Duet 2 Heated Bed with DC-AC Solid State Relay Setup

[jens55]

@Charily_Antics_343, if you want to go with a DC bed you need to make sure that your DC power supply output matches the heater rated voltage and that there is enough power available for the bed. 180W is quite doable in a DC heater but unless your printer is very small, you will not be happy with the end result. As an example, my 300*300 print bed printer uses a 750W AC heater!
If your printer is enclosed and small, you might get away with lower power. Be aware that there is more to life than PLA and a lot of entry level cheap commercial printers with DC heaters will not have enough power to heat a bed for PETG or ABS.
To sum it up, go with an SSR controlled AC heater!

[Charily_Antics_343]

@jens55 My print bed is 152.4x152.5mm (6inx6in). So I don't think I will need more than 180W.... It is relatively small thankfully!

I appreciate your recommendation! My goal is to print with some high temp thermoplastics and have a max heated bed temp of 170C. I'll do my best to stick with the AC heater and figure out how to use it safely with a good SSR!

[jens55]

@Charily_Antics_343, using an SSR is pretty darn simple. Bed output positive to SSR DC input positive, bed output negative to SSR DC input negative. One AC wire goes directly to the heater, the other goes through the SSR AC terminals to the heater. I personally like connecting neutral directly and 'live' via the SSR but the other way works as well (but isn't as safe). Connect ground to the bed. You should also have a thermal fuse but that is not a requirement for basic operation. If you do install a thermal fuse then run the live wire from the SSR to the thermal fuse and from the thermal fuse to the bed heater. If you expect the bed to run up to 170C (only one heater that I know of is spec'd that high) then you will want something like a 200C thermal fuse.
If you are running the bed at that high a temperature I take it that the printer is enclosed. Keep in mind that if the motors are in the enclosure and exposed to the heat, your maximum enclosure temp is probably around 70C unless you have specific high temperature motors which might give you another maybe 30C (verify the spec's!)

Based on your stated level of experience and what you are attempting to do, I suspect you are in for a lot of frustration and hurt .... good luck!

[A Former User]

@Charily_Antics_343 Another thing to watch out for. Cheap SSR's couterfeit SSR's from eBay, Amazon and a few others. If it says FOTEK and comes from Amazon or eBay odds are it's not real and will have overrated triacs inside it. Like ones rated for 12 amps or less inside a 40 amp device. So make sure you buy a real one not something that will fail and possible burn your house down.

Edit. I thought I had avoided this by buying a Mager 40 amp from what I thought was a reputable site and found it cooking on the extrusion it was bolted to. Removed it and after visiting the Mager site found mine was also counterfeit. So I bought one from Digikey cost a bit more than from other sites but I know this is real. Runs nice and cool powering the 1000 watt 120v heater.

[dc42]

@Charily_Antics_343 said in Duet 2 Heated Bed with DC-AC Solid State Relay Setup:

@deckingman Thank you for this info! I just started looking at DC bed heaters since they might pair more easily with the board and be a bit safer for beginners. Do you think there would be any issues with connecting a DC power silicone heated bed directly to the board?

While DC heaters are arguably safer for beginners, AC heaters are much more practical for large beds. So I suggest you stick with an AC heater if you need more than 240W of heat (assuming 24V power to the Duet). That said, if you only need 180W of bed heating power and you are running the Duet from 24V then a DC heater is practical and it can be driven directly from the Duet.

There are indeed counterfeit SSRs around. The counterfeit DC-AC ones can work ok as long as you run them well below their rated current. The counterfeit DC-DC ones are useless.

Edit: I just checked that heater and I see it is about 150mm x 150mm. So DC heating is practical. I recommend a heating power of about 0.4W per square cm. Your heater has 0.8W per square cm, so in the event of a fault that leaves it on at full power, it will get very hot indeed. Therefore I suggest you install a thermal cutout on the bed or heater, if it doesn't have one built-in.

[Charily_Antics_343]

@jens55 Thank you so much! I have done a lot of research on the framing and structure, motion system, and other factors involved, but I was very new to electronics for with heating beds. That said, I built the system with temperature effect on electronics (especially the motors) in mind from the start, so all of my electronics and wires will be outside of the heated area/enclosed chamber with the exception of the wires coming from the heated bed.

I greatly appreciate your help!

[Charily_Antics_343]

@KenW Thank you so much for bringing this to my attention! I had noticed that many of them seemed counterfeit on the sites you mentioned as well.

Currently, I am sticking to looking at those recommended by Duet, namely Auber Instruments MGR-1DD80D100 or Crydom DC100D40. I'll look for these on Digikey per your recommendation, thank you!

If you come upon any other reputable suppliers please let me know!

[Charily_Antics_343]

@dc42 Thank you for these notes! I do only need 180W, but I will probably stick with the AC heater I have to prevent heating issues or increased warm-up time.

[Charily_Antics_343]

@jens55 What motherboard do you use with your heater? Or I suppose what method do you use to control it?

I have been looking at sensors to pair with my bed for temperature control. It seems that a PT1000 would pair best with the duet 2 board I have, and would easily read the temperature range I am looking for. (and there would be no need to purchase a daughterboard) However, I have heard that thermocouples (mainly type k) have been used more often in higher-temp applications.

Do you have any thoughts or recommendations in this area from your experience? Thank you again so much for your help and patience with me!

[jens55]

@Charily_Antics_343, I run both Duet2 and Duet3 boards, all with AC heaters. I have a mix of thermistors and PT1000 sensors (I am transitioning to PT1000 which IMHO are better)

[Charily_Antics_343]

@jens55 Thank you! Going to find some now

[A Former User]

@Charily_Antics_343 You mention you might plan to use an AC bed but the two SSR's you linked are both for DC-DC. Just thought I'd mention that. If you are interested in Auber here is the link to their site. They sell on amazon for small purchases but the link from them would be to a valid part.

Here is a link to a site that shows how they wire the SSR in. I used a fuse in place of the circuit breaker and include a thermal fuse on the bed in case the SSR fails closed. The DC version is simpler as that uses power from the 24v power supply. I have one of those on a printer too. That one is also fused with both a thermal and regular fuse.

[A Former User]

@dc42 Based on that idea I used a DC-AC 40 amp Fotek from Amazon with a 120v 250W PTC heater for a homemade PID controlled SMD soldering plate. That should have been way below the capability of the SSR at a little over 2 amps. Could have cooked an egg on it. The Omron 10 amp replacement from Kb3d did not even get warm.

Feel sorry for the real Fotek if they still exist as they seem to be the number one choice for fake devices.