fuel pump 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=130412
Printed Date: April 26, 2024 at 6:00 PM
Topic: fuel pump relay?
Posted By: hotstix
Subject: fuel pump relay?
Date Posted: January 28, 2012 at 3:25 AM
Hello all, Im a super noob here, so be kind.
Im installing an aftermrket fuel system in my car and have an issue with wiring.
Basically I have a terminal (switch) on the pump controller that needs a 12+v signal to turn on, and 0 to turn off.
My problem is the input signal I want to use for the controller is constantly putting out between 9v (low load) and 14v (high load).
So my question is: Is there a relay configuration that I can use to take that 9-14V wire and make it an on/off swtich that either is putting out 12+ volts or nothing?
Thanks.
Replies:
Posted By: i am an idiot
Date Posted: January 28, 2012 at 3:46 AM
Yes, a standard Tyco Single Pole Double Throw relay will do what you need. Ground terminal 85, connect your 9 to 14 volt wire to terminal 86. Terminal 87 should be connected to the battery via a fuse. Terminal 30 will power your new fuel pump.
Posted By: howie ll
Date Posted: January 28, 2012 at 10:22 AM
Craig on your configuration wouldn't you need 87a to be connected to ground?
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: howie ll
Date Posted: January 28, 2012 at 10:25 AM
It's just the poster's use of "0".
Poster, do you mean 0 volts as in "open circuit", i.e. nothing, or do you mean "0" as in ground?
I'm assuming the first case is correct and therefore so is Craig.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: hotstix
Date Posted: January 28, 2012 at 11:56 AM
howie ll wrote:
It's just the poster's use of "0".
Poster, do you mean 0 volts as in "open circuit", i.e. nothing, or do you mean "0" as in ground?
I'm assuming the first case is correct and therefore so is Craig.
Sorry for the confusion. Yes, by "0" I am referring to an open circuit.
If I wire the relay according to the first post, what will trigger the relay to close and output the 12v signal? The variable voltage input wire reaching a value ofe 12 or higher?
Posted By: howie ll
Date Posted: January 28, 2012 at 1:08 PM
Yes, keep to Mr. Idiot's answer. Ave 12V+ Bosch/Tyco relay, the coil will act when the the voltage reaches about 7.5V+.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: hotstix
Date Posted: January 28, 2012 at 2:42 PM
howie ll wrote:
Yes, keep to Mr. Idiot's answer. Ave 12V+ Bosch/Tyco relay, the coil will act when the the voltage reaches about 7.5V+.
But the input voltage to the relay will always be 9v minimum. So does that mean the coil will ne constantly triggered?
Posted By: howie ll
Date Posted: January 28, 2012 at 6:30 PM
Maybe a 1K resistor on the trigger wire or sub a 24volt relay just to see.
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: oldspark
Date Posted: January 28, 2012 at 6:39 PM
Or a few diodes to predictably drop the voltage.
Maybe a zenor diode if a high drop is needed.
Posted By: hotstix
Date Posted: January 28, 2012 at 8:04 PM
At what voltage will the coil actuate on a 24v relay?
Posted By: howie ll
Date Posted: January 29, 2012 at 12:39 AM
9-12volts? Peter, explain this one please.
Could it be the dreaded oil pressure switch scenario?
-------------
Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
Posted By: oldspark
Date Posted: January 30, 2012 at 1:35 AM
howie ll wrote:
... the dreaded oil pressure switch scenario?
You mean... no!!... not people that use oil-pressure to control f..ff.fff.fuelpumps?  
Thou art cruel!
But no, I'm merely responding. Earlier I was thinking some high-impedance voltage may be being measured (ie, the 9V) - not that charging system variation has been discounted - but I thought KIS. Or, not yet... at least.
And using a relay-coil's pull-in and drop-out behavior as a voltage window sensor has worked often for many. (IE - drop the voltage. A resistor may be ok, but diodes have a essentially a constant voltage drop that is more current independent.)
In some cases that easier than diatribe.
Besides, if the 9V output becomes a "normal" 0 (off or low or 0V), then just remove the add-ons above.
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