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Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
I've got a 340mm (13") tall x 188mm (7.4") diameter cardboard tube with a wall thickness of 5mm (0.2") that I would like to use as the secondary for a DRSSTC.
Are there any issues with using cardboard as the secondary? Any special treatment that I should consider?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Sure, just sand off the gloss from the surface (if it has any) to make sure possibly conductive ink is removed. I wound some of my smaller coils on cardboard due to heating issues.
It may not be as sturdy as plastic pipe but many people seem to use it and will surely offer advice.
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
Fascinating, I didn't know what a sonotube was until now
These tubeas used to hold 7" surface mount component reels and have some shipping labels and KEMET printed in blue ink on the outside. I've got two of them, so I can afford to try thing out on one
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
I was chatting to Richie Burnett at the Notts Gaussfest yeasterday and he had brought a 1kW CW SSTC running on a cardboard tube secondary with 2100 turns. We observed after running it that there was quite a lot of moisture that came out of the coiform.
I was thinking about drying the secondary out in my kitchen oven (electric fan) at home at about 50C for an hour or two to drive the moisture out. I'd then varnish the coil inside and out straight away to seal it against future moisture ingress.
This coilform will be used for a 1KW+ DRSSTC design. This obviously won't run CW but the overall power levels will be similar. Will this affect it?
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
My big DRSSTC (5-8kVA) uses a cardboard form. I spark tested it a little first to make sure it wasnt *too* conductive. It was just some sono-tube (concrete forming tube) with the outer labeling peeled off (since it was black). I coated the form and sanded it smooth, wound it, then coating it about another 10 times. Havent had any problems with the form breaking down, even when getting near 3X the winding length in sparks. It flashed across the entire coil at one point (rather than through the cardboard), which i think is a testement to its performance as an insulator. Of course, not all cardboard is created equally.. as they say, your mileage may vary. Id suggest spark testing a bit of it to see if its particularly conductive.
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Cardboard Tube Secondary?
