Alternator Wire and Ammeter

[sdowney717]

the boat of course has 4 amp meters.
twin engines plus flybridge
Amp meters register charge from the alternators.
Amp meters are not in the circuit that caries current to the positive buss bar which runs much of the boat.

the wire apparently from the alternators runs into the appropriate amp meters and have not really looked into where they eventually hook up. Perhaps the positive buss bar or perhaps the battery selector switch.
Should it be changed or just leave it as is.

What this means is any drains on power the amp meter wont show. If it was changed, then all the boat power except starters would have to run thru some long runs of gauge 4 wire. And that is likely not good idea.

Another question is what about running the ac battery charger output into the output line from the alternator. Then that might show up in the ampmeters when the AC battery charger is pushing current. The charger has its own internal ampmeter and allows for 3 banks of charging batts.

[David M]

The sensor wires on ammeters are always wired to a shunt. Any other wires on the ammeter are for powering the ammeter such as for its back light or for digital ammeters, to power its logic circuitry.

Are you ammeters analog or digital?

Example of adapter on shunt....
http://www.google.com/products/catal...ed=0CDIQ8wIwAw

For measuring an alternators current, you need to measure it on the positive side, since the negative side is grounded to the engine. If the meter is digital then you need to install an adapter for the shunt.

If the ammeter is analog then you put the two sensor wires across opposite sides of the shunt with no need for an adapter.

An ammeter simply measures the voltage difference across the shunt. The difference is directly proportional to current. You just have to get the polarity of the analog ammeter wires correct. There is no damage if you get it wrong, just reverse them.

[sdowney717]

ammeters are analog, old style round gauges, the shunts are internal to the gauge. I forget the amp numbers on the gauge face.

I will have to look at what side is wired, they show positive charging when the alternators are spinning. Meaning the needle leans to the right charge side, not the left discharge side.

I think if the power comes from one side needle moves one way, if the power comes from the other, neelde moves the other way?
Is that how those ammeter gauges work?

Since I dont draw any power thru the gauge from the batteries, they never will show a dischrge. If I drew power from the alternator output wire, it should show a discharge, correct?

The wire feeding power to one of the main positive buss bars from the main large heavy duty battery buss bar is perhaps a 2 gauge wire which is bigger than the alternator output wires.

[Cowboy Sailer]

I suggest that you leave like it is. Think of the ammeters as indicators of the alternators output they are connected to and that is all. If an alternator belt breaks you want to know it right now. Don't try to rewire the system to indicate anything else.
I have a separate ammeter that shows the current that is flowing out of the house bank. I also have a voltmeter on the house bank that tells me the current state of charge of the house bank. It requires some knowledge and experience to interpet those two meters.
Other people use newer sophisticated state of charge equipment. They too require knowledge and experience to interpet.

[David M]

Ok, so you have the older style, relatively low amp ammeters where you run the primary power wire through the gauge.

They should always show current flowing from the alternator to the rest of your DC system. If you ever see current flowing from your DC system to your alternator then you have a problem. Your alternator should never be drawing power.

The primary power wire from the alternator to the ammeter should be the same gauge as the wire from the ammeter to your DC system. The wire gauge is based on knowing the maximum output of your alternator and the wire run from your alternator to your DC system. It should be gauged for a 3% drop at most.

I agree with Cowboy in that if it is doing its job of accurately telling you the alternators output then there is no need to fuss with it.

[sdowney717]

Ok, thanks, sounds good to leave it as is then.
Been like this 40 years and still fine.
All the wiring for the alternator output is 4 gauge in the entire circuit.