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Re: [TCML] Treadmill Motor Question

I used to run my ARSG with a G10 wheel mounted on a Pacific Scientific 90V DC treadmill motor. The input to the motor was the simple unfiltered output from a monolithic full-wave 120v rectifier (one of those square bricks about 1" per side by 1/4" thick - don't remember the pn - but they're available everywhere). I fed the input to the rectifier from a 15A variac. As someone else on the list said, the inertia of all the components involved would keep the wheel moving smoothly irrespective of the ripples on the rectifier output.

There were several others here on the list who used the exact same setup years ago - i.e. I didn't get the idea to do that myself ;)

The downside to the approach is that inevitably the monolithic rectifier would fail. When it failed, it would sometimes but not always short the AC input, and thus the fuse on the variac would blow. In fact, once I started running reasonably high power - like around 5kva from my pole pig, the system would fail every time after about 30 seconds. I could always trace it back to a fried full-wave rectifier.

I tried all sorts of things to alleviate that problem. Filter caps on both input and output. MOVs. Shielding the rectifier from the RF. Etc. I could never stop the rectifier from frying and the arcs never (visibly) hit the rectifier, the input cables, or anything in the ARSG/powersupply circuit. But clearly some sort of transient was whacking the rectifier.

I still have a box of about 50 of those rectifiers from the days I ran my coils with the ARSG/pole pig supply. I just got in the habit of replacing them every run.

Now - in conversing with those here on the pupman list I found that this problem was common, and that nobody had figured out a sure-fire solution, other than to use a different drive technique. You can do a search back in the annals of TCML and find those conversations.

Hopefully there's some use to my mentioning that experience for you.


On 9/10/2013 5:30 AM, Yurtle Turtle wrote:
Question for the list experts. If one were to employ a DC rsg motor with full wave rectification, are filter caps needed? Is the ripple any worse than pulsed AC from an inverter or pulsed DC from a cheap SCR speed controller?

  From: David Rieben <drieben@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Monday, September 9, 2013 7:45 PM
Subject: Re: [TCML] Treadmill Motor Question
Yes, that's what I am doing with my current ARSG in my big Green Monster coil. It's a sweet treadmill motor that I got off
eBay several years ago that was easy to mount and to mount a G-10 rotor to and it required no external fan blades to keep
it cool. I'm using a small variac and a FWB rectifier (and a 3900 uFd, 400 VDC rated 'lytic for some filtering) to run the mo-
tor. I ended up getting a local machine shop to drill the holes in the G-10 rotor for me. That's what I would do with any future
RSG mounting project as well. There's just no way that I could get it smoothly balanced and get all of the holes drilled true
with my facilities.

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