Author Topic: Yokogawa CW-10 or Wattman HPM-100A  (Read 13018 times)

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Offline The Electrician

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Re: Yokogawa CW-10 or Wattman HPM-100A
« Reply #25 on: March 21, 2014, 01:41:12 am »
Has anybody had experience with either of these units? How they perform, accuracy wise, with small loads < 10W?

A lot of my work is in energy efficiency and I would like to have a decent instrument for measure the power consumption of AC devices. I have a few Kill-A-Watts and they are fine as far as they go, but they are pretty inaccurate. I have units that differ by more than 5%. Also, they are not very helpful for very small loads like the "vampire" loads of many standby power supplies that have relatively high crest factors.

A low-cost solution to your problem occurred to me.  The Kill-a-watt has an internal shunt consisting of a short piece of manganin wire.  I bought another Kill-a-watt at Fry's, removed the shunt and measured it.  It's a 2 milliohm shunt.  I then replaced that shunt with a .2 ohm, 2 watt 5% wirewound resistor, choosing the most accurate one from a bunch of them.  Now the modified Kill-a-watt has 100 times the sensitivity.  I was able to measure the no load draw of a modern wall wart at .077 watts.  The maximum power measurable is now 18 watts.  I compared the reading with my high sensitivity, low power factor Yokogawa wattmeter, and it was very close.

For the final accuracy check, I just set the modified Kill-a-watt to measure current with a small load, and compared that to the simultaneous current reading meaured with a DVM.  The modified Kill-a-watt reads 2% low.  A person could trim the .2 ohm shunt, or just add 2% to the reading.  To trim, I would start with a .2 ohm resistor that measured high with full length leads, as measured with a 4 terminal ohmmeter, and then you could solder in the resistor with near full length leads, and then shorten them as a method of trimming.  Or, solder in a .22 ohm resistor and solder in an additional resistor in parallel to trim.

You probably don't need exceptional accuracy for vampire loads, and this solution is well within your budget.
 

Offline djacobow

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Re: Yokogawa CW-10 or Wattman HPM-100A
« Reply #26 on: March 21, 2014, 01:46:46 am »
I've already got two Kill-A-Watts so this seems like a reasonable hack to try. Thanks!

 

Offline JayF

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Re: Yokogawa CW-10 or Wattman HPM-100A (Standby power measurment)
« Reply #27 on: April 07, 2014, 10:02:03 am »
There are a few power analyzers out there designed for accurate low-power standby measurements.

Yokogawa WT310
http://tmi.yokogawa.com/products/digital-power-analyzers/digital-power-analyzers/wt300-series-digital-power-meters/
Tektronix PA1000
http://uk.tek.com/power-analyzer-series/pa1000
as well as ZES LMG95 below


>If accuracy at low loads is important, then the LMG95 from ZES Zimmer
> could be the right device.
> http://www.zes.com/english/products/single-phase-precision-power-analyzer-lmg95.html

Yes, that is the primary aim, measuring and analyzing standby power.

I'm so glad this thread came alive. I have a lot of units to check out now!
 

Offline JayF

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Re: Yokogawa CW-10 or Wattman HPM-100A
« Reply #28 on: April 07, 2014, 10:06:34 am »
There are a few power analyzers out there designed for accurate low-power standby measurements.

Yokogawa WT310
http://tmi.yokogawa.com/products/digital-power-analyzers/digital-power-analyzers/wt300-series-digital-power-meters/

Tektronix PA1000http://uk.tek.com/power-analyzer-series/pa1000]
[url]http://uk.tek.com/power-analyzer-series/pa1000
[/url]

as well as ZES LMG95 below


Quote from: djacobow on March 02, 2014, 04:48:33 AM

>If accuracy at low loads is important, then the LMG95 from ZES Zimmer
> could be the right device.
> http://www.zes.com/english/products/single-phase-precision-power-analyzer-lmg95.html

Yes, that is the primary aim, measuring and analyzing standby power.

I'm so glad this thread came alive. I have a lot of units to check out now!
 

Offline pol098

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Re: Yokogawa CW-10 or Wattman HPM-100A
« Reply #29 on: February 07, 2015, 10:09:22 pm »
A low-cost solution to your problem occurred to me.  The Kill-a-watt has an internal shunt consisting of a short piece of manganin wire.  I bought another Kill-a-watt at Fry's, removed the shunt and measured it.  It's a 2 milliohm shunt.  I then replaced that shunt with a .2 ohm, 2 watt 5% wirewound resistor, choosing the most accurate one from a bunch of them.  Now the modified Kill-a-watt has 100 times the sensitivity.  I was able to measure the no load draw of a modern wall wart at .077 watts.  The maximum power measurable is now 18 watts.  I compared the reading with my high sensitivity, low power factor Yokogawa wattmeter, and it was very close.
...
For anybody coming to this oldish thread:
This has been discussed in another (older) thread here, with some oscilloscope measurements:
https://www.eevblog.com/forum/projects/measuring-standby-power/30/

I also made a note of other URLs a while ago, haven't looked recently and don't remember details:
http://ecorenovator.org/forum/appliances-gadgets/3597-hacking-kill-watt-very-low-power-measurements.html

HTH
 


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