[Home][2018 Index] Re: [TCML] VTTC MOT question [Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TCML] VTTC MOT question

I am using a 10 amp Superior Electric variac strapped for 140 volts. It does get warm after a while but not unreasonably so probably because I am using staccato. The Superior Electric spec sheet says that they can be over-driven for short periods as long as excessive heating is avoided and an adequate cool-down time is provided. The current MOT that I am using is similar in size to the one shown in your pictures. The very old MOT that I have is quite a bit bigger and came from a 1970s vintage Amana Radarange. It has about 40% more iron than the MOT I am currently using or any other MOT that I have seen. It also does not have any shunts. If you run across any Amamna Radarange microwave ovens from the mid-1970s be sure and grab the MOT out of it. Those MOTs are almost like a plate transformer.

I did figure out how to wire the HV terminals of the Amana Radarange MOT. I tried this bigger MOT but did not see a difference in performance so I took it back out and went with my original MOT. At 140 volts on the variac (actual 135 volts to the MOT), the current pulses at about 17 amps peak as closely as I can read on the amp meter.

Today, I tried adding an additional 1 uf of capacitance to the voltage doubler circuit. This gave me a total of 3 uf. Performance was improved somewhat, adding about an inch to the streamer length at 140 volts. Performance was also more consistent at 140 volts. My current spark length with this change is 19" to 20" depending on how I look at it.

I have larger variacs but in the interest of portability I want to stay with the 10 amp unit. Right now everything fits nicely into a single chassis which weighs about 50 pounds.

Another modification that I am working on is a way to soft-start the 833A filament. It won't improve the performance but it should extend the tube life. I tried a thermistor today but it didn't work as well as I hoped. Even after the thermistor came up to operating temperature, it still dropped 0.5 volt across it which dropped my filament voltage too low at 9.5 volts. So I will be trying other methods such as a switched resistor or I may use the thermistor for soft-start and then flip a switch to short across it to eliminate its voltage drop.

Steve

----- Original Message -----
From: "Chris Reeland" <chrisreeland@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, February 22, 2018 7:46:23 PM
Subject: Re: [TCML] VTTC MOT question

Hi Steve,

Look familiar?  See picture links.
Practically the same I think of the more iron one you mentioned... This is
what I have been using on my T-200 at 120v. Other pictures are modifying
for 140v use.

Links:

https://photos.app.goo.gl/IJ7Kb95KVVMyhfoG2

https://photos.app.goo.gl/EtbPMRSEbbWuogiB2

https://photos.app.goo.gl/0pfqWO5W4AR0VZDg2

https://photos.app.goo.gl/60HhKCiQdIWDXeyf1

https://photos.app.goo.gl/rvkanOMrHbyjcIw02

https://photos.app.goo.gl/D03VZhVaZ64fLro13

https://photos.app.goo.gl/dhurmGu98D5lC4692

More coming on other things...

Chris
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxxxxxx
https://www.pupman.com/mailman/listinfo/tesla