Measuring power consumption and multimeter qtn

A

awdark

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This is kinda an extension from the post about house wiring... but I think its worth my own post so I dont steal his thread.

How can I find out how much power say.. my computer uses?
Can I just pull out the plug a little and stab at it with my multimeter in amperage reading mode? :D

I dont think that idea is very smart much less safe. I have a digital multimeter.. but dont know how to measure amperage..
Voltage in dc I know how to measure.. resistance.. sure.
But I dont like to get near AC current without proper guidance.. the instruction manual is um.. not very useful. For amperage, I have no idea how to even begin measuring that for either ac or dc.. I know I blew a fuse once in it so I havent tried again after that.
SO..
Any way of measuring how much power I am using?
How do I go about measuring amperage?
eh might as well
How do I measure ac? just stick +/- in prongs?

:) Thanks for your time, I ask so I wont end up killing myself thats all. I have read the manual if you care but it wasnt very enlightening to me.
 
With most meters you have to measure amps when the meter is connected in series with the circuit.
In this case you are prolly better off leaving it be or using a clamp style meter. ;)
 
Current (amps) can only be measured my multimeter when it is in series with the device. Basically not worth doing, as you'd have to build a go between to be able to put the multimeter inbetween the PC and the outlet (on the hot prong).

Best bet is to just estimate: http://www.jscustompcs.com/power_supply/ Note that is *max* current draw estimated, not how much it consumes normally. (estimating high is a good idea though)

As far as measuring A/C voltage, just set your multimeter to 'ACV' of at least 120Volts and put the red and black in each of prong holes.
 
Hmm oh series...
I think I tried to measure parallel to a power source when I killed the fuse. I will have to try that.
Hmm sounds simple enough... dont some people use the third prong for something though?
 
awdark said:
Hmm sounds simple enough... dont some people use the third prong for something though?
Click to expand...
Are you talking about the ground? Or a third prong on a multimeter or something?
 
There are devices being sold which do exactly what you want. They're plugged inbetween the outlet and the device(s) of which you wish to measure the electricity usage.

They're definitely a lot safer than poking around AC sources with a DMM.
 
Its much easier just doing the math if you know the consumption of the device in question in watts if the amps are not listed, like on an electric motor. The formula

watts / volts = amps

works great every time. Example, a 100 watt light bulb divided by 120 volts = .83 amps.
You can use your volt meter at the wall receptacle to get your true volt reading. Probably somewhere between 115 and 130, depending on your power company.
 
SarverSystems said:
Good way to blow the meter, too.
Click to expand...

Ya I know thats possible and I dont want to do that hence my asking

Why find out like that? its more of a curosity thing esp to just figure out how much power I am using
 
Why find out like that? its more of a curosity thing esp to just figure out how much power I am using
Click to expand...
It is also a good way to kill yourself if you don't know what you're doing. ;)
 
one word

clamp meter

just put it around your power cable... and like magic... your power consumption :D
 
Mister X said:
It is also a good way to kill yourself if you don't know what you're doing. ;)
Click to expand...

na, i could think of much funnier/better/amusing ways to kill myself :p
 
FLECOM said:
one word

clamp meter

just put it around your power cable... and like magic... your power consumption :D
Click to expand...
Almost. With most clamp meters(except the more advanced ones), you need to isolate one of the wires(hot or neutral) and put the clamp meter around that one wire. If you put the clamp meter around both the wires then they effectively cancel each other out.
 
2Busy said:
works great every time.
Click to expand...

Every time you do the computation for an resistive load. But not for inductive loads.

.B ekiM
 
tom61 said:
Basically not worth doing, as you'd have to build a go between to be able to put the multimeter inbetween the PC and the outlet (on the hot prong).
Click to expand...

Fluke used to sell such an adapter. Part number: AC-10. I have one. They quit selling it, and I guard it with my life, now.

.B ekiM
 
If you are a bit more adventurous and have a spare IEC cord (computer power cord), then follow me :D

WARNING: I will not be held responsible for any injuries sustained in this endeavour, whether due to cutting yourself or electricity, or anything else really. YHBW.

First, you have to scrape the outside plastic off a bit to see the wires. Take either the black or the white, and snip it in half. Connect these to your meter, and voila! Your own current-measuring cord. :D
 
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