[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: TC coil experements 7 years ago



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Gary,

Actually, a heck of a lot changed with "simply" geometry of the secondary. Here's a list (view with fixed width font or the table will be really ugly): BTW, my model included full coil, toroid, center disc, etc.. at a base ht of 20" off the ground and if I would have measured them in my own garage surroundings.

Coil   h/d   Fr(kHz)  Imp(ohms)  Les(mH)  Ces(pF)   ACR(ohms)    Q
Coupling
4"    5.3:1   303      26900      14.0     19.7        95       281
0.112
6"    3.42:1  204      38900      29.9     20.3       126       307
0.149
8"    2.56:1  154      49700      50.8     21.0       152       323
0.181

Everything flows at it should. Easy to see why the larger diameter did better (k at 0.18 = Wow!). My point is simply that far more changed than DCR. ACR increased a little, reactance doubled, Q increased a little, but coupling made a major jump from the 4" to the 8" coil. There is a more that changed than is listed above. The energy transfer time changed slightly (14.6uS for the 4" to 17.6uS for the 8") and 1/2 cycles to quench from a high 8.9 on the 4" down to 5.5 on the 8". The 4" turns for resonance was 8.4 and 13.6 for the 8", so about a 40% change in L1 impedance which certainly affects the gap (di/dt). Many variations occur for what we assume is a simple radius increase. Spark length should certainly increase considering the data.

What also would have been a good test was to keep mutual inductance the same and disregard the 2" pri to sec clearance. That really isn't important other than ensuring the sec doesn't arc to the pri. However, the mutual inductance plays directly into coupling ratios, energy transfer times, etc.. So, keeping M the same would be good even if it involved raising or lowering the secondary a little to achieve it. In the coils above, probably the 6" with a 0.149 k would be where I would move the 4" up to and the 8" down to (and besides, that particular coil is closer to the norm for coupling). But, it was 7 years ago wasn't it. Likely too long ago to even mess with now. But hey, there are a lot of new coilers on the list and now is their time to look at these things and tell the list what they find out. More "power" to them (pun intended).

Take care,
Bart

Tesla list wrote:

Original poster: gary350@xxxxxxxxxxxxx
Vanderbelt University did some research on Tesla Coils. The best length to diameter ratio is 3 to 1 according to them. Research shows 3/1 is better than 4/1 and that is better than 5/1. If you are going for absolute maximum output try 3/1 ratio.

I did some experenents with this myself and built 3 Tesla Coils. The 3 TCs are identical only thing that changes is the secondary coil diameter to length ratio.

TC #1, 950 turns #24 wire 20.5 inches in length wound on 4" PVC pipe.

TC #2, 950 turns #24 wire 20.5 inches in length wound on 6" PVC pipe.

TC #3, 950 turns #24 wire 20.5 inches in length wound on 8" PVC pipe.

I used the same 15K 60ma neon sign transformer.

I used the same .01 uf capacitor.

I used the same VSVFSG spark gap.

I used the same top load, toroid 14" diameter 4.5" thick.

I built a flat would primary coil for each secondary coil. The inside turn of each primary was 2" from the secondary coil. Primary were all would with 1/4" copper tubing, flat wound, spacing 1/2" center to center, 18 turns each.

The only thing in the circuit that changed was the secondary coil.
The primary coil physical shape had to accommodate the secondary coil.

Spark length increased a few inches with each secondary diameter on each test. The most noticable difference was the appearance of the streamers. The larger diameter secondary coils produced Hotter streamers.

The 8" secondary would produce a streamer 6" longer than the 4" secondary coil in this test.

Next I wound another 950 turns of #24 enamel coated copper wire right over the 950 turns secondary that I already had on the 8" secondary. I connected the 2 secondary coils in parallel. Test showed the streamers were 2" longer. As far as I can tell the 2 coils connected in parallel reduced the wire resistance thats all. Naturally the 2 secondary coils diameters are different by about .0201 inch diameter this might change bandwidth frequency a bit.

Next I wound another 950 turns of #24 enamel coated copper wire right over the 2 layers of 950 turns wire I already had. I connected the 3 secondary coils in parallel. Test showed the streamers were 1/2" longer than before. This does not appear to be much of an improvement just an extra expense for wire.

My conclusion is 3 to 1 ratio is better. Advantages are, streamers are longer and hotter. Disadvantages are, the TC is physically larger, more work required to build it, the secondary coil requires several times more wire.

I later did some experements with multi layer secondary coils. A 4" secondary with 2 layers of wire connected in parallel would produce streamers equal to a 6" secondary with 1 layer of wire. A 6" secondary coil with 2 layers of wire connected in parallel would produce streamers equal to an 8" coil with 1 layer of wire.
Hummm.....interesting.

Some of you many remember this post 7 years ago. There are new people on here that were not here then I thought some of them might be interested in this.

Gary Weaver