Reddit mentions of uxcell Solid State Relay + Heat Sink SSR-25 DA 25A 3-32V DC / 24-380V AC

SSR or Solid State Relay. It's a switch to turn line voltage power on and off using low voltage (3-32VDC).

Here is one on Amazon with a heatsink.

Ok so the heat bed is here:
http://www.aliexpress.com/store/product/200X200mm-400W-12V-w-NTC-100K-Thermistor-Keenovo-Silicone-Heater-3D-Printer-Heater-Heatbed-First-Grade/210086_32230108542.html
and the relay is here:
http://www.amazon.com/Amico-Solid-State-SSR-25-24-380V/dp/B0087ZTN08/
(thanks to BillDaCat)

Where is the metal brace thingy? (or is that part of your printer? Or the fiberglass part?)

Parts list is dependent on what controller you use. This is a decent one.

https://www.amazon.com/dp/B0195V53X8/ref=cm_sw_r_cp_awdb_t1_n5DWCbX7WY6NB

You will need a box or container for the pid and wires. A temp probe that will work in the 500c temps. And a solid state relay. https://www.amazon.com/uxcell-Solid-SSR-25-3-2-32V-24-380V/dp/B0087ZTN08/ref=pd_aw_fbt_328_3/147-7782181-2201822?_encoding=UTF8&pd_rd_i=B0087ZTN08&pd_rd_r=0b211574-6776-11e9-b475-c358acaaf9b4&pd_rd_w=As9SE&pd_rd_wg=uOeRp&pf_rd_p=3ecc74bd-d08f-44bd-96f3-d0c2b89f563a&pf_rd_r=X57XWHY664NJBVVBD0AS&psc=1&refRID=X57XWHY664NJBVVBD0AS&th=1

That's an example, I need to do more digging to make sure its capacity is ok. I think it should work.

In general, a pid controller says "turn on the relay when the temperature is between x and y. Turn off when the temperature reads z.

This type of probe would work

https://www.amazon.com/Perfect-Prime-TL1815-HeadProbe-Thermocouple-Temperature/dp/B0142S9J4S/ref=pd_aw_sbs_79_1/147-7782181-2201822?_encoding=UTF8&pd_rd_i=B0142S9J4S&pd_rd_r=49d6e55b-6777-11e9-af2b-df456cd2a423&pd_rd_w=eR1mx&pd_rd_wg=w1VKC&pf_rd_p=aae79475-6dc9-4a12-80e8-27b63108fa72&pf_rd_r=BHRC8SSGY71B2D18D2Q1&psc=1&refRID=BHRC8SSGY71B2D18D2Q1&th=1

Thanks for the safety advice, that's obviously something I want to be careful with. I'm looking at getting this keenovo 200x300mm heater and this SSR. What kind of fuses do you recommend for something like this?

So one like this or this work? Whats the difference between the two?

I'm thinking this is the route I need to go. With the relay I'm powering a single 120V 500 watt heating element but had considered adding a second element to add redundancy and cover if somehow room temp were to drop so low a single element couldn't output enough heat. I don't think that's an issue though since one element seems to be able to maintain the correct temp even around 50F in my shop. If I'm figuring this right that should need a little more 4 amps to power it correct? I see this relay that is rated at 25 amps so I'm thinking it should work fine for no more than I'm doing even if I do add a second element. Thoughts?

Thanks for the detailed write-up on your safety mods!!

I've seen Solid State relays recommended over/instead of the MOSFETs you linked to. e.g. something like this but rated at 25A.

However I'm having trouble deciding which one on Amazon is compatible. Would I need one that is DC to AC or DC to DC?

Like would this one be appropriate? Or this one?

I'm looking at Amazon only because they ship from the US and I'm hoping to have a Mosfet or SSR in hand by next week.

EDIT: Doing some more research, it seems like one of these is what I need? Amazon results for SSR-40DD The recommended brands are Fotek, Auber and Crydom.