School me on how an ammeter works

[sunandsand]

Ammeter indications -

Ignition on, engine not running, ammeter should indicate a discharge (reads minus or negative) because the alternator or generator isn't supplying any power and anything that is on (ignition, lights, radio, jacuzzi) is drawing power.

After engine start, ammeter shows charge (plus or positive) because the alternator or generator is recharging the battery. (Starting the engine draws the battery down.)

After the engine has been run for a while, and the "debt" to the battery has been "repaid", the ammeter might register a slight charge.

Momentary changes in the charge rate can be ignored, it is trends we are looking for. If the needle stays continuously on the discharge side, the battery will eventually go dead. The further over to the discharge side the needle is, the quicker the battery will die. Note that if the needle is pinned, full scale, there's a short circuit somewhere and that needs to be fixed before the smoke gets out.

Having an oversized alternator or generator won't overcharge the battery, the regulator prevents that. (However, if you hook up the Grand Coulee Dam to a pair of AA batteries, all bets are off.)

Continuous high charge or discharge rates may indicate a defective battery or defective regulator. A bad regulator will either boil the battery (stuck on) or not charge it at all (open circuit in the regulator).


Regulators have two circuits in them. One is the reverse current lockout relay. This compares the battery voltage to the alternator or generator voltage. If the battery voltage is higher the relay opens. This is because generators are stupid - if the engine isn't running and battery voltage was applied to the generator, it would think it was an electric motor and try to start the engine - and that won't work.

I have occasionally replaced the reverse current lockout relay part of a mechanical regulator with a 50 amp 400 piv (peak inverse voltage) diode from Radio Shack. Does exactly the same job, no moving parts, costs under a dollar, now all we have to do is find a Radio Shack.

The other circuit is the voltage regulator relay. This one is set to open (disconnect the alternator or generator) from the battery when the voltage of the battery exceeds about 6.8 volts on a six volt battery or about 13.6 volts on a 12 volt battery. Each cell of a wet cell battery is nominally 2.2 volts but they need a bit more "stuffed" into them to convince them to take a charge.

Modern regulators are solid state instead of mechanical, and are far more reliable. They are also electrically "quieter" - with a mechanical voltage regulator and a radio on your tractor, you may hear it "buzzing" on the radio.

Most trouble free system is an alternator plus an electronic voltage regulator. Least best is a generator plus a mechanical regulator. Of course, it it works, don't fix it . . .

Best Regards,

Mike/Florida

 

[Bentrim]

May I attempt to simplify ( if not already done) The ammeter measure the amount or current (or Amperes) flowing through it weather charging or discharging. Compare it to a tank or water being drained and refilled as gallons per minute. A voltmeter registers the voltage present at the meter. Or as in water the pressure in a pipe (psi). Most ammeters in cars and farm equipment rarely exceed 60 amps. With to days alternators exceeding 120 amps it would take welding cable to wire them in a circuit.
When tractors started using them a generator but out 6 to 10 amps they told the operator if the battery was discharging or charging, if anything else was on the tractor it would have only been lights, no need for a high output electrical system. Back then most were only equipped with a cut out to disconnect the generator from the battery. The operator usually controlled the rate of charge by a three position light switch. Even after voltage regulators were added output was not increased much.
In the 60's alternators replaced generators output increased but only to 32 to 60 amps. As the electrical load became greater due to cabs, air conditioning , more lights, monitors, etc output from the alternators have risen to meet the need some to more than 120 amps that was in the 80's haven't keep up with what they are today.
Of course as with water you need bigger wires (pipes)to carry the additional flow. Electrical wire gets expensive when a manufacturer is using large quantities. They use only the length required and instead of running huge cables from the battery to the dash and then to the alternator they only run the cable from the alternator to the battery. They then replaced the ammeter with a voltmeter that can take a reading of the voltage at any point in the system using smaller wires.
Hope this helps.
Have a wonderful day

 

[lpakiz]

The post below was a belated attempt to explain why an ammeter can’t be wired like a voltmeter.

””Voltmeters connect the hot to a ground.
Ammeters are wired “in series” so electricity flows in one terminal and out the other, like the meter in the gas pump.
If you wire an ammeter to ground, the wires or the meter itself will get hot, throw smoke, start a fire or something on that order, until a wire burns off.””

 

[dpgood1]

If you have a dvm = digital volt meter, use it to check the voltage on your battery. Tractor not running the voltage should be close to 13v. Start the tractor up and the voltage should slowly rise to 14+ volts and then stabilize. The voltage will drop down to the 13+ range after stopping the tractor. This will tell you that the battery is basically good and that you are charging the battery.

 

[Larry D Johnson]

None of these gauges are very good to use for raw diagnostics. I actually would rather have an amp meter than a volt meter. Voltage dose not tell you much about condition of things such as battery. I have tested many batteries that show proper voltage but as soon as I hit it with a load tester the battery falls on its face. No the starter will not run the amp meter. The starter will draw several hundred amps and the amp meter and wiring going to it will not carry that kind of current.

 

[CADplans]

Most ammeters were connected to vehicles with generators, today, most vehicles are using alternators.

I do not think I have ever seen an ammeter that was calibrated up to the 120 amps my truck alternator puts out??

Beyond all of that,, there are 6 or more ways an ammeter can be wired into a charging system,, each method will give different readings depending on what the system is doing, as far as lights on,, etc,,

Has anyone determined how the OP has the ammeter wired?

 

[Richard]

Memory says it has one side going to starter solenoid and other side to alternator.

I might misremember but I followed installation instructions to the letter

 

[WranglerX]

None of these gauges are very good to use for raw diagnostics. I actually would rather have an amp meter than a volt meter. Voltage dose not tell you much about condition of things such as battery. I have tested many batteries that show proper voltage but as soon as I hit it with a load tester the battery falls on its face. No the starter will not run the amp meter. The starter will draw several hundred amps and the amp meter and wiring going to it will not carry that kind of current.

But a volt meter will give good indication of charging system operation at any give moment depend on what the voltage reading is....
Each gauge ( ammeter vs volt meter) will tell a experienced person the same thing but neither will show capacity (as you mention) condition of battery except a load test ...

 

[stevem5215]

To find out the REAL condition of your battery, I'd suggest a tester that can do a IR test of it. This will test the actual capacity that is available in the battery. What you do is to trickle charge it up fully and then disconnect the charger and let the battery rest overnight and then connect up a meter like this one from Amazon. It's what I use to determine my true battery capacity and battery condition. Easy to use and just a quick check will tell you how the battery is holding up over time. If you were to chart it on a piece of paper you'd see it losing it's capacity over time and could actually decide without it actually being dead to replace it on your schedule and not the battery making the decision.

Amazon.com

 

[CausticUrbanCoast]

But a volt meter will give good indication of charging system operation at any give moment depend on what the voltage reading is....
Each gauge ( ammeter vs volt meter) will tell a experienced person the same thing but neither will show capacity (as you mention) condition of battery except a load test ...

You may want to investigate how load testers work.