Re: MOTs & Thoughts

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

Original poster: "David Speck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-davidspeckmd-dot-org>

The simple solution would be to test a transformer before and after you 
remove the shunts.  All the discussions on using MOT trannys for VTTCs 
have recommended removing the shunts before applying them.

I think the opposite would be the case -- that after you remove the 
shunts, the unloaded current would drop.  I was under the impression 
that the shunts were designed to limit power output by providing an 
alternate path for the magnetic flux, thereby diverting it from the 
secondary windings.  I would expect that removing them would 
functionally convert the MOT to a potential transformer.  After all, 
most transformers can accept their rated input voltage unloaded without 
self destruction.

Dave
G2-1170

Tesla list wrote:

>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
>>
>