Re: Terry Blake gap Maximum power?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Rob Judd" <canska@xxxxxx>

My "propeller gap" has worked well for me so far up to approx 7.2kVA from a
14.4kVA pig, with resulting 8'+ streamers.

My motor is a cap start/induction run 3450RPM 3/4 HP, modified to be
synchronous 3600RPM. 3/4 HP is no doubt overkill, but it was on hand, so it
volunteered for the job. All three electrodes are 3/8" x 7" tungsten rod.
The arbor is simple CPVC pipe with a hand made stop collar to secure the
flying electrode inside the arbor. I cobbled it together to be a proof of
concept, but it proved so rugged and reliable as-is, I never bothered to
rebuild it more robustly.

In fact, I've never had the least bit of trouble with it. After a two minute
run at full power, the electrode tips are dull-red hot, but it has no
visible effect on the coil's performance. It works great, easy to build, and
costs a mere fraction of a big G-10 rotor. I wouldn't hestitate to recommend
it!

Here's a few pics from when I built it...
http://homepage.a5.com/~canska/photos/thumbnails.php?album=12

I don't see any reason why larger dia electrodes couldn't be used though. It
may be worth noting that my coil uses a 9 turn flat primary with ~0.0766mH,
which, as you mentioned, reduces the primary current. Your mileage may vary!

Rob Judd - canska@xxxxxx



----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, October 06, 2006 12:53 PM
Subject: RE: Terry Blake gap Maximum power?


> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>
> I assume you're referring to Terry's "propeller gap" configuration?  My
> experience with such a gap goes only as far as using with a 15/60 NST,
> though I know that Terry has used it with at least a PT.
>
> I don't think that the motor size directly limits the power that such a
> gap can be used with.  It's more the diameter of the tungsten rod
> "propeller" and the ability to accommodate temperature rise in the rods
> that determines the maximum power.  I've only seen propeller gaps use
> 5/32" or smaller rods, but I suspect that a much thicker rod could also
> work.  You'd have to try it, maybe reducing the length slightly to
> reduce the rotational mass if it's right on the edge.  And rather than
> using a plastic arbor to hold the rod, use phenolic or G10 to tolerate a
> greater temperature rise.  My synchronous propeller gap may be seen at
> http://www.laushaus.com/tesla/sync_gap.htm.
>
> As far as the motor being able to spin up and synch-lock with a heavy
> rod - I'm not sure that there's any real advantage to using a
> synchronous gap for high powered systems.  Most pig-powered systems seem
> to do better at high break rates with asynchronous RSG's.
>
> One more thing - I'm not even sure that system "power" is the limiting
> thing as much as gap current.  Using a high inductance primary to lower
> the gap current will probably result in cooler operation and higher
> efficiency.
>
> Regards, Gary Lau
> MA, USA
>
>  > Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>  >
>  > Hi All,
>  >
>  > I finally found a Classic Teletype 3600 R/PM teletype motor.
>  > Nostalgic for me because, to date myself, because I used to work on
>  > Teletypes when I was young. How much power do you run through these
> gaps?
>  >
>  > Thanks,
>  > Jim Mora