Simple EE question

I suspect there's a easy answer, and I'm just missing it. I have a 12V power supply, and a small electric motor. When I connect the motor to the power supply, the voltage across the power supply terminals drops to almost zero and the motor doesn't run, which suggests I'm shorting it. The resistance between the motor terminals (when not connected to anything) is about 15 ohms. Should it be this low, or is my motor burned out?

Is your power source rated for that motor? The resistance could be lower but it sounds like your ps isnt strong enough.

Ron's right... :nodi:

Think about it... You can't start your car with eight D-cells wired in series, can you?...

beerchug

-Eric

Review Thevenin's theorem.

The motor nameplate should give you some indication of current requirements.

Actually, if this is a permanent magnet DC motor, it must be quite small. Otherwise, the resistance could be much less than 15 ohms.

Modern power supplies often have a fold-back circuit in them which drops the output voltage to zero when the current limit is exceeded. The output doesn't have to be shorted--just overloaded.

Sounds like you need a power supply with a higher current rating.

Connect it to your car battery. That will make it run or burn. Beware that there is no current limit on your battery!

Here's the answer. The power supply I was running is rated at 1A, and the motor's are rated at about .9A I came to work and hooked one up to a vps and got it to run fine at .6A, but only after I cranked it up, and even then, it started out running slowly. My guess is because I got them as surplus, and they had been sitting around a while, some gunk got into them and made it hard for the motor to start.

Also, thanks, I didn't know this:
Modern power supplies often have a fold-back circuit in them which drops the output voltage to zero when the current limit is exceeded. The output doesn't have to be shorted--just overloaded.

Marcell said:

Connect it to your car battery. That will make it run or burn. Beware that there is no current limit on your battery!

Click to expand...

I forgot I had set aside a power supply for this project, and was pleasantly surprised to remember it. 12V at 14A sure got those motors running.