AC dimmer control using DC signal

Thread Starter

reza v

Joined Mar 8, 2023
Okay so i'm building a large 3d printer, 12v heated bed wasn't enough, i switched to a mains heater, now it heats up too much and too fast so i need a dimmer.

The 3d printer control board puts out a 12v signal that can go up to about 10 amps and if i use that to just control an ssr, it'll overshoot the temp so when you request 60° for example, once the heat gets spreaded it goes up to like 120 which is really bad.

I'm thinking of building a simple triac/capacitor combo dimmer in this video
and put it in series of the ssr. I know that's a bad idea so i'm trying to delete the ssr from the circuit and somehow control the dimmer using the 12v signal from the main board. I basically need to control the potentiometer somehow using the 12v. I could just cut the signal that goes through the potentiometer using a coil relay or some other method but keep it simple. Also no microcontrollers is preferable. Any suggestions is appreciated.


Joined Aug 21, 2008
Yes, you can do that -change to on/off control. You can set the dimmer using a pot to get the degrees per second that you desire and position the thermal sensor at the right distance from (like right on top of) the heating element. Adjusting gain (degrees per second) and delay (distance between the heating element and thermal sensor can help you limit overshoot and oscillation.


Joined Jan 23, 2018
If you can locate an LED/LDR package that will allow the controller to vary the setting of the dimmer. You will need to putvthe variable resistance part of the LDR in parallel with the variable resistor in the dimmer, and then use a resistor in series with the LED in the LDR to limit the current.
It used to be that there were a number of packages with a light source and a resistive photosensor available, but they are much less common presently. But they can be very handy.


Joined Nov 6, 2012
A Triac could create enough Electrical "Noise" to disrupt the operation of any near by Electronics.
Maybe it won't, but just be aware of the possibility.

Would You like to know how to create a Thermostatic/PWM Controller
that will allow You to set the exact Temperature that You want accurately ?

It can be relatively simple if You can build a Circuit on a small Perf-Board.


Joined Feb 16, 2022
This circuit can do the job:

Choose R1 according to power needed. When LED is energized, heater is on.
It was mentioned before concerning electrical noise (EMI)...

There's other AC regulators for heaters, which do not generate EMI. Search for "zero cross regulator" or so.
Such a "dimmer" is applicable for heaters only.
It can be made by building an astable oscillator on the 555' timer, which drives a solid state relay. Here's a good article , look chapter "Varying the 555' Duty Cycle" :


Joined Jan 23, 2018
The big benefit of using an LDR is that there are at least 1000 volts of isolation between the control input and the mains wiring. In addition, all the physical mains connections are already there in a simple to handle package.