not changed, the current will increase. The rating of 10amps in your problem is not necessarily what the motor draws, but what it is rated at. It can handle 10 amps. By increasing the voltage to 24V, you double the current.

Answer 2

M D has it right. If you double the voltage, the amperage will also double since the resistance of the motor will stay the same. This means the wattage will increase by a factor of 4.

The motor, designed to handle 120 watts (12 volts times 10 amps) willl be drawing 480 watts (24 volts times 20 amps). Result, your motor is toast.

Answer 3

zmonte has used an example of a dual voltage motor that is designed to have constant power. Go to the site referenced in his answer and look up the connection diagram and you will see that the motor is connected differently for the two voltages. This is not the situation the asker has described. Some motors can be driven at higher than rated voltages; whether they will overheat depends on the load. An overvoltaged motor will be sensitive to overloading. If it's a DC motor the higher voltage will make it run faster at light loads. You may not be able to draw more power (using more current) from the motor because of overheating.

Answer 4

Actually these people are wrong. Some motors are dual rated. And doubling the voltage actually cuts the current draw in half. This is because the power output of the motor does not change.

Look at the link below

Answer 5

A 12V motor is designed for 12V. 24V would burn it up. You would get approximately twice the amps.

Answer 6

Double the volts= double the amps resistance remaining equal
I=E/R