Mugen Hamster

Foremost, this an ECU fuel cutoff switch question, not a fuel-pump fuel cutoff switch question. Thanks!


Hi guys. I've been reading a lot of posts dealing with connecting relays to make a fuel-cutoff switch for the fuel pump. Im wondering if a relay should be used in order to make a fuel cutoff switch at the ECU under the passenger side kick panel.

Should a 15A switch still be used even if the relay is hooked up to the ecu switch? (im thinking yes). The available car security relay is a 12V 30 A relay.

I guess im a little confused about if i should use the 15A switch AND the 30A relay, just a 15A switch, or just the 30A relay and whatever switch i buy.

Also, if using the relay, does a 1 A diode still need to be connected between terminals 85 & 86?



Please Note: the above diagram is for a fuel cutoff switch AND an ignition kill, i will just be wiring half of that

Thanks!

special_edition

Why is it necessary to run relay and diode? Can you just slice a on/off switch in the ground wire and call it a day?

Mugen Hamster

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by special_edition &raquo;</TD></TR><TR><TD CLASS="quote">Why is it necessary to run relay and diode? Can you just slice a on/off switch in the ground wire and call it a day?</TD></TR></TABLE>

Using a relay is "safer" since it will prevent a generic 15A switch from burning out incase it ever sees an unexpected increase in current. The diode acts a "fail-safe" so that if too much voltage gets passed through the relay, the diode will turn on and prevent the load, in this case the switch, from burning out or melting. It's also more professional and allows for any extra security devices to be wired later on.

vteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AntiRice Superstar &raquo;</TD></TR><TR><TD CLASS="quote">Foremost, this an ECU fuel cutoff switch question, not a fuel-pump fuel cutoff switch question. Thanks!


Thanks!</TD></TR></TABLE>

Sorry, but what is the difference

It looks good. Latching relay setup with diodes added. I don't see the point of the diodes. If your fuel pump pulled 30 amps and blew your relays, then you need a new fuel pump also. The switch will only ever see enough current to trip the relays( a few hundred milliamps).

It has been a long time since physics 101.

Can you please explain how the 1 amp diode is going to protect the 30 amp relay anyway.

BTW, nice pic.

Quad-Damag

Great Layer, Can't go wrong, more layer = good

I would look into CX Boot, product the car boot, looks nice, can't tow ur ****

HondaDriver4Life

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AntiRice Superstar &raquo;</TD></TR><TR><TD CLASS="quote">Foremost, this an ECU fuel cutoff switch question, not a fuel-pump fuel cutoff switch question. Thanks!


Hi guys. I've been reading a lot of posts dealing with connecting relays to make a fuel-cutoff switch for the fuel pump. Im wondering if a relay should be used in order to make a fuel cutoff switch at the ECU under the passenger side kick panel.

Should a 15A switch still be used even if the relay is hooked up to the ecu switch? (im thinking yes). The available car security relay is a 12V 30 A relay.

I guess im a little confused about if i should use the 15A switch AND the 30A relay, just a 15A switch, or just the 30A relay and whatever switch i buy.

Also, if using the relay, does a 1 A diode still need to be connected between terminals 85 & 86?



Please Note: the above diagram is for a fuel cutoff switch AND an ignition kill, i will just be wiring half of that

Thanks!</TD></TR></TABLE>

You'll need the switch to control the throw of the relay unless you have an alarm with a ground-when-DISARMED output. Also, the diodes in your diagram are wired incorrectly. You will definitely cause some damage this way. The cathode side (band side) should ALWAYS be connected to the side of the coil that is positive. In your diagram, the cathode should be connected to 85 and not 86. If you follow your diagram, you will be passing ground to your ignition circuit - something you don't want.

special_edition

Why do you have 2 relay in the diagram? Isn't one good enough? Is it posible to "ark" the power side since you keep engaging the positive side like how they always tell you to remove the negative side of the battery first to not have the electrical spike. Sorry for the question, I still learning

vteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by special_edition &raquo;</TD></TR><TR><TD CLASS="quote">Why do you have 2 relay in the diagram? Isn't one good enough? Is it posible to "ark" the power side since you keep engaging the positive side like how they always tell you to remove the negative side of the battery first to not have the electrical spike. Sorry for the question, I still learning </TD></TR></TABLE>

It is called a latching setup for a momentary switch. Momentaries are like the push button that make contact for a moment and then pop back out. Normally a single relay would be energized and released immediately.

Here is a good tutorial.
http://www.the12volt.com/relays/page2.asp#psk

Hondadriver4life, maybe you can explain how and what the diodes are supposed to protect. I still don't see the point of adding them.

HondaDriver4Life

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">Hondadriver4life, maybe you can explain how and what the diodes are supposed to protect. I still don't see the point of adding them.</TD></TR></TABLE>

The use of a diode across the coil is often debated among installers. Some believe in them, some don't. When a relay is energized, the coil creates a magnetic field. Once the relay turns off (de-energized) the magnetic field collapses and creates a voltage spike. This spike can cause damage to sensitive circuits and reduce the life of the relay. A diode will absorb this spike thus preventing unwanted damage.

I feel it's one of those "better safe than sorry" scenarios especially when relays are being used to interrupt fuel circuits. The worst time for a relay failure is while your driving on the interstate at 70+ mph.

special_edition

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">

Here is a good tutorial.
http://www.the12volt.com/relays/page2.asp#psk
</TD></TR></TABLE>

So with this setup, running 2 relay it allow the fuel to be cut off everytime the ignition if off and you have to push the switch before starting? What kind of switch is that that pops off/on.

HondaDriver4Life

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">Here is a good tutorial.
http://www.the12volt.com/relays/page2.asp#psk</TD></TR></TABLE>

I looked at the diagrams using 2 relays.....you can simplify what they're trying to do with 1 relay. A second relay should be added to increase security (layers) but these examples don't do that.

For the first example with the momentary switch (should be a latching or toggle switch), I would leave the switch connected to 85 on both relays but disconnect it from 87 on the second relay. 87 should go to the key side of the ignition switch and 30 to the coil side. The second example is the same but instead of the switch, the radio is used.

The end result is that the ignition and starter circuits are interrupted.

vteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by special_edition &raquo;</TD></TR><TR><TD CLASS="quote">So with this setup, running 2 relay it allow the fuel to be cut off everytime the ignition if off and you have to push the switch before starting? What kind of switch is that that pops off/on.</TD></TR></TABLE>

Yeah. The switch is called a momentary switch

special_edition

I don't think we can use that switch for the fuel cut off since it will lose contact after it get energize and thus cut out the power for the fuel pump. So we have to use the toggle switch which we have to turn off everytime?
That would be a neat feature to have the fuel pump turn off by itself.

vteg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by special_edition &raquo;</TD></TR><TR><TD CLASS="quote">I don't think we can use that switch for the fuel cut off since it will lose contact after it get energize and thus cut out the power for the fuel pump. So we have to use the toggle switch which we have to turn off everytime?
That would be a neat feature to have the fuel pump turn off by itself.</TD></TR></TABLE>

This is the purpose of using 2 relays in the latching setup. I'll explain it this way. There are 2 options.
1. toggle switch and single relay.
2. momentary switch and 2 relays in latching configuration.

special_edition

I still don't understand how the latching configuration works? If the switch lose ccontact wouldn't it turn off the first relay which no longer will power the second relay?

HondaDriver4Life

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by special_edition &raquo;</TD></TR><TR><TD CLASS="quote">I still don't understand how the latching configuration works? If the switch lose ccontact wouldn't it turn off the first relay which no longer will power the second relay?</TD></TR></TABLE>

You're right. You would have to hold down the momentary switch in order to start the car otherwise neither relay's coil will be energized and the car won't start. This is why I stated before that a latching switch or toggle switch should be used to make the setup more pratical. Can you imagine how much of a pain it would to hold down your switch with your right hand and trying to start the car with your left? Another alternative would be use latching relays instead of the standard SPDT type.

vteg

I have not done one on my car yet, but from my research you only have to have the car in the run position. Then you hit the momentary switch, then you start the car. No need to hold it.

If you had to hold it that would make hiding the switch impractical.

HondaDriver4Life

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">I have not done one on my car yet, but from my research you only have to have the car in the run position. Then you hit the momentary switch, then you start the car. No need to hold it.

If you had to hold it that would make hiding the switch impractical.</TD></TR></TABLE>

That's the problem. You need to have the starter-cut relay energized in order to start the car. In the diagram, the only way to keep it energized while starting is to hold down the momentary switch so that 12v+ is fed to 85. Once you let go of the momentary switch, 12v+ is no longer applied to 85 thus the relay is de-energized. That's why I said earlier, the second relay is useless because it provides no additional security nor the proper latching function.

vteg

I will test this. I have some spare relays lying around.

JBBNJ609

wait if you cut power to the ECU doesnt it reset the settings ( like when you pull the ecu fuses and unplug the battery) . .. im just wondering

special_edition

ECU fuel pump wire output is being hack in this discussion not cutting the ECU power itself.

special_edition

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">I have not done one on my car yet, but from my research you only have to have the car in the run position. Then you hit the momentary switch, then you start the car. No need to hold it.

If you had to hold it that would make hiding the switch impractical.</TD></TR></TABLE>

Don't the fuel pump need constant power. So even if you hook up the momentary switch to work then wouldn't this sequence happen: you press switch, start the car, switch pop up and the whole relay de-energize itself and will cut of the fuel pump relay or am I missing some point? The latching setup allow continuous power to flow after it started? I think not...

rjr162

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vteg &raquo;</TD></TR><TR><TD CLASS="quote">

This is the purpose of using 2 relays in the latching setup. I'll explain it this way. There are 2 options.
1. toggle switch and single relay.
2. momentary switch and 2 relays in latching configuration.</TD></TR></TABLE>


You only need 1 relay to do a latching relay setup. it's actually really easy to do.

1&gt; Connect +12 to a switch, and connect the other side of the switch to pin 85 of the relay.

2&gt; Connect a wire from pin 87 to pin 85 of the relay.

3&gt; Connect a wire from a 12v source to pin 30 of the relay

4&gt; Connect whatever you want to turn on and stay on when you pulse the button "on" to pin 87 of the relay.

5&gt; Connect whatever you want to turn off and stay off when you pulse button "on" to pin 87A of the relay

6&gt; Connect pin 86 of the relay to either:

A&gt; a push button switch that is normally closed. When you push the button it brakes the ground, shutting the latching relay down

-OR-

B&gt; Connect pin 86 to pin 30 of another small relay, and pin 87A to ground. Then hook up the coil pins of the 2nd small relay to whatever you want to control the relay. In this setup, whenever the 2nd relay is "turned on", it will brake the ground connect of the first bigger relay and shut the latching circuit down.


A good use of this is if your car alarm system has a factory alarm arm and factory arm disarm wires. You can replace the switch on the +12v wire on the first relay with a postive pulse control by the factory alarm wire (using a diode between the (pin 87 and pin 85) connection and factory alarm arm wire. (This keeps the +12 of pin 87 from heading back to the alarm). Then you can control the 2nd relays coil by using the factory alarm disarm to brake the ground connection. In this setup you'd connect your fuel pump control wire to pin 87A of the first relay.

You can also replace the factory alarm arm wires in the insturctions above with the doorlock interface wires of your alarm system.

rjr162

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HondaDriver4Life &raquo;</TD></TR><TR><TD CLASS="quote">

You're right. You would have to hold down the momentary switch in order to start the car otherwise neither relay's coil will be energized and the car won't start. This is why I stated before that a latching switch or toggle switch should be used to make the setup more pratical. Can you imagine how much of a pain it would to hold down your switch with your right hand and trying to start the car with your left? Another alternative would be use latching relays instead of the standard SPDT type. </TD></TR></TABLE>

You wouldn't need to hold the push button down. In the circuit drawn, the ignition line stays +12 while cranking.

So the steps would go, turn key to ignition, push button. Relay latchs and turns circuit on (stays latched). Turn key to start, the ignition line is still +12 volts, so the latch doesn't brake. Cars starts, key returns to ignition position, car still runs. You turn the car off (either to the OFF position or to the ACC position), ignition line now reads 0 volts, which causes the latching circuit to brake. Now to re-enguage the latching circuit, you need to once again turn the key to IGN and pulse (push) the push button.

rjr162

if you look at the latching relay circuit, pretty much this is what happens.

The IGN line is activated by the key, causing it to read +12.

You push the button which causes the coil of the relay to energize. The relay then moves the contact being fed by PIN 30 from 87A (normally closed) to 87 (normally open).

87 now reads +12 instead of 0, and is fed back into PIN 85, which is (for this example) the positive side of the coil. Since PIN 85 is still getting +12 volts, the connection from PIN 30 (your +12 volt source) and PIN 87 doesn't reset. The loop from PIN 87 to PIN 85 is simulating you holding the push button down.

You can run whatever you watch to stay on when the relay is "latched" off of pin 87, since it will now read +12 until the circuit is interrupted.

There are two ways to interrupt the circuit. If PIN 86 (other side of the coil) is connected directly to a constant GROUND, then the only way to interrupt the circuit and brake the latch between PIN 30 and PIN 87 is to shut off the +12 source going into PIN 30. With the +12 source being the ignition wire, you'd do this by simply turning the key to OFF (or ACC). If the +12 source going into PIN 30 is a constant source, then the only way is to brake the ground connect going to PIN 86. You can do this by either using either a NORMALLY CLOSED push button switch, or by using some other source to control another relay. Obviously if you're trying to do something controlled by the ignition on your car, the first option is easiest, as the IGNITION wire in your car will read +12 when the key is in the IGN position, along with the START position. (Note&gt; DO NOT USE THE ACCESSORY WIRE, it will only show +12 when in ACC position and in IGN position, but will read nothing when in the START position, which would brake the latching circuit when you cranked the car over... pretty much you're never start your car unless you did infact hold the switch down)