Re: Coil form

>>From bmcpeak-at-gte-dot-netFri Aug 30 21:56:09 1996
>Date: Fri, 30 Aug 1996 16:08:58 -0500
>From: Brad McPeak <bmcpeak-at-gte-dot-net>
>To: tesla-at-pupman-dot-com
>Subject: Coil form

>Hello All,
>My latest coil secondary is wound on a 6.75 od. schedule 80 pvc pipe 20 inches
>wind length with #24 magnet wire, preped with poly before and after winding.
>Input is 12000 volts -at-120ma. With a variac I can get up to 44 inch
>streamers. I wound this with the thick wall pvc before I knew to use thin
>walled coil forms. My question is would it be worth while to wind another
>coil form of  plexiglas  and possibly use larger wire. I believe my primary
>could be tuned for these changes. Would the gain be significant? Thanks.

>Brad McPeak 


The experiment you propose, to wind a different secondary and compare 
its performance to the existing one in a real A-B comparison sounds 
like a wonderful project.  I'd say go for it!  But I think you should 
consider where you are trying to go with your coiling hobby.  
Whenever the construction of a new secondary coil is proposed, there 
is often an opportunity to go bigger.  Bigger may improve present 
performance, or may not, but I think there is a good chance that it 
will.  Bigger will also give headroom for future power increases.  
This depends on if you WANT a bigger, higher powered coil system.

If your goal is to squeek every inch out of your present system 
without increasing its size, then you can wind a number of comparable 
size secondaries, each with one aspect changed, until you determine 
by A-B testing, which changes help.  This could easily result in the winding of
at least a half dozen test coils.  For example, to determine if the 
composition of the coil form alone is conributing to system loss, 
then wind an identical version of your #24 guage, 6.75 inch diameter 
coil onto say a 6.75 inch diameter polyethylene form of 
equal thickness.  To determine if heavier wire will improve things, 
alone, then wind one on the same sized PVC form, but the trouble here 
is your aspect ratio will change (coil will be longer for same number 
of turns) which confuses the results some.

If you just want bigger sparks, and you are not that concerned from a 
scientific interest, (your interest is primarily outcome based), then I'd say
wind a heavier guage coil onto a polyethylene form.  If your primary can
accomodate it, or if you don't mind winding a new primary, I'd suggest increasing
the diameter of your coil at the same time to perhaps 8 inches or even 10 inches.
Make your new coil longer, say maybe 30 inches to 36 inches.  When 
you start developing higher voltages the extra coil length will help 
reduce the tendancy to arc to the primary or strike rail if employed.

As we become more experienced in coiling, we realise that there are 
countless component combinations which can be used and arrive with a 
good working system.  For example there is no reason why you must use 
enamelled copper magnet wire.  My best performing coils employ 
plastic jacketed, 600 volt rated stranded copper wire.  My highly 
successful MTC system uses a 1/2 inch (thick) walled PVC pipe, 
unsealed, 15 inch O.D. close wound to a length of 48 inches with #18, PVC 
covered, stranded, tinned industrial hookup wire.  Everthing I've read on 
this list tells me this form should be lossy and a poor performer!  I was achieving 
six footers off this early on at just 2500 watts input with a good 
quality 0.05 mfd Condesnser Products cap, and a rotary break.  
Topload at that time was a modest 8" X 30" toroid from aluminum dryer 
duct.  This same secondary is now exceding three times its own length producing
12+ foot streamers with system upgrades and just 7500 watts.  This 
allegedly lossy coil form is definitely a top level performer.

Heck if you have the room, make one just like my MTC.  One thing is 
for sure, you won't have to wind another primary and secondary later 
if you ever wish to advance to a pole pig at the 10 kilowatt level, and it will
run just fine at 2 kilowatts for now.  If you do decide to use a 
large diameter PVC form, I'm sure it wouldn't hurt to 'seal' it with 
a couple of coats of varathane after letting it sit in a dry place 
for a few days to let it expunge moisture, before you wind on the wire.

Please excuse me if I've bored you with the obvious.  Good luck, it 
sure looks like you know what you're doing.  Keep us posted with your 
plan, and any results.

Regards, rwstephens