Wiring a Solid State Relay to Ramps

[printbus]

Heat beds typically aren't really polarized, so any + and - reference doesn't matter. The only situation I am aware of where it does is if the heat bed is equipped with an LED to indicate when power is on.

With RAMPS, people normally wire the SSR control inputs to the D8 output that would otherwise power the heat bed. For the D8 output to work, you need 12V connected to the 11-amp power input.

I think most people get an SSR off Amazon. You can search the Makerfarm subforum for "solid state relay" for some threads that provide links. The general comment I'd have is that going higher in a current rating is better, since the higher current relays will typically also have a lower on-resistance. This maximizes the amount of power going to your heat bed and minimizes the power lost as heat in the SSR. You also want to make sure the SSR is for DC loads, not AC. Unlike mechanical relays, that makes a difference for SSRs.

[PyramidDave]

Heat beds typically aren't really polarized, so any + and - reference doesn't matter. The only situation I am aware of where it does is if the heat bed is equipped with an LED to indicate when power is on.

With RAMPS, people normally wire the SSR control inputs to the D8 output that would otherwise power the heat bed. For the D8 output to work, you need 12V connected to the 11-amp power input.

I think most people get an SSR off Amazon. You can search the Makerfarm subforum for "solid state relay" for some threads that provide links. The general comment I'd have is that going higher in a current rating is better, since the higher current relays will typically also have a lower on-resistance. This maximizes the amount of power going to your heat bed and minimizes the power lost as heat in the SSR. You also want to make sure the SSR is for DC loads, not AC. Unlike mechanical relays, that makes a difference for SSRs.

Thanks for the info printbus. I will do some research before deciding which one to buy.

[longjohn119]

. You also want to make sure the SSR is for DC loads, not AC. Unlike mechanical relays, that makes a difference for SSRs.

AC SSRs use triacs and DC SSRs uses MOSFETs .... One advantage of the higher current rating SSRs is if you get one rated at 100A you can ditch the heatsink for a 15A-20A heater. Frankly once you approach 20A@ 12V DC it's time to raise the voltage to 24V or go to an AC heater. Things just get too lossy, connections more problematic, etc. It's a big part of the reason I went with a 10" rather than the 12". I have my doubts about the longevity of that 12" pcb heater at 12V. Look at all the trouble they go to for the 12V high amp connections on a desktop computer with 4 parallel 12V lines to the motherboard and 2 or more in parallel to a video card