relay for turn on lead
Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=1655
Printed Date: July 23, 2025 at 4:45 PM
Topic: relay for turn on lead
Posted By: DjRDifacs
Subject: relay for turn on lead
Date Posted: July 02, 2002 at 1:03 AM
i wanna hook up a fan for my amp. would it be possible to use a computer fan? how would i wire it up using a relay? thanks russ
Replies:
Posted By: Velocity Motors
Date Posted: July 02, 2002 at 7:46 AM
Hey Russ, as long as the fan is rated for a 12 volt power supply, it will work. You need to hook up a relay like this: - 87 : Constant 12 volts
- 86 : GROUND
- 30 : To (+) wire on FAN
- 85 : Remote turn on lead ( + ) input wire
- 87a: NOT USED
------------- Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: mobiletoys2002
Date Posted: July 02, 2002 at 7:23 PM
just wanted to point out that jeff must have misstyped. pin 85 will go to your remote turn on lead ...
Posted By: Velocity Motors
Date Posted: July 02, 2002 at 9:19 PM
What !! Your wrong , look again  . ( JJ ) Sorry about that, I corrected the error. It was early when I did that, that's my excuse  ------------- Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: DjRDifacs
Date Posted: July 02, 2002 at 10:03 PM
thanks jeff .....another question, the fuse rating on the fan is 0.87amps, wut fuse rating should i use for that? and should i fuse the wire going to the amp? wut fuse rating should i use for the amp??
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Posted By: Velocity Motors
Date Posted: July 03, 2002 at 5:11 AM
If you fuse the fan trigger wire at 5 amps, that should be ample. What is the output ( RMS & peak ) for the amp that you are using ? Most of the time 80 amps is sufficient for anything under 1000 watts. Let us know and someone will be able to help you out. ------------- Jeff
Velocity Custom Home Theater
Mobile Audio/Video Specialist
Morden, Manitoba CANADA
Posted By: DjRDifacs
Date Posted: July 03, 2002 at 9:15 AM
the output is 350W RMS @ 4ohms, 500 @ 2 ohms mono ....600 peak .....i was talking about the remote turn on lead from the relay to the amp.
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Posted By: mobiletoys2002
Date Posted: July 03, 2002 at 9:39 AM
If your amp was running at 500 watts at 2ohms you will be drawing about 40 amps,when you are running that amp at 350 watts @4 ohms you will be drawing about 28 amps so if you were to use a 60 amp fuse you will be fine. 
Posted By: mobiletoys2002
Date Posted: July 03, 2002 at 9:50 AM
but taking into consideration that you may have more than one amp the total fuse size at the battery may be more,but the fuse size at the distribution block for that amp would be the figures i told you in the above post . That is probably your most current drawing amp. generally you add up the fuse ratings to get the total draw for your main fuse at the battery. And like velocity said a 80 amp fuse will be good for amps at 1000 watts but when i do systems i dont like to over do the fuse when i know im not drawing that much current so i will use the least posible fuse value that i can without causing a problem.hope all goes well also if you plan on upgrading at a later time you should maybe over do the fuse value a bit to compensate for more amps.
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