Ammeter a ticking time bomb?

[KSCHEVYUP]

Not trying to stir up stuff; just something to think about.
But this was is the July 2017 issue of 4-Wheel & Off-Road magazine.
Any thoughts on the subject?
Sorry-Not smart enough to know how to rotate pic?

[Jeff's bowtie's]

Well here you go

[franken]

Zero issues w/ 60s and up (if not earlier) GM vehicles since there is no ammeter and no current flows through it. Look at the gauge. it says battery and has no units. It gives nothing more than an indication of charge or discharge.

Of course 10 people who know nothing about electricity are going to start babbling in response, but facts are facts.

[harpo231]

If ya cant fix it with a BFH then its electrical

[leddzepp]

Franken is correct, there are no issues.

[KSCHEVYUP]

I'm not going to babble; but I am one of the ten people that doesn't know chit about electricals!
Thanks for the clarification
Ron

[clay68c10]

International and others had the generator charge wire to the battery routed inside the cab and thru the amp meter. Horrible idea.
On our trucks it is a low current shunt with fuses, just in case.

[Baradium]

Originally Posted by franken

Zero issues w/ 60s and up (if not earlier) GM vehicles since there is no ammeter and no current flows through it. Look at the gauge. it says battery and has no units. It gives nothing more than an indication of charge or discharge.

Of course 10 people who know nothing about electricity are going to start babbling in response, but facts are facts.

That, sir, is the definition of an ammeter.

A voltmeter is the alternative. What you can do though with an ammeter is put a shunt on the back that isn't full size and the gauge can still work just with less current through it. Having less amperage takes care of the problem, but you do actually have an ammeter if it is reading charge and discharge.

[In The Ten Ring]

44 years and still ticking....that's a very slow fuze.

(1972 truck)

[franken]

Originally Posted by Baradium

That, sir, is the definition of an ammeter.

A voltmeter is the alternative. What you can do though with an ammeter is put a shunt on the back that isn't full size and the gauge can still work just with less current through it. Having less amperage takes care of the problem, but you do actually have an ammeter if it is reading charge and discharge.

Sorry, an ammeter is a device for measuring electrical current, but feel free to babble all you want.

[jocko]

Well, ticking time bomb or not, GM decided to convert to voltmeters for whatever reason in the mid 70’s, around 76-ish give or take a year. And if one wants that indication over what the stock ammeter provides, member TBONE1964 sells a beautiful conversion kit.

[VetteVet]

Here's the definition of an external shunt ammeter which is what we have in our trucks.

An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).

This is the reason there are 2 small fuses in the wiring circuit on our trucks that have battery gauges. They are actually amp meters since they measure amperage differential and not volt meters because there is no connection to the negative side of the circuit.

Here is the engine side of the diagram showing the SHUNT, the fuses (circled in red), and the wiring to the firewall. The two small wires go to pins 1 and 12 on the cluster connector.
If you have the charging light you will not have any of this, only the gauge dashes have the ammeter.

[special-K]

I'm not an electrical expert, not going to babble, and not going to insult other members over such nonsense. All I'm going to say is that article appears to be written by one of the 10 people you refer to because it's nothing but a bunch of hype about an issue I for one have never heard of happening in all my years, all the trucks I've had, and all the people I have talked to about issues with their trucks.

[panhead59]

Yep

[B. W.]

VetteVet, as always, great explanation with pics! Thanks.

[hoseman1979]

So from this diagram, I am a bit concerned that my internally regulated alternator upgrade is sending the full power to the ammeter. Should I be concerned or does the internal regulator have a fix in it?

[Coley]

...good info, and very good respectful info VetteVet...informative stuff!
Now, I have to check those 2 little short fuses to see if they are working these days. To my recollection they always seem to be the primary reason that gauge stops working.

All good
Coley

[VetteVet]

Originally Posted by special-K

I'm not an electrical expert, not going to babble, and not going to insult other members over such nonsense. All I'm going to say is that article appears to be written by one of the 10 people you refer to because it's nothing but a bunch of hype about an issue I for one have never heard of happening in all my years, all the trucks I've had, and all the people I have talked to about issues with their trucks.

You are correct that the article is a bunch of hype and it was written by someone looking for shock value instead of correct information.

He has conflated the amp meters of the pre 62 trucks with our 63 and later ones with ammeters, correctly called battery gauges, because they show current flow to and from the battery. As was pointed out by our friend Franken.

The earlier ones were used on Generator charging systems and maybe some of the early alternators. In both cases all the charging current and battery current ran through the amp meter which was in the vehicle dash. I don't recall many problems with them unless the terminals were shorted to ground which could easily cause a fire or a burnt harness.

Here's the diagram which shows the current path of the earlier harnesses.




These systems were designed for 30 to 60 amp currents and would not be adequate for our modern 100 amp alternators although it is possible to use one if it is wired correctly. I wouldn't recommend that setup unless the alternator was wired to a main junction first. I don't want to get into that in this discussion.

I hope we've alleviated the OPs fears about his ammeter and explained it so that anyone else who read that article won't panic.

[RichardJ]

Below is an Ammeter. An Ammeter consists of a shunt wired in Parallel with a meter movement. The meter movement is a D'Arsonval Galvanometer. The shunt is basically a resistance. A meter movement wired in Series with a resistance would be considered a Voltmeter, except a voltmeter isn't placed IN the circuit.

In the drawing you can see I drew a FAT Red line showing that 90% of the current flows through the shunt resistance and maybe 10% of the current flows through the meter movement.

The shunt can be mounted inside the meter movement. The shunt can be mounted on the back of the meter movement. The shunt can be mounted in a remote location any distance from the meter movement.
If you look for Stewart Warner or VDO, Marine Gauges, you will find gauges that must be used with remote mounted, stand alone Shunts.
The two wires from the shunt to the meter can be very small because they carry very small amounts of current.

The 20 Amp gauge pictured has an internal shunt. The two 60 Amp gauges in the picture, have the shunt mounted on the outside for better cooling.

These three automotive gauges with built in shunts, required a large gauge wire run through the firewall from the battery and another large wire from the gauge back out to the generator.
The 67-72 chevy truck used the remote shunt setup, so the two small fused wires Vettevet mentioned, carry a very small current.

The reason they stopped using Ammeters is the same reason the 67-72 truck doesn't have markings on the gauge face. The vast majority of the drivers, don't know how to read the gauge.
When all is right with the World, the battery is fully charged, the generator is putting out the same current that the lights, radio and ignition are drawing, the Ammeter says "0. Amps". "0 Amps", My God my car is broken. They sold me a defective car. Imagine a dealer trying to explain to some soccer Mom that Zero Amps is a good thing. Easier and cheaper to put in the aptly named idiot light.

The article from the OP is about '70s and earlier jeeps. They mentioned Mopar also used the same Ammeters up until the same era.
The 20 Amp gauge I pictured I think is from a '20s ford even though it doesn't say ford on the face. The one 60 Amp is obviously very old, but I have no idea and the last is SW.
Back in the early days of the auto, current drawing options were nonexistent and generator output was lower even though they were 6 volt systems. Gauges with built in shunts worked fine.

[davepl]

VetteVet has it covered with respect to our trucks, which do NOT have ammeters.

I, however, am someone who's had an ammeter melt. It was an aftermarket gauge and I was driving along and it melted/caught fire. For reasons I do not understand, it smelled like Chinese food.

But that's a case where it's a real ammeter and all the current in the system was flowing through the gauge. A "bad idea".

In my '69 Pontiac 2+2 I have the rally gauge package with the ammeter, and I've changed to a 120A alternator, and it'll peg the gauge due to the unexpectedly higher differential (vs the 35A stock unit). Not sure if that's actually bad for anything... I don't think so.

[RichardJ]

This is the same wiring that Vettvet posted earlier, but with most of the non essential circuits removed for clarity.

All copper wire has resistance. The smaller the wire diameter, the greater the resistance. The longer the wire the greater the resistance.
The copper wire between the battery junction block and the Junction below the alternator has a specific resistance because of its size and length. This section of the 12R wire serves two purposes for the price of one.
This wire segment serves double duty as the shunt for the meter movement.
The 18B fused wire and 18B/W fused wire carry a small amount of current to the Ammeter gauge.
If the battery is pushing more current across the shunt than the gen is producing the gauge shows discharge. If the gen is pushing current across the shunt to the battery, the gauge says charging. When the gauge says Zero Amps, the battery is fully charged and the gen is putting out only what is needed above that.

[RichardJ]

>> It was an aftermarket gauge and I was driving along and it melted/caught fire. For reasons I do not understand,<<

If it was working correctly at the time of the installation, because of the exposed nature of the posts on the back, I'd say something fell down and shorted it out.

>>my '69 Pontiac 2+2 I have the rally gauge package with the ammeter, and I've changed to a 120A alternator, and it'll peg the gauge due to the unexpectedly higher differential (vs the 35A stock unit). <<

Did you increase the load demands at the same time the new alternator was installed?
Was the original 35 Amp Alt unable to keep the battery charged and showing a discharge much of the time?
If the 35 Amp alt was able to charge the battery and show 0 Amps soon after starting the motor and while driving, then the 120 Amp Alt should not have had to put out any increased power above the 35Amp Alt. You would have brighter headlights at idle, but little else should have changed.

I can't say I've ever messed with a Pontiac that had the Rally gauges.
I did have to straighten out some wiring on a friends 1st gen Camaro that had the Rally gauges. That was 40 + years ago.

Ok, with the Chevy, they had different wiring and used a different voltage regulator with the Rally Gauges. The regulator has only one relay inside it and with no idiot light, there is no resistor wire in the dash harness.

You switched from a 35A externally regulated alt with no field relay in the Reg to an internally regulated Alt. Three wire or one wire Alt?

I'm just guessing that the Pontiac is like the Chevy and that the conversion was based on the typical External to Internal conversion.

[toolboxchev]

Originally Posted by davepl

VetteVet has it covered with respect to our trucks, which do NOT have ammeters.

I, however, am someone who's had an ammeter melt. It was an aftermarket gauge and I was driving along and it melted/caught fire. For reasons I do not understand, it smelled like Chinese food.

But that's a case where it's a real ammeter and all the current in the system was flowing through the gauge. A "bad idea".

In my '69 Pontiac 2+2 I have the rally gauge package with the ammeter, and I've changed to a 120A alternator, and it'll peg the gauge due to the unexpectedly higher differential (vs the 35A stock unit). Not sure if that's actually bad for anything... I don't think so.

Although it melting is not a funny situation, I find it absolutely hilarious that an aftermarket product burning and smelling like foreign food!

[special-K]

Originally Posted by toolboxchev

Although it melting is not a funny situation, I find it absolutely hilarious that an aftermarket product burning and smelling like foreign food!

My gauge was made in India and when it burned up it smelled like red curry! Just kidding!!!

I really appreciate you guys who know automotive electrical systems. I'm good with finding shorts but have little knowledge of how charging systems work in their entirety. Thanks! Hey, what's that smell? Smells like hamburger. Must be an original part!

[Gromit]

Great post and very helpful responses and discussion - I'd been worried about this issue too - a couple years ago someone at American Autowire made the passing comment that the updated C10 harness kits modify the ammeter and require a later type voltmeter.. Since I wanted to stay with the Original Equipment style I still chose their "Factory Fit" product but I always remembered the comment and noticed they went to all the trouble to substitute the voltmeter in their updated kit. And face it is a pain to get the different gauge and install it and change the wiring diagram.

Quote:

"I don't recall many problems with them unless the terminals were shorted to ground which could easily cause a fire or a burnt harness."

I'd like to add that while refurbishing my gauge panel I did notice it would be awfully easy to short the terminal studs on the metal backing plate. Because it is a fine line between the 8-12 inch pounds called for as max torque on the terminals - (so risk of overtightening) verses the risk of not tightening them enough - and if they are too loose then the gauge itself can twist just a few degrees and allow or cause the posts to contact the grounded metal backing plate and short out.

I don't have a good photo to show how close the terminals are to the holes in the backing plate but I have the instructions to repro parts that point out the danger of the terminal studs not being lined up properly and a photo of the terminals (although with the trouble spot covered by the washers and nuts - so not much help but hey it gets us in the neighborhood)..

Though I think what I have learned from this thread is so long as everything is installed correctly even if those ammeter gauge posts short out it should only blow one or both of the two small fuses up in front near the grill.