Relay Grounding Issue

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=143416
Printed Date: May 04, 2024 at 9:09 AM

Topic: Relay Grounding Issue

Posted By: ryanschofield10
Subject: Relay Grounding Issue
Date Posted: July 31, 2017 at 7:35 AM

I am having an issue with an external relay (Tyco V23234-C1001-X005) that I am adding to an automotive application. I am using a user defined output (ground) from my ECU to control a relay that powers a pump. When the ground from the ECU (terminal 85) is activated the relay should power terminal 87 to power the pump. The problem is when the 12V switched power is attached to terminal 86 on the relay the ground from the ECU at position 85 “loses” its ground thus making the relay inoperable. As soon as the 12V switched power if removed from the relay the ground is then present. I have tried multiple relays (with an internal diode) all with the same result. Terminal 30 on the relay is a fused 12V from the battery and terminal 87 is the connection to the pump.

I have measured the voltage on the relay with a multi-meter on the 12V switched (terminal 86) using the ECU output ground, while activated (terminal 85) this yields 0.3 V (not activating the relay) vs. 13.8 V when I use a alternative chassis ground (activates the relay properly). I have included my wiring diagram for reference. Thanks in advance

Ryan

Replies:

Posted By: ryanschofield10
Date Posted: July 31, 2017 at 7:42 AM

Forgot to attached the wiring diagram, here it is.

Posted By: the12volt
Date Posted: July 31, 2017 at 7:54 AM

When is the output from the ECU supposed to be active? When the output is supposed to active, does it show continuity to ground when not connected to the relay?

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Posted By: ryanschofield10
Date Posted: July 31, 2017 at 8:05 AM

The output from the ECU should be active whenever the water/methanol switch is active (that is the input that activates the ground). The switch will always be on unless I run out of the water/methanol mixture. So for arguments sake lets say the ECU will always be outputting a ground. I have confirmed in the ECU software that it is indeed properly outputting the ground. Yes, when not connected to the relay it grounds properly...

Posted By: the12volt
Date Posted: July 31, 2017 at 8:10 AM

Sounds like the ECU output is not strong enough to activate the coil of the relay. Since it should be on anytime the switch is on, I would use the output of the switch to activate the coil of the relay.

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Posted By: ryanschofield10
Date Posted: July 31, 2017 at 8:14 AM

That's exactly what I was thought the problem was also. However, I can not bypass the ECU because the ECU needs to know when it is activated to make corrections to the fuel and ignition timing. Do they make relays that use a lower output to activate?

Posted By: the12volt
Date Posted: July 31, 2017 at 8:45 AM

Yes, you may be able to use a 6V, 5V, or 3V relay, though I'd probably use a PNP transistor to provide 12V+ to the coil of the existing relay, then ground the other side of the coil. You can find some PNP transistors here and search for relays too.

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Posted By: i am an idiot
Date Posted: July 31, 2017 at 9:02 PM

Try this

Left leg of transistor to ground output of the ECU. Right leg to 85 of the relay.
Ground the tab or the center leg.