Wiring in a relay?

[snowracer69]

I want to wire in a relay from a switch on my new console panel to replace the switch for my fuel transfer pump. I bought a 5-prong 30 amp (I believe) relay from Checkers, but am unsure of how to wire it in. A buddy showed me what he thought was the correct way, but he wasn't 100%, so I didn't trust him. The way he said to do it was: 12v in on top prong, 12 v out on bottom prong, left prong is grounded, right prong is switch. This doesn't make sense to me, as the switch should require two wires to go to the relay, correct?



Here are pics of the relay and the schematic on the side of the relay, that I don't understand (symbols I've never seen in electrical engineering classes... go figure).



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Thanks for any help. Josh

 

[Thomas]

Bosch Relay is the standard.

 

[AggieJustin]

Pins 85 and 86 drive the relay coil. One of these should be connected to ground, the other connected to the output of your switch.



Pin 30 is supply from the battery.



Pin 87 and 87A are the pins for the load toward the pump. This is a changeover relay, since the power comes out of one of the two pins depending on whether or not the relay is energized.



Since you want the pump to run only when the switch is energized, you should wire the pump into pin 87. 87A will have power whenever the switch is off.



Edit: Or, just look at the diagrams in Thomas' link. I'll have to bookmark those, I couldn't find any when I needed them.

 

[DavidC]

85 & 86 are relay coil wires. One will go to ground the other from switch (does not matter which one). 30 will be your 12V hot. I cannot make out the top right number which will be your Transfer pump. 87 will have 12V when switsh is off. All schematics on devices are given as shelf condition (not energized).



Dave

 

[snowracer69]

Ok, for future reference for anybody else who needs to know this and knows how to use the search function:



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I'm going to use the second one, although I don't think I'll need to wire the 12v+ into both the 30 and 86 terminals, right?



Here's my plan:



Ground 86, switch wire into 85. 12v+ into 30 and output to fuel pump out of 87 so it comes on when switch is turned on...



Make sense? Will that work correctly? And it won't hurt anything to not have anything wired to 87A, will it?



Josh



EDIT: Ok, looking at it again, I DO NEED to wire 12v+ into both 30 and 86 so that the coil will energize across 86 and 85. Am I right now?

 

[KLockliear]

Lemme see if I can make it a little simpler (maybe not ).



You've got it straight up there. For ease of reading, look at it this way: A circuit requires a pos and a gnd. When a circuit is complete between 85 and 86 (regardless of which one gets + and which one gets - ), the relay will close the contact between 30 and 87 (regardless of if that's + or - on 30 or 87; all it does is close the contact).



Does that help at all?

 

[snowracer69]

Yep, and that's what I finally figured out in my head, which is why I finally decided one way or another I had to have power going across the switch.



I got her in and it works like a charm. So far I like my new console w/ the gauges and switches, but I haven't got to race anyone yet to see how hard it is to see the gauges and the road at the same time..... only time will tell if I'm gonna keep it.



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Josh

 

[Cummins4Life]

Turned out nice!

 

[NPloysa]

How many amps is it safe to run off a switch and inline fuse?



I mean how do I know if a relay is needed? Say for an air compressor or solenoid valves for horns?



Thanks, Nick

 

[snowracer69]

Nick,



My guess would be to figure out what the air compressor or solenoid pulls for amps, and then either find a switch/fuse that can handle that much load, or run it as a relayed setup.



The switch I'm using to run the relay is rated at 6 amps, and I've got a 5 amp inline fuse for the transfer pump, so in theory I could have just used the switch, but I really wanted the experience of wiring a relay in, as well as not running 12 gauge wiring up into my console.



Not sure I helped, but that's the way I go about figuring out how to run stuff.



Josh

 

[JR2]

The two air horn setups I have done did not use a relay for the solonoid, I just spliced into the current horn wires and hooked up the solonoid to them.



The air compressor needs to run from a relay. I used a relay and had the pressure switch for the air tank as the switch on one system but that left the compressor able to run when the truck was turned off. This cost me a compressor when the tank got some ice in it and plugged the switch... . The next set of horns I ran a dual relay set up. The first relay is on with ignition power and it send power to the second relay that triggers when the pressure switch calls for air. The realys I used where 15 amp which is way too big, but they are cheap and available. I protected the system with a inline fuse. The fuse needs to be rated for what the compressor will draw plus a little bit. Most electric motors (used in compressors) have a higher draw when they start then it drops off to a somewhat constant draw.



JR2

 

[snowracer69]

Originally posted by JR2

Most electric motors (used in compressors) have a higher draw when they start then it drops off to a somewhat constant draw.



JR2

which is why you just buy a slow-blow fuse and call it good... they allow for that extra amperage needed at startup... they're rated to allow x-many amps for y-time, then after that they cut back to a smaller amperage... .



Not saying that I have ever used them either, but that's the way the theory works... heck, I just put fuses in and go with bigger and bigger ones till they quit blowing... hahahaha... that's a good system, right?