Basic relay question
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Post Fiend
Joined: Sep 2000
Posts: 8,238
Likes: 3
From: Oregon
Basic relay question
Yet another ignorant electrical question 
Overcoming my fear of my electrical system I've been cleaning up my trucks rat nest and have now wired in an auxillary fuse box. I plan on wiring a bosch 87 relay into it so that juice is cut to the auxillary stuff when the trucks shut off. My question: These relays are rated at 30 amps......is that the max draw that can pass through the relay or the max amp that can hit the line which opens/closes the circuit? I've got @ 50 amps of goodies drawing juice through this fuse box (amplifier, fuel pump, KC lights, etc) but the line which would energize the relay would of course bear only 12.5-14.5 volts. Now if I can only figure out volts vs. amps....
Overcoming my fear of my electrical system I've been cleaning up my trucks rat nest and have now wired in an auxillary fuse box. I plan on wiring a bosch 87 relay into it so that juice is cut to the auxillary stuff when the trucks shut off. My question: These relays are rated at 30 amps......is that the max draw that can pass through the relay or the max amp that can hit the line which opens/closes the circuit? I've got @ 50 amps of goodies drawing juice through this fuse box (amplifier, fuel pump, KC lights, etc) but the line which would energize the relay would of course bear only 12.5-14.5 volts. Now if I can only figure out volts vs. amps....
Elder User
Joined: Oct 2000
Posts: 642
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From: Nebraska
Basic relay question
Ok, the 30a rating is how much current it can handle through the contacts. (how much you are switching).
Higher ratings are available.
The coil is rated at 12 volts (nominal) and won't pull much current)
Think of voltage and current as water through a hose:
Current is the amount of water that flows through the hose.
Voltage is how much pressure you are using to push the water through the hose.
The Hose is resistance, the bigger the hose, the more water (current) can flow through it.
Higher ratings are available.
The coil is rated at 12 volts (nominal) and won't pull much current)
Think of voltage and current as water through a hose:
Current is the amount of water that flows through the hose.
Voltage is how much pressure you are using to push the water through the hose.
The Hose is resistance, the bigger the hose, the more water (current) can flow through it.
Moderator
Joined: Jan 2001
Posts: 56,980
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From: Virginia
Basic relay question
If you have a common cheap 30 amp relay, and can't find one reasonably priced with more amperage, you could split your auxiliary fuse box in two, and use two 30 amp relays to give you 60 amps. Just make sure you have a heavy enough wire feeding this fuse box. And hopefully it's not too far away from the battery. I believe I would use at least a #6 guage wire for 50-60 amps. Or run two #10 guage wires side by side to feed two 30 amp relays into the split fuse box.
Thread Starter
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Post Fiend
Joined: Sep 2000
Posts: 8,238
Likes: 3
From: Oregon
Basic relay question
Thanks for the input guys, I suspected as much but wasn't sure. I remember seeing a real heavy duty relay in JC so I'll just go for that. I've got 8g running to the auxillary box, but its not to far from the battery. Thanks again!
