[sdiy] Power question

KA4HJH ka4hjh at gte.net
Tue May 22 08:44:43 CEST 2001


>>If I have a device that draws 12 volts at 500ma, will
>>it function perfectly off of an ac adapter that puts
>>out 12v at 1000ma?  Am I correct in thinking that it
>>will only draw what it needs from the power supply?
>>
>yes, but....
>you need to know whether the gear needs regulated power.
>Also, if a tranny is rated 1000ma and you draw less, the
>voltage delivered will be 'slightly' higher.
>Sometimes this is a problem.
>
>paul perry melbourne (currently getting a measured 15v from
>a nominally 10v plugpack)

I've seen some pretty wild differences between the rating on the label (or
molded into the plastic) and the unloaded output of a wall wart. Some
experimentation is usually in order to be sure.

Even if the device in question has onboard regulation you could overheat
the regulator, blow a filter cap, etc. if the voltage is too high. I had a
KORG multi-effects footpedal that worked fine with one wall wart, blew a
transistor in the power supply with another (slightly higher current rating
on that one). The difference in output voltage *under load* was just enough.


-- 
Terry Bowman, KA4HJH
"The Mac Doctor"



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