Relay Circuit to Switch on Higher Amperage Project

Thread Starter


Joined Apr 15, 2017
Hello. I've never really worked with relays before, so I was hoping for some guidance.
My project is a battery powered robot with a single motor that pulls about 5 or 6 amps. I want to use a power switch that is very small and rated for less than an amp.

The top image is what I'm working with now. 12v Lipo Battery which runs through a switch which goes into my microcontroller/mosfets/etc.
Can I switch this out for something like the bottom image? Where the batteries are hooked up directly to the switch AND relay. SO I can just hit the low-rated power switch and the relay completes the circuit? Where even if the motor is pulling 6 amps and the switch is only rated for say 500mah, it wont get fried?

If this is correct, can you recommend the most compact solution for the relay? One thing I lack is space for a large component in terms of height, which is what I see a lot of relays looking like. I can do long and flat. But Tall is tough.

Any help is very appreciated!



Joined Jan 15, 2015
Will a common off the shelf automotive relay fit? That would be about 1 cubic inch. Any auto parts store has everything you need and most relays have a mounting tab with a screw hole. They also can easily handle 30 amps DC. The pins are standardized with a numbering system.



Joined Jan 15, 2015
Pretty close to as drawn. Here is what you would have:

auto Relay.png

So pin 85 goes to ground or common. pin 86 goes to the light switch a normally open switch which then connects to 12 VSC power (Battery +. terminal 87 also goes to battery + and terminal 30 to your loads.The terminals are 1/4" spade lugs and yhe parts store will have mating connectors. Not much to it,



Joined Jul 18, 2013
If you have an automotive wrecker in your area, you can get a handful for a couple of $$'s usually.
We have a strip-your-own-parts one here which is nice.