Re: [TCML] Mot power supply question

[Andrew Webster <andrew600rr@xxxxxxxxx>]

All,

First of all I want to apologize for not responding over the last few
days. Been quite the weekend.

Anyway, I cannot thank you all again for your help on this.

While I understand that the 6 pack will be less reliable and much more
trouble than a 4 pack, and also Peter, I see your point also in making
it the best, but I did I set out to build my 8" coil for a certain
power level and in turn this would (hopefully) give me the performance
level I have been after. While I have found it to either be much more
expensive or downright impossible to find a pig I felt this was the
next best thing.

I was able to get it running this weekend. I pulled the shunts,
cleaned them up as well as I could and just go all out and do
everything I could think of in prepping them even it if was over kill.

I coated the cores where there might be flash over issues, floated the
last four in the run and wired it just for 120 operation and ballasted
it down to 12 amps under load. I then warmed all of them in the oven
for an hour and buried it in oil and let them soak. The next day was
the the first real test and I hooked up a quick makeshift Jacob's
ladder. Presto! No flash overs! I ran this for a few minutes and
watched closely for any signs of trouble, once I was comfortable, I
opened the ballast up to 39 amps and ran the ladder again. Worked like
a charm. Pulled the coil out and ran it testing both the supply and
trying to tune the coil in. The supply did great! Although my coil is
in need some more tuning but I started to develop quite the crowd and
decided the show was more important. More tuning tonight if the
weather holds.

Now, this leads me to a few more questions if you don't mind as I get
my head around things.

First of all it seems the ballast is causing quite the loss in power.
I measure 124.2 out of the wall but only 98 at the input of the
transformer case. I am currently using two matching MOTs in series for
the ballast and am thinking of winding my own as I have a few spare
cores now. But the second part of this is running the pack from 240,
if I parallel the primaries I should get 120 per leg but my
understanding of this is that it will increase the current output of
each of the mots, am I correct in this? Then keeping in line with
this, how do I ballast it correctly? Do I need a matching ballast on
each leg, or can I just ballast one side of my 240? My thinking on
this and please by all means correct me if I am wrong, is that I can
just use the 2 opposite phases of the 240 with no neutral and the
center grounding to the rod I buried just for the transformers.

Also, in determining power levels, while I understand that in
transformers as you step up the voltage you step down the current, so
if you have a 10:1 transformer and put 1 volt in at 1 amp you get 10
volts out at 10ma. How does this hold true in a stack? Does this same
rule still apply? According to my testing I have basically a 1:123
transformer, I confirmed this by running 2 volts in and testing my
output, this also matches what each of them measure by them selves and
added up. Now running this at my measured 98 in I am getting 12054
out. This also means that if this rule holds true I am drawing 39 amps
which gives me 317mA out. Or is the current only determined by the
center two? Something I read on the list had me questioning this.

Thanks again for everything, you all and this list have been an
invaluable resource in my endeavors.

In case any of you are interested you can see it in action here.
https://www.youtube.com/watch?v=7vxziADjpd0 - Just remember I do have
some tuning to do. This was literally first light. ;)


Best Regards,

Andrew


On Thu, May 16, 2013 at 10:48 PM,  <coils@xxxxxxxxx> wrote:
> Hi Andrew,
>
> I dont know what will cause your problem.  Is it the secs or the primarys that burns?
>
> Like others whom have responded, I also have a "six pack" mot psu, and have never had a problem.  My primaries are wired two in parallel, then three sets of two in parallel for 240 in.
> All secondaries phased in series, with the center grounded, inside cores grounded, outer four cores isolated from ground (which is important, as they are seeing more voltage
> than they were intended to).  The inside four cores are also disconnected from secs.  As a precaution from high voltage flash overs, I packed the disconnected secs with epoxy.
>  I ended up with almost 14000 volt secs, and generally drive it up to 280 volts in. I also removed all shunts in the cores.  It is also under Shell DialaAX oil.  So far, I have only used a sync rotory gap and
> I use variable external inductive ballasting, and due to my coil geometry, I use a large Cp and start with a small gap in my ballast, then open it up empirically.
>
> BTW, when I built my bank, I seried all secondaries, and left all primaries open,  I then back fed the secondaries with 12 volts ac,  and phased the primaries together with a volt meter.
>
> This is all probalbly redundant to you, and i dont have the theoretical comprehension that many on this list do... Im more trial and error. learn from my mistakes type.  I do know that when graduating to
> high power levels, things get more complicated.  Especially in engineering the PSU.
>
> Thad
>
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