Sciencemadness Discussion Board

dimmer temp controller modification

modgod - 25-2-2012 at 18:30

I've been reading up on using a dimmer switch to control a heating mantle. I know that dimmers suffer when adjusting at low voltages, and that this can be rectified with a simple modification. I seem to have found the schematic that bio2 posted around 2008, but need help understanding it. Summary of the mod below -
Quote:

Quite simple as only 4 diodes and 2 resistors need to be added and is the same concept used on the commercial triac type mantle controllers.



There was also several references to using ceiling fan controllers rather than light dimmers, seems they dont suffer from the dropout problem. What would these commercialy be called? I'm having trouble googling for one. Details below
Quote:

A ceiling fan controller is also a phase controlled triac same as an incandescent dimmer. These can be used also and have the advantage that they are more stable at low settings (no dropout) and have a minimum voltage (speed in the case of a fan) potentiometer. This offers some range adjustment which allows better linearity of the dial.



Are the ebay chinese PID temp controllers worth a look at? I understand that they need a well placed thermocouple to be effective, but at $20-30 they seem a good deal in comparison to hacking apart a dimmer switch.

any input welcome, I did my searching, so please be kind if I missed anything obvious

modgod - 29-2-2012 at 18:24

bump, is this in the wrong section? should this be in reagent and equipment acquisiton?

watson.fawkes - 29-2-2012 at 19:20

How could anybody possibly understand a schematic that you don't post? Nor do you post the "several references" you talk about. And I'm fairly sure you don't understand what "adjusting at low voltages" means for a triac circuit.

Also, there was a thread on this selfsame topic within the last few weeks. Post your search terms.

smuv - 2-3-2012 at 11:19

http://www.allaboutcircuits.com/vol_3/chpt_7/6.html

diac needs 30v to reach breakover voltage in order to allow the triac to trigger. Therefore, triggering late in the second or fourth quadrant of the AC cycle is very hard. As watson said, how can we help if we don't know the schematic.

[Edited on 3-2-2012 by smuv]

magnus454 - 13-3-2012 at 19:57

Humm, I bought a lutron 2000 watt light dimmer (with built in heat sink) and added it to an external Outlet Box and a couple of rubber cord grips, and a 14 gauge extension cord chopped down to make a controller for my line voltage hot plate, lets me run the element wattage up and down as I need to maintain the right heat output