How many watts is safe?

I just purchased a silicone heat pad for my makerfarm i3 with Ramps 1.4. The pad is 12V 200watts. If I plug this into the ramps will it blow? Or will it just draw as much as the Ramps puts out, which is probably less than 200 watts.

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Antslake
I just purchased a silicone heat pad for my makerfarm i3 with Ramps 1.4. The pad is 12V 200watts. If I plug this into the ramps will it blow? Or will it just draw as much as the Ramps puts out, which is probably less than 200 watts.

There is a PTC resettable fuse on the RAMPS specifically for the heatbed and it is specified for 10~11 A. 12V 200W means something like 15~16A. So definitely it will trigger the fuse.

Also the RAMPS is not designed for currents above 10~11A so I definitely advise you to NOT use this silicon pad connected directly to the RAMPS. If you still want to use it, add an SSR to the circuit.

It's not the power supply that determines the amount of current flowing, it's the load. 200W at 12V = 200/12 = 16.66 amps. As AndrewBCN correctly states, this will trip the PTC fuse. It also may exceed the current carrying capacity of the RAMPS traces (which is why the fuse limited to what it is). Also, you don't give specs on your PSU, but this could also exceed its maximum too, which is something you'd want to avoid.

Using an SSR is good advice. Your RAMPS triggers the SSR at a much lower current draw, and the SSR turns the heated bed on and off. Just make sure the SSR is appropriately rated.

I figured it would over draw, just wasn't sure if the ramps was current limiting.
I am using a pyramid 20amp power supply. I can dedicate it for just the heat bed and use a 12amp for the rest.

Any good places to get a SSR relay? I see a lot of difference in pricing.

Thanks for the help.