The Stovebolt Site Forums The Shop Area The Electrical Bay Wiring the 3 wire alternator

I'm getting around to wiring the 3-wire alternator I bought from Autozone ('74 Monte Carlo $45 w/lifetime warranty) and wanted to check with everyone to see if I've got it right:

The alternator has a terminal on the back where the juice comes out and a two-pronged plug on the top to tell it to make the juice, how much juice to make and to let me know if it ain't workin' right.

The terminal on the back ( the 'battery' terminal) gets hooked up to the starter using a fusible link and heavy guage wire with some resistance. You can get the resistance using 'resistance wire' or a solid state resistor/diode. The resistance is so that the alternator doesn't overheat when its charging a low battery and doesn't heat up the battery too much when it is low, causing the fluid in the battery to evaporate and possibly frying the alternator by overheating it. The fusible link is to protect from a short in the starter.

The two-prong terminal on the side (AKA the 'DA') is marked terminal one (1) and terminal two (2).

Number two (2) terminal on the DA (thicker wire than NO. 1) is the voltage sensing terminal that tells the alternator how much juice to make depending on the state of the battery. The reason this thing exists is because from the factory the wiring used a junction box. The battery ran to the junction box and all the accessories hooked up to the junction box. To measure the voltage at the junction box you needed this extra wire. In the truck you can hook it up to the battery terminal on the alternator but you are better off hooking it up to the junction box (if you use one) or the starter, becuase that'll give the alternator a more accurate reading on volts. Whether this line runs to the Bat terminal, junction box or starter, it should include a fusible link to protect your alternator from a short circuit.

Number one(1) is the 'exciter' and hooks up to the ingnition switch (and optionally to an indicator light.) Somewhere between the alternator and the ignition switch I need to install a resistor (10 ohm 10 watt), so that when the car is turned off juice doesn't flow backwards from the battery through the exiter to the ignition switch and then to the coil, which would keep the truck running even after I take the key out. The 10 Ohm 10 Watt resistor is available at any radio shack (Part 1N4001, 4 for $3.50 I think). You can also buy this resistor from some vendors who sell it for $30.

Right?

do it the way you are comfy with,,but you are over killing the install...doc

You do not wan,t any resistance in the main bat. term. wire. A fuseable link is desired. For a resister in the exiter circuit I use an ignition resister. They are cheap & easily obtained.The voltage sensing wire does not have to be as heavy gauge as the main bat wire. The preferred way is like you discribe but I run it right off the bat term on the alt. Many cars come that way including Cadillacs.

a resistor does not stop power from running 'back'.

Read my page about this Here

The factory uses resistance wire in the harness. I wired my 55 with a ignition resistor & have never had a problem.

NM51... SEE:

http://www.madelectrical.com/electricaltech/onewire-threewire.shtml

http://www.madelectrical.com/electricaltech/chevymain1.shtml

also you CAN make your own fusible link wire: LAPS (local auto parts store) (southern auto/carquest) has bulk fusible wire and you need to remember that that fusible link is TWO wire sizes smaller than the copper wire you use to the electrical item you wish to power.
ie a 8ga. copper uses a 12ga. fusible ~~ 12ga. copper wire uses a 16ga. fusible link and the link wire should be about 6'' long. @ bulk prices the roll of fusible wire costs about $4.50-$5.00

should help ya

Thanks everyone!

I checked the Mad Electric and Alan Horvath's website before I posted.

I also talked to a guy at NAPA who said what you really need is something that reduces the voltage in the exciter line, from the ignition, and that he used to put a bulb in the exciter line. I'm going with the diode just to be safe.

I guess an ignition resister in the exciter line would work the same as a bulb or diode. What OHM resister did you use Wrenchbender?

I used a universal single ignition resister available at any parts store for $3-4. They pretty much use the same one for GM & mopar anymore. I have used a light bulb & put it in an empty hole in the inst. panel. It gives you a warning light. It must be a 2 wire insulated socket though. If the bulb would burn out you would have a charging system failure.

OK...here's a stupid question...

I just completed a re-wire on my '63 using an EZWiring 21 harness and the instructions that came with the harness said that the only time I should use the resistance wire that was included was if I planned on using an alternator that put out more than 80 amps. Why would the alternator amperage have anything to do with it?

another stupid question NM51

why use a diode?? ... i thinking a diode allows current to go/travel in one direction.

or am i thinking of something else.........

I use one on my ignition wire. It's stops engine "run-on" from happening when you turn the engine off -- it's great!

I'm not the expert on this stuff- I read all the websites I could find, talked to some people and then posted to see if what I came up with is correct. Here's what I understand:

The three wire alternator (delco 10si or 12si?) has two spade terminals and a battery terminal-

The battery terminal charges the battery. Usually a line runs from this terminal on the alternator to the starter and from the battery to the starter.

The two spade terminals are labled 1 and 2. The number one terminal controls how much charger the alternator produces by sensing the voltage in the system. This line is the thicker of the two when looking at the 'da' plug that fits the two spade terminals. If you use a junction box it is best to run the sensing line to the junction box. If you don't use a juncttion box you can just run a line from terminal one to the battery terminal and that'll be enough.

Terminal two is the 'exciter' terminal- It actually turns the alternator on by 'exciting' the electrical field. You must have some juice to this. Normally this is connected to the ignition switch so that when the switch is in the on position juice gets to the alternator and when the belt turns it produces electicity.

The coil also gets juice from the ignition switch. Many times the Coil Wire and the Alternator Exciter wire are connected to the same terminal on the ignition switch. When you turn the ignition switch off you cut power to the coil.

If the Alternator Sensing wire is hooked to the BAT terminal on the alternator or a junction box it is basically hooked up directly to the battery (via the starter). Electricity can flow from teh battery to the sensing wire, through the alternator and back through the exciter wire to the ignition switch. If the coil wire and altenator wire are on the same terminal, turning off the ignition switch will not cut the power to the coil and the car/truck will keep running without the key in it because the flow of electricity to the coil hasn't been interrupted. That is what Alan means by 'run on.' The diode in the exciter wire is to prevent electricity from flowing 'backwards' to the ignition switch, because the right diode only lets electricity flow in one direction- From the Igntion switch TO the alternator, but not the reverse.

I think that is right, but I would be happy to be corrected!

In my last post I switched terminal one an two= TWO is the sensing terminal and ONE is the exciting terminal, my bad.

This is the best way to hook everything up:

[img]http://alanhorvath.com/54chevy/chevypics/wiring_1.jpg[/img]

Feeding the #2 wire to a terminal in the engine bay the way I did is best because you want your alternator to read wht the components need and jumping the #2 wire to the BAT connection, like most people do, gives the alternator an inaccurate reading to go by.

More info Here

Alan...I understand what you are saying, but how is it different jumping the #2 wire straight to the Batt terminal vs the way you described above? The voltage reading would be the same at either point...no? The only real difference I could see is that if the #2 wire reads voltage at the alt you eliminate any resistance that is in the #1 wire. If #2 wire reads voltage at terminal 1 it should be the same with the exception of a miniscule (probably undetectable) drop due to the length of #1 wire. It would seem to me that jumping the wire to the Batt terminal simply uses less wire to achieve the same purpose. In fact I don't really understand why this isn't done internally to the alternator.

Not trying to be difficult, just a little confused.

The real difference lies in the fact that I am supplying power (a full 14 volts) to everything from that terminal and my alt. is reading from that same source, thereby supplying what my system needs in a very real sense.

Without the terminal, however, we would only be reading the battery and everything in the system, which is actually being supplied less voltage, and from a more distant source, is not being properly read by the alt.

I agree w/ Alan in that the #2 sensing wire registers the voltage being used @ a location where the power is distributed from. There is a slight voltage drop because of the distribution to all accessories drawing power after the key is turned to ON/RUN, @ any given time. This constantly changes during load draws from radiator fans, A/C, electric windows, heater, heated seats, etc. If the #2 wire were attached directly to the BATT lug on the alternator (what 3'' long) the alt. would always sense high voltage w/o a drop.
I don't see the #2 wire connected to the BATT term on the key switch. Shouldn't the #2 be connected to the 'ON/RUN' post. I'm going to have to go look tonight @ my key switch and wiring diagram @ home.... more &/or a correction tomorrow. But if I think about this my power lead to my key switch goes to the OFF post. Once the key is turned it provides a connection to either ACC, ON/RUN, or START posts.

Some set ups (which have a key start position, 4 post key switch) would wire the #2 wire w/ a diode.??? ... yes?? to the ON/RUN post??
imput anyone.....
AND

I realize others have a simple 2 post key switch and a foot start. Then I could see having the diode in place on the RUN post. But if (say Alan has a V8 & probably a 4 post [[acc,off,on/run,start]] key switch in his truck) then the #2 sensing wire would be connected to the ON post. I have a 6'' jumper wire from the 'ON/RUN' post to the 'START' post as all the start does is provide power to the starter solonid for a couple seconds & using the 'ON/RUN' wire for that purpose.

Diode ... yes. Eliminates run-on after turning the ignition off.


That's me.

Correct-a-mundo.

Thanks Alan

and that is a simple 12v-50v diode??
or is there a specific one @ the local friendly neighborhood auto parts store (LFNAPS).
PART # ??

You can buy a 4-pack of diodes from Radio Shack for only $3 or $4: Part #1N4001

ive got two vehicles that work fine just running the #1 wire to the generater light in the dash.

Yup ... in effect, the generator light achieves the same thing.

where does the alternator idiot light on the dash get hooked up to??

so in escence the 3 wire alt. is a four wire....

I don't use the idiot light ... just the diode.

Some resistance in the # 1 (exciter) line is enough to stop the run on.

A diode is one way to create the resistance, an 'ignition' resister is another.

And a bulb, which is basically a glass jar containing a piece of high resistance wire that heats up so much it glows, is another.

The following can be seen in it's entirety: This is a VERY COOL INFO LINK.......
He covers everything: petronix, generators, alternators, cooling systems, relays, suspension, brakes, electrical components, trannys, carbs. and more..

http://www.rowand.net/Shop/Tech/AlternatorGeneratorTheory.htm

Alternators
The more modern and more capable alternator is explained here. Every modern vehicle uses an alternator - and for good reasons. It is more complicated than a generator, but that added complexity brings a few very good features that you will most certainly want on your vehicle - mainly the fact that it will charge the battery at idle and can support the higher amperages needed to run all of the electrical equipment on a modern vehicle. Alternators tend to be more reliable than a generator and have fewer "hard to diagnose" problems as the system ages - particularly the internally regulated models. The internally regulated models are also very easy to service if something goes wrong - there is only one part to fail (the alternator itself) and replacing it is a simple 30 minute job. This all adds up to the performance and reliability that is expected in a modern vehicle.

The key different between an alternator and a generator is what spins and what is fixed. On a generator windings of wire (the armature) spin inside a fixed magnetic field. On an alternator, a magnetic field is spun inside of windings of wire called a stator to generate the electricity. This allows the wires to be directly and easily connected to their outputs without the need for sliding contacts to carry the relatively high output current. The magnetic field is still generated via electro magnets mounted on a rotor, and the relatively small field current that powers them is supplied to the rotor by two small brushes that each ride on a separate and continuous slip rings. These smooth slip rings (unlike the comparatively rough contacts on a commutator in a generator) and the fact that the relatively heavy windings are fixed instead of rotating allows the alternator to be spun to much higher speeds. This allows it to reach it's maximum output sooner and to be spun fast enough at engine idle speeds to produce enough electricity to power most (if not all) of the needs of the car without relying on the battery.

There are typically three separate windings of wire in the stator that are all set to so that the AC current that is generated is slightly out of phase in each one. The peaks and valleys of the rising and falling current do not happen at the same time, rather they are staggered a bit. This increases and smoothes the electrical output of the alternator much the same way that a 8 cylinder car runs more smoothly than a 4 cylinder one does - there are more power pulses happening in each revolution allowing more total power and better smoothness.

The process of rectifying the AC current into DC current is handled inside the alternator by something more complex than a commutator - diodes. A diode is a "solid state" device that allows current to flow in one direction only - "solid state" means it does this without any mechanical or moving parts. It relies on the different electrical properties of the materials it is made of to act as a one-way valve for current. By arranging diodes so that current from each of the three stator wires is only allowed to pass in one direction, and by connecting the three outputs together, you get a reasonably smooth and stable DC output without any moving parts. (This arrangement is typically manufactured as a single part and is referred to as the diode pack or diode trio.) This lack of moving parts makes the alternator not only very reliable - but also comparatively inexpensive to build and repair. That diode trio costs well something trivial like $1 to produce in large quantities.

Alternators do not need to be polarized after installation. You mount them to the engine, plug them in, and go. This is an advantage for not only manufacturing the car but for servicing it as well.

On externally regulated models, there are typically four connections on the alternator - the large output terminal (BAT), the ground terminal (GRD) which may be "implied" though the metal mountings of the alternator, the field connection (F), and terminal #2 on the regulator is a separate connection to one of the three poles on the stator (R). Unlike on a generator, the BAT terminal is directly connected to the battery and the rest of the cars wiring system, while only the F, R, and GRD connections will connect to the regulator. Also, terminal #3 on the regulator (if present) is connected to the main junction block for the wiring system and serves as a "remote voltage sensing" wire. Terminal #4 on the regulator will be connected via small wires to the charge indicator light on the dashboard of the car and the charge resistance wire. The regulator itself can be a mechanical or solid state device. A typical externally regulated alternator wiring diagram from a 1963 Buick is below for reference - click on the image to see a larger view.




On internally regulated models, there are also four connections on the alternator, but there is no separate regulator in the system - it is inside the alternator and constructed of solid-state components. The connections here are the large output terminal (BAT), the ground terminal (GRD) which may be "implied" though the metal mountings of the alternator, and two connections typically labeled simply 1 and 2. Terminal #1 on an internally regulated alternator is the same as terminal #4 on the regulator of an externally regulated system - it connects to a small wire that is goes to the charge indicator light on the dashboard of the car and the charge resistance wire. Terminal #2 on an internally regulated alternator matches terminal #3 on an external regulator - it is connected to the main junction block for the wiring system and serves as a "remote voltage sensing wire". If you are comparing to the externally regulated wiring, then you will note that the F and 2/R wiring connections are done inside the alternator. A typical internally regulated alternator wiring diagram from a 1973 Buick is below for reference - click on the image to see a larger view.


Regulators
What exactly does that little black box on your inner fender do? What's the difference between internally and externally regulated alternators? The regulator does just what it's name implies - it regulates the output of the generator or alternator to the proper voltage and current by controlling the field current that is supplied.

For all generators and externally regulated alternators, the regulator is a small device mounted somewhere on the firewall or the inner fender of the car. It is connected with relatively long wires to the generator or alternator. It is usually a mechanical device that works by rapidly opening and closing the contacts of several relays to create the correct "average" voltage and to limit the current supplied to the correct amount. These mechanical regulators need periodic adjustments and can be somewhat noisy in operation. They also have moving parts that will fail after a period of time. Some later-model and aftermarket replacement regulators are solid-state devices that are quieter and longer lasting even though they look pretty much the same externally as a mechanical unit.

For internally regulated alternators, the regulator is a solid state device (no moving parts) that is mounted inside the alternator casing. These units will never need replacement separately from the alternator and will last for many, many years giving trouble-free service. There are no separate wires to run between the the two units, and there are only a few simple connections to make at the alternator itself.

Remote Voltage Sensing
Both regulator styles can have what is known as a "remote voltage sensing" feature on them - many thanks to the explanations on the MAD Enterprises site for finally making this clear enough to me so I could explain it here. They have details on the remote sensing feature, 1-wire vs. 3-wire alternators, and a great description of a typical musclecar-era Chevy charging system. The details are interspersed throughout those documents, but together they provide very valuable insight into how the typical alternator-based charging system works, and how to modify your charging system to work correctly using an alternator. All internally regulated systems come with the remote voltage sensing feature, but not all externally regulated systems do. Basically, the remote sensing wire should be connected to the main junction point for the entire electrical system. This is because the voltage at the place this wire is connected to will be maintained at the proper level. If this connection is at the alternator or regulator, then that's where the maximum voltage will be with lower voltage out in the rest of the electrical system. If you connect this wire to the main junction point, then the main junction point will have the proper voltage. The difference that results from this can be very noticeable, especially in cars with the battery mounted somewhere besides the engine compartment. A 1V drop is common between the alternator output and the main junction point in many cars, so if you have 14V at the alternator and only 13V at the junction point, you may not be doing much better than 12V by the time you get to the actual devices that need to use that voltage. In this theoretical 1V drop scenario, by connecting the remote sensing wire to the main junction point, you will have 15V at the alternator (yes, 15V - it's OK and desired here), 14V at the junction point, and then 13V at the accessories.

Dashboard Indicator Light
If you have an alternator and are using the factory style indicator light on your dashboard, it is a pretty helpful thing. It helps kick-start the alternator into working at idle speeds when you first start the car, and it tells you if the alternator is putting out less voltage than the battery has in it, indicating a problem. The light is connected on one side to the field current system inside the alternator and to a switched ignition power source on the other side. When you turn the key on but have not started the car yet, the field acts as a ground and power flows through the light and out to ground - lighting the bulb so you know it works. Once you start the car, the voltage at the field is powered internally by the output of the alternator. If this value is exactly the same as the battery voltage, then you have the exact same voltage on each side of the indicator light and they balance each other out - kind of like a tug of war in reverse. If all goes well, the light never comes on, and you drive happily around knowing all is well with your alternator. If the output of the alternator should drop due to a slipping/broken belt or due to certain kinds of electrical faults inside the alternator itself, there will be less voltage on the field side of the light and more voltage on the switched ignition side of the light. The result is that some amount of electricity will flow through the light and into the field and the light will glow proportional to that voltage difference. This is how a slipping belt or an overloaded alternator will cause the light to glow very dimly, while a full-on failure will cause the light to glow very brightly. Note that if you disconnect (or forget to connect) the wire at the alternator, the light will never come on and the alternator will not charge properly.

The dashboard indicator light circuit also typically has an extra wire with a calibrated resistance in it. This wire is run in parallel to the indicator light and has about a 10ohm resistance. It's purpose is to allow slightly more current to flow to the alternator field current system at initial start-up to make sure the alternator begins producing power as soon as the engine starts. About 1 amp total current is flowing to the field current between the light and the resistance wire, with the resistance wire supplying about 3/4 of an amp. This extra resistance wire does not affect the functionality of the indicator light in any way.

NOTE: I've been informed by my readers that a Radio Shack 10 ohm 10 watt 10% wire wound ceramic resistor (part #271-132) has worked well on their GM vehicles. Use caution if you decide to do custom wiring work with resistors as they can get hot and melt stuff.

Conversions and Customizations
Many "hot rod" style conversions use a modified internally regulated alternator to eliminate the two small wire connections and only leave the single large BAT connection to be hooked up. This is usually referred to as a "one wire" alternator - you only have to run one wire to it instead of the usual three wires. In this conversion, the dashboard indicator light is eliminated entirely, the field terminal is connected to the BAT terminal internally, and the connection to the other terminal is made inside the alternator. Conceptually, this conversion works like a factory system without the indicator light on the dashboard and with the remote voltage sensing wire connected to the back of the battery. There are several major drawbacks to this setup. One is that you have to to rev the engine up to approx 1100rpm once after the engine is first started for the alternator to begin charging - the alternator has to reach a high enough RPM so that it "self-excites". Another is that the field connection inside the alternator can allow a small current draw while the vehicle is not running, and this can cause a dead battery if the car is stored for a period of time. Lastly, you do not have the advantage of the remote voltage sensing feature and that means poor electrical system performance - dim headlights, slow wipers, and various other maladies. There are some great details on this at the MAD Enterprises website - check out their articles on the remote sensing feature, 1-wire vs. 3-wire alternators, and a great description of a typical muscle car-era Chevy charging system for more details.

I personally do not recommend the "one wire" conversions - the dubious improvement in under hood aesthetics just isn't worth it. Your neighbors will probably not appreciate you revving your car up to 1100 rpm each morning at 7am before you head out to work and it makes your otherwise cool ride annoying to drive. Many "tamer" drivers (like your wife, if she's anything like mine) will often start the car and drive for some time before making it to 1100 rpm for the first time. During that entire time, she would be draining the battery if the vehicle was using a "one wire" conversion - and that's not cool. It is very simple to hook up the extra wires for the indicator light and the remote voltage sensing feature. It also makes the car much more pleasant to drive - you have one less thing to worry about when you just want to get in the car and go. In addition, many of the vehicles that use the 1-wire conversion tend to be specialty use vehicles and thus do get stored for a long time between uses, so the battery drain could be an issue. If you do go that route, consider a battery disconnect or some form of "battery maintainer" to keep your battery charged between vehicle uses. Lastly, the problems with reduced voltage as a result of not having the remote voltage sensing feature can be a very big deal.

If you are still pondering a "one-wire" conversion, it should be noted that you can partially eliminate the second wire by using a short pigtail to hook it directly to the BAT connection on the alternator. If you examine the diagram above for an internally regulated alternator, you will see that this wire eventually ties back into the wire that is attached to the BAT terminal anyway. When I originally wrote this webpage I was not aware of the remote voltage sensing feature and the possible issues with connecting the remote sensing wire directly to the alternator output, and now that I am, I believe I understand a few problems I was seeing in the operation of my 1973 Electra. For the record, I'm going to be making some changes to the electrical systems in my vehicles now that I understand this - I think it's that big of a deal now that I understand how this all works.

A final word of caution is to think twice (and then think about it again) before deviating from the way the factory did things if you want to customize your charging system. Modern factory charging systems are amazingly reliable and trouble-free. There is a reason the factory did what they did. Adding those extra lengths of wire probably costs them about $1 a car - and although that may not sound like much, when you make a million cars, $1 per car is a $1,000,000 less in potential profits. That's some serious money - and that's just for a few pieces of wire. (This detail is why the factory goes crazy trying to save every penny possible when building the car - it really adds up fast and they like making all the money they can.) Also, when you make a million cars and find out something is wrong with them (fire hazard, doesn't always charge the battery, etc.) it ends up being very expensive - both in real dollars and from a public-relations perspective - to repair the problem. Melding two factory-style systems to upgrade your vehicle to newer standards is a worthy goal and often a very easy thing to do - just be sure you get all the details right so you can enjoy your vehicle for many trouble-free miles to come. Take the time to make sure each wire you put into the car or change the function of (aka, push more current through it) is up to the task you are placing before it.