Measure power usage with a Clamp Meter.....

Bluefront · Post by **Bluefront** » Tue Aug 15, 2006 12:22 pm

Well I always wanted one of these things....a clamp meter. This one was on sale at Harbour Freight for $11 (cheap....usually cost much more). Cen-Tech #DT266.

I always thought you could just clamp around a power cord and it would register amps....wrong. You have to clamp around a single wire...the hot or neutral. I carefully cut open a small extension cord....pulled out the white (neutral) wire and used it.

My P4-3.4 idles at .7A (77watts) and maxes out at 1.4A (154watts)....about right. This is a useful device....doubles as a VOM and comes with leads and a case. Not bad for $11.

zenboy · Post by **zenboy** » Tue Aug 15, 2006 12:33 pm

I saw one of those at Harbor Freight and was trying to justify it to myself, and I think you may have sold me on it.

larrymoencurly · Post by **larrymoencurly** » Wed Aug 16, 2006 5:18 am

Here: http://www.fatwallet.com/forums/message ... word1=kill

is a thread about deals on the Kill-A-Watt power/amps/volts/PFC/energy measurement device.

Does anybody know of deals for cheap DC clamp-on ammeters or clamp-on probes? I bought a probe for $35 + shipping, but the dealer has since increased the price by a lot.

Post by **Rusty075** » Wed Aug 16, 2006 6:23 am

What's it sensitivity like on the low end of the spectrum? ie, Do you think it could give meaningful numbers from 12v DC sources like HDD's or fans?

Oleg Artamonov · Post by **Oleg Artamonov** » Wed Aug 16, 2006 7:02 am

Bluefront wrote:My P4-3.4 idles at .7A (77watts) and maxes out at 1.4A (154watts)....about right

This is wrong unless you have PSU with ActivePFC.

Without ActivePFC, TrueRMS clamp meter will give you RMS current and therefore apparent power, not active power. Non-TrueRMS meter will give you some completely meaningless values.

Oleg Artamonov · Post by **Oleg Artamonov** » Wed Aug 16, 2006 7:20 am

Rusty075 wrote:What's it sensitivity like on the low end of the spectrum? ie, Do you think it could give meaningful numbers from 12v DC sources like HDD's or fans?

Usually resolution of clamp meters with 300...600A range is 0.1A and absolute error is about 3 to 5 digits (= 0.3...0.5A). So you can't measure low currents with such clamps.

But there are low current AC/DC clamps with resolution two orders higher, like that one: http://us.fluke.com/usen/products/LH41. ... eProducts)

zenboy · Post by **zenboy** » Wed Aug 16, 2006 8:09 am

And they don't cost $11 either.

Bluefront · Post by **Bluefront** » Wed Aug 16, 2006 3:07 pm

Well the PSU in this setup I tested is Active PFC....a 300w fortron. And it registers down to .1A (AC).....3.5 digits.

The P4-3.4 runs about 95W at max. Here's the rest....

MATX board (ASRock)
2 512mb ram sticks
2 maxtor 3.5" drives
Fortron 300w PSU with active PFC
1 120mm fan
1 92mm fan
1 80mm fan
1 60mm fan
AIW 8500DV
Wireless pci card
AMR modem
5 port USB card
a few small internal lites

154W sounds about right at max usage (CPUBurn). The readings are completely stable. It's a keeper for me. The clamp only registers AC amps...not DC. That's pretty normal for these things.

Measure power usage with a Clamp Meter.....

Measure power usage with a Clamp Meter.....

Re: Measure power usage with a Clamp Meter.....