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12 volt relay to start a 24 volt motor

I need an on/off switch to start a 24 volt 42 amp trolling motor. i assume that means using a 12 volt relay to do this. Or, I can just plug / unplut it. I want to put the switch in a wired remote control box with as little wiring as possible leading to the box. Where do I find a 12 volt relay to powere the 24 vdc 42 amp power circuit?
 
You could use a couple of 12V automotive relays with coils in series and output contacts in parallel.

Remember to put a flywheel diode across the relay coil and also the motor to protect the contacts during switch off.
 
Paralleling relay contacts isn't a good idea as you can't guarantee them both pulling in at the same time - one will ALWAYS take a greater load, even if only for a very brief period, and wear the contacts in no time.
 
A relay with 12V coil is perfectly useable to power a 24V trolling motor. Just power the relay coil with 12V, which may be tapping only to one 12V battery.
 
Paralleling relay contacts isn't a good idea as you can't guarantee them both pulling in at the same time - one will ALWAYS take a greater load, even if only for a very brief period, and wear the contacts in no time.
I do not think that much heat will be generated in a millisecond or so. Contacts wear due to the generation of an arc at switch off, the diodes will suppress this.

The automotive relays seem to be rated at 40A so a couple should be able to pass 42A without trouble. 12V automotive relays are readily available from car dealers and scrap yards.
 
Why use two when one will do? The 24v relay isn't 'rare' so use the right part for the job - is my motto.
The reason is that 12V relays are common. I can take a walk over the fields and Rich will give me a couple free, he also lets me use his compressor to blow dust and spiders out of old radios. If I speak to him nicely, he would bring me the relays when he comes down to his mum's for lunch.

24V relays are used on large vehicles but I would need to travel many miles to get to a service depot or order and wait for the post. 24V 100A relays are probably quite common but I have not looked into this.
 
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