Author Topic: SSTC - Triac the Amazon module a cheap alternative to variac???  (Read 135 times)

Offline corny90

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Hi everyone,

Three months ago I made my first SSTC with a single mosfet driver (IRFP460) and with manual tuning. I had nice result at 333kHz RF (without topload) with around 3 cm continues sparks and with the mosfet cold (40V input).

Now I pass to a half bridge driver with this circuit of Kaizer:
http://kaizerpowerelectronics.dk/tesla-coils/kaizer-sstc-i/

The only thing that I add, is another 555 timer for manual tuning (their is a jumper that allow me to choose manual or auto).
On the output of 74HC14, with the coil off I have a perfect 50Hz (of my main house I think). Switching ON the coil I have a very "nice" mix of 50Hz with RF and duty cycle of pulse.
I tried to put the driver one meter away from main AC or supplies but the same result... It disappear only if I switch OFF all mains in my room.

Now, I have 3 big questions, and hope someone can help me:
1. Is it normal to have less results with this half bridge driver, like 1cm spark and drawing about 400mA at 40V?
2. What can I do to remove that 50Hz? A hi pass filter on the input of 74HC14 will help?
3. A triac-diac module is a cheap solution to a variac (I found in amazon to control motors until 4000w)? It will work? Is a good solution to use this module before full bridge rectifier?
(the triac-diac: https://www.amazon.com/WINGONEER-Electronic-Regulator-Thermostat-Controller/dp/B01LXLU3SD/ref=sr_1_6?ie=UTF8&qid=1523648449&sr=8-6&keywords=voltage+regulator+ac)

I would like to connect my SSTC at the maximum power to 220VAC soon, but I will like to slowly smooth step up the input voltage (if I will solve the 50Hz problem).

Thanks in advance, and hope someone can help me,
Best regards

Offline CCX191

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Re: SSTC - Triac the Amazon module a cheap alternative to variac???
« Reply #1 on: April 14, 2018, 12:41:54 PM »
You might want to watch this youtube video as to why using a Variac is better than a Triac. I had the same question before then too!


Offline profdc9

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Re: SSTC - Triac the Amazon module a cheap alternative to variac???
« Reply #2 on: April 14, 2018, 05:28:11 PM »
A triac conducts only when the line voltage exceeds a threshold, and stops conducting when the current in the triac falls to zero.

The waveform from a triac is discontinuous because the voltage turns on abruptly.  You might be able to heavily filter this output, but chances are that creating such a filter would be no cheaper and probably inferior to just using a variac.  The peak currents through the triac would be high and might burn it out.

One solid-state alternative that actually might be somewhat cheaper would be to design a buck converter, as is commonly done in power factor correction circuits.  These are not easy to design but are common on high efficiency switched mode power supplies.  You could use use a full-wave-bridge to rectify the line voltage directly, and then input this to a IGBT that would chop it with a particular frequency or duty cycle.  If the frequency is high enough, this is relatively easy to filter.  You would need a good heatsink on the IGBT because it would be hard-switched.  I don't have a lot of experience with these, being relatively new to power electronics, but it seems like this could be a good alternative to a variac.

Dan

Offline corny90

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Re: SSTC - Triac the Amazon module a cheap alternative to variac???
« Reply #3 on: April 15, 2018, 11:54:56 PM »
Thank you very much CCX191 and profdc9! I was thinking that the cheap triac circuit must have something strange... In the description and the comments of that triac module people are well driving motors untill 4000W but I think is availabe on AC motors not DC, they do not specify.

Anyway, I think I will have to do an investment and buy a Variac to smoothly test my SSTC.

High Voltage Forum

Re: SSTC - Triac the Amazon module a cheap alternative to variac???
« Reply #3 on: April 15, 2018, 11:54:56 PM »

 


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