basic switch/relay?

I have two circuits, one is 48 V and one is 12 V. they are both DC. I need to have a switch that turns on both of them at the same time, while still keeping the two circuits isolated from each other. I had a rather complicated circuit drawn out with two relays in it. The only problem is that it would be sending high current through the part of the relay that is supposed to be low current. I was looking at the switches on radioshack.com. they use relay jargon (DPDT, SPST, etc) but they don't really explain how they work. some of the switches have 4 prongs on the bottom. Do they make a switch that can turn on and off two seperate circuits? And do they make anything that can handle 48 V and about 30 amps?
Thanks for any help you can provide.

Use a DTSP Switch.


I wouldn't put 48v 30A through a switch thats what the relay is for. I will work on a diagram. You should be able to use one switch to control two relays that will turn on you equipment.

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Just because you've done something for a long time doesn't mean you're any good at it.
Cable Ties Rock!

You can actualy use a SPST switch  (the one with two posts ).

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Just because you've done something for a long time doesn't mean you're any good at it.
Cable Ties Rock!

thanks for the diagram. i think that would work.
two questions:

1) i know that relays consume a very small amount of power. but it seems almost like when that switch is closed that there would be a short circuit between the 12V battery (going through the switch) to the chassis ground. Should there be an LED or something in there?

2). The 12 V is running a ventilation fan (in a car). it has its own switch, which has 4 settings. settings 1-3 use resistors (1 is highest ohm, 3 is lowest) to control the speed of the fan. setting 4 has no resistor. when the 48V device is on, i want to have the fan on full power (Setting 4), which would mean no resistor in the circuit. so basically there will be two way to turn on the fan, either by the SPST toggle switch, or the rotary fan switch.
Now if the SPST toggle switch is closed, and the rotary fan switch is on a setting 1-3, this would be like having the fan motor in parallel with the resistor on the fan switch. And if its a low resistance resistor, as compared to the fan motor, it would get too much current and burn up. Is this correct?

answers:
1) the relay coil is the load of that circuit. It consumes 80 - 150 mA. It will only take the amps that it needs. Just go straight to Chassis ground

2)I dont quite understand your question, but the fan power is running through the relay ( 30 - 87) It is the same as if you were directly connecting power from 48v to the fan power input. If the fan has different settings built into it with the rotary switch, it should not affect how the power is supplied to the fan.

Hope this helps.   What kind of install are you using fans for? And where are you getting 48 volts? Just curious..   

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Just because you've done something for a long time doesn't mean you're any good at it.
Cable Ties Rock!

Check this out , for errors. 

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Just because you've done something for a long time doesn't mean you're any good at it.
Cable Ties Rock!

I could n't fit it on the IM....

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Just because you've done something for a long time doesn't mean you're any good at it.
Cable Ties Rock!