# Wall Warts Stop Working



## Doc Doom (Aug 28, 2008)

Some of you may remember my head turning prop Drew Buriedmoore. I used a 12 VDC wall wart to power an air vent motor and pair of LEDs. Pretty simple, basic set up.

Previous operation has been testing only. I set her up yesterday and after about an hour noticed she had stopped working. Based on my meter, the wall wall wart stop working. I did notice that it was hot to the touch. It was 12 VDC, 300 ma. I replaced the wall wart with a 12 VDC, 700 ma one and was back in business, I thought. After about another hour she had stopped again. THis time the transformer was not hot at all.

Anybody got any idea what's going on? The moter simply rotated the head on a central spindle, no heavy torque loading going on.

Thanks,
Doc


----------



## Frighteners Entertainment (Jan 24, 2006)

what was the rating on the vent motor?


----------



## DynamoBen (Nov 9, 2008)

Frighteners Entertainment said:


> what was the rating on the vent motor?


This was the direction I was going to go in. It sounds like you are drawing more current than the power supplies can provide. What is the current draw on the motor (amps)?


----------



## Frighteners Entertainment (Jan 24, 2006)

I'm thinking around 1 amp?


----------



## Doc Doom (Aug 28, 2008)

Frighteners Entertainment said:


> what was the rating on the vent motor?


Good question.

Answer: I don't have the foggiest idea. I used the same little black vent motor about a dozen props. Have never had this problem before. I've used wall warts varying from 300 ma to 1.5 amps.


----------



## Otaku (Dec 3, 2004)

Those motors have some issues with their power connectors. I wonder if you have a short in there somewhere? Shorting a wart will kill it fairly quickly.


----------



## Doc Doom (Aug 28, 2008)

Otaku said:


> Those motors have some issues with their power connectors. I wonder if you have a short in there somewhere? Shorting a wart will kill it fairly quickly.


Soun like you may be onto something. How can I confirm if I have a short? One problem is that I can only get to the ends of the wires going to the motor and LEDs unless I tear the whole thing apart.


----------



## Otaku (Dec 3, 2004)

Do you have a DMM? I have a couple of those motors at my work that I can test for the resistance across the motor terminals. If your DC resistance value is really low you may have a short. I'll test my motors first thing in the morning and post results.


----------



## lostskeleton (Aug 30, 2011)

Do you know if you have a protection diode on your motor? Any time you drive an inductive load you should have one. It is possible to have an inductive spike blow your supply when switched from on to off. Or when you are dealing with any sort of ripple at all.


----------



## Otaku (Dec 3, 2004)

Good point, lostskeleton. I use these diodes on 12VDC solenoids:

http://www.radioshack.com/product/index.jsp?productId=2062578

FWIW, the DC resistance across the motor leads is ~257 ohms. I don't know if this is relevant for determining a short or if it has a high degree of variability from one motor to another.


----------

