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

Guest
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.
 
boyntonstu@gmail.com wrote:

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
Click to expand...
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"
 
boyntonstu@gmail.com wrote:
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.
Click to expand...
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
 
In article
<668bd2d8-a5db-463a-aba9-a40e588e63c6@l37g2000vba.googlegroups.com>,
<boyntonstu@gmail.com> wrote:
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.
Click to expand...
Measure the output of the eliminator when it's connected to the HF meter.
My guess is there's no output from it due to the load being too small
which is common with SMPS types. A non SMPS one should work ok - that will
be heavier than a similar output SMPS one. Or add a load large enough to
switch the SMPS on - an LED and resistor selected to draw 20mA should be
enough. 390 ohms in series with a standard red LED should be ok. Make
sure you get the polarity of the LED correct.

--
*Rehab is for quitters

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> writes:

boyntonstu@gmail.com wrote:

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

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| 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.
 
In article <eiz4ek7b.fsf@repairfaq.org>,
Samuel M. Goldwasser <sam@repairfaq.org> wrote:
To clarify (I think): Many digital meters require that the power
supply be isolated from the circuit being measured.
Click to expand...
Wouldn't all wall warts do this for class II status?

--
*I never drink anything stronger than gin before breakfast *

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
 
On Jan 14, 10:08 pm, jakdedert <jakded...@bellsouth.net> wrote:
boynton...@gmail.com wrote:
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
Click to expand...
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
 
"Dave Plowman (News)" <dave@davenoise.co.uk> writes:

In article <eiz4ek7b.fsf@repairfaq.org>,
Samuel M. Goldwasser <sam@repairfaq.org> wrote:
To clarify (I think): Many digital meters require that the power
supply be isolated from the circuit being measured.

Wouldn't all wall warts do this for class II status?
Click to expand...
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.
 
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