AC Amp Meter For Genset

[RickB]

buy a meter with a range as close (but above) to that as possible.

The most accurate reading on any analog meter or gauge is in the middle third of the scale. Ideally, the "normal" reading should be at the center of the range.

 

[Daddyo]

We have this setup from Marinetics Corp. The meters show both legs of the source selected by a separate selector switch ie: 50A shore power, 220V genset output or as shown the 110V inverter output. Works great for monitoring or switching which legs feed which devices.

 

[rwidman]

The most accurate reading on any analog meter or gauge is in the middle third of the scale. Ideally, the "normal" reading should be at the center of the range.

Fine, but the maximum current cannot exceed the maximum rating of the meter. For a 30 amp system, he will probably have to use a 50 amp meter and let the "normal" current fall wherever it falls. Of course, a digital meter would be best and would read accurately at any current within it's capacity.

 

[Tom.B]

Fair enough, Ron, but I don't think absolute accuracy, like to the 1/10 of an amp, is needed.

 

[Moonstruck]

My analog 115 volt AC gauges for volts and amps are accurate. On the DC side my analog gauges read .4 volts higher than the digital gauge for the inverter. Measuring at the batteries my multi gauge tester agrees with the digital. That's what I go by. I have a 50 amp shore service that will run everything, so don't need to watch power usage too closely. The generator is 12 kw NL.

At anchor on the inverter power is when battery levels have to be watched carefully. I will probably add a SOC meter.

 

[Moonstruck]

OK, I have been checking out some state of charge (SOC) meters. With an accurate digital read out of the house battery bank is one really necessary? It seems to me that if 12.2 volts is a 50% state of charge, the object is to never let it go below that. Any ideas as to why this is not enough information?

The charger compensates for temperature variations. The plan is to upgrade the 80 amp alternator dedicated to the house bank to a small frame 120 amp unit with a 3 stage voltage regulator, or would the 80 amp with an upgraded voltage regulator be large enough? When under way about 25 amps DC is the most the inverter would use.

 

[Larry M]

OK, I have been checking out some state of charge (SOC) meters. With an accurate digital read out of the house battery bank is one really necessary? It seems to me that if 12.2 volts is a 50% state of charge, the object is to never let it go below that. Any ideas as to why this is not enough information?

The charger compensates for temperature variations. The plan is to upgrade the 80 amp alternator dedicated to the house bank to a small frame 120 amp unit with a 3 stage voltage regulator, or would the 80 amp with an upgraded voltage regulator be large enough? When under way about 25 amps DC is the most the inverter would use.

Don: I guess it depends on what you want to look at. Our SOC meter, in addition to DC volts, also lets us see how many amps are going in and out of the house bank. I like to monitor what our DC loads are and what is going back into the batteries from the charger or alternator.

I would would keep the 80 amp alternator and just upgrade your voltage regulator. An 80 alternator only requires a single belt. Depending on who you talk to, a 120 amp alternator may require 2. If the batteries aren't getting fully charged when motoring, then I would consider the upgraded alternator.

 

[psneeld]

OK, I have been checking out some state of charge (SOC) meters. With an accurate digital read out of the house battery bank is one really necessary? It seems to me that if 12.2 volts is a 50% state of charge, the object is to never let it go below that. Any ideas as to why this is not enough information?

The charger compensates for temperature variations. The plan is to upgrade the 80 amp alternator dedicated to the house bank to a small frame 120 amp unit with a 3 stage voltage regulator, or would the 80 amp with an upgraded voltage regulator be large enough? When under way about 25 amps DC is the most the inverter would use.

From my experience...the voltage reading has to be done at just the right time and with a no load condition...one where there is no inflated voltage from a recent charge....waiting for that to happen and not using any DC while waiting for it is a bit difficult when cruising.

Much like knowing the amperage of my AC electric and amount of fuel left...I prefer the old time "know what was running for about how long" and you should be able to figure the rest...not as accurate but accurate enough if you have it down pretty well.

The bottom line is neither voltage or a SOC really can tell you the health of the battery...only a load tester (I think) can.

 

[rwidman]

Fair enough, Ron, but I don't think absolute accuracy, like to the 1/10 of an amp, is needed.

Of course it's not for general purpose on a boat. The argument was made that an analog meter would be most accurate in the middle of its range. I think for our purposes here, the accuracy of an analog meter at any point in its range would be just fine, but if one were to try to measure loads in the one to two amp range with a 100 amp meter, it would be pretty difficult to read. That's why we have different "ranges" on most analog VOMs and that's why I made the suggestion that I made.

 

[Moonstruck]

Thanks, guys. I think the simple, inexpensive thing is the first to try. So, it will be the 3 stage voltage regulator. The 80 amp alternator is already driven by a double belt set up, so the 120 amp alternator would probably be just a bolt on addition.

Reading the battery voltage is a tricky thing. I have noticed that when there is a load of any kind on the batteries the read out will be about .2 volts lower. When only a small load the voltage read comes back up. So, I take it that the light load reading is more the true state of the batteries. The batteries have been tested under load and show as new.

 

[FF]

"The 80 amp alternator is already driven by a double belt set up, so the 120 amp alternator would probably be just a bolt on addition."

Perhaps , but it could also be a larger frame size , as most truck units are.

The key is the alts HOT amperage rating.

A rewound car unit will give loads of amps for a short time , but the hot cont rating is usually better with larger units with better cooling.