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Old 08-25-2017, 06:03 PM   #21
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I use a Magnum inverter setup that will start a generator (usually 3 cylinder Onan) when the batteries get low. When the generator comes on line, a relay turns on my water heater (3500 watt), the start battery charger and the inverter draws power to recharge the house banks. Seems to be enough.
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Old 08-25-2017, 08:04 PM   #22
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The arguments in this thread remind me of my early days as a mechanic.
I used to believe that the sphere of my personal experience accounted for more than the microscopic slice of the world that it was.
In other words, if I'd never seen it in the 50 or 100 examples of a model or brand that I serviced, it was unusual.
In time I began to understand just how insignificant my percentage of the world my little piece was.
Manufacturers see more of the entire picture with more data points than I/we ever can.
Our Northern Lights 6Kw generator had some rather unusual "issues" when it was new. As we were close to the company's base, I met some pretty experienced staff as they addressed the problem. To a person they insisted that the best way to keep a generator running for a looooong time was to keep it loaded.
50% or more was what was suggested was appropriate.
With proper care and use, they claim our generator might easily last some 15,000 to 20,000 hours.
Who am I to argue? I keep it loaded!
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Old 08-25-2017, 09:05 PM   #23
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Good input Bruce.

When we start the generator it gets loaded well with the bulk phase. As the amps come down I add the water heater.
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Old 08-26-2017, 07:44 AM   #24
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"Manufacturers see more of the entire picture with more data points than I/we ever can."

TRUE , but the mfg has way different goals than the boat owner.

So his advice is centered on his needs , not ours.

WE hope for reliability , long trouble free service life and modest fuel use.

The Mfg just wants to get by the warranty period with no problems.

This is why the mfg love to request a prop that will make full throttle RPM .

Most any pullback will lower the engine output nicely , and things like slobbering , underloading , or noise underway are not his problem.
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Old 08-26-2017, 09:22 AM   #25
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"Most any pullback will lower the engine output nicely , and things like slobbering , underloading , or noise underway are not his problem.[/QUOTE]

What the heck is "slobbering?" Is it something one does when they graduate to a nursing home?
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Old 08-26-2017, 09:40 AM   #26
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Slobbering is when you have unburnt diesel and or lube oil coming out the exhaust.
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Old 08-26-2017, 10:54 AM   #27
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Many boats have an analogue ammeter on the power panel that will show full AC load as it is coming into the boat's AC system from either shore power or the genset. It will be right after the selector. There you can see exactly how many amps are being used.

My boat has a 30 amp shore power cord. The total load on the shore power cord should never be allowed to exceed 30 amps, so the breaker is sized accordingly. The genset feeds the same breaker, so is also sized accordingly at 4 kw.
The loads are all the same, whether from shore power or from the genset. When generating, I usually have cold water, so 10 amps go to heat water, low batteries, so 8 amps go to the charger, and a few smaller loads, not exceeding the 30 amp total. I frequently need to remind my wife to turn off the water heater before turning on the hair dryer or using the microwave, and that caution applies whether on generator or shore power.
I usually let the generator run past when the water heater shuts down, past when the hair dryer is done, past when the microwave will be used, till the charger has ramped down from its initial high rate, through a gradually declining bulk charge rate to a float rate of under 20 amps DC, so by then the AC load has dropped to 5 amps or less. This means the genset is under a very light load. I have been doing this consistently since I got this boat, and in 23 years have had no issues relating to genset underloading.

In the first several years my charger was incapable of doing much, as it was the old ferroresonant style, coupled to the batteries through an automotive style regulator that was incapable of supplying full power to the batteries for more than just a very few minutes. I hate to think just how little of the generator's capacity was being used then, though I know I was never able to stay out for more than a few days at a time without getting back to shore power for an overnight charge.
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Old 09-03-2017, 06:46 PM   #28
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Originally Posted by firstbase View Post
Thanks for all the replies. Why would my ammeter gauge, which I think shows the output of the alternators, read 0 when running? Why would only one, port side, read 5-10 amps or so when I am running with the generator on but the starboard read 0?


Engine ammeters generally report battery current. Panel ammeters generally report load current. I've seen a meter report alternator current on some aircraft.
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Old 09-03-2017, 07:17 PM   #29
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Originally Posted by koliver View Post
Many boats have an analogue ammeter on the power panel that will show full AC load as it is coming into the boat's AC system from either shore power or the genset. It will be right after the selector. There you can see exactly how many amps are being used.

My boat has a 30 amp shore power cord. The total load on the shore power cord should never be allowed to exceed 30 amps, so the breaker is sized accordingly. The genset feeds the same breaker, so is also sized accordingly at 4 kw.
The loads are all the same, whether from shore power or from the genset. When generating, I usually have cold water, so 10 amps go to heat water, low batteries, so 8 amps go to the charger, and a few smaller loads, not exceeding the 30 amp total. I frequently need to remind my wife to turn off the water heater before turning on the hair dryer or using the microwave, and that caution applies whether on generator or shore power.
I usually let the generator run past when the water heater shuts down, past when the hair dryer is done, past when the microwave will be used, till the charger has ramped down from its initial high rate, through a gradually declining bulk charge rate to a float rate of under 20 amps DC, so by then the AC load has dropped to 5 amps or less. This means the genset is under a very light load. I have been doing this consistently since I got this boat, and in 23 years have had no issues relating to genset underloading.

In the first several years my charger was incapable of doing much, as it was the old ferroresonant style, coupled to the batteries through an automotive style regulator that was incapable of supplying full power to the batteries for more than just a very few minutes. I hate to think just how little of the generator's capacity was being used then, though I know I was never able to stay out for more than a few days at a time without getting back to shore power for an overnight charge.
Keith brings up a good point. The initial load on the genny may be a high percentage, but after a couple hours the loads usually drop off.
Air conditioner compressors start cycling off, water heater cycle off on temps, battery chargers reach absorption voltage and current drops off, cooking is finished, etc. That only leaves air con fans, water pump, a few lights and TV. Probably less than 10 amps or 1200 watts of load plus a few minutes runtime of an air con compressor. Nowhere near 50%.
My 8 BTD only gets over 50% for the first hour of operation at best. After that its only over 10% if I leave the cabin doors open. Probably what killed it with only 2200 hours. The last PO started it before unplugging shore power and only shut it down after plugging back in. So, if you don't have an AC ammeter on the panel you should determine what loads are full time and what cycle or taper off.
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