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How to fire thyristors in a 3phase phase angle controller

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Larry80:
Just want to chip in, which is not found in the literature. Be mindful about the energies which flow trough the RC snubber. All capacitors also act as resistor in AC circuit, which will flow trough even when triac is turned off. Use non-flammable resistors and X capacitors, at least in the end. You can estimate the amount of energy quite well by measuring the body temperature of your test resistor against the manufacturer charts. Factor in the ambient levels too, if you test at 20C flat and finished product is 50C vertical, how would it effect that equation? I would keep resistors nominally under 60C and it must not become dangerous if capacitor shorts.

duak:
The optocoupler could drive an intermediate triac rated at 10 to 20 A that could then drive the main triac.  Make sure the gate currents are within specification - some series resistance in each stage to limit current may be needed.  Also, gate bypass resistors may be needed to handle any leakage current from the previous stage.

Larry80 points out that the RC snubbers will also let a leakage current through even the triacs are not triggered.  Also remember that the triacs cannot be considered fail-safe. ie., there must be definite opening of the line phases with a mechanical switch or connector.

Small amounts of chlorine and hydrogen will be evolved even with AC, especially with hot or boiling water.  The chlorine will tend to stay in solution and attack copper.  Hydrogen is flammable and the combination with chlorine is explosive if allowed to collect in litre volumes.  It can be triggered by light too.

Take care,

jbb:

--- Quote from: MagicSmoker on July 22, 2019, 07:01:08 pm ---Another note - electrolysis of saltwater is how bleach (NaOCl) is made industrially, though with DC, of course. Now, with AC the cathode and anode switch places 50 or 60 times per second, so ion migration can't really happen, but I do know that gases are produced in water resistors even when AC is applied, so beware. You might find it is altogether preferable to submerge coils of stainless steel wire rope into a barrel of deionized water to use as a water-cooled resistor, rather than use salt water itself as the resistor. Also, the coils of wire rope will definitely have enough minimum inductance.

--- End quote ---

Mmm, bleach.  It may be a bad plan to tip that back into the ocean - do you have a plan for safe disposal?

I just remembered a trick on the salt water resistors.  If you don't need super-fast response, you can use a mechanical sliding stage to bring the bars into the barrel to varying depths; this makes a variable resistor and will have much better power factor than an SCR bridge.

I also remembered that you can purchase resistors made from stainless steel sheet: see the HPR Grid Resistors here for an example.  These can be immersed in deionised water as MagicSmoker suggests.

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