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Sigurthr

Thu Jan 29 2015, 02:38AM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

Also, you can't measure the primary circuit resonance with the secondary not in place. The mutual inductance of the secondary will affect the resonant frequency of the primary, and vice versa.

I find most builders have better results by plugging data carefully into JavaTC to model the expected approximate resonance points than they do by trying to measure it directly. I say give the program a go.

Kolas

Thu Jan 29 2015, 06:40AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

I'm not going to say anything that hasn't already been said.
I agree that

might be a Huge help to you now.
What you guys need to do is an "asbuilt" using your current configuration.
While much better performance comes from synthetic materials, Glass capacitors are certainly the cheapest route. I don't like them but they will do you well. Expect some bottles to break.
MOT's are very resilient and don't care much about be shorted.
Beef up your wiring, its just too small a gauge, everyone is saying it.
Remember the ring down is hundreds of amps. And those charges need "room" to move. I'd like to say that the primary winding should be the smallest in the system, but that is likely not going to happen. Every bit of wiring that isn't "coupled" to the secondary is leakage inductance. and yes, 1 inch matters. The entirety of the primary should no be used. The larger your hookup conductors, the lower their inductance.
I think the biggest problem is the size of your tank cap. 24 NF is TOO SMALL!!! You're pumping all this power, and you've got a tiny tank cap. The first thing I think you should do is at least double the size. Doing this will let you decrease the number of primary turns. Java TC will let you determine the resonant frequency of the primary. It is very important to try and calculate it out.
I like that you youngsters are playing around with this tech. Keep it up, and _Don't ever quit!_
The moral of my story.... get more tank capacitance. Try to calculate the capacitance for about 10 turns on the primary. Just like Matt said.
The look of your coil is secondary to it's function. So don't worry about that. Machine techniques evolve with time. Once this one is functional, I'm sure the next one will be quite pretty.

skyler

Thu Feb 05 2015, 04:17PM

Registered Member #42712 Joined: Fri Jan 10 2014, 01:21AM
Location:
Posts: 21

Thanks everyone for the help. Got the coil to work better with a little bit of your suggestins and something else- the ballast.

At first, I had a tiny MOT as the ballast and I replaced it with a bigger MOT and it worked so much better. I then took the ballast off, and the spark gap didn't even fire properly until I just let it free slow down. At some speeds, I got strange giant arcs.

So in general, I am using a MOT with secondary shorted as power ballast.

The question: What does the ballast have an affect on the coil other than the power output?

Hazmatt_(The Underdog)

Fri Feb 06 2015, 03:36AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

It's basically going to limit the surge current and act like a resistor. The voltage drop across the inductor is V = L di/dt, where di/dt is the rate change of current over time.

The resistance the circuit "sees" or reactance, is Xl = 2*pi*f*L, so you can see how this translates to a resistance, and how the resistance interacts with the current di/dt by the relationship

V = Xl di/dt = 2*pi*f*L di/dt

The amount if inductance that you have can also be varied by changing the degree of shorting of the secondary due to the mutual inductance and coupling of the transformer.

k = M/(sqrt(L1L2))

If you measure the inductance of the primary when the secondary is open, the inductance will be higher then when the secondary is shorted. So if we control this with a large rheostat, we can control the degree of the effective inductance reflected back to the primary, but this is just theory.
It would take a substantial rheostat to control the secondary of the MOT because we're dealing with a 20:1 ratio or so, so you would need a 250W rheostat at maybe 500 ohms or 1000 ohms, which would be an interesting experiment.
You would be changing the secondary reactance and resistance which changes the primary impedance by the impedance ratio.

Anyway, there are some intersting things going on with the transformer as a current ballast.

Kolas

Mon Feb 09 2015, 05:26AM

Registered Member #102 Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169

this sounds a lot like the beginning of a variable reactor. which may not be entirely impossible.

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