# Can the primary coil of a Tesla coil be inside the secondary coil?

I'm building a Tesla coil and the secondary coil (about 800 turns of 0.85 mm diameter enameled copper wire) is wrapped around a cardboard tube (about 8 cm diameter and about 1 m long).

I was planning to wrap the primary coil (about 10 turns of >= 1 mm diameter insulated copper wire) around a smaller cardboard tube (about 4.5 cm diameter and about 40 cm long) that will fit inside the larger tube with the secondary windings, however, most Tesla coils I have seen have the primary coil on the outside of the secondary coil and I could not find any information regarding this.

(Not to scale) I hope this rough diagram helps with understanding.

• Will the Tesla coil work with the secondary windings (red) on the outside of the primary windings (yellow)?
• If not, what is the reason for this, but if so, will I have to reverse the polarity or direction of the windings since the magnetic field is going in the opposite direction on the outside of the coil to the inside?
• And finally, would the inner tube's diameter be large enough for the primary coil to work?
• seems like the primary is too far away from the secondary ... try using a 7.5cm tube for the primary – jsotola Mar 12 '18 at 6:35
• How many volts to you want from the top end of the secondary? How many volts do you expect half way up the secondary? haven't you got the primary a little close to the secondary? paper isn't going to stop an electric arc, neither is the lacquer on the wire. – Jasen Mar 12 '18 at 7:42