Voltage from a plugpack measured with no load

[T.T.]

I have a no-brand plugpack that is labeled "output 9V DC".
If I try to measure the voltage using a DMM, I get a value of 14odd volts.
I believe trying to read the output voltage of such a device without load
gives unreliable results.
Is this so?
If so, how can I check the output voltage on this plugpack?

 

[T.T.]

What is the current rating for the plug pack?

Load the plug pack with say 50%, 75% of the rated current output and see
what the voltage supplied is.

If you dont have power resistors for a load try using automotive globes.

That was quick! Thank you.
The plugpack is labeled 9Volt DC 1 Amp. It is from an old Casio music
keyboard.
I will hunt around for a suitable globe.

 

[T.T.]

Perhaps more importantly, what load did you want to run off the plug pack?
How much will it draw?

I don't know. The keyboard must be twenty years old, and I was asked to look
at it by the organist at the church. The keyboard had died and at first
sight it looked as if the plugpack was dead. A closer look revealed that the
coaxial plug that plugs into the keyboard had pulled out of the two-pin
connector on the end of the cable from the plugpack. It wasn't easy to see
because the join was covered in heat-shrink. It was hard to see which way
the co-ax plug had been connected to the cable, and I assumed that the
centre connector was the positive and the outer was the negative. That is
when I used the DMM, to check the polarity. And that is when I became a bit
worried about the high voltage reading. I'm still looking for a globe.
I guess the correct answer to your question(s) is I will be running whatever
load was being required of it before.

 

[atec77]

I don't know. The keyboard must be twenty years old, and I was asked to look
at it by the organist at the church. The keyboard had died and at first
sight it looked as if the plugpack was dead. A closer look revealed that the
coaxial plug that plugs into the keyboard had pulled out of the two-pin
connector on the end of the cable from the plugpack. It wasn't easy to see
because the join was covered in heat-shrink. It was hard to see which way
the co-ax plug had been connected to the cable, and I assumed that the
centre connector was the positive and the outer was the negative. That is
when I used the DMM, to check the polarity. And that is when I became a bit
worried about the high voltage reading. I'm still looking for a globe.
I guess the correct answer to your question(s) is I will be running whatever
load was being required of it before.

I would check the input for possible voltage and resistance , it might
have electros in there or a diode which should offer a clue as to polarity

 

[T.T.]

I would check the input for possible voltage and resistance , it might
have electros in there or a diode which should offer a clue as to polarity

All is well. With a taillight globe the voltage read about 9V.
I was wrong about the polarity. Centre pin is negative and the outer
connector is positive.
Thanks again for your help.

 

[Tom]

I don't know. The keyboard must be twenty years old, and I was asked to look
at it by the organist at the church. The keyboard had died and at first
sight it looked as if the plugpack was dead. A closer look revealed that the
coaxial plug that plugs into the keyboard had pulled out of the two-pin
connector on the end of the cable from the plugpack. It wasn't easy to see
because the join was covered in heat-shrink. It was hard to see which way
the co-ax plug had been connected to the cable, and I assumed that the
centre connector was the positive and the outer was the negative. That is
when I used the DMM, to check the polarity. And that is when I became a bit
worried about the high voltage reading. I'm still looking for a globe.
I guess the correct answer to your question(s) is I will be running whatever
load was being required of it before.

Lot of problems I've noticed with DC plugpacks are dried out electrolitic capacitors. Affected plugpacks show reasonable valuevoltage under no load but at normal operation produce excessive ripple that affect powered circuit. I observed a lot of that with modems, routers and other stuff with microprocessors.

I guess the best test to find out if the plugpack or the keyboard is faulty is to get another 9-12 V known good power supply and power the keyboard from that.

Tom

 

[Baron]

T.T. Inscribed thus:

That was quick! Thank you.
The plugpack is labeled 9Volt DC 1 Amp. It is from an old Casio music
keyboard. I will hunt around for a suitable globe.

Oddly enough I have one of these in my Daughters old toy box. It is
marked as you say 9V 1A. The manufacturer is "Niko" who ever they
are ! Off load it measures 14.52 volts, into a 15 ohm resistor load it
drops nicely to 9.15 volts.

HTH.