Rectifier

There are many companies that make just firing boards for SCR controllers, no need to re-invent one from scratch. In fact many of the people who made complete controllers would use the boards made by companies like these. One such company is Phasetronics in Clearwater, Florida, another is Enerpro in Goleta Calif.

But if you want to find one in your country, simply do a search for "SCR firing boards" and the name of your country, you will likely find one.

I thought it is easy to design a firing module. Anyway if anyone comeup with a circuit please let me know.Definitly not going to buy a module because it may cost more than my pocket money.

Hi Hithuanand, I hope you are well.

Easier to repair what you have than to design one!

1. Do you mean 3 phase, 3 thyristors (SCRs) and 3 diodes? Or 6 thyristors in bridge?
2. Or single phase, two thyristors,two diodes? This is at a power where it might be single phase.
3. What kind of components on firing module? Transistor only or integrated circuit? Is it a printed circuit?
4. Are there any circuit diagrams or functional descriptions or parts lists? Specifications? Makes life easier.
5. What load does it feed? [possibility for test].
6. Is it "part working" or "dead" at present? Often "dead" is easier - start with power supply failed. Any obvious burnt bits?
7. Any "bells & whistles" you did not mention yet, like it is controlled by speed feedback? Or it is -220 to 0 to +220V DC variable?
8. Can you read the maker's name and type codes on the thyristors?
   

Yes I am fine, thank you. In a Polytechnic machines lab we want DC supply to conduct experiments on DC motor(one at a time). The rectifier unit here is old and its firing module not responded. Unfortunately i dont have the firing module with me now.Some experienced lab assistants from other collage took it for mounting their circuit on that so that it is easy to fix in rectifier unit.Now i know it was a bad idea to do so. They tested their circuit and when we installed it for testing it failed and smoke came out of the circuit they designed. The module is irreversibly damaged to repair. We have 3phase,415V input supply(27KVA transformer having 205V as secondary voltage) and 0 to 300V DC Voltmeter,0 to 100A Ammeter. Pot to thyristor module to Vary voltage output. They used small three 6V transformer and a 15V transformer to power their module.They said they used CRO to verify the output of their circuit.

Score so far : theory 0, reality 1. Smoke requires distinct degree of incompetence!

1. Are all three SCR cathodes bolted together, usually the big lead which is not the SCR body? This makes direct connection from firing circuit possible. If not, pulse transformers are necessary to isolate each gate trigger. This bolted common would be POSITIVE of DC output. Watch out for reverse polarity SCR which has cathode to case!
2. The 15Vsecondary gives DC power for the control circuit. The 3 transfo with 6V secondary give reference timing wave for firing pulse.
3. Unless something was very wrong in the firing circuit, connected to the SCR gate, it is difficult to blow up a firing circuit - unless the SCR fails. Are your SCR still OK - if not short circuit, probably OK.

Must depart, letter to post.

They did it successfully

I see a breadboard with around 30 components, maybe 20 jumper wires. I'd give it around 20 hours of an engineer's time at an absolute minimum, at least $30US for components. Both values are likely very low.

You could have bought a new firing board for $230 US. Than makes your engineer's time worth no more than $10 per hour.

Good investment.

What if the experience of designing a firing module makes the Engineer happy worth your yearly salary .

In theory, yes. In reality, are you willing to pay in money and time? It is sophisticated enough, that you pay anyway. Your choice.

Here we have thyristor controlled fan regulator.I dont think its much sophisticated. I do agree the firing module must be sophisticated to protect the whole power and control circuit.We just want to trigger 3 SCR for a 3 phase supply.

There are a 100 & 1 ways to build your circuit but more information is needed.

I suggest you find the book in your library called "General Electric SCRs and Triacs"

If not you can purchse from http://www.amazon.com/gp/offer-listing/0137967632/ref=dp_olp_used?ie=UTF8&condition=used

If you study this it will give you the infomation to do some repairs.