12V DC adaptor showing 19V

[damunk]

I was checking polarity using multimeter on some 12v DC adaptors I have.
Doing this showed me the voltage. Here on my readings:

12V DC 200ma = 19V
12V DC 500ma = 16V
12V DC 1000ma = 14V


Question 1): Why are they not showing 12V? Is this because all happen to be unregulated?
Question 2): Why when Amp is higher the voltage drop?

 

[Specialist]

The only proper way to test the output is when they are under load, the open circuit voltage will always be much higher. Especially when measured with a high impedance multimeter.

 

[Wilko]

Agree with Spec, especially if it's an unregulated one. What is the rated current of it please? A pic?

 

[damunk]

It's a philip dc adaptor 12V200ma. It measured 19V under no load.
I then connected it to a servo controller which required a 12V DC power source to open up a resistor which allows the servo to be enabled.

So I powered the servo controller up and I measured the voltage of the philips DC adaptor and it was outputting about 18.5V so it hardly takes up any load. All this 12V power required is for opening up a resistor on a circuit.

So I turned it straight off after I took that reading.

 

[Specialist]

The servo controller would be drawing next to no current if not connected to anything other than the power supply.
If you look on it's rating label, it should tell you the idling current it draws.
It's also possible that the power supply is just badly made & poorly regulated, although it's more likely that your not drawing enough current for the regulator to work efficiently.
Get hold of a 1.5 to 2 watt 12v bulb to use as a load, then check output.

 

[damunk]

To save all this messing ,should have just though about itabit more and get a regulated one. steady 12v. Nothing to worry about.

 

[Specialist]

To save all this messing ,should have just though about itabit more and get a regulated one. steady 12v. Nothing to worry about.

Not necessarily, but the fact that they're unregulated won't cause problems with the majority of things. May with your servo controller though, they normally work best on a clean well regulated voltage supply.

 

[damunk]

That's right mate. With the servo controller I have a feeling it's only drawing 20-50ma. If so then the voltage it'ssucking could be 17V-18V when the controller is switched on.

 

[Specialist]

Don't forget though, the servo controller may have it's own regulation circuit on board & may run happily on a 17 - 18v supply.
Without having the units in front of me on the bench, it's really difficult to give specific advice.

 

[damunk]

Yeah you right. DC 12v-24v . Checked in manual. Thanks for your help.