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Help with resistive cartridge heater and variable control circuit

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Still trying to understand why the diac is a requirement.
It is required for zero crossing control. The heater is a pure resistive load and can be handled by a regular lamp dimmer. Your fan is an inductive load and requiers a different dimmer to run a motor like a celling fan speed controller. It is still a triac but has more stuff for inductive loads mainly a coil. Still much stuff on the web for this stuff google is your friend. Andy
 
It is required for zero crossing control. The heater is a pure resistive load and can be handled by a regular lamp dimmer. Your fan is an inductive load and requiers a different dimmer to run a motor like a celling fan speed controller. It is still a triac but has more stuff for inductive loads mainly a coil. Still much stuff on the web for this stuff google is your friend. Andy
I'm no expert on dimmers and speed controls, but I don't think this is the reason diacs are used. I found this on the Electronics and Radio Today site:
One of the major uses of diacs within triac circuits. The diac is placed in series with the gate of a triac to provide a more symmetrical switching characteristic. It is found that triacs do not fire symmetrically as a result of slight differences between the two halves of the device. This results in harmonics being generated, and the less symmetrical the device fires, the greater the level of harmonics produced. It is generally undesirable to have high levels of harmonics in a power system.
To help in overcoming this problem, a diac is often placed in series with the gate. This device helps make the switching more even for both halves of the cycle. This results from the fact that the diac switching characteristic is far more even than that of the triac. Since the diac prevents any gate current flowing until the trigger voltage has reached a certain voltage in either direction, this makes the firing point of the triac more even in both directions. In view of their usefulness, diacs may often be built into the gate terminal of a triac
I found similar information on several other sites.
 
Thanks for the replies guys. yes, this circuit is one of a few that will have to be put on a PCB. I have little experience with triacs and mostly work with DC stuff so this will be a bit new to me. There is also a fan control and device protection circuit that will have to integrated.

Yeah, it is always frustrating that you can literally go buy a complete device for less than you can get the parts for. Go look at a radio controlled gadget at Wal Mart in the kids isle. I guess I was just hoping there would be a stupid simple way to regulate the voltage to this device but sounds like not...

If you could better explain this project there may be some simple and viable solutions. For example you have a 100 watt cartridge heater element. That can be manually controlled as simply as using a common very inexpensive dimmer switch. Why buy pices and parts?

You mention a fan. If the fan speed is going to be manually controlled possibly a simple F-Stat or button thermostat could be employed to turn a fan on with temperature rise. Unless you absolutely need variable speed and since it would be manual vari-speed I don't see the point?

This would go much better with a more detailed explenation of the overall project.

Ron
 
I need to run a cartridge type heater with a variable voltage control. Just looking for opinions as well as a potential supplier for the heater.

Rough specs (not set in stone)
Heater - 120V, 100watt, .25-.500" diam x 1-2" long
Really would like to find a source for these in a smaller bulk orders.

Google: cartridge heaters
Cartridge and Insertion Heaters for Heat Transfer and Uniform Temperatures in the Heating Element Industry
Cartridge Heaters:
**broken link removed**
SunRod 1/8" and 4mm Cartridge Heaters from Sun Electric Heater
And many more!
Ken
 
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