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I'm forgetting about the time I jacked up the front of my FD without the car in gear or e-brake on, and it rolled backwards into my garage door. There are still cracks in the bumper paint that I pretend aren't there...
Sorry to resurrect this thread from the dead, but this is one of the better alternator threads in the first gen section and I found this friggin' amazing diagram in the 3rd Gen FSM that lays out SUPER clearly the path for each terminal on the alt.
B terminal goes straight to the battery for charging.
Sense wire (S Terminal) goes straight to the battery without a load on it for sensing.
L terminal goes from the battery, through the ignition switch and a fuse to the warning light in the Instrument console, then on to a diode before connecting to the Light (L) terminal of the alt.
I'm highlighting the diode because I've been having problems with my Instrument Console lights, and I think this might be key here. In the 1st gen, the path for the L wire goes Battery --> Ignition Switch --> Choke/Check Relay --> L terminal, and it's the Choke/Check relay that toggles from "Normally Open" to "Closed" to ground out the console warning light and make it turn on.
In order for the Alt Light (L) wire to toggle the Choke/Check relay, the L terminal needs to have a lower electrical potential than the signal from the battery via the ignition. When the alt isn't spinning, this is true. If my understanding is right on this, when the alt isnt spinning the coils are basically grounded, or close to it. The power from the 12v positive wire actually charges the coils up so that they can generate a magnetic field which will make power once the alt starts spinning.
So if you're in just "IGN" mode with the engine off, power is flowing from the battery, through the ignition, through the Choke/Check relay (thus toggling it and changing the two relay switches inside it) and to the alt coils. But once the car is running the alt is generating enough power that the voltage potential between the coils and the battery is basically equal, so the Choke/Check relay clicks off again and your alt light goes out.
The idea being that if, say, your alternator belt snaps while you're driving, the alt will stop spinning, the coils will stop generating current, and start pulling 12v through the wire again, flipping the Choke/Check relay and turning the "battery"/alt warning light on.
I feel like I'm 90% of the way to understanding my problem... There is no diode on this wire on the FB, so I'm thinking of adding one between the alt's L post and the Choke/Check relay. I don't think that'll solve my console light issue though so I'm thinking that maybe something in my alt is bad and the L terminal isn't grounding out properly when the ignition is on but the engine isnt running? Not sure. More investigation required.
Last edited by vipernicus42; 10-04-23 at 08:07 PM.
Electricity always flows from highest potential to lowest potential (which is usually, but not always, ground). The electrons actually move in the opposite direction but that's confusing so let's ignore that for now.
Diodes ensure that power only flows one way, so that if the relationship between which side has the higher potential flips, current can't flow back that way.
So what that means is that when the alt isn't spinning you've got 12v at the battery, but 0v (ish) at the L terminal. Diode says OK, let the power flow.
So what circumstance flips that relationship? If the L terminal has a higher voltage than the battery - which likely happens when the car is running.
So the diode is there to make sure that if/when the L wire has a higher voltage, the power doesn't flow "backward" through the circuit.
Of course the difference in voltage at that point would be like 1-2v (battery through ignition would probably read like 12-13 to the alternator's 14) so I don't know if that would even be enough to toggle the light/Relay... But it's good protection I guess?
I could be understanding it wrong though. I'm not an alternator expert. Just trying to figure things out from diagrams.
Electricity always flows from highest potential to lowest potential (which is usually, but not always, ground). The electrons actually move in the opposite direction but that's confusing so let's ignore that for now.
Diodes ensure that power only flows one way, so that if the relationship between which side has the higher potential flips, current can't flow back that way.
So what that means is that when the alt isn't spinning you've got 12v at the battery, but 0v (ish) at the L terminal. Diode says OK, let the power flow.
So what circumstance flips that relationship? If the L terminal has a higher voltage than the battery - which likely happens when the car is running.
The alternator gets generates power when it is spinning AND gets power to the L terminal which excites the Field. After the field is excited the L terminal is no longer needed until the alternator stops spinning.
So the diode is there to make sure that if/when the L wire has a higher voltage, the power doesn't flow "backward" through the circuit.
Of course the difference in voltage at that point would be like 1-2v (battery through ignition would probably read like 12-13 to the alternator's 14) so I don't know if that would even be enough to toggle the light/Relay... But it's good protection I guess?
I could be understanding it wrong though. I'm not an alternator expert. Just trying to figure things out from diagrams.
Learning about Transistors more specifically NPN (since that's what is used in our alternator but the concept is more or less the same) should help you understand how the voltage regulator works. I recommend watching those videos and anything that you don't understand find a video on that topic and diving in. Sure it may seem to be boring or whatnot but before all this my understanding was more or less it's magic.. now I know its physics and with a side of magic
Here's a post I made when I was trying to figure this out for myself as far as wiring the whole thing goes. https://www.rx7club.com/1st-generati.../#post12572695 Though it seems I have at least one contrarian but didn't really offer much to tell me how I am wrong. So YMMV.
Yeah, I had a decent idea of how it all worked, but after watching the first video it helped to solidify my understanding of what's going on and give me the right terms to use.
Before the alternator is turning, it uses the battery to power up the coils of the electromagnet side of the alt (the rotor) and generate that magnetic field which, once spinning, generates current in the coils of the power generating side of the alt (the stator). Since there is no solid-state magnet in the alternator, if we were to just spin it with no battery it wouldn't be able to power itself because the rotor doesn't produce a magnetic field until it's powered and the alt doesn't produce electricity until there is a spinning magnetic field. In a way, it takes power to make power.
So when the car is in IGN position but the engine isn't running, it's the L wire which provides the voltage from the battery that creates the magnetic field. Electricity goes from positive terminal of the battery to the L terminal, through the coils of the rotor, then back out to the battery via the ground connection - which is the body of the alternator itself. That's why you don't see a ground wire on the alt, and why the L wire should be grounded when the engine is off.
When the car is running, the 3 coils of the stator generate AC current, which gets turned to DC by the rectifier. The voltage regulator then uses the voltage on the Sense wire to determine whether / how much to reduce current to the rotor to keep the voltage from going off the charts and frying things.
Coming out from the voltage regulator we have the B terminal charging the battery, and an internal connection to the rotor coils to power them (and thus also connected to the L terminal from the inside).
So in normal operation the power coming out of the voltage regulator and connecting to the rotor will be around 14-15v, but due to losses through the system the voltage on the other end of the L terminal wire (via the choke/check relay, the instrument console, and the ignition switch) will be a bit lower, so power would tend to want to flow back that way. Hence the diode in the FD's wiring diagram off the L wire.
So yeah, going to add that diode to my L wire. But I also need to figure out if the voltage regulator on my alt is fried because I'm not grounding out on the L terminal when I think I should be. This wouldn't be the first time I fried a voltage regulator on these alts - which is why I'm trying to understand all of this so that I can avoid frying them in the future.
I think that *not* having upgraded my charge wire might be why I'm frying things (combined with the added load of things like my e-fan). If you try to draw a whole bunch of current through too small of a wire, you get quite a voltage drop. So I think when my e-fan and everything else is drawing power the system voltage drops, and the alt has to produce something ridiculous like 20v to end up with 14v on the other end of the sense wire because of the big current load on the inadequate stock charge wire. So I've got to upgrade that.
10-04-23, 08:03 PM
