Why won't a multimeter work on a 9V plug?

[[email protected]]

I have several multimeters, including a Fluke and some cheapies.

I wish to use a pair of cheap $2.99 HF meters as dedicated digital
panel meters.

They work fine on a 9V battery.

I would like to hard wire them in.

None of the above will work with an AC battery eliminator.

I am puzzled by this.

Please explain.

 

[Jamie]

I have several multimeters, including a Fluke and some cheapies.

I wish to use a pair of cheap $2.99 HF meters as dedicated digital
panel meters.

They work fine on a 9V battery.

I would like to hard wire them in.

None of the above will work with an AC battery eliminator.

I am puzzled by this.

Please explain.

Most likely you have the newer, worse model Virtual Ground
power rail, cheapy meters.
Make sure you don't allow the (-)/(+) power lead to come in
contact with the (-)/(+) probe of the meter.

Also, put a cap and a small load across the wallwart, most likely
have one hell of a ripple on it and over voltage.


http://webpages.charter.net/jamie_5"

 

[jakdedert]

I have several multimeters, including a Fluke and some cheapies.

I wish to use a pair of cheap $2.99 HF meters as dedicated digital
panel meters.

They work fine on a 9V battery.

I would like to hard wire them in.

None of the above will work with an AC battery eliminator.

I am puzzled by this.

Please explain.

My guess would be that the battery eliminator is a switching type that
needs some sort of a load to start up. Does it weigh less than a few
ounces? If so, it's almost certainly a switcher.

Use Ohm's Law to determine a proper resistive load, if it's less than
100 ma. Put an appropriate resistor across the output and then measure
it. A light bulb of the proper size (which you must determine by the
output capacity) would be easier to obtain if the output is more than
100 ma.

Post the milliampere rating of the supply here and someone will help you
figure the proper load.

jak

 

[Samuel M. Goldwasser]

Most likely you have the newer, worse model Virtual Ground
power rail, cheapy meters.
Make sure you don't allow the (-)/(+) power lead to come in
contact with the (-)/(+) probe of the meter.

To clarify (I think): Many digital meters require that the power
supply be isolated from the circuit being measured.

Also, put a cap and a small load across the wallwart, most likely
have one hell of a ripple on it and over voltage.

And, make sure the battery eliminator actually measures 9 V without a
load, since the meters won't be much of load.

--
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[[email protected]]

My guess would be that the battery eliminator is a switching type that
needs some sort of a load to start up.  Does it weigh less than a few
ounces?  If so, it's almost certainly a switcher.

Use Ohm's Law to determine a proper resistive load, if it's less than
100 ma.  Put an appropriate resistor across the output and then measure
it.  A light bulb of the proper size (which you must determine by the
output capacity) would be easier to obtain if the output is more than
100 ma.

Post the milliampere rating of the supply here and someone will help you
figure the proper load.

jak

Hi!

Thanks.

I pulled a 1K trimmer from an old board and set it about half way.

Diddled it to see the max resistance effect and it still worked.

Works fine!

Thanks again

BoyntonStu

 

[Samuel M. Goldwasser]

Wouldn't all wall warts do this for class II status?

Yes, for a single meter AND with neither power supply connection also
attached to one of the meter inputs. And assuming he didn't try to
measure the wall wart's voltage with the meter!

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.