why does variable AC adapter always test at max voltage?

J

Jack Tyler

Guest
When testing a variable voltage AC->DC adapter (the type with generic
tips), I get the max 12-13 volt reading regardless of the voltage
setting. This is an IMA M-100 adapter with a polarity switch and
voltage increments of 1.5, 3, 4.5, 6, 7.5, 9 and 12 at 7W & 300ma. The
multimeter being used to test it is a Radio Shack Micronta 22-174.

I notice the reading drops very slowly when I leave the meter leads
connected, though I haven't left them on long enough to see if it
finally reaches the specified voltage (i.e. 3V). The adapter works fine
when hooked up to different gadgets and won't power them unless you set
it as specified, so this testing "oddity" must be common. Does anyone
know the reason for it?

JT
 
"Jack Tyler" <jctyler_67@yahoo.com> wrote in message
news:1110760232.616980.307150@l41g2000cwc.googlegroups.com...
When testing a variable voltage AC->DC adapter (the type with generic
tips), I get the max 12-13 volt reading regardless of the voltage
setting. This is an IMA M-100 adapter with a polarity switch and
voltage increments of 1.5, 3, 4.5, 6, 7.5, 9 and 12 at 7W & 300ma. The
multimeter being used to test it is a Radio Shack Micronta 22-174.

I notice the reading drops very slowly when I leave the meter leads
connected, though I haven't left them on long enough to see if it
finally reaches the specified voltage (i.e. 3V). The adapter works
fine
when hooked up to different gadgets and won't power them unless you
set
it as specified, so this testing "oddity" must be common. Does anyone
know the reason for it?

JT
The filter capacitor charges to the top voltage and as you told us it
Click to expand...
slowly decays with the tiny load of the multimeter.
Any real load that the PS is capable of will quickly discharge the
capacitor to close to the set voltage.
--
John G

Wot's Your Real Problem?
 
I agree, attach a load and you should get a good reading


"John G" <Greentest@ozemail.com.au> wrote in message
news:0C8Zd.219$8O2.2935@nnrp1.ozemail.com.au...
"Jack Tyler" <jctyler_67@yahoo.com> wrote in message
news:1110760232.616980.307150@l41g2000cwc.googlegroups.com...
When testing a variable voltage AC->DC adapter (the type with generic
tips), I get the max 12-13 volt reading regardless of the voltage
setting. This is an IMA M-100 adapter with a polarity switch and
voltage increments of 1.5, 3, 4.5, 6, 7.5, 9 and 12 at 7W & 300ma. The
multimeter being used to test it is a Radio Shack Micronta 22-174.

I notice the reading drops very slowly when I leave the meter leads
connected, though I haven't left them on long enough to see if it
finally reaches the specified voltage (i.e. 3V). The adapter works
fine
when hooked up to different gadgets and won't power them unless you
set
it as specified, so this testing "oddity" must be common. Does anyone
know the reason for it?

JT
The filter capacitor charges to the top voltage and as you told us it
slowly decays with the tiny load of the multimeter.
Any real load that the PS is capable of will quickly discharge the
capacitor to close to the set voltage.
--
John G

Wot's Your Real Problem?
Click to expand...
 
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