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How do I use a multimeter to check my PSU's voltage?

post #1 of 13
Thread Starter 
So I got a multimeter today to prove lemons produce voltage(my best one gave about 1.9V!), and now I'd like to check my PSU's voltage. How would I do this? It says something about a 10A max DC current, and I know my PSU supplies a lot more than 10A. How would I go about this?
    
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post #2 of 13
Your not measuring amps at all..
Your simply reading the voltage that is being produced, Nothing more..
Set the Multimeter to ~DC 20 v ( whatever your DMM has, Needs to be higher than 12, for 12v ), then just stick your DMM leads into an open molex connector , There is a 5v+ , GROUND, GROUND, 12v+ ... Its actually pretty easy tbh
post #3 of 13
Thread Starter 
Thanks, +REP.

I just measured the voltage on the 12V rail of an old, terrible PSU which I have done a lot of bad things to(lit on fire by bridging rails, etc) and it's 12V is at 17.7V LOL
    
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post #4 of 13
Quote:
Originally Posted by Lostintyme View Post
it's 12V is at 17.7V LOL
Meh, close enough.
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post #5 of 13
Thread Starter 
Quote:
Originally Posted by fazio93 View Post
Meh, close enough.
I tested my PSU in my rig right now, and at BIOS it is at 17.8, I think something is wrong. I might have gotten lemon juice on the leads, would this affect anything? Is it safe to wash the lead? Thanks!
    
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post #6 of 13
Quote:
Originally Posted by Lostintyme View Post
I tested my PSU in my rig right now, and at BIOS it is at 17.8, I think something is wrong. I might have gotten lemon juice on the leads, would this affect anything? Is it safe to wash the lead? Thanks!
Lemon juice won't cause increase voltage.....

Is there any load on the +5v or +3.3v?
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post #7 of 13
^This.
If your power supply is an older group regulated design, there needs to be a minimum load on the minor rails for the major rail (12V) to work properly.

However, I doubt it can be as bad as 17.7...
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post #8 of 13
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
Lemon juice won't cause increase voltage.....

Is there any load on the +5v or +3.3v?
I think my PSU has either 4 or 6 rails. The bad one I tested with has 1. With my rig on as I type this, 17.8V is what I get from a local molex. I have the multimeter on DCV 20. What is wrong?
    
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post #9 of 13
Are you using the opposite ground wire to test in your molex? For example
+ - - +
______
/o o o o\\
----------
^ ... ^
|| ... ||

Often recommended in this manner, possibly to avoid potential leakage/crosstalk? Just a thought.
Not sure what unit you have, but if you have it heavily crossloaded and it's not designed to handle that it could also pull your unit out of spec. Rails or no rails.
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post #10 of 13
Quote:
Originally Posted by ocpokey View Post
Are you using the opposite ground wire to test in your molex? For example
+ - - +
______
/o o o o\\
----------
^ ... ^
|| ... ||

Often recommended in this manner, possibly to avoid potential leakage/crosstalk? Just a thought.
Not sure what unit you have, but if you have it heavily crossloaded and it's not designed to handle that it could also pull your unit out of spec. Rails or no rails.
Crosstalk isn't important when you don't care about signals. Crosstalk is important with data transmission and when measuring ripple or EMI. Plain voltage, it doesn't matter.
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