Over Voltage with New Battery Disconnect Switch

-
Dana67Dart said:
You would wire it the same as the diagram I posted but instead of interrupting the charge wire you would interrupt either of the field wires. (SOMEONE ELSE NEEDS TO JUMP IN HERE AS I DON'T HAVE EXPERIENCE WITH A TWO WIRE FIELD ALT BUT.... as understand one of the wires provides voltage to the field and the other provides ground to the field DON'T QUOTE ME ON THAT!)

You could test out my theory by disconnecting one of the field wires while the engine is running and the alt is hooked up in stock fashion if the car voltage goes from 14 ish to 12 ish indicating no charging, also the amp meter should read large discharge.



as in the diagram it would be from the source after the disconnect switch but before the car stock wiring
Click to expand...

This is all starting to make a lot more sense. Disconnecting one of the fields wires (either with relay or the master disconnect) definitely sounds like the way to go.

If anyone could tell me which field wire is what I think I can play with this tomorrow.

Thank you both so far with all your help
 
Last edited:
Just saw a flaw in my diagram. the hot wire after the disconnect switch will be energized by the alt when the engine is running. SORRY I missed that Not going to work this way.

Let me think on this a bit more.
 
What you really need is a 2 pole single throw disconnect switch.

upload_2018-10-6_22-57-8.png
 
One way to kill the alternator side is to ground it out. One switch, no extra wires or relay needed.
 
Dana67Dart said:
explain this a bit more
Click to expand...
It would need a switch with a grounded terminal.
So it would look like this. (Starter cable could be on either side, whatever the rules say, drawn here assuming a switch that could handle 100 + amps)
Kill-switch-ground.png


When running, everything is the same. Once battery gets recharged all current flows to ignition and field.
Kill-switch-ground-running.png


When the kill switch is closed, alternator output takes the quickest path to ground. Ignition and field are left without power.
Kill-switch-grounded.png

Engine dies because the ignition has no power.
The alternator stops producing any more power because the field demagnatizes and the engine is no longer turning.
 
Last edited:
What I don't like is dumping full alternator charge current to ground while the engine is running . seems like the fusible link will end up doing its job a blow.
 
Dana67Dart said:
What I don't like is dumping full alternator charge current to ground while the engine is running . seems like the fusible link will end up doing its job a blow.
Click to expand...
I don't think the alternator ever gets a chance to increase its power output.
Lets say the alternator output is 2.5 amps to the field and 3.5 amps to the ignition. Total of 6 amps out at 14.2 Volts.
Flip the Kill switch to off.
6 amps takes the short route to ground. Even if the voltage regulator sees a voltage drop in time to go full field, electricity isn't going to flow through the windings instead of the direct route through the kill switch. So the alternator never has a chance to go to maximum output.

I'm not saying grounding the alternator is without its faults, I just don't think the fusible link will be harmed during a test.
 
I think the double pole switch looks like my favorite solution so far. I need a "second switch" to disconnect one of the field wires. I've been trying to think of a way to do that with my single pole switch and a relay but I am going to call flaming river to see if they offer a double pole switch in the long remote kind (I don't see any on their website).
 
Dana67Dart said:
you going to test that out for gradedcatfood :poke:
Click to expand...
Nope. LOL. At least not now. When I move my battery to the trunk, it will get a kill switch, and yes I may set it up to ground the alternator out.
Ever shut off a lawnmower engine by grounding out the sparkplug? Now, that was always fun. Hints. Don't use your bare hand and don't be hesitant about it. LOL.

While putting idea out there. A self powered alternator, like the GM 10SI and 12SI series, can cause the same type of issue. The factory solution was to wire a resistor in between the ignition feed and the field wire. A diode will do the same thing. So where this is going is... cutting the power to ignition is probably the key thing - whether its coming from battery or the alternator, keeping it from the ignition will kill the motor.
 
Just looked at your switch. You could get a second and make a mechanical linkage that would shut off both at the same time.

I would also look into what 67dart273 pointed out about voltage drop etc.

Lastly... 60s ford starter relays are cheap and beefy. Could use them to do the disconnecting and use your switch to do the controling. Dont know if it would qualify for NHRA????
 
Thought things over and spoke with my dad. I think instead of breaking the main wire from the battery I am just going to break the MSD ignition wire and fuel pump. Should still pass NHRA tech as the car will shut off and I wont have to deal with this alternator stuff.

I will have to run a couple more wires back to the switch but it will simplify things greatly.

It's funny I was also thinking of a mechanical linkage secondary switch!

Thank you again for all your help and I will update you guys when I execute with this new plan. This alternator stuff has me going :BangHead:
 
Dana67Dart said:
Lastly... 60s ford starter relays are cheap and beefy. Could use them to do the disconnecting and use your switch to do the controling. Dont know if it would qualify for NHRA????
Click to expand...
I've seen a number of cars using them, mounted on the battery case and other places. So probably yes. Probably depends on the details.

Here's another way to kill all power to the engine. If that's the sole intent of the rule, then it will work. If the goal is also to kill all battery power going forward, then it won't do. My impression was the starter cable does not have to cut off by the switch. If so, then probably the alternator feed can stay hot as well.

Kill-switch-alt.png


^This^ is basically the same as the intent in the diagram below from post 1.
5951863-2postfullcutoff-jpg.jpg

The way I drew it, the regulator should work fine and the kill switch will stop the engine from running as well power getting to field.

The original black wire from the alternator to the main junction can be hooked up to the starter relay or the junction where the 1 AWG wire terminates. That would then provide two parallel wires from the fender to the original main junction.
 
Last edited:
Mattax said:
The way I drew it, the regulator should work fine
Click to expand...
I think that is how the OP has it hooked up but due to some interactions like 67Dart273 pointed out the OP is getting excessively high charging voltage.
 
Little update. I think I have found the best way forward for my situation. I plan on "breaking" the red and black wire that runs in series with the amp meter under the dash. I have already deleted that gauge and they are currently connected together via a nut/bolt.

With how I wried my ignition box and fuel pump relay switch when I disconnect those two wires the car shuts off. So my plan is to run a 10ga wire from the red wire to the master disconnect, then run another wire from the other side of the master disconnect back to the black wire which should take care of all this.

I know it wont shut the entire power off to the car but I believe this will meet NHRA rules as the car and fuel will shut off with 1 push of the switch (accessed from outside the car of course)

Thank you again for all your help
 
gradedcatfood said:
Little update. I think I have found the best way forward for my situation. I plan on "breaking" the red and black wire that runs in series with the amp meter under the dash. I have already deleted that gauge and they are currently connected together via a nut/bolt.

With how I wried my ignition box and fuel pump relay switch when I disconnect those two wires the car shuts off. So my plan is to run a 10ga wire from the red wire to the master disconnect, then run another wire from the other side of the master disconnect back to the black wire which should take care of all this.

I know it wont shut the entire power off to the car but I believe this will meet NHRA rules as the car and fuel will shut off with 1 push of the switch (accessed from outside the car of course)

Thank you again for all your help
Click to expand...

I don't think you want to do that. Do you remember the "old wives tale" about "testing" alternators? The "old wives tale" says if you disconnect the battery cable and the engine keeps running, the alternator is good. If the engine quits the alternator is bad

There's a couple or more things wrong with this:

1....If you do this "test" and the alternator is running slow, it might not be charging enough to run the engine, and may die, falsely telling you "it is bad."

2...If you do this test and the alternator only partially works (couple or 3 bad diodes.........) it may output enough to run the engine and little else, giving you the false notion "it is good."

3....UNHOOKING and alternator under load causes a HIGH VOLTAGE SPIKE and can be hard on electronics in the car.

ALSO

Having some sort of disconnect that leaves some wiring "hot" I BELIEVE (my opinion) does NOT meet the spirit or intent of the rules. But it's your neck.
 
You must log in or register to reply here.
-

Back
Top