Easy current measure/recording in power strips?

[[email protected]]

I'm looking for an inline plug-in type of AC current
meter that will tell me how many amps are flowing through
a particular power strip - i.e. I'm willing to unplug a
power strip from a receptacle, plug in a "gizmo", then
plug the power strip into the gizmo.

This is a 'temporary' kind of basis... just measurements
over a short period (5-15 minutes), not a permanent
installation.

Background:

I have a number of equipment cabs in my data center than
have dual 115V 60HZ vertial power strips in them. The
cords on these strips have 'ordinary' 15A male 3-prong
plugs and they are plugged into receptacles that are fed
from individual single-pole breakers back in the PDU
(power distribution unit). Some of these breakers are
15A, some are 20A.

For each cabinet, I want to survey the current draw on
each power strip when both are on, then each strip being
the lone power source for that cabinet. Nearly all of the
gear in the cabs have dual power supplies, with a power
cable from each to a separate power strip.

My budget is such that I cannot afford a full-blown
"Dranetz" analysis/recorder type of device, and that's
overkill for what I need to do anyway.

A pair gizmos like a "Watts Up?"
(http://www.doubleed.com/) would be great except that it
is 15 amps max - I may have some strips pulling more than
15A.

Is a device available similar to the "Watts Up?" but just
a little beefier and (mabye) better quality?

I guess I could buy/build a simple short pigtail with
separate wires to enable me to use a clamp-on ammeter,
but it's not as "pretty" of a solution.

Thanks!

 

[[email protected]]

Is a device available similar to the "Watts Up?" but just
a little beefier and (mabye) better quality?

There is a similar device (with the same 15 A limitation) called
a Kill A Watt.
http://www.p3international.com/products/special/P4400/P4400-CE.html
There are pictures of it disassembled here:
http://cafeelectric.com/killawatt/
It looks like the current measuring shunt is a loop of wire in the
neutral line. Depending on the gauge of wire, it _might_ be OK for 20 A
for a relatively short period of time. The open question is whether the
microprocessor is programmed to give up / indicate an error if it sees
more than 15 A or not. I haven't used one of these, but they seem to
sell for about US$30, plus or minus.

I guess I could buy/build a simple short pigtail with separate wires
to enable me to use a clamp-on ammeter, but it's not as "pretty" of
a solution.

If you want pretty, you can buy one already made up
http://www.testequipmentdepot.com/meterman/electricaltesters/els2.htm
but these are often only rated at 15 A.

You could measure the voltage drop across a chunk of wire. I am
thinking something like some 12 gauge cable, a plug, and a receptacle.
Wire it up like an extension cord, but also include a 3" pigtail off of
the hot wire on either end. Measure (carefully) between the two pigtails
to get the voltage drop in the cable when it is supplying a known load,
like a few 100 W light bulbs. Then, put the cable in the circuit of
interest, measure the voltage drop there, and do the math.

You could even do it by brute force. Look up the rating on the breakers
involved, then add a 100 W light bulb to the circuit and wait to see if
the breaker trips. If no trip, add another light bulb. Keep doing this
until the breaker pops, then calculate the original load by
(breaker rating - (0.833 * number-of-bulbs)). Yes, this is a moderately
silly way to go about this...

Matt Roberds

 

[Guest]

This is a 'temporary' kind of basis... just measurements
over a short period (5-15 minutes), not a permanent
installation.

Actually, at one time, Amprobe had a model that included exactly this item.
It had 3 windows in it for various current values and was to do exactly what
you describe..and it was pretty. The clamp on meter went thru the chosen
window and then you could read the current on the meter. This is just a
'pretty' version of the 'multiple loop' homemade device described by others.

I dunno if it is still available or not...check Amprobe...and check Ebay
(who knows?!)

whoops...here it is....

http://www.contractor-books.com/AM/AM-Clamp-on_Acc.htm

 

[Andy P]

If youve got time (you said you only wanted to measure for a few
mintues) why not jsut use a clamp on multimeter and watch it. load it
down for peak amps, and then that'll probably give you a good indication
of what's going on. It's a much simpler way of doing things if ya ask
me. More time consuming in man hours, but cheap and easy.