Re: MOTs & Thoughts

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Steve,

I tried this too.  Here are the numbers I got with various input voltages
to my single open loaded MOT:

VAC	AAC (true rms)
30	0.4
40	0.5
50	0.6
60	0.7
70	0.8
80	1.0
90	1.2
100	1.7
110	2.7
120	4.9

I "think" (but I don't "know") removing the shunts would tend to drive more
magnetic flux into the core and make the saturation worse.  

Interesting, I didn't realize they saturated so badly...  I wonder if the
core is less likely to saturate if it had a load on the output?  Or, if
that makes it worse still...  A PFC cap may also do something "odd"...

This saturation is a big concern in some tube coils and other uses where we
want just a "nice" HV transformer.

Cheers,

	Terry


At 11:49 PM 7/20/2002 -0600, you wrote:
>I took some no load measurements on a 4 MOT stack that some of you might
>find interesting.  All 4 MOT primaries are in parallel, and are powered by a
>120 volt variac.  Here are no load primary volt vs amp measurements:
>
>Volts                    Amps
>below 75              less than .5
> 80                         1
> 95                         2
> 90                         3
> 95                         4
>100                        5.5
>105                        7.5
>110                      10.5
>115                      14.5
>118 (max)           17.6
>
>As you can see, the MOT cores start serious core saturation at around 100
>volts, or about 85% of their rated voltage.  The moral of this story is to
>design your MOT stacks to produce the output you need without exceeding 85
>or 90% of the normal primary voltage.
>
>Question:  Suppose I knock out the magnetic shunts.  Would the above
>measurements be much different??
>
>Another thing to be aware of is that above 90% of normal input voltage
>causes significantly distorted sine waveforms that sometimes have strange
>effects on DVMs, causing them to indicate quite inaccurate measurements.
>
>--Steve Young
>
>