Amp Meter + and - current flow

[chconger]

Hi All

For a boat that still has the + / - amp meter, it hooks up basically between the output of the alternator to the positive post of the battery (at the starter)

So I understand, when the engine is running and the battery is charging, current will flow into the battery through the meter, indicating a + reading on the meter.

What is happening when we see a - reading on the amp meter? Is current flowing into the alternator? It's the only thing hooked up in the other direction, so I don't get this circuit.

Really perplexed

Thanks
Chris

[sastanley]

If you are seeing (-) on the ammeter it means the battery is discharging. The A-4 takes a few amps to run. If I am at idle, I see negative on my ammeter, but I have a negative shunt digital Blue Seas meter, the value is something like 3 or 4 amps. Normally, those +60/-60 ammeters don't have enough range on the needle to show the miniscule draw of the motor...
I'll try to remember to take a pic just for posterity.

[ndutton]

To get the +/- ammeter to read the way you expect, connect the house panel feeder to the alternator output post rather than the battery.

[ronstory]

If you look into the diagram, when the amp meter is detects a "negative flow" it just means that alternator voltage is lower than the wire on the other side of the amp meter. Yes, when a alternator fails, a bit of current 'flow' will occur... but it's usually minor and just sinking thru bad diodes and the like.

Voltage is just like water height. A column of higher water will want to equalize with a connected water system to an average height that will always be lower that the highest height. Voltage is the same.

When the alternator fails and can't provide a voltage higher than the connected system, the current flow is reversed from "normal" operation. Now that flow is not as large as current flow during "normal" operation because the device that is trying to 'sink' or absorb the current, and it was not designed for that operation. Any current absorbed is due to some failure in the alternator or a component inside the alternator.

[joe_db]

Hi All

For a boat that still has the + / - amp meter, it hooks up basically between the output of the alternator to the positive post of the battery (at the starter)

So I understand, when the engine is running and the battery is charging, current will flow into the battery through the meter, indicating a + reading on the meter.

What is happening when we see a - reading on the amp meter? Is current flowing into the alternator? It's the only thing hooked up in the other direction, so I don't get this circuit.

Really perplexed

Thanks
Chris

The way the ammeter is rigged it only shows alternator output. If it ever goes negative you have issues like shorted diodes.
It is usually a big improvement to ditch it for a voltmeter and avoid the long wire run for the alternator output.

[JTG1160]

Ammeter readings

I have a stock ammeter gauge and alternator installation. Generally when I start the motor the gauge moves all the way to the +30 reading until I throttle up a bit and then settles into a +5 or +10 reading. Does this sound like "normal" operating levels?