On 11/11/21 9:00 AM, Joshua Thomas wrote:
> Hello all,
>
> Thanks for your earlier help. I've got the varnish drying on my new
> secondary coil, which I'm fairly sure was my problem. By the way, if anyone
> knows a good way to wind coils with few gaps I'm interested. I made a jig
> for winding and used a cordless drill, but even still I get the occasional
> gap in the winds. Is this just one of those "experience and patience"
> things?
>
> On to my real question: Is there a method for sizing a topload correctly
> for a coil? Assuming a toroid, you can choose different dimensions that
> give the same effective surface area and therefore the same effective
> capacitance. Are there useful rules-of-thumb for the proper sizing of a
> topload, as a function of the other parameters of a TC?
>
> Thanks in advance,
>
> Joshua Thomas
>
Yes, experience and patience. I use double stick tape on the form - a
couple strips the length of the form, and that helps hold the wire in
place.
A foot switch is nice, because then you can have one hand on the form,
with a finger laying the wire, and the other holding the wire in a
glove, coming off the spool.
An old trick is to put the spool on the floor and feed the wire up
through a funnel over the spool (open end of funnel facing down). But
really, it's about the tradeoff on tension.
I wound one secondary on a lathe - that was a mistake, because it's not
something you can start and stop quickly, so it was: get ready, hit the
start button, and hope everything goes ok.
As far as topload sizing - My conceptual thoughts are "topload outer
diameter should be comparable to height of coil, and no less than 1/2
height of secondary winding. The idea being to have a fairly uniform
field along the secondary. If you need more C, you can stack more
toroids on top.
ANd then, there's all the practical details - if you're using a piepan
or pizza pan as the center of the toroid, and aluminum flex duct as the
toroid itself, there's only certain sizes available. If you're cutting
aluminum tubing and tig welding a cage style toroid, your trade space is
much larger.
A lot of design decisions come from handling - "will the toroid fit in
the back of the car?"