ENOS Wiring problem

[PeterR]

I suspect there are a number of reasons ammeters have fallen out of favour in production passenger vehicles, and surprisingly none of them has been raised in the posts above.

1.  In dem olden days before alternators, typical auto generators had an output of 19amp and the real big heavy-duty models had an output of 26amps.   Even though cars of those days were not loaded up with accessories, driving on a wet cold night with the load of ignition, lights, wipers and demister fan meant the generator would be struggling to cover the demand and any small deterioration in performance inevitably resulted in the battery being drained.   This meant the charge light alone could not be relied upon to indicate a satisfactory charge condition.

When alternators came along their output was almost double that of the generators they replaced.   If the charge light did not illuminate then the driver could be confident the alternator would be producing sufficient current to cover demand so there was little need for an ammeter.

2.  If a generator equipped engine is switched off or running at low revolutions the generator output voltage is lower than the battery voltage, and if permanently connected the battery would discharge into the generator.   To prevent this a low-voltage cut out relay in the charge lead isolated the generator under these conditions.

Also, the armature resistance of a generator is very low (less than 1ohm), accordingly the source resistance of a generator is small. Similarly a battery has a very low internal resistance and if the battery is almost flat the generator will attempt to pump in current at a rate beyond the safe capacity of the armature windings.   To prevent permanent damage from excessive current, generators had an external current limiter.

The low-voltage cut out and the current sensing coil were within the voltage regulator which was usually mounted on the firewall.   This meant heavy gauge wiring was already at the firewall and extending it a few inches to run an ammeter was not an expensive exercise.

Though the primary function of the rectifier pack in an alternator is to convert the AC voltage off the coils to DC, it also prevents current flowing backwards into the alternator eliminating the requirement for a cut-out relay.   The stationary coils in an alternator have a large inductance and as there is AC flowing through these an alternator is inherently current limiting making over-current control unnecessary.   These two features allow an alternator to be connected directly to the battery.   Typically the charge cable from alternator to battery post is about two feet, but has to be extended by at least ten feet if a dash ammeter is fitted adding to the cost and introducing undesirable voltage drop in the charge circuit.

3.  After the introduction of alternators as standard equipment some vehicles retained ammeters however they frequently caused driver anxiety.   The regulators used at that time were the mechanical type with three stages of charge; low, medium and flat out.  If an engine idled for some time the regulator would go to the highest setting, then when the engine revved up, the charge rate rocketed to maximum pegging the ammeter until the regulator dropped down a notch.   The solution to this was fitting a voltmeter instead of an ammeter.   As long as the needle remained in the green zone the driver felt content, and as a bonus these cost about a quarter of the price of an ammeter, and avoided the long runs of heavy gauge cables.
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The reality is that when used in automobiles modern alternators with solid state regulators do not require meters at all, a simple charge light is quite adequate.

The long leads associated with internal shunt ammeters cause voltage drop in charge circuits but if routed correctly are not dangerous as some suggest.

To be useful a voltmeter must read to fractions of a volt making the modern cheap thermal movement voltmeter connected to a heavily loaded ignition circuit serve little more purpose than to fill a hole in the dash.

The situation in marine and aero applications where the consequences of failure may be life threatening is different, but even here the argument of whether to use an ammeter which indicates trouble looming ahead, or voltmeter that confirms there is already trouble will go on forever.   Installing a remote sensing voltmeter and remote shunt ammeter settles the argument by providing all the attributes of both without any of the disadvantages of either.

[Bruce Dorsi]

Thank you, Peter, for taking the time to do all that typing!  

As usual, your explanation was thorough, clear, and VERY informative.  ....I always learn something from your posts!  

Thank you!

~~~~Bruce

[model a vette]

I built my dash using gauges from a '64 Malibu. It came with a shunt type ammeter as described above. On the Malibu setup the shunt looked like a ballast resistor. Long story short: it broke and ALL the charging current went thru the tiny wires to the ammeter. Smoke filled the interior. I changed to a cheap ammeter that put the charging current thru the ammeter. I never really liked it and it was difficult for my old eyes to see a discharge. I finally changed to a voltmeter. It is much easier to see a problem.

[PeterR]

story short: it broke and ALL the charging current went thru the tiny wires to the ammeter. Smoke filled the interior

And what does that indicate you forgot to do during the instalation.

[HOTRODSRJ]

Install a voltmeter!

This used to be a common problem on some models.  If the shunt which is the low impedance path opens, then all the current is trying to go thru the meter directly and hence fries the small wires and not to mention the gauge.

[model a vette]

Peter-
I assume you mean either a fusible link or Maxi-Fuse. My only defense is that the install was in 1976 and I didn't know as much about wiring then. The car now has a fusible link but I'll probably change to a Maxi-Fuse when I convert to a higher amp alternator this spring.

[Ed ke6bnl]

what exactly is a maxi fuse and how do they differ from regular fuses and resetable fuses. I believe I have herd the term used on tv when refering to large wattage stereo systems. Ed ke6bnl

[Skip]

I built my dash using gauges from a '64 Malibu. It came with a shunt type ammeter as described above. On the Malibu setup the shunt looked like a ballast resistor. Long story short: it broke and ALL the charging current went thru the tiny wires to the ammeter. Smoke filled the interior. I changed to a cheap ammeter that put the charging current thru the ammeter. I never really liked it and it was difficult for my old eyes to see a discharge. I finally changed to a voltmeter. It is much easier to see a problem.

How does a volt meter tell you there's a problem?

All a volt meter tells you is that there's a specific voltage at the back of the meter.  It DOESN'T tell you whether this voltage is sufficient or if the battery is slowly going south because it isn't being charged.

Some of the new, maintenance-free batteries need a charge voltage WELL ABOVE what an old lead-acid battery requires.  How do you know what voltage is "enough" and what's not enough.  What's too much?

With an ammeter, anything over an amp or two (once the starting voltage has been replenished) is too much.  If the charging system isn't up to the task, the needle moves towards "discharge".  If it's straight up, it's good.  If it's pushing to either side, you have a problem.  Pretty simple when you compare it to a volt meter.

[PeterR]

Whenever the words voltmeter or ammeter are uttered there is that bizarre reaction similar to discussions involving front steer vs rear steer, carb vs injection, stick vs auto, drums vs disks.

For some reason utterly beyond my comprehension there is a belief that an ammeter is the fire breathing dragon and a voltmeter the knight in shining armour.  

Most of the criticism directed towards ammeters has been based on fault conditions of poor installations, when it should have been directed at the installation rather than the device.  No one has raised the issue of what happens when a fault occurs in a voltmeter attached directly to the ignition switch and the main feed does not have a fusible link.

The reality is that they are simply electrical devices and if correctly installed either is safe: if poorly installed both are dangerous.

If there is something intrinsically unsafe about conductors carrying large currents then every automobile with trunk mounted battery would have burned to the ground, there would be smoke pouring from vehicles with a seven pin trailer socket, and dash mounted cigarette lighter sockets would have been banned by insurers.  

Modern alternators with electronic regulators control are extremely reliable, and in the vast majority of applications there is no need for a meter at all.  In the unlikely event a battery goes flat from lack of charge generally the outcome is a mild inconvenience, however if an engine losses oil pressure the outcome is far more serious yet people are quite happy to place their trust in a low pressure light.

[32tom]

Whenever the words voltmeter or ammeter are uttered there is that bizarre reaction similar to discussions involving front steer vs rear steer, carb vs injection, stick vs auto, drums vs disks.

For some reason utterly beyond my comprehension there is a belief that an ammeter is the fire breathing dragon and a voltmeter the knight in shining armour.  

Most of the criticism directed towards ammeters has been based on fault conditions of poor installations, when it should have been directed at the installation rather than the device.  No one has raised the issue of what happens when a fault occurs in a voltmeter attached directly to the ignition switch and the main feed does not have a fusible link.

The reality is that they are simply electrical devices and if correctly installed either is safe: if poorly installed both are dangerous.

If there is something intrinsically unsafe about conductors carrying large currents then every automobile with trunk mounted battery would have burned to the ground, there would be smoke pouring from vehicles with a seven pin trailer socket, and dash mounted cigarette lighter sockets would have been banned by insurers.  

Modern alternators with electronic regulators control are extremely reliable, and in the vast majority of applications there is no need for a meter at all.  In the unlikely event a battery goes flat from lack of charge generally the outcome is a mild inconvenience, however if an engine losses oil pressure the outcome is far more serious yet people are quite happy to place their trust in a low pressure light.

Yes I agree. Ammeter is a buzz word.  I do put in a fusible link in the 10 ga. wire not for fear that the ammeter will fail but for fear that the highly reliable alternator might fail. (again) I had an alternator short out while driving. The 10 ga wire carried every amp left in the battery staight to ground inside the alternator. The old SW ammeter handled the load with no problem, unfortunately. Even without an ammeter the charging circuit would have melted all the wires in the loom. A cheap fusible link would have blown instantly saving the wires. I don't think anyone would think that a GM alternator is dangerous. I don't but, a fusible link is cheap insurance. IMHO

[model a vette]

Skip-
As I stated I couldn't see the ammeter well enough to determine a slight discharge vs. a "zeroed" needle. The voltmeter tells me that the alt is charging, when I start, because it shows 14+ volts going to the battery and the rest of the system. If it shows 12 volts I know something is wrong. If the voltmeter drops to less than 12 volts I know I have too much load or the alt or battery took a dump.
How does a ammeter show a bad battery? It would still show a charge flow even if the battery was going bad.
In the end both the ammeter and voltmeter have their good and bad points.

[Skip]

if it drops below 15 volts with a current generation battery you have a problem.

the trouble is, you need to know what generation of battery is under the hood to be able to make any sense of an ammeter.

An idiot light tells you a LOT more about the charging system than a volt meter does if all you want to know is if it's charging or not.

Ammeter is best, idiot light is next and the volt meter is the least usefull for this particular task.

[HOTRODSRJ]

if it drops below 15 volts with a current generation battery you have a problem.

the trouble is, you need to know what generation of battery is under the hood to be able to make any sense of an ammeter.

An idiot light tells you a LOT more about the charging system than a volt meter does if all you want to know is if it's charging or not.

Ammeter is best, idiot light is next and the volt meter is the least usefull for this particular task.

I have to respectfully disagree if evaluating the overall application.  If the voltmeter shows more than the full battery charge voltage(12.65V for lead-acid) then you know the alternator is holding the charge up...it's that simple. Don't make it toooo complicated.  I don't have any idea why you think anything below 15 volts is an issue when in fact most alternators won't produce that under most conditions.  What's up with that? Please explain further whereas I can't figure that statement out?

Idiot lights are inherently subject to higher failure rates due to the bulb aspect failure alone.  LED indicators would be far more trusting to split hairs here for the idiot light.

While I will agree that properly installed amp meters are okay.... in alot of these cars with heavy loads (my 57 pulls in excess of 85+ amps in full tilt position) and I sure am not going to pull all that thru a wire to the interior for sure.  Modern OEM wiring systems use a "tree" style desigin with alots of branches and relays to keep high loads off the main bus and relay everything over 10amps.  This is done for reliabililty, voltage drops and safety. As I have pointed out earlier, safety experts have lobbied to get high current carrying devices out of the interior due to their designed and inherent ability to carry very high currents under "shorted" conditions making for a greater likelihood of fire or fuel ignition.  I could offer a library of information here on that, but all of these articles are copyrighted to authors or schools or companies. Join the American Society of Automotive Engineers and subscribe to their series to learn more.

I also point out that ammeters will show so little deflection on the meters scale that most people are not aware that they are operating effectively, if at all.....or can't read them.  This was an inherent problem of the "ergonomics" side of this subject and witnessed right here in this forum with an anecdotal post.  I think that is a very good reason to go away from ammeters.

FWIW, I too have always been a proponent of fusible links.  Some people use them...some not unfortunately.  But, you can have a "limited" fault on highly "fused" lines that can provide as much of a problem as a short.  So, very high current one wire sources and protected as such are vulnerable to these problems.

"The reality is that they are simply electrical devices and if correctly installed either is safe: if poorly installed both are dangerous."  I agree completely.....but...these designs can be improved on as proof by the modern automotive electrical system.

"If there is something intrinsically unsafe about conductors carrying large currents then every automobile with trunk mounted battery would have burned to the ground, there would be smoke pouring from vehicles with a seven pin trailer socket, and dash mounted cigarette lighter sockets would have been banned by insurers."... well "every automobile" is a little strong...don't ya think?...... and moreover ..... we are talking perhaps 100+ amps potential ....not a measily 10amps or 20 for that matter?? Completely different realm of current and these examples are not considered heavy loads by any means.  

FWIW, I have seen three trunk mounted battery vehicles in fact in minor rear-end collosions and burn to the ground because the positive lead shorted to ground with no protection.  This is why I put a master fuse (150amps) within 18" of my positive lead at the battery to the starter.  So, it does happen to turn your example around.  

Just my two sense.

[Ohio Blue Tip]

FWIW, I have seen three trunk mounted battery vehicles in fact in minor rear-end collosions and burn to the ground because the positive lead shorted to ground with no protection.  This is why I put a master fuse (150amps) within 18" of my positive lead at the battery to the starter.  So, it does happen to turn your example around.  

Just my two sense.[/quote]

Since you folks seem to be well versed in electrical systems, what and where do you recommend master fuses or fusible links and what capacity for general street rods.
I have, over the years, done a fare amount of rod wiring and usually use a master disconnect switch in the batter positive cable. The last car I did we used a master fuse in the battery, alternator, starter loop.  I would like more of this protection incorporated into wiring systems and as I do most jobs from scratch, I would like to know capacity and location that would be best to protect most rods.
Thanks, Ken

[river1]

FWIW, I have seen three trunk mounted battery vehicles in fact in minor rear-end collosions and burn to the ground because the positive lead shorted to ground with no protection.  This is why I put a master fuse (150amps) within 18" of my positive lead at the battery to the starter.  So, it does happen to turn your example around.  

Just my two sense

Since you folks seem to be well versed in electrical systems, what and where do you recommend master fuses or fusible links and what capacity for general street rods.
I have, over the years, done a fare amount of rod wiring and usually use a master disconnect switch in the batter positive cable. The last car I did we used a master fuse in the battery, alternator, starter loop.  I would like more of this protection incorporated into wiring systems and as I do most jobs from scratch, I would like to know capacity and location that would be best to protect most rods.
Thanks, Ken

GREAT QUESTION maybe it can be put in a new thread so as to allow it to be saved in the tech section.

thanks jim