alternator question

[jovial_cynic]

Based on simplified wiring diagram for an internally regulated alternator (shown in this post: http://forum.ratsun.net/showpost.php?p=64159&postcount=3), I'm trying to pin down the exact error in my setup to determine whether it's a wiring problem on my end or a problem with the alternator.

 

First things first - I don't have a harness. I'm cobbling everything together manually, which isn't too bad, but it makes for a headache after a while, when you're tracing down a gremlin and you didn't exactly color-code everything to specifications...

 

Anyhow, near as I can figure, the S/N and A/B terminals both go to positive on the battery. My battery is in the trunk, so I'm running the wires from S/N and A/B to the positive side on the starter. E is grounded at the alternator chassis, so nothing to do there.

 

L/F appears to connect to the fuse block at the flasher, which doesn't go hot until the key is turned to the #2 position. But I don't have a keyed ignition; I have a starter button and an ignition toggle, which simply turns on the fuse-box. That said, there's no #2 position - the L/F wire is just wired into the fuse-box.

 

So... after swapping the known bad alternator with the tested-at-auto-zone alternator (passed on the charge, but failed on the diode), my (thankfully) installed volt meter went from a battery-only 12 volts at idle to a (OH-NO!) 18 volts and beyond at anything over 2k rpms.

 

Is this the sign of a failed internal voltage regulator, or did I possibly wire the alternator incorrectly?

[datzenmike]

The L/F wire is connected to the charge light not the fuse box. Check the bottom diagram. There is 12 volts on the fusebox side of the charge light. As long as the alternator is charging there is the same voltage on the other side if the light and it can't light as there is equal voltage on both sides. If the alternator stops charging power flows from the fuse box through the charge light (lighting it) and into the alternator. This wouldn't cause your problem but you should have your charge light wired in right.

 

You said you replaced a bad alternator with one that passed the charge test BUT failed a diode test? Sounds like it's the alternator.

[jovial_cynic]

Oh - failed to mention that I had a blinking diode inline with the L/F wire. I was messing with it today and it blew out, so I just bypassed it, thinking that the power from the fusebox went to the alternator through the L/F wire, and not the other way around...

 

Hrm. Bypassing the LED may be the cause of the voltage spike?

[banzai510(hainz)]

http://datsun510.com/photopost/showphoto.php?photo=124&size=big&papass=&sort=1

 

 

 

 

 

You said you replaced a bad alternator with one that passed the charge test BUT failed a diode test? Sounds like it's the alternator

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[jovial_cynic]

Hainz - you mentioned this in my other thread. But I also wanted to make sure that my understanding of the wiring wasn't a part of the problem -- that L/F line was my main concern.

 

I do plan to swap the alternator out with a new one, but I still wanted to make sure that I understood the circuit. Specifically, if you run a direct line from the L/F terminal to the fusebox, are you going to see the same18+ volts in the system, even with a new alternator? Or was that specific to a bad diode in an alternator?

[]2eDeYe]

The only problem I have with that diagram on the internal regulated alt. is that the field has constant power.

 

With the S/N and A/B terminals both going to positive on the battery. Your telling your alternator to charge at all times, even when your in the house reading ratsun.....

 

This will kill the regulator over time. It's like leaving the key in the run position without actually starting the car. The main output lug (not sure which is which going by the diagram) should go to battery and the spade terminal should be ignition power.

 

The L/f wire does not need even need to be hooked up, but if it is, it should run to the charge light not the fuse box. It says that in the diagram, CHG circled in red ;)

 

[jovial_cynic]

2eDeYe;66017']With the S/N and A/B terminals both going to positive on the battery. Your telling your alternator to charge at all times' date=' even when your in the house reading ratsun.....

 

This will kill the regulator over time. It's like leaving the key in the run position without actually starting the car. The main output lug (not sure which is which going by the diagram) should go to battery and the spade terminal should be ignition power.[/quote']

 

Ah... good point. This shouldn't be a problem for me to rewire.

[datzenmike]

2eDeYe;66017']The only problem I have with that diagram on the internal regulated alt. is that the field has constant power.

 

With the S/N and A/B terminals both going to positive on the battery. Your telling your alternator to charge at all times' date=' even when your in the house reading ratsun.....

 

This will kill the regulator over time. It's like leaving the key in the run position without actually starting the car. The main output lug (not sure which is which going by the diagram) should go to battery and the spade terminal should be ignition power.

 

[/quote']

 

 

I see what you are saying, power is on one end of the field coil but that might not matter as it may be the other end that is in effect run to ground by the internal regulator. The regulator varies the field current to vary the output. I doubt if power is flowing while you are in the house else the battery would eventually go dead. I think instead it just sits there waiting for the pully to be turned. Wiring to the ignition switch sure won't hurt it though.

[]2eDeYe]

I've toasted a few internal reg. alternators with them wired that way. After I figured out what was happening, I wired the field to the ignition and haven't had any charging issues since.

 

I've also cooked a few ignition modules as well. After my jeep was stolen, I was having to hotwire it for a while. I'd kill it with the clutch and forget to disconnect my hotwire. :)

[datzenmike]

2eDeYe;66017']The only problem I have with that diagram on the internal regulated alt. is that the field has constant power.

 

With the S/N and A/B terminals both going to positive on the battery. Your telling your alternator to charge at all times' date=' even when your in the house reading ratsun.....

 

This will kill the regulator over time. It's like leaving the key in the run position without actually starting the car. The main output lug (not sure which is which going by the diagram) should go to battery and the spade terminal should be ignition power.

 

The L/f wire does not need even need to be hooked up, but if it is, it should run to the charge light not the fuse box. It says that in the diagram, CHG circled in red ;)

 

[img']http://i138.photobucket.com/albums/q251/datzenmike/wiringdiagram510internallyregulated.jpg[/img]

 

I knew I shouldn't have done this at work to-day. Memory ... not... good.

 

The field coil isn't under power all the time at all. The E (earth, ground) and the F (field) are the two ends of the field coil. The s/n and a/b terminals are for the armature coils.

 

You can have 12 volts on both the A and N terminals as they are connected together through the armature coils. The diodes only allow current flow in one direction to ground, and the way they are wired in it can't happen.

 

I have my '78 IC regulated alternator wiring diagram and it clearly shows the s/n and a/b terminals joined together just as in the above diagram. Anyway, no harm having it switched.

[]2eDeYe]

Interesting, maybe my diodes were what was cooking....Don't have those alt's anymore either to check.

 

Maybe, because they were AC Delco alt's. Maybe it's because they we're in my Jeep. It's done weird shit electrically since it was stolen.

 

I wired my Saturn alt in my '77 620 well after I had burned up the 2 in the Jeep so I wired the field the ignition.

 

When the new one goes together it will be wired to the stock configuration, unless 78 isn't a IR system?

[datzenmike]

IR started in '78s.