How to physically measure power draw?

[crimsonjax]

I was wanting to measure how much wattage my system currently pulls under full load. How and what do I need to do this? I have a multimeter but not sure how to use it too measure this. Thanks.

 

[GoStumpy]

Kill a Watt:

http://www.newegg.com/Product/Produc...82E16882715001

With a multimeter I would assume you set it to 120v AC (or whatever range that falls into) and put each terminal on the + and - of the plug? Definitely get confirmation before doing that though!

 

[The Boston Dangler]

you could use an amp clamp:
http://www.fluke.com/fluke/usen/com...ticlecategories/dmms/access_current_clamp.htm

the kill-a-watt (and others just like it) are fine for home use.

 

[Mark R]

You need to use a power meter (also called a Wattmeter). Simple plug in ones are easily available for a few $.

Cheap DMMs won't measure AC current, and I wouldn't recommend using a DMM for measuring AC current because of the danger of splicing into mains wiring (unless the DMM has a current clamp).

Just one thing to bear in mind is that if you just measure the current with a clamp-meter, you can't necessarily calculate the total power from that (especially not for comps). If you multiple Amps * Volts (as measured by a DMM), you will get an upper limit for Watts (but the actual Watts may be quite a lot less). See this pic from my home-made power meter for an example of this problem.

 

[cantholdanymore]

You need to use a power meter (also called a Wattmeter). Simple plug in ones are easily available for a few $.

Cheap DMMs won't measure AC current, and I wouldn't recommend using a DMM for measuring AC current because of the danger of splicing into mains wiring (unless the DMM has a current clamp).

Just one thing to bear in mind is that if you just measure the current with a clamp-meter, you can't necessarily calculate the total power from that (especially not for comps). If you multiple Amps * Volts (as measured by a DMM), you will get an upper limit for Watts (but the actual Watts may be quite a lot less). See this pic from my home-made power meter for an example of this problem.

Correct, voltage and current have different phase if the load isn't passive, like your PSU.

 

[pm]

Just one thing to bear in mind is that if you just measure the current with a clamp-meter, you can't necessarily calculate the total power from that (especially not for comps). If you multiple Amps * Volts (as measured by a DMM), you will get an upper limit for Watts (but the actual Watts may be quite a lot less). See this pic from my home-made power meter for an example of this problem.

What if you used the clamp ammeter to measure current on the DC output side instead - like clamp all of the +12V wires, measure, then repeat with +5V, etc? While you lose measurement of the inefficiencies of the supply, wouldn't it solve the power factor issue?

 

[Zap]

I wouldn't recommend using a DMM for measuring AC current

Agreed. Don't do it with one that doesn't specifically state it can be used for AC, unless you want the DMM to make a loud pop in your hands and stink up the place after you let the magic smoke out.

BTW Meritline has the basic Kill-A-Watt model P4400 for $15 with free shipping using coupon code MLCKCYBERNL1.
linky

 

[crimsonjax]

Cool. Exactly what i was looking for, thanks!

 

[GoStumpy]

I just ordered one as well 🙂 I can finally know how much power all these things the wife leaves on consume!

 

[BoomerD]

For our purposes, the Kill-a-Watt units are accurate enough...and easy to use.