Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

My kids have been tearing apart a number of different gadgets, from RC cars, to toys, to coffee makers.

There are a variety of cool little motors and lights in these devices that we would like to use on oddball projects. (For serious projects, I prefer to spec out the component and purchase it directly)

So far, I've been using a variable voltage DC power supply to guess the right voltage based on what seems to be the correct speed, brightness, etc... without burning the item out.

Is there any scientific or mathematical technique that can be used to know when you are at a correct level of current or voltage for a given device, or does it simply depend on the specifications of the device?

share|improve this question

alt text

share|improve this answer
hey, that's what I do with LEDs! – Matt Williamson Jan 2 '11 at 19:51

You may be able to deduce the operating voltage from what they came out of - for example, in a toy count the number of cells in the battery pack.

Things in plug-in appliances may be more complicated. Components may not be meant for the full mains voltage - for example I recall a curling iron where a small can motor was probably in series with (part of?) the heating element.

For small motors, there's also the can you touch it after it has run for several minutes (and had power disconnected) test. Many toys (especially cars/planes/helicopters) will push motors harder than this and get away with it for a lifetime comparable to the rest of the toy's brief endurance. But if it stays cool enough that it's not painful to touch, there's a good chance you aren't overdriving it.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.