Voltage from a plugpack measured with no load

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
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?



Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it

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.



Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it
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.



Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it

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



Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it
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.



Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it

I'd be confident the plug pack is ok and wouldn't worry about testing with a
globe.

Centre positive is common but not always the case, I'd suggest opening up
the keyboard and working out what the polarity should be, perhaps there is a
protection diode off the power connector that would indicate polarity -
otherwise look for filter capacitors or a voltage regulator.

Perhaps look for dry joints / cracking where the power connector is soldered
to the PCB.




Re: Voltage from a plugpack measured with no load
Quoted text here. Click to load it
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

--
X-No-Archive: Yes


Re: Voltage from a plugpack measured with no load

Quoted text here. Click to load it
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.
Quoted text here. Click to load it



Re: Voltage from a plugpack measured with no load
Quoted text here. Click to load it

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

Re: Voltage from a plugpack measured with no load
T.T. Inscribed thus:

Quoted text here. Click to load it

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.

--
Best Regards:
                          Baron.

Site Timeline