Can the output on the extruder controller board be used for a SSR?

My heater is not heating up much at all at 12V. I'm going to buy a nozzle heater that runs at 120v AC. Can some one help me with this question? My understanding is that the makerbot extruder control takes info from the thermocouple and switches on and off the 12V dc to make the nozzle hotter or colder. I was wondering if I can us this output to control a solid state relay such as:

[www.photosensor.com.tw]

It takes 3-32V input and controls AC current on the output side. Think it'll work?

Edited 1 time(s). Last edit at 03/26/2011 08:50PM by HereinCS.

How big is your nozzle that you need 120VAC to heat it? I don't see why you need that much voltage unless you're extruding really large plastic filaments.

You can control a SSR with any of the power MOSFETs on the extruder controller. Note that one of the output is at 12 V and the other is switched to ground by the power MOSFET to complete the circuit.

Extruder temperature is measured more commonly with thermistors than thermocouples. Either way works.

I'm using a small cartridge heater. It's meant to run at 120ac, I tried it at 36v DC. It does get hot, but not 260' hot and is so slow.

What's the advantage of using that instead of one of the many methods that have been shown to work and are much safer than messing with 120 V?

Neater looking. Very similar to that on the Up! machine. More reliable. No shorting issues, etc. Can heat to much, much higher degrees, potentially more flexible for other materials.

I didn't think there were shorting issues with the 6.8 ohm ceramic resistor and brass or aluminum block described in the wiki. There's also plenty of power to heat up to 300C with 12V. If you want higher T, you can use a lower resistance. The tip on the Up! looks like it uses a similar design to this. Is the Up! using 120VAC on the extruder tip?

The up machine uses a lower voltage heater. I just happen to have a 120v heater sitting around to play with. Perhaps I'll buy a lower voltage one.

To switch the mains, i think a triac would be needed, and to control the triac mainly a dedicated optocoupler is needed, which in turn can be with zero crossing or with random point. Solid state relays are something like these two packed together, but usually in my case, its much more expensive than the separated parts (e.g. i used bta140+moc30xx [www.fairchildsemi.com] series for another app and i could buy 10 combos like that for the price of the required ssr equivalent). Lots of schematics on the net, and even some discussions on arduino forum on switching mains, and i also think i read at some point an application on the microchip site for a light dimmer on mains via a pic the same way, which was a good read - after all heater or light its same thing. I think in general zero cross should be best, as it means that it will switch not when the command is received, but instead will do it next time when the wave crosses zero, which goes nice and smooth. And the random point i think switches when the command gets there regardless at what point the wave is at, which can raise issues like transients, snubber design, or use of snubberless triacs for inductive loads etc, needed if you want to control a motor, but else i think its both beyond my head and beyond the discussion here. Also a thing to consider, I guess looking at the firmware would also make some sense, for example if you want to pwm control the heater, and at which freq, that can bring some further considerations into the problem. Or just change the firmware and take out the pwm and simply use on-off. Or, just step back and think it through, alot of things can go wrong and leave heater on at full power, and if it runs mains with significant power increase, it can make more mess than 12v 6r8 variant, which is simple enough, cheap and fairly safe somehow. Sorry if my post was not better, cant figure out what else to say. Good luck either way