Electrical Lesson Again Needed

[KVH]

Am I correct that a TR3 or TR4 will not start if the Ammeter Gauge is blown?

If so, why is that?

Either way, I think I need another lesson from the technicians here as to the relationship between the ignition, the solenoid, ammeter gauge and voltage regulator.

Thanks.

 

[DNK]

The power go through that on the way to somewhere else?

 

[TR3driver]

Someone give that man a cigar!

Power from the battery passes through the top terminal of the solenoid, the ammeter, and then the control box (aka voltage regulator) before it powers pretty much the entire car, including the ignition and starter solenoid. But if the ammeter is not passing current, you won't see the fuel gauge come up, nor the "ignition" light, so it's pretty obvious that something is wrong.

When the solenoid is energized (or you push on the 'button' on the back of it), it connects the starter directly to the top terminal (not through regulator or ammeter).

Does that answer the question?

 

[KVH]

When the solenoid is energized (or you push on the 'button' on the back of it), it connects the starter directly to the top terminal (not through regulator or ammeter).

The direction of the current is what I'm unclear about.

Based on the wiring diagram I have, and from what you say above, I'd assume that the battery lead to the solenoid engergizes the brown lead that goes from the solenoid to the ammeter and out of the ammeter with a brown and white lead to the control box.

Then power apparently goes from the control box, via a brown and blue lead to the ignition, meaning that the source of all power to the ignition must be that brown and blue wire (from the control box)? That would explain why a dead ammeter would mean no ignition.

Finally, I guess that would mean that the white and red wire from the ignition to the solenoid carries current only when the key is turned, and that's the current that closes the solenoid connection to send power to the starter.

Do I have it correct?

(If so, I'll go back and read why the red ignition light in the dash should go out after the engine is running!)

 

[TR3driver]

The direction of the current is what I'm unclear about.

Well, that's kind of a slippery concept. For the sake of simplicity, I generally think of it as flowing from "hot" to "ground", regardless of the polarity involved. It's really just a convention, either way, the results are the same.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Based on the wiring diagram I have, and from what you say above, I'd assume that the battery lead to the solenoid engergizes the brown lead that goes from the solenoid to the ammeter and out of the ammeter with a brown and white lead to the control box.

Then power apparently goes from the control box, via a brown and blue lead to the ignition, meaning that the source of all power to the ignition must be that brown and blue wire (from the control box)? That would explain why a dead ammeter would mean no ignition.

Finally, I guess that would mean that the white and red wire from the ignition to the solenoid carries current only when the key is turned, and that's the current that closes the solenoid connection to send power to the starter.

Do I have it correct? [/QUOTE]
Yup, all good.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:](If so, I'll go back and read why the red ignition light in the dash should go out after the engine is running!) [/QUOTE]
One way to look at it : the "ignition" light compares the output voltage of the generator to the voltage in the ignition circuit. With the engine and key off, both are zero, so no light. When you first turn the key on, the ignition circuit gets power through the switch (and the path above), but the cutout relay in the control box is still open, so no voltage at the generator output and the light is on. Once the engine starts, the output of the generator comes up, the cutout relay closes (connecting it to the battery) and the voltages match again, so the light goes out.

 

[Member 10617]

Randall or anyone else,

Randall: Your last explanation is very helpful to those of us mystified by the ammeter.

Could you indulge me by explaining in similar terms the following:

(1) What is happening when the ammeter reads below "0"? (Car drawing from battery?)

(2) What is happening when the ammeter reads above "0". (Car drawing from generator?)

(3) What is happening when the ammeter reads "0" (Generator and battery match?)

 

[TR3driver]

Pretty close, but above zero indicates that the generator is recharging the battery (in addition to supplying whatever the car needs).

Zero indicates that the generator output matches the car's load (not the battery); but that could be either because the battery is fully charged (hence the regulator is reducing the generator output to match the car), or because the generator can only keep up with the car.

 

[Member 10617]

Randall,

And below "0" indicates that the generator cannot keep up with the car?

If so, does this mean that the car is essentially running on the battery? And if so, what is to be done to correct this?

 

[TR3driver]

And below "0" indicates that the generator cannot keep up with the car?

Yes.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]If so, does this mean that the car is essentially running on the battery? And if so, what is to be done to correct this? [/QUOTE]
Well, it doesn't necessarily need "correcting", it's normal for the ammeter to go negative under some conditions (low rpm, heavy electrical load). Just the way it was designed (which was pretty much standard for all cars back then). Think of it like a cordless drill, it runs on the battery when needed and then the battery gets recharged to be ready for the next time it is needed.

But if the ammeter stays negative at higher rpm, then likely there is a problem with the generator and/or control box that should be located and corrected. Or possibly there is some unusually heavy load (like an electrical short) that needs prompt attention.

Or possibly it's just normal for what you have. My TR3 has extra brake lights, higher power headlights, and an electric radiator fan; along with the stock generator. It just cannot keep up with all of that at once, but hopefully there are enough periods when not everything is in use that the battery remains charged enough to start the car next time. It is something of a balancing act (especially since I have a somewhat smaller battery than original). And eventually I probably will convert to an alternator. The alternator still may not keep up with the load at idle (the 60 amp on my TR3A would not), but the extra output at higher rpm means it can recharge the battery faster.

 

[Member 10617]

Randall,

Your explanation is just what I have been looking for over the past nine months! Finally the whole situation with the ammeter is clear to me (at least as clear enough for my purposes). Thank you very much for this explanation of how the thing works.

My ammeter goes into the negative when I am running with lights on and driving at a slow speed or idling, but immediately recharges or goes to "0" when I am moving along. From what you say, this is normal.

I won't worry about it any more!

Again, many warm thanks.

PS: As I've written before -- you should write a book!

 

[Member 10617]

Randall,

One last question.

When the ammeter goes into the negative, the red ignition light comes on signaling that the generator is not keeping up with the load. Is this just a redundancy in the electrical system, as the ammeter should be enough to signal what is happening. Other than indicating that the car is ready to start when the key is turned on (light on), do the light and the ammeter indicate the same condition?

 

[TR3driver]

Well, they aren't quite the same condition. The ammeter can read negative while the generator is still putting out current; but the light should not be coming on until the generator is actually taking current (trying to act like a motor) rather than producing it.

For example, idling at around 1000 rpm (indicated, I think my tach reads a bit high), my generator produces about 5 amps. That's enough to keep up with just the ignition, but if I step on the brake pedal, the needle swings to discharge (a handy way to check if the brake lights are working). However the ignition light doesn't come on until much lower, like 500 rpm.

So the ammeter shows "enough" or "not enough", while the light only comes on for "none". But I guess you could say it's redundant to some extent.

 

[Member 10617]

Hi, Randall,

My light has always come when the tach falls to about 1000 rpms, even after three new voltage regulators, a new generator, and rebuilt and recalibrated tach. The car idles at 1000 to 1100 rpms. The guys around here who work on the car say that is "normal".... but I have always thought that 500-800 was "normal." For the time being, I guess I'm sticking with 1000 rpms.

Once the car is warmed up, etc., etc., my generator produces about 5 amps at around 1100 rpms.

Here is another sign of my ignorance. I thought that the generator only produced current but did not take it. I thought that the cut-out relay in the voltage regulator prevented current from flowing to the generator from the battery when the generator's output voltage was lower than the battery voltage.

I thought the light came on only at start-up and when the generator is not producing sufficient current.

 

[TR3driver]

I thought that the cut-out relay in the voltage regulator prevented current from flowing to the generator from the battery when the generator's output voltage was lower than the battery voltage.

Well, kind of. In fact, once the cutout has closed (normal operation), the voltage at the generator output is exactly the same as the battery voltage, because the cutout relay has connected them together. So the cutout relay also has to sense current from/to the generator, so that it can open when current starts to flow into the generator even before the battery voltage drops.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I thought the light came on only at start-up and when the generator is not producing sufficient current. [/QUOTE]
No, the light should only come on when the cutout relay is open, and it should not open until the current from the generator actually reverses.

I'm not sure why your light is coming on at idle, but since your generator seems to be working fine at higher rpm, it doesn't seem like something to lose sleep over. It's also quite possible that your tachometer is reading a bit high (not unusual for them to read as much as 500 rpm high).

Also, the "book" idle rpm is 500 rpm, but if your engine has been modified (mine has) or is a bit tired (mine is), it may not like to idle that low. It really doesn't matter anyway, unless you are spending an awful lot of time idling, or the idle is so high that the engine tends to run on. (I always kill mine with the clutch anyway, so even an occasional tendency to running on isn't a problem.)

I also find that, with modern fuel and SoCA heat, the idle rpm tends to vary quite a bit depending on current conditions. Having it set just a bit high makes the engine less likely to die when the idle rpm goes down.

 

[Member 10617]

My engine was rebuilt and, I believe, modified to some degree, altough I don't know the exact details. So perhaps, as you say, that is why it idles at 1000 rpm. At that speed, it sounds great and doesn't sound like it is racing or anything like that. It seems a bit high to me... but not too high.

And, thanks to traffic patterns here in western Virginia, I don't spend much time idling.

The tachometer was rebuilt recently, but I can't guarantee that it is absolutely accurate. It may be a little high...

I think the ignition (dash) light will remain a bit of a mystery to me, but as long as it seems to be doing what it should do, and the ammeter is functioning properly, I won't lose sleep over it.

I notice on this forum that from time to time others have similar questions about the light. It would be extremely helpful if someone with a keen knowledge of the proper functioning of this system -- voltage regulator, ammeter, ignition light, battery, generator -- could write up an explanation (not too technical) of how it all works (or how it should work) and how the guage should appear when the system working properly.

 

[Twosheds]

I used to be known far and wide for my excellent aircraft generator/voltage regulator/current limiter/reverse current cut-out lecture. I used overheads, chalkboard, hand-outs, arm-waving, show-and-tell, and a generator/regulator test machine. I received many compliments on this lecture from students who were retired electrical engineers.

That was years ago and now I am merely a disabled, depressed, confused Old Fart reduced to banging away at this keyboard. Oh, well...

The reverse current cut-out gets its name because reverse current (flowing from battery to generator) is what opens it. Of course, once it is open, the current stops flowing. Reverse current flows any time battery voltage is higher than generator output voltage.

The Randall will probably correct me here, but I think, if you go through all the lefthand rule stuff for motors, that the reverse current will try to run the generator as a motor in the OPPOSITE direction that the fanbelt is turning it. The current through the armature would be reversed, but the current through the field windings would remain the same, reversing the direction of rotation.

The generator would fight the engine!

My friend put a new wiring harness in his TR3 that he was restoring, but the electrical system didn't work. I went to help. He turned on the ignition and I heard a grinding sound. This sound was the generator turning like a motor! Luckily, he had left the fanbelt loose. He said that he had had a hard time soldering the ignition light in. Sure enough, he had left a solder trail between the ignition light contacts. Since the ignition light is in parallel with the reverse current cut-out, this has the effect of shorting the reverse current cut-out and allowing battery current to flow to the generator.

 

[TR3driver]

The Randall will probably correct me here, but I think, if you go through all the lefthand rule stuff for motors, that the reverse current will try to run the generator as a motor in the OPPOSITE direction that the fanbelt is turning it. The current through the armature would be reversed, but the current through the field windings would remain the same, reversing the direction of rotation.

The generator would fight the engine!

An interesting question. I won't claim to be able to go through all the "lefthand rule stuff" (especially and get it right the first time!) but I do believe you are mistaken about the direction reversal.

The generator is basically configured as a parallel-wound DC motor, and as a DC motor comes up to speed it starts to generate what is known as "back EMF". Back EMF reduces the current drawn by the motor (which is why they draw such huge amounts of current at startup), but that means the generated voltage is the same polarity as the applied voltage. At no load (ignoring drag in bearings and such), the back EMF matches the applied EMF and the rotor current drops to zero. If you then overdrive the motor in the same direction, the back EMF exceeds the applied EMF and the motor becomes a generator in the same polarity you started with.

I have also observed that when my radiator fan (a permanent magnet motor) was wired directly into the ignition circuit, it kept the engine running for several seconds after I turned off the key. Since I had several devices that would not like reverse voltage (including the electronic ignition), I don't believe the voltage reversed.

Third example: Some small engines (eg outboard motors or lawnmowers) use the same motor as both starter and generator, with the case being a common connection (hence no polarity reversal possible).

But as always, I'm open to discussion. I definitely don't have all the answers (and I'm not too clear on the questions either

)

PS, it would be easy enough to find out. Just take the belt off, and mash the cutout contacts closed with your thumb, then look to see which way the generator runs. I might even try that, next time I have the belt off for some reason.

 

[Member 10617]

Obviously I am in the presence of experts regarding generator/voltage regulator/current limiter/reverse current cut-out matters! The forum is lucky indeed to have such sources.

Dr. John -- I would have enjoyed hearing your lecture! As a retired history professor/college administrator, however, much of it probably would have gone well over my head.

I am reminded of a cartoon I once saw of a mathematics professor lecturing at the blackboard. He had strings of equasions on the blackboard, all leading to the conclusion: "At at this point a miracle occurs."

That's about how I look on the workings of my TR3 electrical system. I say a little prayer each time I take the car out that nothing will melt down, blow up, break down, or fall off! So far, so good.

 

[Twosheds]

An interesting question. I won't claim to be able to go through all the "lefthand rule stuff" (especially and get it right the first time!) but I do believe you are mistaken about the direction reversal.

I knew it!

Yes, the Back EMF is what makes the generator hard to spin. It's also what makes a generator self-regulate at about 18V for a 14V generator when you give it full field during troubleshooting.

Ed, my lecture was sort of like Popular Mechanics: "Written so even you can understand it".

Until you got to "college administrator". Now I'm not so sure! I have a sore spot about college administrators' intelligence. But it's not your fault!

When I get my scanner hooked up again, I'll look for the overhead I used. It is the simplest I've seen.

 

[Sarastro]

That was years ago and now I am merely a disabled, depressed, confused Old Fart reduced to banging away at this keyboard. Oh, well...

Not sure I follow. How does that make you different from the rest of us? :wink:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]

The Randall will probably correct me here, but I think, if you go through all the lefthand rule stuff for motors, that the reverse current will try to run the generator as a motor in the OPPOSITE direction that the fanbelt is turning it. The current through the armature would be reversed, but the current through the field windings would remain the same, reversing the direction of rotation.

The generator would fight the engine!
[/QUOTE]

I had never thought about this before, but I think you're right.