Power Supply

Carlinux

Hi,

I'm making a project with a 12vdc motor (came from a hospital bed). It works fine with my big power supply that I use for HAM radio or from a car battery but these are just to big for that. Today, I bought a small 13.8vdc power supply from Radio Shack. www.radioshack.com/product/index.jsp?productId=2103959 When I plugged the motor to the power supply it started to run like a stepper motor with pulse of about 500ms !! Then I checked the output on the scope. When both neg and pos are hooked to the scope it shows 13.8vdc but when I remove the neg I can see the pulse (attached image).

Do you think that I can fix that with a bridge rectifier and a capacitor? If yes can you tell me which parts I need exactly ?

Thanks for your help.

Carl

Mike Green

I'm not sure what you're describing. Do you mean that you see that tracing if you have only one lead from the power supply connected to your scope? If so, you're seeing noise, possibly coupled from the AC supply. I suspect that your motor draws too much current from your power supply and the power supply is protecting itself by shutting itself down briefly, then trying again to see if the "short circuit" has gone away. You just need a power supply matched to your motor. You also need to measure how much current your motor draws, both at heavy load and lightly loaded so you can properly choose a power supply.

Carlinux

Thanks Mike. That answers my question!

sam_sam_sam

Carlinux

Here is where you can find a 10 amp transformer

http://www.mpja.com/prodinfo.asp?number=7846+TR

I hope this helps

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Sam