help with tesla coil topload

[lokeycmos]

this is my 1st post on this forum. i am very experienced with high voltage. check out my site in my profile. i am in the process of building a tesla coil. im pretty sure there are others on this forum with tesla coil experience. what im looking for is ideas to secure the top lead of the coil from stress and at the same time being able to interchange different top loads during experimentation. i have attached a few pics of what im working with. im wondering if it is a good idea to just secure the top as i did the bottom and use a jumper to the topload, but concerened about losses or possible arcing. if you have built tesla coils before please share your ideas with me! thank you in advance!

 

[DerStrom8]

this is my 1st post on this forum. i am very experienced with high voltage. check out my site in my profile. i am in the process of building a tesla coil. im pretty sure there are others on this forum with tesla coil experience. what im looking for is ideas to secure the top lead of the coil from stress and at the same time being able to interchange different top loads during experimentation. i have attached a few pics of what im working with. im wondering if it is a good idea to just secure the top as i did the bottom and use a jumper to the topload, but concerened about losses or possible arcing. if you have built tesla coils before please share your ideas with me! thank you in advance!

Hi lokey! Welcome to ETO!

As you know, I have some experience with tesla coils, myself. I think the most common way to secure a topload to the secondary is with an inverted bolt on the top, so that the torroid or sphere can simply screw on. If you choose to go with this method, a round-headed bolt would be a good idea to help avoid corona leakage. Something like this is also a popular choice:
**broken link removed**
Good to see your project is still going well!
Der Strom

P.S. Sorry for the huge image....

 

[lokeycmos]

i was kinda thinking the same thing in the image too. ive read a lot of horror stories about internal arcing to the bottom with metal electrodes inside the tube. i could glue some wooden baffles inside though. would it be a good idea to fix the top the same way i did on the bottom in the pic and attach a jumper to whatever the top load is?

 

[DerStrom8]

I've heard those stories of internal arcing, too. That is why I would suggest putting the bolt well above the top-most winding of the secondary, with the wire connecting to it. Also, several coats of a urethane wouldn't hurt at all. I don't think it would be a good idea to do to the top what you did on the bottom. The voltage is so high at the top that it will come out of the sharp edges rather than the torroid, and you won't get the full potential. Everything needs to be as smooth as possible. I would do what he did in the photo I posted. Just cover up the wire connecting to the bolt with urethane to prevent arcing.
That's what I would do, anyway
Der Strom

 

[shortbus=]

How about using a thick, around one inch piece of plastic for the top plug. Instead of drilling a hole clear through it and using a bolt, you would only drill half way through the plug and tap it. Then you could put a piece of 'all-thread' or a long set screw in the blind tapped hole, to connect your top load to.

 

[DerStrom8]

How about using a thick, around one inch piece of plastic for the top plug. Instead of drilling a hole clear through it and using a bolt, you would only drill half way through the plug and tap it. Then you could put a piece of 'all-thread' or a long set screw in the blind tapped hole, to connect your top load to.

Yes, that would work too, but seems like a lot more work. But, Lokey, if you're willing and able to do that, then that's actually a really good idea. A dab of glue inside the tapped hole will also help keep the threaded rod snug.

Good one, shortbus=
Der Strom

 

[lokeycmos]

what do you think of this idea? i can cutout an area to embed and epoxy a nut into the top cap and permanently attach the wire to the nut. then i can just use different bolt lengths based on how thick the load is. this is important to me, because i plan on experimenting with both a sphear and a toroid.

 

[DerStrom8]

what do you think of this idea? i can cutout an area to embed and epoxy a nut into the top cap and permanently attach the wire to the nut. then i can just use different bolt lengths based on how thick the load is. this is important to me, because i plan on experimenting with both a sphear and a toroid.

That could work too, but having a huge collection of bolts with the same thread size and differing lengths may not be the best idea. This is all up to you, though. I still like the idea with the threaded rod, personally

 

[lokeycmos]

That could work too, but having a huge collection of bolts with the same thread size and differing lengths may not be the best idea. This is all up to you, though. I still like the idea with the threaded rod, personally

the thing is with the bolt idea is that my first load will be a sphear about 9 inches tall. if i go with that length bolt, then switch to a toroid i need a much smaller bolt otherwise i will have a tall bolt sticking out much higher than the hight of the toroid....

 

[DerStrom8]

the thing is with the bolt idea is that my first load will be a sphear about 9 inches tall. if i go with that length bolt, then switch to a toroid i need a much smaller bolt otherwise i will have a tall bolt sticking out much higher than the hight of the toroid....

You wouldn't need a 9" bolt to go through the entire sphere. You only need one a couple inches long--just enough to fit through the base of the sphere to hold it on. Same with the torroid. One bolt that is just the right size would probably be enough.

 

[lokeycmos]

what do you guys think of my setup? i like the idea of being sturdy. i will cut the bolt to length. then attach the wire to the bolt. im using a T nut in the PVC cap. i like this too, because the load is well above the top of the coil. LMK TY!!

 

[lokeycmos]

more pics

 

[DerStrom8]

Hi Lokey.

Looks pretty good. Just be careful about those rough edges. You'll lose a lot of electrical energy through corona around anything even remotely sharp, especially the edge of the head of the bolt, and the bottom of the bolt (inside the cap). That corona discharge on the inside of the tube is what causes the damage to the secondary. You'll need the bolt to be as short as possible, which makes attaching different size toploads with the same bolt difficult. That is why I agreed with shortbus earlier that a bolt coming up through the bottom of the topload and into the middle would be best. That way, all the charge would be carried away from the sharp edges of the bolt within the topload and will collect on the outer "shell". It wouldn't be too hard to do. Just mount a nut on the inside of each topload, and permanently fix a short bolt (perhaps an inch and a half long) so that it sticks up from the cap.

What you have there may work, but it is kind of risky. I would definitely consider the idea that shortbus mentioned previously, and what's described here.

Regards,
Der Strom

 

[lokeycmos]

im going todo the way you suggested. i attached a couple pics. if you look at my diagram should i run the wire under the pvs cap in a groove or into the side of the pvc cap through a hole? i chose a brass screw so i can solder the wire into the groove. ty

 

[lokeycmos]

1 more

 

[DerStrom8]

Hi Lokey. Looks great. I, personally, would try putting the wire on the outside of the PVC cap, just so you can see if there's any corona loss through it. If you had it on the inside, and you had it leak, it would damage the coil and you wouldn't even know what caused it. A groove along the outside of the cap would be ideal, with the wire epoxied in, perhaps covered with a couple coats of urethane.

Der Strom

 

[lokeycmos]

just to clarify, it would still hookup on the inside. but i would drill a hole and run it from outisde in?

 

[DerStrom8]

just to clarify, it would still hookup on the inside. but i would drill a hole and run it from outisde in?

If you plan to connect the wire to the bolt from the inside, you should have the wire so that the least amount of wire is actually within the cap. In other words, have it go inside right next to the bolt, if possible.

 

[lokeycmos]

how high up should i mount the pvc cap? if you look at the pics, i could go low or high. i have about 1.5 inches of "wiggle room"

 

[DerStrom8]

how high up should i mount the pvc cap? if you look at the pics, i could go low or high. i have about 1.5 inches of "wiggle room"

I would put the topload as close to the last winding of the secondary as possible. This reduces the amount of wire between the two, which in theory reduces the risk of corona leakage. In other words, you'll want to push the cap as far down as it will go.