# Re: [TCML] My first ballast results

```Hello Ted,

That sounds like the basis of a good ballast. The fact that it is running cool is a good sign. Without doing the detailed calculations, 12 square inches of laminations on the center leg of the E should be good for at least 40 amps at 240 volts and 60 Hz with the proper number of turns. I am a little confused by your statement at the end that says that your minimum current is with no gap and the current decreased as the gap increased. I assume that you intended to say that the current increased as the gap increased. This would be the expected behavior. As you reduce the number of turns, the minimum current with no gap will decrease and smaller air gaps will be needed for the same current. But you can't go below the minimum number of turns or you will get core saturation. I keep telling myself that I am going to make a spreadsheet with the ballast calculations but I haven't gotten around to it.

I have a question about your stated number of turns of 118. Since you used 3 conductors in parallel as a single composite conductor, does the 118 turns mean that you have 118 turns of your composite conductor corresponding to 118 x 3 = 354 turns of 14 AWG wire? Or do you have 118 / 3 = 39 turns of composite conductor? Hopefully not the 39 as that would be too few turns.

As a point of reference, I designed my adjustable air gap ballast using transformer equations. My design goals were a maximum of 40 amps at 240 volts and 60 Hz. It has 14 square inches of iron on the center leg of the E. The number of turns is 73. My minimum current with no gap is about 5 amps. The gap spacing for 30 amps is 0.06 inches. I would have to do the calculations but 0.7 inches seems quite large. I am also surprised that your no-gap current is 20 amps. That seems high if you really have 118 turns of your composite conductor. Is this with 240 volt operation?

Maybe you already know this but you can test your ballast without the pole transformer. Just short the 240 volt input leads of the pole transformer together.

I would not run the pole transformer with more than 240 volts. You may exceed the insulation rating of the secondary.

Steve White
Cedar Rapids, Iowa

----- Original Message -----
From: "Tedd Dillard" <tedd.dillard@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, December 20, 2018 6:44:05 PM
Subject: Re: [TCML] My first ballast results

Gentlemen,
I am not an electrical engineer but have worked around machinery in power
plants all my life.
I also worked in an electric motor rewind shop while I was in school, not
bragging or complaining just being open about were I am coming from.
I have a 10 kva pole transformer that I intend to use to drive a good sized
coil. I have assembled a power supply for the transformer with four variacs
so I can vary the voltage up to about 290 volts with a 240 volt supply.
I constructed a ballast from three golf cart battery chargers by combining
the lamination's and winding a coil for the center post.
The lamination's are E and I shapes. The E lamination's were welded
together and the I lamination's were welded together in the chargers and
then the I lamination's were welded to the E lamination's after the charger
coils were installed.
I was able to carefully grind out the welds between the E and I and bolted
three sections of E lamination's together and three sections of I
lamination's together to make a core that has about 12 square inches of the
center post of the E lamination's.
The core weights about 40 pounds. I wound a coil from three parallel number
14 magnet wire because I could not get number 8 wire.
I have about 118 turns if I remember correctly. By adjusting the air gap
between the I lamination's and the E lamination's I can vary the current
from about 20 amps to, I have it at 42 amps for now. It is quite and does
not heat up at all. The air gap is about 0.700 inches at that current. I
have not yet completed the tesla coil and have only used the pole
transformer to drive a 10 foot traveling arc.
I say all this because the amps were the lowest when the air gap was zero
and the amps were reduced as the gap was made larger.
This tells me that your problem is not that you do not have enough copper
but that you do not have enough iron.
Both the Phils use large iron cores as does Richy Burnett.

On Tue, Dec 18, 2018 at 7:38 PM Tyler LaVite <tlavite@xxxxxxxxx> wrote:

> NSTs or MOTs but good luck they smoke out in mere seconds.  I built a
> ballast by winding 500 feet of 10 gauge THHN around a 2 inch piece of PVC
> and could adjust the current draw by adding or removing welding rods from
> the inside of the PVC pipe. It worked quite well and had a decent duty
> cycle but the problem was the pipe would get hot from the rod heading up
> and it would want to sag.  Could build one like that and submerge in oil.
>
> Sent from my iPhone
>
> > On Dec 18, 2018, at 7:57 AM, Daniel Kunkel <dankunkel@xxxxxxxxx> wrote:
> >
> > Tyler and David,
> > Yes, as much as I hate to give up more valuable floor space in the shop
> to
> > another welder, it seems inevitable. I will get one someday, but I am
> > waiting for something priced so right, I can't say NO. So in the
> meantime,
> > I just need to scrounge up an additional 3.4 mH of inductance using stuff
> > around the shop. Hence the old NST core idea, which is not heavy, does
> not
> > take floor space, and has no additional cost involved.
> > ~Dan (streamers on a budget)
> > Kansas City area
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxxxxxxxxxx
> > https://www.pupman.com/mailman/listinfo/tesla
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxxxxxx
> https://www.pupman.com/mailman/listinfo/tesla
>
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