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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Resurrection!
Among the projects I have planned this summer is an arc welder, and this circuit is perfectly suited for power control. The one thing I don't understand is the ratings of the main power triac. Often 1200V and many, many amps, more than most circuit breakers can carry. If I'm going to be powering 5 MOTs, what is the minimum size of triac I would need? I thought a 600V, 16A MAC16M would be plenty, but I just want to make sure.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
This is probably a circuit I'm looking for, but where can I get the component values? Firkragg, would you mind if I ask you what component values did you use? Also, it is not evident from the schematic, is there a connection between C and Rd/P? Thanks
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Uzzors: 5 mot's at 230V (7000 watts or so) is already 30 amperes at least. I would use biggest triac I can find, something in 50-100A range would be optimal, with large package and heatsink to dissipate power. Can you actually provide that much power from a single phase?
Auxiliary triac is actually more problematic, and it is the reason why I don't like this circuit too much. It needs to be sensitive type with lowest possible holding current, otherwise large amounts of power need to be dissipated in power supply resistor in order to keep it on.
The auxiliary triac triggers at same time as the main triac, and then it shorts out the potentiometer, drastically reducing the RC time constanc of relaxation oscillator, wich runs at higfh frequency generating a pulse train until zero cross.
jmartis: just copy the example arc-welder control schematic. The diode bridge thing across the capacitor is absolutely necessary for voltage synhronization mode.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
I was looking at the ST application note posted earlier, and I plan to use my SCR module as the triac with the SCR's back to back. However, after looking on the application note, I just now noticed that the circuit is designed for 220V. So- a couple of questions: What values (if Any) need to be changed for 120VAC operation? Also, are the two pots in that circuit a coarse and fine adjustment? I think this may just be a circuit from heaven- not even one transformer or 7805
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Control of inductive loads by a triac - 'solid state variac'
