The Stovebolt Site Forums The Shop Area The Electrical Bay Amp meter or Voltage Meter

Which is the correct terminology for the gauge used in the 1946 Chevy Truck?
I see it referred to in posts as both a Volt Meter and an Amp Meter. The Gauge Cluster shows Battery. The parts book calls it an Amp Meter.
Is it indeed an AMP meter?
Thanks,
Harold

Harold
I've been learning more about this stuff recently than I'd imagined, had I even been inclined just a few months ago.

My understanding is the '46 dash gauge as factory delivered came with an Ammeter. Some owners afterward, preference or otherwise, sometimes have changed them to higher amperage gauges or bypassed the ammeter gauge in place of a volt meter.

Voltmeters did not start being used on production vehicles until the mid-1970's or later. All the stovebolt trucks had either ammeters or idiot lights to indicate the performance of the charging system. Some people who don't understand charging system operation very well prefer to install a voltmeter, thinking that it will give a better indication of the health of the charging system.

In actuality, it would be necessary to have a voltmeter, an ammeter, and a method of monitoring the specific gravity of the battery acid to make a well-informed evaluation of the charging system, plus enough knowledge to interpret all those readings. That would take virtually all vehicle owners, and at least 90% of professional mechanics out of the equation!
Jerry

Actually the best thing to have is a light. Most folks don't look at the meter until there is trouble starting the motor, or lights are low or whatever. Then it's too late and most don't know what the gauge is then telling them. Anyway, 90% of the time it's the battery and 10% it's the charge system which takes the battery down 90% of the time but 10% of the time it doesn't. I like a light to go on...on the dash, then the light goes on in my head, 100% of the time. We all think and tell the auto manufacturers that we demand gauges!!! and right now!! We are not idiots! But the battery still goes dead before we know it, on a dirt road, at night, in the rain, all alone and no tools and no cell phone coverage.
People like volt meters because you don't run the entire truck amperage thru it like an ammeter and it tells the same info. Autos with ammeters have the same breakdowns as idiot light autos. It's a false control syndrome and the name idiot light bugs us. I've chattered on this before and no one has ever agreed with me yet. I'm at peace though. The modern, well tested, high tech, automotive engineered vehicles use a dozen lights to warn us and they give digital and analog meters at the same time. Never know if an idiot or a gauge watcher will buy the truck.
Harold: Forget the ammeter and put in a bulb. Gotta stop now, the nurse is coming down the hall..

I too like the warning light as well as a volt meter. The light goes off, you look down and see the voltage has fallen below normal. Might save you a burnt up engine if the fan belt has broken or come off and was no longer turning the water pump.

I had one vehicle fire due to an ammeter burning up. Don't care too much for the ammeter.

If you have a 3 wire alternator, you can hook up a light real easy. The small terminal closest to the main terminal on the alternator is the idiot light connection. Run that to a 12v gauge bulb and put a 1N5401 diode (stripe facing the alternator) in between the alternator and the bulb. Now whenever the alternator is not charging, like after turning on the ignition but before you start it, the light will come on, then once its running and charging the light will go out.

If you stick with the Ammeter, use a fusible link at the battery.

Why diode and bulb? I've run a diode when no bulb was to be used, but never a bulb and diode and never any problems.

I was also wondering about that diode. I know that you can put one in place of a relay for the fan which wil act as a motor and try to keep car running. But the bulb is passive. We will see what the reason is.

He also failed to mention there needs to be 12V to the other side of the bulb.

As Cletis indicates, Switched 12V to one side of bulb. Other side of bulb to Alternator. I.E.- Motor off (IGN on): Alt is ground, bulb lights. Motor on: Alt generates 12V and equalizes both sides of bulb, bulb goes off. Alternator or charging circuit malfunction: Bulb glows weak or off/on.

A diode may be used in the IGN to Alt wire to prevent "run on". It is not necessary for the indicator bulb circuit operation. Remember it prevents flow in one direction and may cause the warning bulb not to operate properly. It would seem like it has to be between the Ign and bulb, not between bulb and Alt. I would not mess with a diode as Roy and Beltfed say. If you have "run on", then we'll talk.

As Deve says. Fusible link is a must. There are several big wires on our trucks which are not fused. Not good. Add fusible links 2 gauges smaller than wire. Usually right at the battery. (sized by gauge 1, 2, 3, 4 NOT 2, 4, 6, 8)

The diode is because the alternator isn't really ground. It's a low. Since its a low it SHOULD have a diode in the line so you do not backfeed the positive voltage to a potential higher than is safe for the alternator. Sure just a bulb works, but why not do it right? The diode protects the circuit. The diode in the circuit makes it work the same as if there was no diode in the circuit. I didn't decide to put the diode there, it's in many schematics. I never thought I would be in a position to save any of them to prove it, so do your own research.

I assumed he knew to put 12 volts to the bulb. Did he think a dangling wire was going to work? You guys are a tough crowd sometimes. Jeeze!

I did research on Diode before posting. There was no evidence for it. Your explanation sounds made up. Use one if you like, it won't hurt my feelings.
When we help someone, we can't assume they know the "rest of the story". The comment was not being "tough", just completing the info.

You'd be surprised how many people think electrical circuits involve magic.

After digging around in some old books and looking around the internet I can't find any diagrams showing where both the bulb and diode would be needed if the bulb is used in the wiring.

I find a lot of diagrams showing the indicator bulb in the circuit, or the diode in the circuit if no warning light is used.

A few diagrams also indicate you can use a 15 ohm resistor in place of the bulb with no diode.

So I would be interested to see a diagram showing the need for a diode if a warning lamp is used in the circuit. Could be I'm doing something wrong and just don't know it.

Well, I have never been wrong before. I take that back, I was wrong once before. It was when I thought I was wrong, but I really wasn't. My recall isn't what it used to be and since I did this:

http://www.devestechnet.com/Images/Projects/WarningSystem/CriticalSystemsWarnSchematic1.jpg

I had researched the Alternators behavior (low vs ground) and remembered I needed a diode. In looking at it, yeah, it doesn't belong there. It took me awhile to decide what resistor value was needed for an LED instead of an incandescent, but yeah, no diode for incandescent. The schematic above works flawlessly, but I have no idea how I managed that!

If it's any consolation..... I'm almost constantly wrong about something.