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Re: LOW Inductance Ballast





---------- Forwarded message ----------
Date: Thu, 9 Oct 1997 16:08:08 +0100
From: Julian Green <julian-at-kbss.bt.co.uk>
To: tesla-at-pupman-dot-com
Subject: Re: LOW Inductance Ballast

> 
> Julian,
> There is a simple method to allow you to keep the wire rolled up and
> still keep the inductance near zero. The method was first used by
> Nikola Tesla to fabricate wire wound resistors with low inductance.
> The method is simplicity itself. Take the 100 meters of wire and
> locate the center. At this point bend the wire over (and tape it if
> desired). Use electrical tape to secure the half-way point to the
> spool you will be winding the wire onto. As you roll the wire back
> onto the spool, just keep the two wires always adjacent. When you
> have the wire all back onto the reel, except for a few inches, tape
> the surface down with a layer of electrical tape. The two wires that
> you now have will exhibit almost zero inductance, because the current
> through them is equal but of opposite direction.
> 
> I usually use this technique with much smaller reels of wire, but it
> should work well at almost any scale. It is simple and very easy to
> implement, and allows you to have a much more convenient high wattage
> resistance. Works for any wire that has insulation.
> 
> I believe that the general principle behind this was mentioned on
> this list recently, but I am posting this in case you missed it, or
> missed its implications in your particular case.
> 
> Hope this helps.
> Fr. Tom McGahee
> 
> 
Yes I know that there is no inductance even if the extension lead remains
rolled up because the 'go' and 'return' conductive paths run parallel
and any magnetic fields generated by one conductor are cancelled out 
by the other.   If however you run too much power down a coiled 
extension lead it gets hot and you end up melting the insulation.

I did this and was completely unaware of what was happening at the 
time.   The outer layers exposed to the air only got warm, but the 
layers below had melted and formed a solid lump of PCV.    My extension 
lead was ruined.

Julian Green