KY-019

Can you use KY-019 relay to control power from the house mains in a simple on / off fashion? I see it can be used with 125 or 250 VAC but the 10A has me confused?

It would be helpful if you post a link to more information on this part, ideally a datasheet. Use the chainlinks icon on the toolbar to make the URL clickable.

10A is the current rating of the relay. That is the maximum amount of current that can be switched. If you don't know what that means you need to learn it before you mess with mains voltage.

I did a Google search of the relay that you referenced, I must say in my opinion this relay is totally unsuitable for 120V AC. In fact I would be hesitant to use it on anything more than 24V DC. You need to look at the underside of the board. There should be as much separation between the relay contact traces as possible. There should be a cutout between the pole connection of the relay and all low-voltage components/traces. This includes the ground plane. Also for high current applications, the traces for the relay contacts should be on both sides of the relay board. Although I have seen worse boards, this one is extremely bad. Never assume that because the relay is marked at a high voltage/current, that the board will take that same voltage/current and still be safe. you need to do some research, and make sure that you get a board that is safe for your application.

promacjoe2: I did a Google search of the relay that you referenced, I must say in my opinion this relay is totally unsuitable for 120V AC. In fact I would be hesitant to use it on anything more than 24V DC. You need to look at the underside of the board. There should be as much separation between the relay contact traces as possible. There should be a cutout between the pole connection of the relay and all low-voltage components/traces. This includes the ground plane. Also for high current applications, the traces for the relay contacts should be on both sides of the relay board. Although I have seen worse boards, this one is extremely bad. Never assume that because the relay is marked at a high voltage/current, that the board will take that same voltage/current and still be safe. you need to do some research, and make sure that you get a board that is safe for your application.

Makes sense. Thanks for the tip on looking at the bottom of the board. I wasn't aware of that.

I think I'd be best to shell the $30 and get an SSR designed for this application. I'm thinking an element like this. Looks sufficient to handle the house mains.

For reference I'm making a fire prevention system for my 3D printer so I'm comfortable printing unattended. The idea is using a combination of temperature sensors and thermistors/thermocouplers inside the "electrical cabinet" (actually inside machine housing) and mounted on the hot end itself. Most typical failure modes (for a machine fire) are bad connectors / connection on the electronics and a loose / bad thermistor on the hot end. Set some thresholds for the monitoring sensors and if a particular element or the electrical cabinet in general starts to heat up, kill the power at the source with the relay before it gets anywhere nearly combustion temps.

Caution with SSR's they require a minimum current to work. Seems to be in the order of 150 ma.

I don't know your temperature goal but you might consider this (as a standalone or added protection).

http://www.ebay.com/itm/4PCS-KSD301-60C-140F-NC-Thermostat-Temperature-Thermal-Control-Switch-/232016056057?hash=item36053c0ef9:g:cqAAAOSw32lYuMEH

They are designed exactly for application like yours (i.e. over temperature protection)

As promacjoe2 suggested. Keep AC as far away from your other circuits as possible. If you find the SSR works, it should be in an electrical box with the control wires coming out of a different hole from any of the AC wires. You wouldn't want to toast your setup if lightning strikes near by.

Another question:

How is the printer powered? Could there be less lethal ways to power it down?

Good luck

JohnRob