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What's up with this transformer! Answered

Hey I have a litte problem! (sorta, not yet!)

So, I have one of those wall adapter things, and it says it outputs 12vDC and 1 amp. Out of curiosity, i hooked up my volt meter to it and the output was a whoppin 20 volts! Why was it 20 instead of 12 like the transformer said? This is making me worry about my other ones!



6 years ago

It's most probably an unregulated power supply. The open circuit voltage (when no load is present) is higher with simply (or badly) designed supplies. Once you add a load that draws about 1A, the voltage will drop to 12V, the nominal value.

Should you worry? Well, that depends on what you connect. Simple LED strips etc should be no problem, delicate electronics might get destroyed.


Reply 6 years ago

Hey thanks a lot! Prolly just a cheep thing!


6 years ago

Ok thanks guys!


6 years ago

as verence explained perfectly, Open circuit voltage is often higher than the nominal.
Also very often the nominal voltage in not at max load but at moderate load of anywhere from 20-80%.
Often at max load the voltage isnt the nominal anymore...

If you want to play on the save side and protect your electronics from overvoltage of such critters (They also might have nasty voltage-spikes), i normaly use a linear regulator.
Cheap, sturdy and if the voltage is not too much off and the current is not too high, the cooling is no problem.
Fir 12V i suggest taking a simple one with imprinted voltage rather than one with variable voltage (configurable by resistors). So i would go for a LM7812 or similar.
See http://www.porcupine73.com/pics/misc1/LM7812.gif for an example on how to use them.