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Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi Marko,
The hand-held box is the interrupter for my DRSSTC, and the pots are rep rate, burst length, fine tuning and DC bus voltage. I just used the so-called "solid-state variac" circuit already in my DRSSTC, and wired the NST up to it, to see if it would work.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
With a dimmer rated for 300 amps you can probably only safely dim about a 30 amp load.
That's why soft start was invented :p
Modern high-power dimmers also have 'preheat' setting in case where lighting needs to be ramped quickly from 'off' to on: they continuously keep small current through the filaments to keep them hot, but without producing any significant visible light. This favors both the lamp life and dimmer itself as it doesn't need to suffer extreme peak currents if ramped up rapidly.
The hand-held box is the interrupter for my DRSSTC, which also has the voltage control pot for the SS variac on it. I just used the circuit already in my DRSSTC, and wired the NST up to it.
Huh, I would have never guessed
I actually noticed that transformers like NST's aren't especially demanding about dimmers. I actually made simple voltage-synchronized circuit to work without problems - triac seems not to have trouble staying on with inductive load like this.
I was planning to drive my DRSSTC with this and the current draw is around 17A I just have these large parts on hand and needed to know if it would work, it seams because it is a capacitive load it might not like it but right now my variac is rattling so I dont have another choice.
edit
I really need it so if I could have a go ahead to start I would be much obliged. This will only be temporary but I am planning it to dimm a 240 line to 140VAC-0VAC at max 20A normal run conditions will be around 15A feeding a 2,400uf 900V bank I think I should add an inrush current limiter. Or slowly bring up the power. I will also be running it as a 120VAC dimmer for 0-90% AC in. Another question is would it be better to use 600V 80A ultra fast recovery diodes for the bridge?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Such a thing will not work for a filtered rectifier. All you can do is blow the IGBT.
Even still it's silly to use a 300A IGBT brick where a small TO220 triac would do the job.
For your DRSSTC you shouldn't need more than few amps on 230V line unless it is really inefficient. Like 10 amps at most.
Look here at the circuit at page 10. Jut build it as it is, and add an inductor in series of about few mH. Triacs with low holding current like TLC221 are hard to find, but I think rest is very simple.
Other, look at steve's controller:
It's somewhat more complex but still straightforward and robust. Note how he constructed series inductor. Primary of an low voltage transformer in range 100-200VA will probably also serve, although you may need to saw some airgaps into it.
I dont know why IGBTs arnt better for this but ok I just have 10 of the modules and need to do something with them. I will try to build steve's controller though. the puls transformer is just a GDT right. and I can use any huge SCRs.
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30A DRSSTC dimmer
