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Re: Ballast Resistance For Pig Coils (fwd)



---------- Forwarded message ----------
Date: Sat, 27 Oct 2007 08:23:36 -0700 (PDT)
From: Yurtle Turtle <yurtle_t@xxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Ballast Resistance For Pig Coils (fwd)

How much would you want for them (offlist)? I've got
several duct heater elements, and a loaner VFD braking
resister (six BIG 7.7 ohm "heating elements"). I'm
gonna play around and see what I really need.

What concerns me is the fact that inside my cabinet,
my 120 volts jumped 1/8" to ground. I don't know
whether that was a one time thing or a continuous
thing, even when the Powerstat wasn't thumping. That
can't be good for my VFD.

Of course, if I knew how to calculate what was going
on, perhaps I could simply bypass the
"resonant/unwanted" ballast inductance, and go for
more power. I've seen "poor" designs for
pump/motor/vfd, where harmonic/vibration problems were
"solved" by simply skipping past the problem speeds.
Maybe I can just mark the "bad" spots on my slide
choke and avoid them. That's assuming the problem will
go away at higher powers, which I'm afraid to try at
the moment.

I did some reading and saw a post where someone
suggested using a relatively high resistance/low
wattage resistance across the ballast. He suggested
calculating the transformer's leakage and stray
inductance, and the capacitance seen on the pig's LV
side as Cpig=Ctank(pig turns ratio)^2. Using that, one
could use a resistance = 1.54sqrt(L/C) to provide
"critical damping". That's over my head, but sounds
better than dumping kW's of heat. Has anyone tried
this?

Adam

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> 
> ---------- Forwarded message ----------
> Date: Sat, 27 Oct 2007 13:37:42 +0000
> From: David Rieben <drieben@xxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Cc: drieben@xxxxxxxxxxx
> Subject: Re: Ballast Resistance For Pig Coils (fwd)
> 
> Hi Adam,
> 
> I have used resistive ballasting in series with my
> inductive ballast
> in my control panel for my big coil before. As far
> as the "thump-
> ing", I have experienced it, but only on a few
> occasions. I think 
> the thumping is a result of the inductor resonating
> with the trans-
> former so that would probably explain why it goes
> away when 
> you change the BPS rate. I was using huge power
> resistors for
> about 1 ohm of additional resistance to the
> ballasting circuit. 
> However, I do not like the resistance approach as
> large amounts
> of power are wasted in the form of heat. I had to
> run forced
> air across the resistors and they would still glow
> cherry red! It
> made for a nice incidental shop heater during the
> coldest winter 
> days, but wasn't worth a crap the rest of the year,
> especially du-
> ring that long string of 100 degree + days that most
> of the south-
> ern US experienced this past August. Actually, I
> rarely get to 
> fire my big Green Monster coil since I have to roll
> it out on the
> driveway and fire it outdoors in front of suburban
> neighbors but
> I do use the control panel pretty often to fire my
> monster Jacob's
> ladder inside. I think many bigpig coilers manage to
> get around
> the power-wasting (and voltage dropping) power
> resistors in 
> their ballasting circuits these days. I would try
> either going back
> to the welder ballast or adjusting my breakrate to
> stop the 
> thumping before I'd break down and use resistors.
> However,
> if you're determnined to go the resistor route, I
> still have the
> big resistors that I was using in my control panel
> that I would be 
> willing to sell since I have no intentions of going
> back to resis-
> tance ballasting at pole pig power levels. ;^)
> 
> --
> David Rieben
> 
> -------------- Original message -------------- 
> From: "Tesla list" <tesla@xxxxxxxxxx> 
> 
> > 
> > ---------- Forwarded message ---------- 
> > Date: Fri, 26 Oct 2007 17:41:37 -0700 (PDT) 
> > From: Yurtle Turtle 
> > To: tesla@xxxxxxxxxx 
> > Subject: Ballast Resistance For Pig Coils 
> > 
> > What size resistance are you folks using inline
> with 
> > ytour ballast for their pig powered coils to
> prevent 
> > "thumping"? I decided to tune up my coil this
> evening 
> > in preparation for Halloween. I recently started
> using 
> > two slide inductors instead of my welder. This
> evening 
> > all was running well, as I slowly cranked up the
> amps. 
> > As I got to around 25 amps, the actuator motor
> died on 
> > my Powerstat stack. I replaced the fuse, and it
> blew 
> > again. I decided to set the voltage, then remove
> the 
> > fuse, to keep from risking damage to the stepper 
> > controller board. As I continued to run, I heard 
> > several hard thumps from my powerstats. I quickly 
> > turned up the breakrate, which solved the problem.
> 
> > However, I noticed that the line in to the
> Powerstat 
> > actuator had flashed over to the chasis.
> Apparently I 
> > am getting some nasty spikes that I hadn't
> experienced 
> > with the welder. 
> > 
> > I know folks have advocated using resistance in
> line 
> > with their ballast. Is there a way to calculate
> what 
> > resistance is effective at certain configurations,
> or 
> > is it more trial and error? 
> > 
> > The reason I'm concerned is I don't want to blow
> up my 
> > Powerstat actuator or my VFD. 
> > 
> > I have EMI filters between my incoming power and
> my 
> > pig/ballast, but maybe I should consider something
> for 
> > voltage spikes. While a spark gap for 120/240
> sounds 
> > silly, and hard to set, the 120 volt input to my 
> > actuator jumped 1/8" to the grounded chasis.
> Without 
> > having access to some kind of power monitor, I 
> > wouldn't know if MOV's would last for years or 
> > seconds. 
> > 
> >
>
http://www.hot-streamer.com/adam/bigass_coil/schematic.pdf
> 
> > 
> > thanks 
> > Adam 
> > 
> > __________________________________________________
> 
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> > 
> > 
> > 
> 
> 
> 


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