Electric Heater Controller Using Thyristor

[kshong]

Hi guys,

I really need your help on this. I'm doing a project on Electric heater 15kW 30A using thyristor controller. There must be a high temperature trip and i'm planning to use trip amplifier. Can any experts who did this before tell me how to assemble all this together? How should the whole system connection looks like? What should be considered?
If there are visual examples then it will be really great.

thank you!!

 

[Hero999]

Are you just building a thermostat?

I assume it's AC to you'll be using a TRIAC.

I'd suggest running the control circuit at a lower voltage (5VDC to 24VDC) and be isolated from the 500V supply using a pulse transformer or an opto-isolator.

I found an 800V opto-isolator whcih should do the trick, it features zero crossing which is what you probably want. There are plenty of circuit on the datasheet which show you how to use it to control a TRIAC or a couple of SCRs. The IR diode could be activated by a simple comparator and thermistor or you could opt for more complicated microcnotroller based design.

https://www.fairchildsemi.com/ds/MO/MOC3083-M.pdf

 

[kshong]

I'm building a heater for a closed drain vessel. There should be Hi temperature trip which i will use trip amplifier. The thyristor controller should control the temperature of the heating element. Then there should also be a auto manual mode in case i need to adjust the temperature manually. If i could get a similar single line diagram or AUTOCAD drawing of such application then it would be the brightest day ever!

Thank you so much!

 

[Hero999]

Sorry but you're expecting too much: this is not a free design service, the aim of this forum it to help people with their electronic problems by helping them to learn how to do for it themselves, not by doing everything for them.

I don't see why you need an amplifier? A comparator is all that's required. When it's too hot, the resistance of a thermistor will be low which can be detected by a comparator which can switch the heating element off.

Here's a couple of sites which should help you with comparators.
LM311 Light/dark detector/thermostat
**broken link removed**

The idea is to use a comparator to switch on the IR inside the MOC3083 which is coupled to the SCRs (see the datasheet I linked to above if you don't know how).

A manual override could be implemented by bypassing the comparator's open collector output (see the comparator tutorial I linked to if you don't know what this means) with a switch.

This is assuming it's possible to use a thermistor; you haven't already decided to use a thermistor and that it's AC power but because you haven't provided this information, assumptions are all I have to go on.