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Registered Member #102
Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169
Ok, I've seen countless TC's of all types with primaries on the outside of the secondary. This serves it's perpose when the secondary dia is 1-6". However, what would be the main draw back to putting a primary inside the secondary of say, a 12" secodnary?
I've scrateched the small secondary I asked about stripping yesterday because I found 12.5" pipe. And I wanted to use as large/tall pipe I could get and this offers just that. So my proposal, since this is a VTTC, is to have a helical priamry inside the secodnary with the secodnary wound as usuall.
Not only would this save on primary winding length, but it would also possibly help reduce the possibility of primary/secodnary flashover.
Registered Member #305
Joined: Sat Mar 11 2006, 04:27PM
Location: Liverpool, UK
Posts: 29
an interesting idea, but wouldnt the field be reversed? also i imagine the risk of primary to secondry strike would be higher, as the electrically charged field would be high and concentrated inside the tube of the secondry?
Registered Member #205
Joined: Sat Feb 18 2006, 11:59AM
Location: Skørping, Denmark
Posts: 741
I have made several coils with this type of primary, and although a couple of them still are functional, I don`t recommend it anymore.
The electrical field strength in the area btwn. the primary coil and the secondary is high, and at the primary coil this leads to the formation of corona. You cannot insulate your way out of a corona problem. If you add more dielectric into the space, the field strength in the remaining air goes up.
So unless you cast the primary into potting compound, and completely avoids voids , there is inevitably going to be a corona induced failiure.
I have seen this happen, with the acompanying zoot, and carbon tracks all along the inside length of the secondary, to avoid this kind of primary coil.
Registered Member #99
Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637
I have used a primary inside the secondary before...I never had any trouble whatsover. it was an 8.5in diameter secondary, and I used 6.5in diameter form for the primary. Primary wire was 14awg insultated hookup wire.
This was with my old DRSSTC(power levels up to 1kw, 3 foot arcs)...
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Though, this was an attempt to save wire as far as the primary goes, consideing it's such pricey stuff. Being a 12" diameter secondary.
You do realize, that if your primary diameter is smaller, you need more turns, right? I think the amount of wire required stays fairly constant. The actual number of turns isnt what is crucial, but the inductance. That said, there are certain geometries that will maximize inductance per foot of wire (i think when H=R its pretty good).
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inner Primary proposal
, there is inevitably going to be a corona induced failiure.
