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Old 06-11-2017, 02:49   #46
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Re: WHAT IS A GOOD GENERATOR ??

Sometimes you need more AC power than a normal inverter can supply. Hot water heater and space heaters, for example. Unless you never use your boat much in cool weather.
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Old 06-11-2017, 03:13   #47
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Re: WHAT IS A GOOD GENERATOR ??

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Sometimes you need more AC power than a normal inverter can supply. Hot water heater and space heaters, for example. Unless you never use your boat much in cool weather.
Is that an argument against DC generators?

I run my 1500 watt hot water heater off my inverter sometimes. It works fine.

But it's inefficient to heat water and do space heating with electrical power you generate on board. Much better to produce the heat directly by burning diesel fuel in a heater of one kind or another. I have an Eberspacher 10kW hydronic furnace for that.

I do have an AC generator, but this issue wouldn't stop me from having a DC generator.
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Old 06-11-2017, 03:17   #48
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Re: WHAT IS A GOOD GENERATOR ??

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I would like a built in generator. My needs are minimal, and although the above is relatively compact, light and cheap it's still, huge, heavy and expensive compared to a 2kv Honda.

I dislike using gas, I don't like the fumes but don't need more than 2kva. It would be great if there was a true diesel Honda equivalent that could be built in.
Now that we have inverters with power boost, suddenly 2kW of generating capacity becomes really, really useful. Even 1.5kW.

It would be really cool if someone would make a small low speed DC generator, and somehow make it very very quiet.

Of course, lithium batteries change the game again -- can be charged with short intense generator runs. Lithium batteries might make it worthwhile to just use a massive alternator on the main engine and call it done. You lose the redundancy from having a separate generator, but if the alternator is big enough, it will put a decent load on the main so you don't have to worry about compromising its health, at least.
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Old 06-11-2017, 07:37   #49
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Re: WHAT IS A GOOD GENERATOR ??

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Why would you operate it at constant RPM if you don't have to?
Sure if something off the shelf was that sophisticated, but my own needs don't require that.

My only need for dino juice power would be charging the bank, and that means just 30 min to an hour per run, at pretty constant load, given an LFP bank.

When loads are small in relation to bank size maybe only a few times a week, even with zero solar.

With lots of solar, then only when insolation conditions are poor.
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Old 06-11-2017, 07:40   #50
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Re: WHAT IS A GOOD GENERATOR ??

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Sometimes you need more AC power than a normal inverter can supply. Hot water heater and space heaters, for example. Unless you never use your boat much in cool weather.
Heat from electricity only makes sense if you have a large cheap surplus of energy.

Webasto-style Hydronic system, directly burning your propulsion fuel makes a **lot** more sense.

Everything being very well insulated helps keep things sufficient.
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Old 06-11-2017, 08:00   #51
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Re: WHAT IS A GOOD GENERATOR ??

I hauled a high end ( for me $ 4K ) Honda generator down to a friends house in Rockport, TX after the hurricane. It was a fuel injected model and would match the engine rpm to the load by controlling the fuel injection circuit. Once started you flip a switch and engine rpm decreases to just off idle for low loads. This generator sipped fuel. It was worth every penny. If you had asked me before this salvage trip I would have scoffed at paying that much for a generator.
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Old 06-11-2017, 08:42   #52
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Re: WHAT IS A GOOD GENERATOR ??

DC generator efficiency is much lower than you may think. Last time I looked, an inverter generator (like the ubiquitous Honda) is close to 70% efficient while a simple alternator is around 40% efficient (just the ratio of input power vs. generated power). Hence you do not see DC generators. Also, high loads and 12V DC power do not mix well. This, if you are an AC boat (cooking, watermaker, heating) use an AC generator. Keep the DC for small loads.
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Old 06-11-2017, 08:53   #53
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Re: WHAT IS A GOOD GENERATOR ??

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DC generator efficiency is much lower than you may think. Last time I looked, an inverter generator (like the ubiquitous Honda) is close to 70% efficient while a simple alternator is around 40% efficient (just the ratio of input power vs. generated power). Hence you do not see DC generators. Also, high loads and 12V DC power do not mix well. This, if you are an AC boat (cooking, watermaker, heating) use an AC generator. Keep the DC for small loads.
actually there are lots of dc generators available. They do have their uses.
An alternator is not a dc generator. It produces AC power that is rectified to dc. Hence the low efficiency. A large dc generator comes into its own when large dc loads are present. ( charging large banks, electric propulsion etc.).
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Old 06-11-2017, 09:19   #54
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Re: WHAT IS A GOOD GENERATOR ??

Phasor marine.

Best deal under the sun

Phasor Marine Generators
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Old 06-11-2017, 09:31   #55
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WHAT IS A GOOD GENERATOR ??

I donít think you will find many if any true DC generators, I bet you will find large alternators almost exclusively because they can generate much more power for lighter weight and less money.
Way back when I was a contract welder in the oilfield, my old 200 Amp Lincoln was a true DC generator and weighed, Iíd guess at least 1000 lbs and had a flat head four cylinder Continental engine to run it.
You could buy a Kubota I think it was little Diesel that was claimed to be 300 amps that was small and light enough that a Toyota pickup could carry it. It was obviously an AC alternator machine, rectified to DC.

The Lincolnís arc was smooth as it was real DC, the Kubotaís arc was not as it was pulsed DC.
It also melted down one day, but thatís another story.

Alternators are of course air cooled, by internal fans, the faster they turn, the lower the field current needed to make power which keeps heat down and the faster the fans turn and that keeps heat down too, lower operating temps lead to longer life.
You would want to keep the RPM up to make it run cooler and get a longer life out of it, besides an engine turning say 1500 RPM or so is usually pretty smooth and quiet anyway.

If you ran a serpentine belt with a huge engine pulley, you can keep side loads down to next to nothing and not harm the engine and still draw all the power off of a belt that an engine can make without harm.
Nex Gen does this with their AC machines as the gen is belt driven off of the crankshaft.
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Old 06-11-2017, 09:34   #56
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Re: WHAT IS A GOOD GENERATOR ??

Ass-u-ming an A/C generator. Phasor's are 1/2 the price of northern lights and just as rugged. Also, very simple ... no electronic boards to fail ... they just run and run.
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Old 06-11-2017, 09:35   #57
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Re: WHAT IS A GOOD GENERATOR ??

Also the phasor compact series will save weight if that is a big issue.
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Old 06-11-2017, 10:15   #58
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Re: WHAT IS A GOOD GENERATOR ??

Quote:
Originally Posted by Pizzazz View Post
DC generator efficiency is much lower than you may think. Last time I looked, an inverter generator (like the ubiquitous Honda) is close to 70% efficient while a simple alternator is around 40% efficient (just the ratio of input power vs. generated power). Hence you do not see DC generators. Also, high loads and 12V DC power do not mix well. This, if you are an AC boat (cooking, watermaker, heating) use an AC generator. Keep the DC for small loads.
This is just not true. Leece Neville school bus alternators like mine (just to name one example) are more than 70% efficient, and a good inverter something like 95%. Generator heads used in commercial DC generators are more efficient yet. You only "pay" 5% or so (or less, depending on the efficiency of the AC generator) to run an AC load off a DC generator through an inverter. And you get it back by not converting AC power to DC when you charge batteries. There is really not much to choose between AC and DC generators, in terms of efficiency, even on boats like mine with a lot of AC consumers.

Anyway, what do you think an inverter generator does? The Honda produces DC power first, then inverts it, just like we do by using an inverter with a DC generator.
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I behold from the beach your crooked inviting fingers,
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We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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Old 06-11-2017, 10:45   #59
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WHAT IS A GOOD GENERATOR ??

Iíd go out on a limb and guess the Honda produces AC and rectifies it as opposed to producing DC.
On edit, it does,
https://powerequipment.honda.com/gen...tor-advantages

What I have always wondered is why are there no big inverter / generators? Seems as if a bigger one would take over the market?
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Old 06-11-2017, 10:53   #60
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Re: WHAT IS A GOOD GENERATOR ??

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Iíd go out on a limb and guess the Honda produces AC and rectifies it as opposed to producing DC.
On edit, it does,
https://powerequipment.honda.com/gen...tor-advantages

What I have always wondered is why are there no big inverter / generators? Seems as if a bigger one would take over the market?
Why "as opposed to"? That's what rectifiers DO - they produce DC power from AC. Honda inverter generators make DC just like any alternator, and then run the DC power through an inverter.
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We must have a turn together . . . . I undress . . . . hurry me out of sight of the land,
Cushion me soft . . . . rock me in billowy drowse,
Dash me with amorous wet . . . . I can repay you."
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