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Microwave Transformer Currents

A while back someone wanted me to post input voltage vs current draw of a re-wound microwave transformer. The transformer is labelled YEC DPC YSH-200 Y800TC

115V 60Hz 86-02 394416

The transformer is rewound with a 60 turn secondary, and is unloaded in these measurements.

The rms values are V I P

5 0.1 0.5 10 0.148 1.48 15 0.182 2.73 20 0.211 4.22 25 0.238 5.95 30 0.264 7.92 35 0.29 10.15 40 0.316 12.64 45 0.345 15.525 50 0.375 18.75 55 0.408 22.44 60 0.445 26.7 65 0.486 31.59 70 0.531 37.17 75 0.583 43.725 80 0.645 51.6 85 0.722 61.37 90 0.818 73.62 95 0.944 89.68 100 1.127 112.7 105 1.384 145.32 110 1.796 197.56 115 2.418 278.07 120 3.29 394.8 125 4.49 561.25 130 5.98 777.4 135 7.67 1035.45 140 9.87 1381.8

Not sure if this will still be of value, as it was requested months ago, but now I definantely see why everyone kept recommending running two in series for continuious duty, the growth over 60V is clearly exponential. Are these transformers ferro-resonant? I only assume the jump in current is from the core saturating. The reson I'm working on these is I'm trying to build a 40V @ 25A or so supply (my original plans for 80v were pretty much pointless, I realized). I already have a transistor bank that can handle a max of 1380W, I'll probably run it around 1000 just to play it safe, I have the capacitor bank, diodes, and now I'm working on the transformer. I'll also probalby go with the recommendation to tap switch to keep power down. I had originally planned on building a triac pre-regulator, but I'm no design engineer and I think this will probably just be the weak point of the supply. Does anyone have another recommendation of a relatively cheap ($50 or so) transformer that could supply these currents? All thoughts and input always appreciated.

Thanks for reading, Steve

Reply to
sck0006
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Yes, I think I see my mistake now. I never really grasped the concept of VA vs W, except that they are different. Please bear with me, I'm trying to understand...

So you're saying that the transformer is mostly reactive, not resistive, being that the resistance is low

Reply to
sck0006

Thanks very much for your reply. Fan cooling them is not a problem, I had planned on it, and since it shouldn't be more than say 40 turns, I don't forsee it being a problem winding them very closely the same, as long as I can find a good way to get the terminals for tap switching mounted. I'm still keeping an eye out on ebay, I've found a couple good transformers with moderate power ratings, but they all seem a bit pricey, but if I gotta pay for it, I gotta pay for it...

Thanks again for your help! Steve

Reply to
sck0006

( V I P )

** The primary resistance of that tranny is likely to be less than 1 ohm.

So the real "power" figure at 120 AC is more like 10 watts copper loss plus a few watts of iron loss.

394.9 is the reactive power draw in VA.

........ Phil

Reply to
Phil Allison

** To measure power in watts with a reactive *non linear* load requires a "wattmeter". Such a meter effectively multiplies the voltage and current value at each instant to derive instantaneous power, then averages the result.
** Yep.

Good old " I squared R " .

** The iron core dissipates energy in being heavily magnetised and then re-magnetised in the opposite direction 60 times a second. Makers often specify this as so many watts per kilogram of iron , depending on the grade.
** I expect a "wattmeter" would read that sort of number.
** Not really, a saturating transformer is a non linear load as well as an inductive one.
** Once you put a load on the secondary, the primary copper losses will increase but the iron loss reduces. Of course, the secondary gets hot too - so the overall heat loss will rise to something like 30 watts. I suspect the secondary can deliver about 500 VA before the whole caboodle gets too hot to be safe.

Microwave oven trannys are "cut to the bone" designs and need fan cooling to achieve the rated output continuously. Running one with no fan means de-rating it by a large margin - maybe 2 or 3 to 1 in terms of VA.

Connecting two with their primaries wired in series means their secondaries must be wired in parallel and the two units be very close in ratio.

........ Phil

Reply to
Phil Allison

Pardon me for butting in on the tail end of this thread. I suggest that you might buy a Kill-A-Watt meter for you experimentation. These meters are really great instruments in that they provide readings of watts, V-A, KWH, power-on time, power factor, line frequency, line voltage, and load amps, all in one unit. You can find them on Ebay for $20 - $30 US plus S/H. I have two of them that I use on old radios and audio systems that I repair. They have paid for themselves many times in that use.

The watts vs. V-A confusion will be shown at the push of a button, and you can immediately see the effects of any changes you might make to your circuit.

Cheers!!!!

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in 
the address)

Never take a laxative and a sleeping pill at the same time!!
Reply to
DaveM

I'll look into it. I always love buying new toys on ebay. I work in a cal lab, and all the meters of this sort I've seen have been of the high dollar kind. The last one I saw used four current transducer clamps, four voltage inputs, had a paper printout, computer interface, graphical interface, measured just about everything under the sun....didn't think about looking for one in my price range. Thanks for the input, I'll probably pick one up.

Steve

Reply to
sck0006

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