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Setting up SPST Relay...
https://slantsix.org/forum/viewtopic.php?t=53528		 Page 1 of 2
Author:  kxracer728 [ Mon Oct 07, 2013 9:38 am ]
Post subject:  Setting up SPST Relay...
I'm going to add a relay to my hei setup...i'm going to use the alternator output wire for the main 12v feed. When i tested this wire it looks like it gets voltage even when the key is off

I assume that means the module will still get voltage when the key is off? Or does the relay act as an interrupt when the key is off? Is that what the trigger feed does?
Author:  Reed [ Mon Oct 07, 2013 9:48 am ]
Post subject: 
The alternator output wire is not an acceptable trigger for the relay because, as you have identified, the output wire is always hot since it connects directly to the battery. You need a feed that is off when the switch is off but on when the engine is cranking and running.

The trigger feed on a relay is exactly that- then a current is passed through the trigger terminal, it triggers the relay and allows current to flow through the relay and to the device being powered. The purpose of a relay is to allow a smaller current to trigger the flow of a larger current.

You can use one of the field wires on the alternator as the switched feed, or use the wire powering the electronic choke thermostat assist.
Author:  Rick Covalt [ Mon Oct 07, 2013 9:58 am ]
Post subject: 
Quote:
i'm going to use the alternator output wire for the main 12v feed
Sounds like he is using the alternator for the main feed to the relay, not the trigger. That would be no different than having it come from the battery, correct? That is how mine is set up. (to the battery)

Rick
Author:  Reed [ Mon Oct 07, 2013 10:07 am ]
Post subject: 
Oh, maybe I read it wrong. If you are using the battery feed of the alternator as the main power feed to the relay and using some other switched feed a the trigger, then yes, the relay will act as a power interrupt and the HEI module will not get power when the car is off.

Apologies if I misread the original post.
Author:  kxracer728 [ Mon Oct 07, 2013 10:15 am ]
Post subject: 
Yes, i was going to use the alternator output wire for the main 12v feed instead of the battery. Because it's on the same side as the module, coil, (shorter wire run...)

In the HEI article it says to put a 15A inline fuse close to the power take off point. So i'll put that close to the ALT

Quote:
The trigger feed on a relay is exactly that- when a current is passed through the trigger terminal, it triggers the relay and allows current to flow through the relay and to the device being powered. The purpose of a relay is to allow a smaller current to trigger the flow of a larger current.
Thanks...that helps me understand what the relay does

The article says "#86 is your trigger feed. This one needs a 16ga wire that's live when (and only when) the ignition is switched on."

Does the trigger wire need a START, RUN or just a RUN trigger?
Author:  Reed [ Mon Oct 07, 2013 10:41 am ]
Post subject: 
The trigger wire needs to have a + power feed to it in START and RUN. Think about it- the trigger is what turns on the HEI module. If it had no feed in START then the plugs wouldn't fire when you were trying to start your engine.
Author:  mattelderca [ Mon Oct 07, 2013 10:43 am ]
Post subject: 
Just use the original coil positive for the trigger. Works just fine even with the ballast resistor in place, although it is not required.
Author:  Reed [ Mon Oct 07, 2013 10:53 am ]
Post subject: 
Quote:
Just use the original coil positive for the trigger. Works just fine even with the ballast resistor in place, although it is not required.
+1.
Author:  kxracer728 [ Mon Oct 07, 2013 10:59 am ]
Post subject: 
Quote:
The trigger wire needs to have a + power feed to it in START and RUN. Think about it- the trigger is what turns on the HEI module. If it had no feed in START then the plugs wouldn't fire when you were trying to start your engine.
Makes since to me :)

That's another confusing thing about the HEI Electronic Ignition Retrofit How-To that's on the forum...somebody needs to revise that thing to make it more usable and understandable for simpletons like myself :lol:

The article says to: "#87 is your power output. Connect this via a 14ga wire to the coil + and to the module's power terminal."

I'm just wondering if this reduces some of the voltage going to both + coil, hei power terminal?
Quote:
Just use the original coil positive for the trigger
That's what i'll do...
Author:  Reed [ Mon Oct 07, 2013 11:06 am ]
Post subject: 
Quote:
The article says to: "#87 is your power output. Connect this via a 14ga wire to the coil + and to the module's power terminal."

I'm just wondering if this reduces some of the voltage going to both + coil, hei power terminal?
Possibly, but if you use the coil (+) terminal as the junction point for the coil feed and the HEI module feed, than you would be talking about a millivolt level difference between the coil and the module feed.
Author:  emsvitil [ Mon Oct 07, 2013 7:49 pm ]
Post subject: 
I'd be reluctant to use the alternator output because of the ripple voltage.

It might do something weird with the HEI module.........
Author:  wjajr [ Tue Oct 08, 2013 6:15 am ]
Post subject: 
Emsvitil:
Quote:
I'd be reluctant to use the alternator output because of the ripple voltage.
Good advice.

Running a wire from battery will provide a clean steady voltage to HEI. Battery acts like a voltage shock absorber that levels voltage peaks and valleys from alternator output.

Alternator is an alternating current (AC) three phase device that uses diodes (an electron one way valve, rectifier) to clip half of voltage sine wave off to mimic DC so system sees three constant streams of zero to 18 to zero volts many times a second 120 degrees apart and they average out to say around 13.8 v or whatever the real numbers are. Some electronics don’t like this waving voltage. For the nerdly crowd’s reading pleasure click here.
Author:  kxracer728 [ Tue Oct 08, 2013 8:53 am ]
Post subject: 
Quote:
I'd be reluctant to use the alternator output because of the ripple voltage. It might do something weird with the HEI module...
Yeah, it's better to be safe than sorry with electronics...i better work something out with the battery instead
Author:  Joshie225 [ Tue Oct 08, 2013 10:14 am ]
Post subject: 
One fair size capacitor, 1000uf or so, near the HEI module will keep it happy. In other words, I would keep the feed from the alternator and put a 1000uf, 35+ volt capacitor between the input side to the relay and ground.
Author:  kxracer728 [ Tue Oct 08, 2013 7:29 pm ]
Post subject: 
Quote:
One fair size capacitor, 1000uf or so, near the HEI module will keep it happy. In other words, I would keep the feed from the alternator and put a 1000uf, 35+ volt capacitor between the input side to the relay and ground.
#30 is your power input. Connect this via a 14ga wire to a good, solid source of line voltage. Good options for where to pick up this power feed include the battery positive terminal, alternator B+ terminal, large terminal on the starter relay, large terminal on the starter. Put a fuseholder in this wire as close as possible to your power takeoff point. You'll want a 15A fuse, and you'll want to carry spares.

#85 is your trigger ground. Run a 16ga wire from this one to any decent ground.

#86 is your trigger feed. This one needs a 16ga wire that's live when the ignition is switched to start, run.

#87 is your power output. Connect this via a 14ga wire to the coil + and to the module's power terminal.

So, are you saying #87 or #30? On radio shacks website it has radial and axial capacitors does it matter which one is used?
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