# Can a 2 HP DC motor drives a 5 kW DC Generator?

• xiv_wolf
The red line is the power output that the motor can handle before it starts to overheat. The yellow line is the power output that the motor can handle without over-heating. The green line is the power output that the motor can handle with acceptable ductility and life.The red line is the power output that the motor can handle before it starts to overheat. The yellow line is the power output that the motor can handle without over-heating. The green line is the power output that the motor can handle with acceptable ductility and life.

#### xiv_wolf

Sorry for this noob idea but I'd like to know what happens if:

A 2 HP DC electric motor is coupled to a 5kW DC Generator, will the 5kW DC Generator produce a 5kW output? What will happen to these two equipment. Thanks for the Reply!

It will work just fine under 2Hp (approx. 1.5kW). The power rating just tells you what the safe operating conditions should be. You could run a 2Hp motor at 5kW but it will have a shorter life span.

When you go past the rated power, you are drawing more current than than intended for the rated voltage. It could overheat. Also, the torque in the rotor is proportional to power being run through it so the metal has to be strong enough to handle it. If you hooked a 2Hp motor up to a 10,000Hp motor in a train, you could be sure that the big motor would just tear it to shreds.

In other words, the electrical input of the 2 hp motor will always be greater than (after efficiency losses) the electrical output of the 5 kW generator.

Okefenokee said:
It will work just fine under 2Hp (approx. 1.5kW). The power rating just tells you what the safe operating conditions should be. You could run a 2Hp motor at 5kW but it will have a shorter life span.

When you go past the rated power, you are drawing more current than than intended for the rated voltage. It could overheat. Also, the torque in the rotor is proportional to power being run through it so the metal has to be strong enough to handle it. If you hooked a 2Hp motor up to a 10,000Hp motor in a train, you could be sure that the big motor would just tear it to shreds.

Ok so there's no argument re: the power output of the Genset but on the lifespan of the motor. Is the RPM of the motor considered?

xiv_wolf said:
Sorry for this noob idea but I'd like to know what happens if:

A 2 HP DC electric motor is coupled to a 5kW DC Generator, will the 5kW DC Generator produce a 5kW output? What will happen to these two equipment. Thanks for the Reply!

Why would you be wanting to run the 2HP/1.5kW motor so far past its rating? You looking for a high-tech way to start a fire?

berkeman said:
Why would you be wanting to run the 2HP/1.5kW motor so far past its rating? You looking for a high-tech way to start a fire?

I just want to sure that energy balance is still the bottom line and driving an electric generator through an electric motor was not a good practice. Anyway, this forum helps a lot, so thank you very much!

xiv_wolf said:
Is the RPM of the motor considered?

Oh yeah, that's important. If you overload it to the stall torque(power) of the motor, that will stop it completely. The motor will just sit still and draw a huge current.

ETA:

I was sitting here at work and starting wondering if I gave a good answer. I really didn't.

Here is an ideal speed-torque curve for a DC motor. It shows the speed, torque, and power relationship.

I got it from this http://lancet.mit.edu/motors/motors3.html" [Broken] and added some annotations.

Note the regions that I marked. DC motors do have a theoretical limit on how much power they can throughput. The range for normal operation will end long before that.

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