Choosing AC bed heater + SSR

Nxt-1

I am currently running a 310mm diameter PCB heater from my 12V PSU. To take the some of the load away from the PSU (which heats up quite a bit => fan noise) I am looking to get myself a AC heater and an SSR to control it. I've got two points that I'd love you guys' feedback on.

Would something like this SSR 40DA + the heatsink to suitable?
I'm looking a into silicone heater like this one. Is there a reason to not pick a million Watt heater for fast initial heat up.

dc42

SSR-25DA or SSR-40DA is suitable, or even SSR-10DA (which is what I use) if your mains is 230 or 240V and the heater power is no more than about 400W. You don't need the heatsink.

I suggest you choose the heater power to be around 0,4W/sq cm so that if the heater remains on then the temperature is likely to be limited to a safe value, perhaps 200C or a bit less. If you choose a higher power, add a thermal cutout.

Nxt-1

@dc42 said in Choosing AC bed heater + SSR:

SSR-25DA or SSR-40DA is suitable, or even SSR-10DA (which is what I use) if your mains is 230 or 240V and the heater power is no more than about 400W. You don't need the heatsink.

I'll probably go with the SSR-40DA, the price difference is negligible anyways. While I'm at it the heatsink is going in there to, you can never be to cool :).

@dc42 said in Choosing AC bed heater + SSR:

I suggest you choose the heater power to be around 0,4W/sq cm so that if the heater remains on then the temperature is likely to be limited to a safe value, perhaps 200C or a bit less. If you choose a higher power, add a thermal cutout.

Since I would love really quick heating times, I think I will go with a higher power heater and a thermal fuse like this one, Have you got any recommendation with regards to a temperature or how to let the fuse make proper (thermal) contact with the heater?

dc42

Bear in mind that the body of that type of thermal fuse is generally live, so it must must be insulated from the bed plate.

Nxt-1

@dc42 said in Choosing AC bed heater + SSR:

Bear in mind that the body of that type of thermal fuse is generally live, so it must must be insulated from the bed plate.

That's good to know, thanks. Do you think attaching it in the center of the heater on the underside with some kapton tape would suffice with regards to thermal conductivity? Also over/under (depending on how you look at it hehe) the tape would go an aerogel insulation pad.

pawPrinter

How about using these for a thermal cutout. They are available in various temperature ratings, and are easily re-settable manually. I have got a couple but haven't tried them in anger yet. I get the impression that they are quite reliable. I can't imagine that these are live on the body because they are meant to be held in contact with the surface that they are measuring, but I will be checking carefully!! I have applied heat sink compound to ensure a good thermal connection with the bed (and heated build chamber)
http://sinolec.co.uk/en/manual-reset-thermostat/1211227-thermal-cut-out-130c-nc.html

Nxt-1

@pawprinter said in Choosing AC bed heater + SSR:

How about using these for a thermal cutout. They are available in various temperature ratings, and are easily re-settable manually. I have got a couple but haven't tried them in anger yet. I get the impression that they are quite reliable. I can't imagine that these are live on the body because they are meant to be held in contact with the surface that they are measuring, but I will be checking carefully!! I have applied heat sink compound to ensure a good thermal connection with the bed (and heated build chamber)
http://sinolec.co.uk/en/manual-reset-thermostat/1211227-thermal-cut-out-130c-nc.html

Generally I am a fan of reusable parts but I plan on never having to reset the fuse and they are more expensive/bulky. Also I'd still have to tape it down since I have no place to screw it down to.

mrehorstdmd

@nxt-1 I would not buy safety devices like thermal fuses via ali-express. TCOs made by well known manufacturers, with multiple safety certifications, are only about $1 each. This is no place to get cheap. If you're in the US, Digi-key and Mouser sell TCOs made by reputable makers, with multiple safety certs.

Don't use tape to hold the TCO to the bed/heater. If the tape fails the TCO won't do its job. Screw or clamp it down mechanically or glue it down with high temperature silicone, like the stuff used to make gaskets for engines, available at any auto parts store.

TCOs have to be chosen for adequate current and operating temperature, typically 20C or so above the expected maximum use bed temperature. Consult data sheet for exact selection criteria.