Alternator wiring

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...........You.........got..........er.............LOL

What these do, is, diodes act sort of like a "check valve" for liquids, that is, they only flow current in one direction. But WHEN they are "flowing," which is known as "forward biased," diodes all have SOME (tiny) amount of voltage drop, which can change with the type and rating of the diode, as well as the current going through it.

So this tiny voltage drop allows some current to "shunt" in parallel with the ammeter, but some goes through the diode.

The reason you need TWO is that when the alternator is charging, one diode is conducting, but if you , say, example, are parked, and are using a load (stereo) off the battery, then the OTHER diode will be conducting.
 
pompis, you drew it perfectly, and 67Dart273 explained it perfectly.

Typical silicone diodes have ~0.7 V forward voltage drop, which is a little too much since that is about the drop you will get across the ammeter at full scale. The diode above and the type I put in my Dart are Schottky type with nominal 0.3 V forward drop. However, I say "nominal" because it isn't constant, but a function of current flow (and temperature), which you can see from the chart in the datasheet. A diode is much better than a resistor for this because it acts more like a "pressure relief valve". It doesn't conduct much for low ammeter readings, then "opens wide" to bypass the ammeter as it reaches high currents.
 


Now the diode has arrived going to install it this weekend probably. Going to fix the overcharging problem first with right drawn cables and new coil and ballast. Will put relays to ignition, headlights, horn and heater switch. I have a 3 speed wiper motor and I think I will put a relay to all three wiper speeds. Is there any more function that's need to put relays on?
 
Your horn is already on a relay, and I haven't had enough trouble with wipers to bother.

You have any other added on stuff, like "big" stereo, fuel/ water pumps, fans?
 
I'm not planning for a stereo now but in the future it's possible, then I will put a relay to start the stereo unit. And have no fuel/water pumps and no fans either. I seen now that the horn has a relay. Maybe it's overkill to put relay to the wipers but I will probably do that anyway or going to replace the cable to the wiper motor with bigger wire than stock.
 
I really don't think the wipers are a problem. They don't have much failure history over the years, nor do the bulkhead connectors show much history of damage in that area.
 
Pompis,

Great, and just how I did it, though have not installed in my Valiant yet since other projects (house, 02 T & C, 60 hr/wk day job, ...). At this point mine is at the status "should work", just like the smaller diodes I used in my Dart. Let us know any measurements you make. I have both an in-line 100 A ammeter and a Fluke clamp-on DC ammeter to measure my true alternator output when I get to measuring things. Make sure you mount it where it gets a good heat sink, like right off the battery. Also, wrap all exposed metal since it will be at 12 V.
 
Bill I have not wire the diode shunt yet, will keep you updated how it works out for me.

I'm thinking of this solution to kill the car. I know there are specific switches to kill both the battery and alternator but here in Sweden it is cheaper to buy a 2 pole switch and a heavy duty relay. I'm going to use a 100A relay in this set up. Is this a good way to go? The down side is to leave the switch on when the car is parked because the relay will discharge the battery.





 
That won't work. The problem with a kill switch that will actually kill a RUNNING car is that the alternator puts out power, and keeps supplying power to the ignition. In your diagram, the alternator will keep the relay coil powered forming a "latching" circuit. In other words, the way it's shown, won't do a thing.

The usual way to "cure" this with a 2 post (single pole) switch is to run the charging wire from the alternator directly back to the battery. But in my opinion, this does not meet the intent of the (NHRA) rules which speaks at some point about "killing all power." That is, the charging wire is still hot from the battery clear up front.

I do NOT understand why the parts suppliers keep selling 2 terminal/ single pole switches. A 4 terminal/ double pole switch makes things SO much easier.
 
You have so right, now I see it would not work. I have to put the alternator charging wire directly to the battery + instead like you said. The reason why I want a kill switch is because insurance rules require some kind of main switch not necessary a "killing all power" system. Can also skip the alternator relay and just break the battery + circuit so thiefs can't start it. But that will not kill the car when running in theory instead.
 
If all you want to do is disconnect the battery for insurance/ theft, I would simply break the battery lead and be done with it. I'm guessing there is no need to have the switch exposed, as for race rules, etc.
 
I put a Battery Brain in most of my cars. I mainly use it to avoid running down the battery when parked, like if a dome light is left on. However, some have a remote disconnect which can help for anti-theft. They suggest putting directly in line w/ the battery, but I usually wire it after the starter so that large current doesn't go thru it (though claimed to handle it). I got most for ~$30 on ebay.

It doesn't fix the problem of the alternator keeping a running engine going (per 67Dart273). Indeed, they have a wire to connect to your IGN so it won't ever shut off accidentally when driving.
 
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