Newbe need some relay
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=144166
Printed Date: April 29, 2024 at 1:07 PM
Topic: Newbe need some relay
Posted By: windsor 393
Subject: Newbe need some relay
Date Posted: February 19, 2018 at 2:31 AM
Hi yall I'm in the process of wiring my efi up on my race car and I have a few question, right now I am wiring the outputs of my efi witch will trigger a relay to turn on say the fan or water pump now I am also going to have a 12v switch to bypass the ecu and turn on the fan or water pump manually. The ecu wire will be on 86 tab to act as a trigger. My biggest question is if I'm using a resistor type relay to prevent any fly back to the ecu would I also need a diode in line with the ecu trigger wire to prevent any back feeding when I use the switch to bypass the relay Here is a drawing of how I am thinking of wiring it up thank you for the help
Replies:
Posted By: eguru
Date Posted: February 19, 2018 at 9:33 AM
In order to suppress back emf from the relay coil you would need to have a Schottky diode across the coil. The series connected diode is not required.
Posted By: windsor 393
Date Posted: February 19, 2018 at 10:57 AM
Ok so a resistor type coil won't work in my application and it would be a diode protected coil ? I'm not sure what a schottyk coil is
Posted By: wirewise
Date Posted: February 19, 2018 at 11:29 AM
A 1N4001/L diode across the coil of your SPDT relay should be fine. https://www.the12volt.com/diodes/diodes.asp------------- ~wirewise~
Verify all wiring with your meter before making any connections!
Posted By: windsor 393
Date Posted: February 19, 2018 at 12:19 PM
Thanks wise now would the diode protected relays wire the same as how I have it in the drawing? And do you have a good source on where I could purchase these at?
Posted By: i am an idiot
Date Posted: February 19, 2018 at 12:29 PM
You do still need the diode on the line coming from the ecu, and you want the switch connected to 86 also. Unless you are planning to use a 40 amp switch.
Posted By: windsor 393
Date Posted: February 19, 2018 at 12:44 PM
If your referring to bypass switch I have that hooked up to a fuse and relay
Posted By: windsor 393
Date Posted: February 19, 2018 at 1:53 PM
If I put a diode in line between the ecu output and and pin 36 wouldn't that be pretty much doing the same thing as as the diode between 85 and 86 just on the out side of the relay
Posted By: i am an idiot
Date Posted: February 19, 2018 at 2:21 PM
The diode across 85 and 86 is needed to protect the ecu from the backlash created when the relay disengages.
Is there a second relay that is not pictured?
Posted By: windsor 393
Date Posted: February 19, 2018 at 2:45 PM
Yes the bypass switch to by pass the ecu relay is also wired in with a relay as well
Posted By: i am an idiot
Date Posted: February 20, 2018 at 11:34 AM
You will not need the diode in line with the ecu and the relay. You should still put the diode across 85 and 86.
Posted By: eguru
Date Posted: February 20, 2018 at 8:52 PM
wirewise wrote:
A 1N4001/L diode across the coil of your SPDT relay should be fine. https://www.the12volt.com/diodes/diodes.asp
Standard rectifiers like the 1N4001 are too slow to properly suppress back emf from the relay coil. A high-speed rectifier (Schottky) like 1N5819 is required. The rectifier needs to be rated for at least 3X the coil voltage and with a current rating at least equal to the coil current.
Posted By: eguru
Date Posted: February 21, 2018 at 8:25 AM
To protect against the back emf from the relay coil you will need a diode that switches faster than the 1N4001 as the peak amplitude of the voltage spike occurs in the first few microseconds after the coil is de-energized. A Schottky diode like the 1N5819 would be a good choice.
Whoops sorry about the double post. I don't know how to delete it.
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