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Re: New wattmeter
Good idea here.. but, the last C&H meter I got had a max current of 5A,
obviously designed to work with a current transformer for higher powers.
And, they are a bit, shall we say, ancient... the fabric insulation tends
to be a bit crumbly, etc. However, mounted into a box, with a calibration
chart that shows "seconds for 1 rev" vs "watts" they work pretty well. I've
used it to measure power factor on AC motors, NST's etc.
Actually, I've also seen (at C&H, for that matter) lab power meters in the
same $50 price range.
One of the newer solid state power meters would be a better bet, although a
bit pricey (>$100 new). Perhaps some shopping around would find one at a
reasonable cost. Say one that was 5 yrs old, or something.
Your local electric utility will often have bins full of old meters at
scrap prices (i.e. $0.10/pound), although, in some cases, they are
deliberately damaged so you can't swap it in for the one they put on your
house. And, of course, it is a "bin" where they've dumped the old meters in
with a bucket loader.
Any of you HV types in Los Angeles should certainly take a trip out to DWP
scrap yard in Pacoima every once in a while. Mostly junk, but occasionally
nice stuff turns up (quasi-dead vacuum contactors, post insulators, etc.).
Make sure you come in a vehicle that can carry the stuff away though,
because you need to take it with you.
>
> One minor comment. One of the differences between expensive and
> cheap current transformers is how little phase shift they
> introduce. Cheap ones can have significant phase shift. Any phase
> shift will appear as false power factor.
>
> If you want to measure power in our range of interest directly, get
> a utility-type watt-hour meter. I see them surplus all the time
> from electronic surplus dealers such as C&H Sales all the time in
> the $35 range, usually with a meter base included. The register
> (dials) record watt-hours but you can measure watts by timing how
> fast the wheel turns. The Kh factor on the dial face is how many
> watt-hours one revolution of the wheel is worth.
>
> John