[Boatanchors] (Another) question about clamp-on ammeters

[N5ARW]

While not an answer to your question.  I got one of these power meters and
mounted it in a box with an outlet and find it very useful for the price to
monitor my line voltage and the current drawn by a device I am testing.
http://www.ebay.com/itm/321969561028

On Mon, Jul 18, 2016 at 8:57 PM, Phil <ko6bb1 at gmail.com> wrote:

> Hi All,
>
> Awhile back I posted a question about using clamp-on ammeters, if using
> multiple turns through the meter was a linear function.  I.E. If 4 turns
> through the sense probe clamp gave 4 times the sensitivity.
>
> Awhile back I DID buy a relatively inexpensive unit, the Harbor 'Fright'
> Cen-Tech 95683.  Think I paid a bit less than $20 with a coupon.
>
> I DIDN'T want to put a lot into one as it will only receive occasional
> use, and those not critical measurements (I DO have several DVMs, from high
> quality down to 'throw-away' meters as well as VTVMs).  So the last thing I
> needed to do was sink a lot into another one ;-)
>
> When I replaced the Astron RS-20M 20Amp PS with the Astron RS-50A I wanted
> to measure and compare the "idle" (no load) current of the supply while
> turned on but not in use (basically I would say mostly transformer losses).
>
> To this end I put one of my freebie HF outlet strips on the bench, opened
> it up and cut the hot wire to the power switch.  I then spliced a 12 inch
> wire between the power cord and the switch, and routed this 'loop' out the
> side of the outlet strip.  This will now be what I use when I want to
> measure AC line current on something. It's long enough to allow multiple
> turns through the ammeter when need be.
>
> 1.  First I measured the RS-20M, it measured between .4 to .65 Amp primary
> with no load.
>
> 2.  Then I measured the RS-50A.  It measured between about 1.2 to 1.75
> amps with no load.  Makes sense, the supply is rated at about 2.5 times the
> current, and it looks like the transformer losses are in a similar ballpark.
>
> HOWEVER: *******************************
>
> What I don't understand is why the large variation in what I read,
> DEPENDING on where the wire was located in the pick-up 'jaws' of the meter.
> If I centered the wire (the hole is about 2.25 inches) it read the least,
> IF I located the wire loop near the edges, especially the left edge it read
> the maximum.  I'm pretty sure that is due the better coupling to the
> (presumed) ferrite in the clamp proper, and that makes sense.
>
> *******************************************
>
> DUH, I just went back and read the 'skimpy' manual again (for the
> umpteenth time) and it did answer the question I was going to ask.  It said
> to locate the wire in the CENTER of the jaws for best accuracy.
>
> At that point I nearly scrapped this email before sending, but thought it
> might emphasize how important it is to read the manual over several times
> before asking stoopid questions. Especially when said manual is in
> "Chinglish" (though this one is better than most that come with Chi-Com
> products).
>
> --
>
> 73 From "The Beaconeer's Lair"
> Phil, KO6BB
> http://www.qsl.net/ko6bb/  (Web Page)
>
> HF/LF RADIOS:
> Grundigs: S-350 (~2006), G6 (2011) & S450DLX (2014).
> HOMEBREW: 7 Tube+Rect 1v3 Regenerative RX for LF (built 2015)
> Icom:     IC-735 Transceiver (~1990).
> Icom:     R-75, Cascaded 250/125Hz CW-Filt, Panadapter. (~2009)
> Icom:     IC-7200 Transceiver (~2015).
> R-Shack:  DX-380 digital portable (~1990).
> SDR:      Softrock Ensemble II LF (built from a kit 2015).
> Zenith:   Royal-7000 Transoceanic Portable (~1968).
>
> ACC:   HOMEBREW  LF-MF Pre-Amp, MFJ-993B HF Auto-Tuner.
>        HOMEBREW  4 Port Multicoupler, Feeds Antenna to 4 RX's.
>        HOMEBREW  8 Hz Audio Filter.
>        Timewave  DSP-599zx Audio Filter.
>        Behringer 1202fx Audio Mixer (for mixing/routing audio).
>
> ANTENNAS: 88 foot Long Ladder-line fed dipole, 35 feet AGL for MW/SW.
>           Active Mini-Whip, 36 Feet AGL for LF/MW/SW.
>           37 foot "Low Noise Vertical", 11 feet AGL for LF/MW/SW.
>
> Merced, Central California, 37, 18, 37N   120, 30, 6W CM97rh
>
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-- 
James True N5ARW
www.boatanchor.com