Thread: 6 volt relays
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Old 12-20-2011, 04:22 PM   #13
Old Henry
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Default Re: 6 volt relays

Quote:
Originally Posted by Joe KCMO View Post
I am interested in your statement. With a positive ground horn relay you ground the circuit and the relay closes , the power comes directly from the negative power source to what ever. So what if it shares the negative. If the relay operates a horn why would not operate something else. Not arguing, trying to learn.
Thanks for your question.

When I first saw the inquiry about a 6 volt relay I had the same thought, "Why not a horn relay?" and was about to post such until I thought about it further.

In the picture and diagram below you'll note that the horn relay has just three connections. One (marked B for battery) is to apply current to the relay which is attached to both the primary and secondary circuits inside. A second contact (marked S for switch) attaches to the wire that goes through the horn button to ground. The third connection (marked H for horn) goes to the horn. When the primary circuit is grounded it completes the circuit that energize the electromagnet and closes the secondary circuit which then powers the horn. That's fine if that's all you want to do - close a switch to a larger load by closing a switch to ground. That's exactly the same as the starter solenoid. But, you can't switch on a load through that kind of relay by turning on the ignition switch. That is because such function requires two seperate isolated circuits through the relay as illustrated and explained below.





The usual use for a relay is to use a low current such as from the ignition switch to close the relay and power a higher current need such as a fuel pump, heater fan, stereo, etc. As you can see in the pictures and schematic below, for it to work like that you need 4 connections. One (85) that takes low current from the primary source such as the ignition switch, a second one (86) to ground for that primary circuit, a third (30) that takes the higher current from the battery, and the fourth (87) that sends the higher current to its higher need.






The only way a horn relay could be made to work like that would be by hooking it up "backwards." You would use the primary connection that would normally come from the battery as a ground. Then run your primary source from the ignition switch to the ground connection on the relay (that would normally go to the horn button.) The accessory to be switched by the secondary circuit would have to have the current go directly to it first then through a ground wire to the horn connection of the relay so that when it was energized it would be grounded and work. It could work like that but you'd have to insulate the accessory from ground and complete the ground circuit through the relay.

Better to just get a standard 4 connection relay for switching high current with low current such as the one I posted in #5 also shown above with the same schematic on the side of that relay as is shown above or a headlight relay that works exactly as described above.
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Last edited by Old Henry; 12-21-2011 at 12:17 AM.
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