Thread: Question on 12 volt wall warts

Tweet

On the 12v wall warts everyone is using, what is the importance, if any, of the mw rating on them. (I have tons of the 12 v wall warts, but the milliwats is different for each one.)

What would you recommend for a computer fan?

I tried to hook one up to cold cathode lighting (for inside a computer) and the wall wart still works, but the transformer for the cathodes blew. Any ideas why?

The transformer may have gotten too much voltage. Even if the label reads 12VDC, the actual voltage may be higher unless it's a regulated supply. Some unregulated 12VDC warts can put out as much as 20 volts unloaded. For unregulated warts, let's say 12VDC, 500mA, the mA rating means that the wart will put out 12VDC with a 500 mA load on it. Anything above or below that load will get something other than 12 volts.
The mA rating is the maximum load that the wart can handle before it starts to drop it's voltage. Putting a higher than rated load on a wart can result in overheating and failure.
I've run 12VDC muffin fans on as little as 200 mA warts, but they were regulated supplies. Most computer fans don't pull very much current.

700ma should cover just about most computer fans . (0.7amps)

most run on 200-500ma.

thanks for the info, I will look at the ratings and see if I should use a different wart in the future.

Possibility that the wallwart (although it says 12vdc) it could be whats called 1/2 wave rectified. If that is the case then some ac likely got through and as mentioned possibly more voltage getting through than needed. Also many of the wallwarts have terrible filtering in them (thus the low cost of the wallwart) to filter out ac ripple on the dc line, again this would likely cause failure in a dc circuit that is relying on good 'smooth' dc current/voltage.