I'm looking for relay boards that can handle 20V/20A DC easily and can be switched with the raspberry pi. I have been googling for days but haven't found anything ready made for DC, only for AC. I want to turn on a cheap tire inflator (12V and 12Amps) with the pi and the power for the inflator comes from a power adaptor. The relays I have found are mostly found in cars and I'm not experienced enough to come up with my own solution as these types of relays require more than 5V to be switched. Can you help or provide a diagram?
if you want to high current capacity Relay for control device you can use Solid state relay
refer this link for SSR Solid State Relay
I can't imagine why you'd have to 'Google for days', but I don't think Google is the best way to find a relay with a particular set of specifications. I'd suggest you use the screens and filters available on the websites of some of the big electronic distributors. I'd probably try Mouser first.
You will note that this relay can not be driven directly from your RPi GPIO pin. You will need a transistor in between your RPi and the relay coil to make this work; i.e. you will drive the transistor directly from the RPi GPIO, and switch the relay coil with the transistor. This is not difficult, and this is the approach I'd take if it were my project. Following is a schematic from another answer that you may find useful:
If you decide to use a transistor to interface your RPi to an electro-mechanical relay, please edit your question to reflect that & we'll help further.