Building an electric motor science kit

I'm a mechanical engineer and I'm building an electric motor kit for kids to learn about electrical/mechanical design. I've made the parts for the motor but my electrical knowledge is low. I want to use a 12V transformer to power the motor. Does it make a difference if I use a 12V DC or 12V AC transformer? The motor runs at about 200 to 300 RPM and draws about 4 amps. I was using a 12V DC battery from my garage opener to test the motor. I then tried using a 12V AC transformer for a halogen light fixture and it wouldn't run the motor. Does anyone have some ideas for an inexpensive power source that would best suit this application? Thanks for your help.

It seems like your design is a DC motor. Therefore, using an AC power supply will not create a single unidirectional magnetic field. The forces that are suppose to make the motor turn are cancelled out due to the Alternating Current.

I suggest you buy a Universal Power Supply which has a 12V DC output.

If it is a brush type motor it will run on AC or DC. I presume it is a brushless type as it isn't working on AC. Just look for a 12VDC "wall wart" type of transformer that hangs on the receptacle. I have a couple in my junk box. You should be able to get one for a phone or radio, just make sure it says DC. Some of the ones for LEDs don't rectify to DC so avoid those.

Thanks for the information. Would it make a difference using AC or DC power source if I used straight copper wire or carbon brushes? Also, many of the inexpensive 12VDC power supplies like the wall wart are only rated below 2 amps. This motor draws 4 amps. When I look for other power DC power sources, it then steps up to a bigger box unit costing over $100. I can't find a cheap power source that supplies the higher amperage.

Look for one that has the transformer in the middle of the wire, like this example: http://www.lightinthebox.com/60w-12v-5a-ac-po...nce-security-camera-ac-110-220v_p1774720.html

They tend to be a higher output. I have a spare one from and old printer

It might draw that current when running. What is the current when the rotor is locked, at startup there is no back enf, and the current requirement is very much larger. You have to make sure the power supply doesn't sag too much when starting. Brush type won't make a difference, aside from the contact area, on a motor like this,
cheers,
Richard

Thanks Richard. I've been using a 12v DC battery from my garage door opener. I
assume the start up current required is higher than 4 amps. I'm trying to find an inexpensive power supply that will run the motor. Batteries need to always be recharged so i was looking for a 110V plugin source. What about a power source like this:
http://www.alibaba.com/product-detail/Constant-Voltage-Single-Output-12V-10A_1496625416.html

Firstly, measure the current with the motor stalled. That will tell you what the peak current is. A good SMPS power supply will have fast acting over current protection, which will normally allow automatic startup once the offending load is removed. So you need to sort out a power supply with that in mind.
It could be that you could pick up a cheap transformer with a suitable rating, put a rectifier on the output, and try that, a grunty old battery charger with a suitable rating might do it, that was all they normally contained. Good quality ones will have a charger controller, but that could be bypassed, in either case, you might find a cheap second hand one locally, just a thought,
cheers,
Richard