jefflaws & cpadpl:

Ok, actually I am somewhat right and wrong. I work with regular motors and generators: AC, DC, steppers, Brushless DC, Brush DC, Slotless, PM motors etc. Never have really worked with auto's.

So first let me apoligize for any wrong information. I don't want to put out bad information. First I am not wrong about alternators putting out AC voltage as jefflaws suggest. jefflaws is correct that the "final" output of the alternator is DC but that is after the AC has been rectified to DC through the diodes located usally inside the alternator. Of course the newer ones may not even use diodes anymore but another circuit all togeather. You can never get DC voltage/current when rotating an wound amature within a wound field it will always be AC until rectified to DC. The DC output of an alternator is not pure DC as like from a battery but is very close with filter circuits.

jefflaws is correct about me having it wrong with an AC voltage to the coil, well kind of. It is not "normal" AC as I stated before but as like jefflaws stated with the DC voltage building then collopsing makes for an AC "effect" so as to create a bigger voltage output on the output side of the coil. As I had said before the coil is nothing more then a transformer and you can not transform DC voltage/current only AC. What I mean by that is if you continusely feed an AC output to the input of a transformer (coil) you will get an AC output in the secondary side of the transformer (coil). If you continusly feed DC voltage to the input side of a transformer (coil) you get "nothing" out of the secondary side. By building a DC voltage then collopsing (i.e. old points system) you create an AC (effect: rise and fall) voltage that can be transformed to a much higher voltage on the output side of the coil. If you were to look at the voltage rise and fall on a scope it would somewhat resemble an AC sine wave.

Alternators which used to be called generators on old cars/trucks have always produced an AC output, but prior to leaving the output side of the alternator/generator was rectified to a DC voltage/current.

The coil is a transformer plain and simple. It has two windings wound togeater inside. One winding is the input, the other winding is the output. The input winding has fewer turns then the output winding (one may have 100 turns or wire, while the other has 1000 turns, in that case if you put 100volts in you would get out 1000volts). If it were just one winding you would not get any higher a voltage from the output (spark plug) side then what was put into it. It would be like a capacitor. A capacitor can be charged and discharged but the discharge is always equal to or less then the initial charge it received. In reality it will always be less, not much but it will.

cpadpl:

Yes the alternator usally produces enough voltage/current to power everything. It also keeps the battery charged if working correctly. alternators are rated for output amps. Not sure what ours is, but for example some are rated for 100amps that is all it will put out. So if you had acessories that demanded more then 100amps it would take power from your battery which is why I had stated before about how you could tell if your alternator was working correctly (i.e. headlights getting dim) that is a good indicator that either the alternator is not doing its job, or there is to much demand on the alternator and thus taking juice from the battery which in turn will drain the battery since it is not able to get a charge from the alternator.

What I meant about needing the battery for the computer is for constant power to the computer when the truck/car is not running. The computer I don't know about as far as if it needs power to it for any outputs that may be needed in order to start a truck/car. Maybe it needs to maybe it dont I just don't know. I do know the only way to re-set the computer is to take one of the terminals off the battery, so then there is no power to the computer. This tells me the computer needs power for some reason when the truck/car is not running.

So as you can see what I had posted before was correct with some minor errors, or just not very good examples from myself. The fact is like I said before once the truck/car is running you don't need a battery if the alternator is working correctly and within its capibility. The other thing to remember is that an alternator/generator will always produce an AC voltage and the only way to get DC voltage from an alternator/generator is by means of rectifing it to DC, many different methods of doing that, use to be, and not long ago because my 79 Camaro had it was diodes located in the alternator.

Just to clear up any questions on older generators and their output being AC prior to being rectified to DC. On older ones they did not use diodes. Rather it was rectified by means of comutators and brushes. The comutator being part of the shaft, and the brushes riding on top of the comutator and the DC output taking off the brushes. It was still an AC output until it went from the comutator and then through the brushes.

 

It is NOT AC current. AC is ALTERNATING current, and the pulse going to the primary of the coil never switches polarity, so therefore it is in no way AC. It is a pulsed DC. It just simply cant be AC without switching polarity. The coils on ALL fords have a constant 12V positive to them when the key is on. The ground side is pulsed by points, or an ignition module. It is NOT AC.

 

Look, I have read many of your post jefflaws and I have a great deal of respect for you and your knowledge. I am not trying to get into a battle here.

I did not say it was AC I said it was an AC "Effect" the rise and fall of the DC voltage is like an AC effect. You can not in any way take 12vDC and make it say 10,000vDC through the coil (transformer) without the rise and fall of the DC. If you looked at it on a scope it would look somewhat (not perfect) but somewhat like an AC sine wave.

Yes you are right the primary side may always be a constant 12vdc, but the secondary side does not see a constant DC voltage supplied to it. As you had stated before with older cars and points. The points would close and open thus causing a pulse of the DC voltage. It is the only way you will ever be able to step up the 12vdc to say 10,000vdc. If the primary side of the coil never collaspes then you can not induce a voltage into the secondary side of the coil (transformer effect).

I am not in any way trying to question your knowledge of Ford cars and trucks. As I said I have read many of your post and learned alot from you. What I do know however is motors, generators, alternators, transformers (coils). I have over 15 years experence working with them, in building, repairing, troubleshooting and develpoing them. Now I will give you this I may not be explaining myself as well as I could and perhaps someone will come along and help me out some.

You are right it is not AC voltage as we know AC voltage. But it is not a constant DC voltage that causes the coil (transfomer) to step up the output DC voltage that creates the spark.

True AC = voltage going from 0 vots to +120 volts to 0 volts to - 120 vlots. (sine wave)

True DC = voltage at 12vdc constant, never changes like from a battery.

DC pulsed, or what I call an AC "effect" (for coil to induce a voltage to secondary side) voltage going from 0 vdc to +12vdc to 0vdc to +12vdc etc.

This rise and fall from 0vdc to 12vdc is like an AC "effect" it is what is needed to induce a voltage into a secondary winding of a coil (transformer) if you never pulsed the DC voltage on the primary side you will never have anything from the output of the secondary side. Or another way to look at it is if you measure the output side of the coil, put voltage into the primary side then cut the power off you will measure a voltage from the secondary side only for a second until it to has collasped. So turning the DC on and off, and on and off will give you an output on the secondary side. This is what AC voltage does except you never have to turn it off since it is going from 0 to +120 to 0 to -120. That is why I explained it as an AC "effect" the on and off cycle.

jefflaws, is that a better way of explaining it? I know what your saying and I agree I am just trying to explane how it works inside the system itself.

 

The best way to explain it is that the collapse of a magnetic field induces a current on the secondary windings of the coil.

That way there is no refernce to AC since it cant be AC without switching polarity. What you are desribing as an "AC effect" is actually a square wave DC signal. Put it on an ocilliscope and you will see that it doesnt even look like a rectified AC sine wave. The 2 things that makes it not AC is 1.) the fact that it doesnt switch polarity. 2.) the fact that there isnt a gradual rise and fall of the wave. It is a square fronted and ending wave. Would you consider turning your headlight switch on and off to be giving your light bulbs AC current??? No, its just a pulsing DC current, just like the coil gets.

What you arent seeing is that it doesnt require AC current to induce current in the secondaries of a transformer. All it requires is a collapse of a magnetic feild. You could apply DC power to the primary for however long you want (called dwell) without producing secondary, but the instant you stop the power and the magnetic field collapses, it will induce a secondary current.

 

Damn your good. I couldn't have said it better myself. Like you said about "collapse of a magnetic field" was the point I was (trying, not successful) to make. With AC you always have the wave form building then collapsing, and like I was trying to point out you could not do that with DC, unless you were collapsing the magnetic field. And you made a very good point that I did not about the DC does not change polarity. I know there is no AC power in the truck even the headlights, and no I don't consider it AC when turning them off and on. I know with good duty cycles you have a good square wave but I would imagen if you looked at the input or especially the output of the coil it would look more like an AC sine (as far as the rise and fall from 0 to +vdc to 0) wave then a good square wave if you know what I mean, as in not a clean square wave form.

Anyhow I wish to thank you on a good conversation in this thread. Wished I had explained myself better in the begining. It is much easier to do in person then writing on here. I work much better with paper, pens, hands etc explaining then just putting down the words here. As I said before I have read many of your post and learned a great deal from you and others and look forward to many more learning experences. I'll get better in the future on explaining things if I have the chance, then again I will always have you around to test me and make me think better on just how I should explain it

As a side note jefflaws, how about going over to the engine forum and maybe giving me some answers on a thread I started. Its titled "Stupid question on oil consumpution" something I have always thought about and was kind of hoping to learn something. I figure you have a lot of experence so maybe you could teach me some more. I know for you guys with tons of experence its a "stupid" question, but God I love learning about these trucks

 

NoProb.