Electrical Lesson Again Needed

[Member 10617]

Dr. John,

Ha, ha! Yes... when I left the faculty and entered the administration, my faculty colleagues accused me of "going over to the enemy." They forgave me when I became a champion of better salaries for faculty members.

If you find that overhead, I would like very much to see it.

For veteran TR2 and TR3 drivers in the forum, I'm afraid that most of my questions are pretty basic, but some of us are new at this, and then there is the younger crowd who will come along and discover these great old cars and will need basic information. Thus, your information, and that of others, is welcome, indeed.

I still wish someone would post a basic description/explanation of what the driver is seeing when he or she watches the antics of the ammeter (from start-up to cruising). And, for that matter, what the other gauges show (except fuel gauge and speedometer) and how to interpret them. A kind of "Watching the gauges for Dummies" kind of posting. As the philosophers might say, gauges are the outward signs of an unseen existence.

 

[Twosheds]

If you find that overhead, I would like very much to see it.

I used to be able to draw it from memory, but those days are long gone!

 

[Member 10617]

Looks like we are of the same generation!

 

[TR3driver]

I still wish someone would post a basic description/explanation of what the driver is seeing when he or she watches the antics of the ammeter (from start-up to cruising). And, for that matter, what the other gauges show (except fuel gauge and speedometer) and how to interpret them. A kind of "Watching the gauges for Dummies" kind of posting. As the philosophers might say, gauges are the outward signs of an unseen existence.

I would be willing to try, except I never know in advance what level of answer people expect. It's kind of like "Why is the sky blue?": do you want to hear the explanation about how Rayleigh scattering depends on wavelength, or why do we call that color "blue" instead of "zibnitz"? Or just the usual "God made it that way" (which translates as "I don't know")?

Ok, I'm being a bit facetious, but the problem is real.

 

[Member 10617]

Well... I think what I have in mind is just a very basic (perhaps too basic) overview or explanation of the guages.

Electricals (What can one expect to see in the guages):

For example: Turn on the key and the ignition light glows. What does this indicate? Current flowing from X to Y...

Begin driving, light goes out and ammeter high in positive territory. What does this indicate? Generator recharging battery? Generator powering electricals?

Continue driving at "normal" rpms. Ammeter eventually settles down to "0" but jumps a little from time to time. What does this indicate? Battery and generator equal? Current flowing from X to Y...

Continue driving but the ammeter doesn't fall... stays at about 20 or 30 without dropping. What does this indicate?


Turn on the lights and the ammeter moves into negative territory. What does this indicate? Lights drawing on battery? What if the ammeter remains in negative territory?

Idle... Ignition light comes on. What does this indicate?



Oil pressure (What can we expect to see):
Start out and oil pressure up around 80. Normal? too high? Depends on following factors: temperature, weight of oil, some other reason?

Continue driving and oil pressure goes down to about 50 at normal speed (say 45 or 55 mph, 2000 or 2500 rpms). Indicates what?

Idle. Oil pressure comes down to 30 or lower. Good or bad? Normal?

Temperature
What is considered "normal" for ordinary conditions (if there is such a thing)? 180-185? How high can it go and for how long before it indicates trouble (before you see steam!)? Can it go too low?


The technical details behind all this could fill a book, I know, but as they say, you've got to walk before you run... and some of us new to these cars are either walking... or even crawling. It would be reassuring to have the "big picture" when looking at all these guages as we cruise down the highway. It would be nice to know what, in theory anyway, they should be doing and if they are giving good signals or signaling a problem. The manuals are good at telling us how these guages work, but fail to tell us how to read them.

In other words, just an answer to the question: What's going on here?

Clearly, what I am asking for involves, to some degree, a consolidation of much that has been said in this and many other threads. But it would be great to have it all in one place.

.... Or... perhaps what I am suggesting just isn't that necessary, helpful, or possible. Anyway... just a thought.

 

[Twosheds]

Not until you spell gauge correctly!

 

[TexasKnucklehead]

Einstein once said everything should be as simple as possible –but no simpler.

I’d like to see that lecture as well, and I’m sure the left-hand principles will be adhered to even in RHD cars. And I’m sure Randall could provide enough information to make me pay much closer attention.

But, Ed, you still need to remember the difference between a gauge and an instrument. Your tachometer is technically a gauge and not a precision measuring instrument. The ‘instruments’ on the dash are all ‘gauges’ and though they have been somewhat ‘calibrated’ and are adorned with numerals, they are intended to ‘gauge’ different things, and not yield exactly accurate values (especially through their entire measuring range). The red light on the dash is also an indicator, not necessarily meaning to show a faulty condition –it’s another gauge to help you know what is going on.

I love discussions that start with a simple question and end up questioning how god might be involved in choosing the name of a color, or how one spells gauge.

 

[Member 10617]

Yow! How did I miss that typo? You caught me. Sorry... about that. Gauge it is! Obviously too much in a hurry to proofread.

I love these discussions also... For me the question is: These gauges are saying something to me, but I don't speak their language yet. Need a Rosetta Stone.

Lincoln once said: For every problem there is a simple solution... and it is usually wrong.

 

[TR3driver]

For example: Turn on the key and the ignition light glows. What does this indicate? Current flowing from X to Y...

Simplest explanation, it indicates that the key is on but the engine is not running (as shown by the generator cutout being open). That is why it is called an "ignition" light.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Begin driving, light goes out and ammeter high in positive territory. What does this indicate? Generator recharging battery?[/QUOTE]Exactly.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Continue driving at "normal" rpms. Ammeter eventually settles down to "0" but jumps a little from time to time. What does this indicate?[/QUOTE]Now we're into "it depends". The jumping may indicate an electrical load of some sort (like brake lights or turn signals). Or it might indicate the VR contacts are a bit dirty and are either sticking or not always making good contact when they close. Or if the rpm is on the low side, it may indicate that the generator has only a little bit more capacity (at that rpm) than is required to meet the requirements (of charging plus load).

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Continue driving but the ammeter doesn't fall... stays at about 20 or 30 without dropping. What does this indicate?[/QUOTE]Either the battery is still not fully charged (it can take 2 hours or more for a deeply discharged battery to fully recharge), or the generator controls are malfunctioning in some way. If you see more than 20 amps (rated generator output) for more than just a few minutes then it's fairly certain that either the charging circuit is malfunctioning, or there is a problem with the battery (eg shorted cell).
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Turn on the lights and the ammeter moves into negative territory. What does this indicate? Lights drawing on battery?[/QUOTE]Yes.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] What if the ammeter remains in negative territory?[/QUOTE]
Eventually, the battery will run down.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Idle... Ignition light comes on. What does this indicate?[/QUOTE]
That the generator is not working at idle.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Oil pressure (What can we expect to see):
Start out and oil pressure up around 80. Normal? too high?
[/QUOTE]Perfectly normal.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Depends on following factors: temperature, weight of oil, some other reason?[/QUOTE]Temperature of the oil (which is perhaps what you meant, but it's not always the same as air temperature). General condition of the engine. RPM of course. Too high or too low may indicate a problem with the oil pressure relief valve (aka pressure regulator).
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
Continue driving and oil pressure goes down to about 50 at normal speed (say 45 or 55 mph, 2000 or 2500 rpms). Indicates what?
[/QUOTE]Within the normal range, I'd say. Possibly a smidgeon on the low side, indicating (perhaps) a grade of oil on the thin side for the prevailing weather, or the bearings are a bit worn (not enough to merit an overhaul). Sometimes oil gets thin with age and use, too, so it might just indicate the need for an oil change. The list of possibilities goes on.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]Idle. Oil pressure comes down to 30 or lower. Good or bad? Normal?[/QUOTE]Reasonably normal. A fresh engine would probably carry somewhat more, but it's certainly not worn out yet.

Mine was down to around 10 psi hot (with 20W50 oil), so I changed the rod bearings. Actually a fairly simple procedure with the engine still in the car; as I recall one of the books recommends it every 30,000 miles.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]
Temperature
What is considered "normal" for ordinary conditions (if there is such a thing)? 180-185?[/QUOTE]
Certainly nothing wrong with that.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] How high can it go and for how long before it indicates trouble (before you see steam!)?
[/QUOTE]As long as you only see steam under exceptional conditions, I'd say it's OK. Generally, the higher it runs under "normal" conditions, the less margin is leftover to handle those "abnormal" conditions (like climbing a big hill on a hot day).
<div class="ubbcode-block"><div class="ubbcode-header">Quote:] Can it go too low?[/QUOTE]
Yes. If it doesn't consistently reach at least 160F, then your thermostat is not working. Not a show-stopper necessarily, but running the engine too cold tends to lead to more rapid wear, poor fuel mileage and so on.

 

[Member 10617]

Randall,

You have given me exactly what I need to start putting all of this into some order. Many warm thanks to you, Dr. John, Texas Knucklehead (?), and others who have patiently reviewed these ramblings of mine.

I have pages of BCF postings, many references in manuals, and several articles from the Internet that I will now attempt to boil down and write up into a clear and simple statement of what the new or inexperienced driver of these cars (like me) can expect to see on the dash when not concentrating on the road ahead. When I get it ready, I'll post a draft on the forum and hope you guys will work it over, correct it, poke holes in it, confirm it, dismiss it... whaterver seems appropriate.

 

[poolboy]

After a while you'll get used to what your gauges indicate as normal for your engine, not necessarily any one elses'.
When your gauge indicates a deviation from normal, that's when their true value to the driver become obvious.

 

[Member 10617]

Poolboy,

Great observation and excellent advice! Many thanks.

As long as "normal" is within the proper range, I think you are right that every engine is going to be a bit different. So, "normal" will be normal for one's own engine.

What I'm trying to overcome is ignorance of what the proper range is. For example, I drove home from a shop once after having a brand new regulator and a brand new generator installed. I, too, was new to the car. The ammeter registered 30 and stuck there, and soon the ignition light came on and remained on. I had no idea whatsoever what was happening, but I had a feeling that things were not right -- a hunch, but no knowledge. When I returned to the shop I discovered that the voltage regulator either had not been set properly or was defective, and that my new generator had melted down. Ignorance, in that situation, was definitely not bliss.

Fifty years ago when I drove one of these cars, I only looked at the speedometer and the gas gauge. I paid no attention to any other gauges figuring that they would do their thing and I had no idea what their "thing" was and really didn't care. Fact is, I got on quite well that way -- but then the car was "new."

 

[Twosheds]

Aircraft instruments are marked with color range markings.

A green arc means that if the needle is in that range, that's normal operating range, a red arc means bad, a yellow arc means caution, etc. etc. etc.

Why don't autos use this convention?

 

[Member 10617]

Dr. John,

Excellent idea! Yes, why don't they use color range markings?

As I search through other threads in this forum and in other forums, I come across others who have no idea what the ammeter is supposed to indicate. You'd think the owners manuals for these cars, electric cars, tractors, etc., etc., would at least give the new owner a "hint." Guess it is knowledge that comes with one's DNA! Ha!

I have also found many experienced guys who say that an ammeter is less than useless in a car. What is needed is a voltmeter. (I can't comment inteligently on this.) The simplest explanation I have found is that an ammeter is like a water meter: it indicates when current is flowing one way or the other. At least this tells the driver that there is current.

There must be a good reason why "modern" cars for the most part don't have ammeters but have voltmeters.

I do plan to write up what I have discovered about the meaning of all these gauges, and I hope it will help others like me to whom all this is new. If not, at least my obsession with all this has kept me off the streets and out of trouble ... at least until the sun shines and the temperature rises to 55 degrees or better.

 

[TR3driver]

Yes, why don't they use color range markings?

Well, particularly in the case of the ammeter, there is no "good" and "bad" reading. +20 amps is perfectly normal sometimes, and a problem other times. Likewise -20 amps is perfectly normal sometimes and a problem other times.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]As I search through other threads in this forum and in other forums, I come across others who have no idea what the ammeter is supposed to indicate. You'd think the owners manuals for these cars, electric cars, tractors, etc., etc., would at least give the new owner a "hint." [/QUOTE]Not if they don't read them!

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I have also found many experienced guys who say that an ammeter is less than useless in a car. What is needed is a voltmeter. (I can't comment inteligently on this.)[/QUOTE]I have tried both. IMO a voltmeter gives you less information, and only tells you what has happened in the past. Slightly better than an "idiot" light, but not much; especially since they very rarely read actual battery voltage.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:] At least this tells the driver that there is current.[/QUOTE]Well, no, not really. As we've discussed, even when the ammeter reads zero, there can still be current. The coil, lights, etc. do NOT run themselves.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]There must be a good reason why "modern" cars for the most part don't have ammeters but have voltmeters.[/QUOTE]Actually, most of them just have idiot lights. The reason for that is because most drivers are idiots when it comes to understanding how a car actually works.

Voltmeters serve much the same purpose, they are much easier to explain to folks that don't understand how the electrical system actually works. The same way a yardstick is "better" than a vernier caliper!

Two more reasons: With modern alternators, keeping the battery charged is much less of a concern. As I pointed out before, generators pretty much always were kind of marginal, so keeping an eye on actual charging is important.

And with a voltmeter, all of the current doesn't flow through the gauge. That means you don't have two big, unfused wires running through the dash.

 

[Darrell_Walker]

There must be a good reason why "modern" cars for the most part don't have ammeters but have voltmeters.

For the most part, modern cars just have "idiot" lights...

One reason for the change is that an ammeter requires all the current to go through that one gauge. As the electrical needs grew, that was a lot of current to pass through the gauge.

Here is one person's opinion:

https://www.egauges.com/ATM_Tips.asp?TipPage=voltmeterammeter.htm

 

[poolboy]

Do modern cars really just have idiot lights ?
I kinda thought that they went out of favor.

 

[Twosheds]

One reason for the change is that an ammeter requires all the current to go through that one gauge. As the electrical needs grew, that was a lot of current to pass through the gauge.

That's why I like the shunt type ammeter. Only a small, but proportional, current flows through the meter; the rest goes through the shunt and then to the electrical system. Therefore, an open failure of the meter does not cause a failure of the rest of the system.

 

[TR3driver]

Do modern cars really just have idiot lights ?

Sometimes they are disguised ... my buddy's Miata had an oil pressure "gauge" that ran from a switch :laugh:

 

[Member 10617]

As if all this were not complicated enough for the average non-electrical engineer driver,consider this: "Since the classical ammeter is hooked up in series, it involves very thick wire (like 10 ga) to be routed all the way to the ammeter in the cockpit of your car. With all that current flowing through the ammeter, a short circuit on the ammeter in the cockpit can be fairly dramatic, and some classic car guys avoid ammeters for the possibility of causing a fire."

A good argument to have an external shunt.

Can an original ammeter be modified to include a shunt?

To give an example of how brief some manuals can be, here is the write-up on the ammeter from Classic Car Electrics. "The ammeter or amp-meter is a handy thing on an older car, as it keeps the driver in touch with the state of the charging system. If not fitted as standard, the an aftermarket unit is worth the trouble to fit. The meter is placed in circuit with the generator, and measures the current as it flows based on the mabnetic field which is produced by that flow." That's it. If you want to know more, you won't find it here.