Replacing Ammeter with Voltmeter- Why?

[Ajax]

Gents,

The new fellow's thread on swapping the ammeter for a voltmeter has me curious. You all seem to agree that getting rid of the ammeter is beneficial.

Can you explain why?
What is the procedure?
Where do you typically wire in the volt meter to get the most reliable readings?

[ndutton]

A panel mounted ammeter requires a lengthy wire run in the charging circuit to and from the panel. Even at #8 wire the length of the run imparts voltage drop due to the inherent resistance in the wire. Eliminating the ammeter eliminates the long charging circuit loop and the efficiency loss. Keeping the ammeter and using bigger wire would achieve the same result.

Typically a voltmeter is mounted in the panel and taps off the ignition wire (purple). As for where to connect it for accuracy, it depends on what voltage is most important to you to monitor. You may feel charging voltage means the most or perhaps instead it's ignition voltage. There will be differences due to wire gauge and length of the various circuits.

[sastanley]

Ajax, Here's my $0.02.

The biggest issue is the long run the charging circuit has to make..From the alternator, to the ammeter in the cockpit, and back to the battery switch/batteries/charge controller/isolator,etc.

To me it is about voltage loss in the long run (and by today's standards usually a small-ish wire that is now 30+ years old.) 8# for a 20' charging circuit??

I put a volt meter directly in place of the ammeter in the cockpit, and it is wired into the ignition circuit (via purple wire in Moyer's diagram). This way you are seeing the voltage in that circuit itself, which I think is a good gauge of ignition health (i.e., coil, what's running thru the circuit, all connections tight, etc.)

I also have an on-demand volt meter on my electrical panel in the Nav station..if I recall it is tapped into the 1-2-ALL switch, and has about a 36-48" run with 4# cable directly to the batteries, so this gives me an accurate reading of voltage at the batteries themselves (I also replaced the charging run from the alt. to 4#.) These two gauges often differ, as there is voltage drop along the ignition circuit run to the cockpit. I see higher voltage at the panel, since all the runs from the alt. to batteries are 4# cable, and it usually matches the voltage if I put a meter on the battery terminals. The ignition circuit is 12#, if I remember correctly, and might be 0.5-0.7v lower.

edit- I am obviously more long winded than Sparky (aka Neil)

[ndutton]

Originally Posted by sastanley

I am obviously more long winded than Sparky (aka Neil)

Prior to that post I composed and deleted a 1500 word treatment of the subject that included wire material, cross sectional area, length, voltage drop, DC vs. AC voltage drop, termination integrity and so on. It was so lengthy it bored even me.

[joe_db]

There are some really long threads on this with all kinds of diagrams and photos. Short story is you change a 10-20 foot charge wire to a 1-2 foot wire
Besides for all that the way the A4 ammeter was wired did not do what you thought it did anyway.

This thread has a ton of info on the subject:
http://www.moyermarine.com/forums/showthread.php?t=6702

[edwardc]

Originally Posted by ndutton

A panel mounted ammeter requires a lengthy wire run in the charging circuit to and from the panel. ...

While this is quite true for the direct-reading style of ammeter that was all that was available when most of our boats were built, the newer shunt-style ammeters only require putting an extremely low (on the order of milliohms) shunt resistor in the charging circuit, which then does not need to be brought all the way up to the panel. Only the tiny sensing wires from either side of the shunt go to the panel. This is the type of current monitor that is used with all the fancy battery charge state monitors too. The downside is that they're much more expensive than the simple direct-reading ammeters.

[ndutton]

I agree Ed except in my direct experience from 1971 on I never saw a single shunt type ammeter installed in a sailboat and that observation covers a variety of manufacturers. It may have been common in older boats however.

Note also the Moyer and Universal wiring diagrams do not incorporate shunt type ammeters.

[edwardc]

Originally Posted by ndutton

I agree Ed except in my direct experience from 1971 on I never saw a single shunt type ammeter installed in a sailboat and that observation covers a variety of manufacturers. It may have been common in older boats however.

Note also the Moyer and Universal wiring diagrams do not incorporate shunt type ammeters.

True. I don't think they were ever common. The only ones with shunts I've ever seen were all retrofits. The direct-reading style, with it's automotive heritage and multi-million unit production runs, were just too inexpensive to allow shunt-style meters to compete economically.

[ndutton]

Interestingly, my main DC distribution panel ammeter is exactly that, a shunt type. Before it's asked, no - not factory.

[hanleyclifford]

Originally Posted by ndutton

I agree Ed except in my direct experience from 1971 on I never saw a single shunt type ammeter installed in a sailboat and that observation covers a variety of manufacturers. It may have been common in older boats however.

Note also the Moyer and Universal wiring diagrams do not incorporate shunt type ammeters.

That's because neither Moyer nor Universal are in the business of equiping cruising boats. The shunt type ammeter is a cruiser's tool.

[Dave Neptune]

I just did a rewire for the positive power feeds, the charging circuit, and complete engine.
I removed over 50 feet of #4 (battery feeds), 50 feet 0f #8 that comprised my primary panel feed and charging circuit. I moved the "main switch" to a battery box bulkhead under the dinett now the longest #4 run is 3 feet to the starter.
I installed a shunt style analog 280 degrees sweep ammeter in the engine panel I have in my nav station with the tach & vac gage. I moved my volt meter from the inside panel to the outside panel with oil, temp & volts read off the switched end of the key.
It is amazing how much more responsive everything is and the lites are even brighter. The "shunt style" meter allowed me to shorten the charging circuit by over 25 feet.
Now I have an ammeter that reeds if I turn on the radio, or leave a light on in a closed storage area. I feel it was worth both the investment in the new VDO unit and moving the main battery switch. Very happy with the results.

Dave Neptune

[romantic comedy]

To me the series wired ammeters are useless. The scale is so small, all i can see is if there is a charge, and not how much.

I have a shunt wired ammeter for my charging circuit. It is 100 amp, and works great.

I also have a 25 amp ammeter, series wired, for the house loads, in my panel.

I have a circuit breaker, for loads over 25 amp. Then I have a way to go around the ammeter, if needed.

A volt meter is very helpful. I have one in the main panel. With the cheap led ones available, I am planing on a few of them.

[joe_db]

I have had fun with the FleaBay meters. Usually $6-$18 or so a piece.

Originally Posted by romantic comedy

To me the series wired ammeters are useless. The scale is so small, all i can see is if there is a charge, and not how much.

I have a shunt wired ammeter for my charging circuit. It is 100 amp, and works great.

I also have a 25 amp ammeter, series wired, for the house loads, in my panel.

I have a circuit breaker, for loads over 25 amp. Then I have a way to go around the ammeter, if needed.

A volt meter is very helpful. I have one in the main panel. With the cheap led ones available, I am planing on a few of them.