Testing an AC adapter using a multi meter - what settings go where?

Posted on 2012-04-03
Last Modified: 2012-04-30
multi meter
Hi the black and red rods have a choice of three holes - which ones?
Also the rotational dial goes where?

Question by:fcek
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LVL 95

Expert Comment

by:John Hurst
ID: 37800311
Most adapters put out 20 Volts or less, so choose a setting like 20 or 50 volts on the meter (rotational dial). Use the DC setting, not AC. Then test the holes in pairs to see if any pair produces 20 volts (or -20 volts, depending on how you connect. ... Thinkpads_User
LVL 62

Assisted Solution

by:☠ MASQ ☠
☠ MASQ ☠ earned 167 total points
ID: 37800380
Good thing about it being a digital meter is it doesn't much matter about the polarity.
Black lead goes in the COM socket and is nominally negative.  For the the voltages your talking about the red lead goes in the socket immediately above.  Set the dial to DCV in the range the adapter says it puts out.
If this is a laptop adaptor you may have a cylindrical plug with a central pin  the cylinder may have separate internal and external surfaces that you need to check the potential across while the pin will have a lower voltage.  The adaptor label should also show polarity for the DC output to give you an idea about whether the outside is positive or (more likely) negative.  If you get a negative reading for DC volts then it just means the surface you've got the red probe on should actually have the black one!
LVL 62

Expert Comment

by:☠ MASQ ☠
ID: 37800396
Which is pretty much what thinkpads_user has already covered.
Shouldn't go for a coffee mid-post :)
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LVL 92

Accepted Solution

nobus earned 333 total points
ID: 37804941
>>  Hi the black and red rods have a choice of three holes - which ones?   <<  see above
the 3rd one is for measuring DC Amperes up t o 10 A DC
>>   Also the rotational dial goes where?   << since most ac adapters output 18 - 19.5 V the 20 V DC position seems the best; if unsure start from the 200V, then switch to lower

to show all, here a picture  :

Author Comment

ID: 37858696
Im going to test the ideas here soon
LVL 92

Assisted Solution

nobus earned 333 total points
ID: 37859311
note that you must load the PS -  otherwise it still can be bad  when connected to mobo

Author Comment

ID: 37898679
Im going to test this over the weekend thanks.

Author Comment

ID: 37912943
Well like the person with new orthopaedic shoes, I stand corrected.


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