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RE: Expensive hobby

Original poster: "Mark Dunn" <mdunn@xxxxxxxxxxxx>


Short the Secondary and put 5 - 10 VAC @ 60 HZ on the primary.  Make
sure your variac or power supply is good for min 5 amps for this test(Z
will likely be 3 to 4 Ohms so at 10 VAC you will draw 2.5 to 3.5 amps).
If not go with even lower voltage or put a resistor in series to drop
the voltage down.  You can work in the mV range and still get good
results.  Then measure current and voltage across the primary and you
can compute impedence as Z=V/I.  You can then choose your current
limiting based on this.

If you want to do full tranformer analysis, you can measure secondary
current as well.  Then you need to repeat the testing with the secondary
open(Obviously, sec I = 0) for this.  From all this data you can figure
leakage inductance, k, etc.

I have approx 20 MOT's and none are current limited by the shunts even
though the shunts are in place.  I have tested MOT's momemtarily across
120 volt mains.  They will pull 30 to 40 amps easy with the secondary
shorted.  If you try be prepared to weld the breaker contacts or weld
the plug into the wall.


Original poster: "Paul B. Brodie" <pbbrodie@xxxxxxxxxxxxx>

Thanks for the info. How are you going about measuring the impedance of
primary? Do your MOT's have shunts? All of mine do. If so, are there
not enough to limit current like the NST's do? Thanks.
Think Positive

----- Original Message -----
From: "Tesla list" <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
Sent: Thursday, April 21, 2005 1:56 PM
Subject: RE: Expensive hobby

> Original poster: "Mark Dunn"
> Paul:
> I have many MOT's. A number are marked 4000 Volt. They are not.
All > of my MOT's have a ratio between 16:1 and 20:1. Most of my MOT's
have > an impedence with the secondary shorted of about 3 to 4 Ohms.
Thus they > will pull 30 to 40 amps from 120 Volt mains with the
secondary shorted > -Don't try that. You test at 10 VAC with the
secondary open I have done > many times to verify ratio. Note you will
be reading 160 to 200 VAC on > the open secondary. Hook up meter
before applying power so you avoid > shock risk. > > Mark > > >
Original poster: "Paul B. Brodie"
> Mike,
> I doubt it because this MOT is substantially larger than the other
coils > > and it has a lot more turns on the secondary. Also, the 4000
V is > labeled > right on the transformer with the manufacturer's
data. Since the > manufacturer doesn't know how the end user is going
to wire the > transformer, they wouldn't put the 4000 V assuming it is
going to be > driving a voltage doubler or anything else, for that
matter. > > I'm curious, where did you get the 1650 vac figure? Almost
everything > I've > read on this list and on countless web sites say
that the majority of > MOT's > are 2000 vac and the heavy duty ones
4000 vac. I am going to drive them > with my variac set to 10 vac and
measure the output from the secondary. > Then, I can extrapolate the
output at 100 vac on the primary. Anyone > have a > better idea of
determining the secondary voltage on MOT's?? > > Paul > Think
Positive > > ----- Original Message ----- > From: "Tesla list"
> To: <<mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx>
> Sent: Wednesday, April 20, 2005 6:31 PM
> Subject: Re: Expensive hobby
> > Original poster: "Mike"
> >
> > Odds are the 4000v is dc after the 1650vac or so from the mot is
> rectified > and doubled under the load of the magnetron. > > Mike
> >