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Ryan Parle

Tue Jun 16 2009, 07:40PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

whilst looking on ebay for a variac i stumbled accross these solid state power controller modules which seem to be an alternative to a variac.

anyone know if it will be suitable for SGTC use?

If so it would make a very neat and cost effective alternative to a big heavy variac. and i would be able to get my entire control system in the spare 19" 2U rackmount enclosure i have.

Arcstarter

Tue Jun 16 2009, 09:29PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

No, unfortunately this will not work for an iron cored transformer. It is a switch mode type of this, pulse width modulated which will give out high frequency and a variable pulse width.

The only kind suitable for iron cored transformers are the large iron cored variacs. There might be something else out there that works, i know someone here used a light dimmer for some MOT sgtc, i am not sure how that worked XD.

teravolt

Wed Jun 17 2009, 01:11AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

the moter controler may not work with transformers but it may be all right with a DRSSTC

Ryan Parle

Wed Jun 17 2009, 03:34PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

ok, thats a shame, i was rather looking forward to having a nice light and compact control box.

the ratings plate on my 10kv 50mA tranformer shows 2.4A current draw from the LV side, would the actual current be the same or will my TC be likely to make it draw more?

a 2.7A variac is only Â£35 but the price seems to be double or even more if you go bigger.

Steve Conner

Wed Jun 17 2009, 03:48PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Says "OK for inductive loads" so I don't see why not. Unless the sheer amount of RFI from your Tesla coil blows it up.

...

Wed Jun 17 2009, 05:08PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I would agree with Steve, its certainly worth a try. I am guessing it is a phase angle controller, like a normal dimmer switch, which should work just fine for a tesla coil. Just make sure to have plenty of line filtering on both sides of the controller.

Ryan Parle

Wed Jun 17 2009, 06:48PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

Cool! I suppose for 20 quid i cant really go wrong. I'll make sure i build a good protection network before i use try this module.

i'm thinking i will want terry filter with safety gaps, and a line filter either side of the solid state power controller. Any advantage to using PFC caps as well? If so how do i choose what value capacitor i should use?

Any other protection devices recomended?

When choosing a line filter are there any particular things to look for?

As well as the power to the transformer i would also like to add the power cables for a vacuum cleaner motor. The motor has three terminals, which all seem to be for power and no earth, the cables go to a small speed controller which has a PIC on board, the speed for the motor is controlled via a potentiometer. My plan was to use a multi core cable to provide power to the NST and the motor, with all the control gear mounted in the control box which will be mounted a safe distance away from the TC. but i am a little concerned about RFI passing up the power cables to the speed controller and zapping its PIC, is this a valid concern? if so what can i do to protect it?

Nicko

Wed Jun 17 2009, 09:19PM

Registered Member #1334 Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615

Ryan Parle wrote ...

whilst looking on ebay for a variac i stumbled accross these solid state power controller modules which seem to be an alternative to a variac.

Its a straight phase-angle controller - I've already spoken with them about this as I get my magnet wire from them - see M028N instructions - nothing special.

Not tried it with a DRSSTC yet, but any similar dimmer should work the same (go to B&Q etc.)

Nick

Arcstarter

Wed Jun 17 2009, 11:40PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

... wrote ...

I would agree with Steve, its certainly worth a try. I am guessing it is a phase angle controller, like a normal dimmer switch, which should work just fine for a tesla coil. Just make sure to have plenty of line filtering on both sides of the controller.

Ah. I just thought this was one of the PWM type things. I did think about it being like a light dimmer type thing, but i thought that the phase angle controllers, since they give a sawtooth wave, would not be suitable for transformers. It would not change the waveform too much and make the charging of the capacitor be weird? Then again, i guess as long as it swings to the peak and trough just as a sine wave would, it would not matter, right?

But do beware, RF might interfere. I used a dimmer switch that was grounded to the mains ground (but unshielded) for my asynchronous rotary spark gap, and it would speed up and down by itself, more at certain break rates. Shielding it with some sort of conductive mesh or foil might help, but you have to make sure there are no 'leaks'. Unless you put the mesh all around your heat sink, but i would just screw the mesh onto the heat sink and ground it.

Hope it works out for you, let us know. This might become the new thing to use!

Steve Conner

Thu Jun 18 2009, 11:05AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

My old Tesla-2 had a rotary gap powered by a vacuum cleaner motor. I controlled the motor speed with a dimmer switch from B&Q. An ordinary dimmer didn't work (it blew up) but a more expensive one worked fine, that was sold as suitable for low-voltage halogen transformers.

And yes, I used the same setup with a remote control box and multicore cable. The only difference was that the transformer power was just controlled by a switch, the output of the coil was varied by changing the gap motor speed. This is only possible with a DC resonant charging coil: a NST based system risks damage to the NST from overvoltage unless the gap is either synchronous, or always runs fast enough to present at least once per half-cycle.

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