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Old 01-08-2014, 09:44   #46
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Re: Are Marine Diesel Generators Pure Sinewave?

Generating AC as the output is more convenient. There are inverter generators which are at their heart DC generators that feed an on-board inverter.

Battery charging with a DC output used for other things requires a regulateable DC-DC converter or a dedicated alternator.

Running high loads requires very large inverters or stacked smaller ones. This becomes more expensive than just buying an AC genset.

DC output becomes more of a problem at larger sizes. A 6Kw AC load is going to require 600A of DC input.

Aquagen is one unit that has been around for many years. People I know with those love them, but they are also constantly fixing them.

Mark
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Old 01-08-2014, 09:52   #47
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Re: Are Marine Diesel Generators Pure Sinewave?

I like the way the little Honda's can vary RPM with load, while maintaining a constant 60Hz, Thought that wouldn't be that difficult a thing to scale up.
See, I don't "need" more than about 2.5 KW, actually usually much less
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Old 01-08-2014, 09:55   #48
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Re: Are Marine Diesel Generators Pure Sinewave?

There are a couple of companies that make DC generators. One is Fischer Panda.

Or you could make your own by adding a "marine" alternator, such as Balmar, to a small engine. 8 to 10 HP will turn a 300A alternator. Search, I remember threads on just this subject.
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Old 01-08-2014, 10:01   #49
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Re: Are Marine Diesel Generators Pure Sinewave?

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Originally Posted by a64pilot View Post
I like the way the little Honda's can vary RPM with load, while maintaining a constant 60Hz, Thought that wouldn't be that difficult a thing to scale up.
See, I don't "need" more than about 2.5 KW, actually usually much less
Yes, the Honda is an inverter generator. It makes DC, then feeds that directly into an on-board inverter. Varying rpm for load is one of the advantages of this type. Fischer-Panda also make inverter generators.

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Old 01-08-2014, 10:02   #50
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Re: Are Marine Diesel Generators Pure Sinewave?

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There are a couple of companies that make DC generators. One is Fischer Panda.
Yes, another company whose customers love the product, but always seem to be fixing them.

Perhaps that is just a generator thing in general?

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Old 01-08-2014, 11:23   #51
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Re: Are Marine Diesel Generators Pure Sinewave?

Making 12VDC is not as efficient as making 120V or 240V AC. Anyway a DC generator is really an AC alternator with rectifiers that turn the AC output into DC. So if you use lots (a few kilowatts) of AC power then it's more efficient to avoid all the conversions and power lost in the high current DC wires.
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Old 01-08-2014, 12:08   #52
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Re: Are Marine Diesel Generators Pure Sinewave?

If you are just looking to charge your batteries, a small DC generator would be OK but in those cases, solar starts to make a lot more sense with maybe a bigger alternator on the engine for when the sun doesn't shine. Or you could go with something like a 1000watt honda to run the battery charger if it will be more frequent.

When you move up into built in generators, people usually want the ability run the air/con or similar large loads for longer durations and DC generators are less efficent due to multiple power conversions and battery storage losses.
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Old 01-08-2014, 12:54   #53
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Re: Are Marine Diesel Generators Pure Sinewave?

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Originally Posted by colemj View Post
Yes, another company whose customers love the product, but always seem to be fixing them.

Perhaps that is just a generator thing in general?

Mark
Yeah, I'll have Fischer Panda in the boat that has a Volvo in it.
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Old 02-08-2014, 00:16   #54
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Re: Are Marine Diesel Generators Pure Sinewave?

Both of you guys are lost in the dark ages.

Get over it, and stop and think about it.

With an AC generator, you have to run it every time the Air-Con, is needed.

But it takes a mighty gen head to run the AC, with the Air-Con, and battery charger, as well as the domestic HW, at the same time. The prime mover must run at a fixed speed no matter the load. The bat charger must convert the AC to DC to charge the bats.

A DC gen coupled to an inverter, an automotive style Air-Con, and domestic HW loop. Can charge the battery at variable speed, provide Air-Con, HW, and run under perfect load.

Sure the DC unit must run to provide Air-Con, but so must the AC unit. The difference is the AC unit must run at constant speed no matter the load.

The DC unit only needs to run at an RPM to support the running load, with the bats being opportunity charged, you have plenty of AC to power other loads by the inverter.

Not to mention all the Domestic HW you need.

Lloyd






Quote:
Originally Posted by valhalla360 View Post
If you are just looking to charge your batteries, a small DC generator would be OK but in those cases, solar starts to make a lot more sense with maybe a bigger alternator on the engine for when the sun doesn't shine. Or you could go with something like a 1000watt honda to run the battery charger if it will be more frequent.

When you move up into built in generators, people usually want the ability run the air/con or similar large loads for longer durations and DC generators are less efficent due to multiple power conversions and battery storage losses.
Quote:
Originally Posted by transmitterdan View Post
Making 12VDC is not as efficient as making 120V or 240V AC. Anyway a DC generator is really an AC alternator with rectifiers that turn the AC output into DC. So if you use lots (a few kilowatts) of AC power then it's more efficient to avoid all the conversions and power lost in the high current DC wires.
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Old 02-08-2014, 11:43   #55
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Quote:
Originally Posted by FlyingCloud1937 View Post
Both of you guys are lost in the dark ages.

Get over it, and stop and think about it.

With an AC generator, you have to run it every time the Air-Con, is needed.

But it takes a mighty gen head to run the AC, with the Air-Con, and battery charger, as well as the domestic HW, at the same time. The prime mover must run at a fixed speed no matter the load. The bat charger must convert the AC to DC to charge the bats.

A DC gen coupled to an inverter, an automotive style Air-Con, and domestic HW loop. Can charge the battery at variable speed, provide Air-Con, HW, and run under perfect load.

Sure the DC unit must run to provide Air-Con, but so must the AC unit. The difference is the AC unit must run at constant speed no matter the load.

The DC unit only needs to run at an RPM to support the running load, with the bats being opportunity charged, you have plenty of AC to power other loads by the inverter.

Not to mention all the Domestic HW you need.

Lloyd
Prior to the advent of inverters that "support" generators I would have agreed with you and often advocated as such.

However, with the ability to run a smaller ac generator and pull battery power to pull the peaks works extreamly well.

In addition with a large lead acid or a modest lifepo4 bank the inverter can hold the load on the generator at the optimum point. If the generator was a DC system it would be running at high load most of its run time also.

I have a 6kva 230v 50hz (could be 8kva 60hz) 1500 rpm westerbeake and an 8kva victron quattro inverter. With 440ah 24v lead acid bank. With lifepo4 I could continue to charge at much higher rates.

The primary change I will make this winter is shifting the engine heat loop for the hot water heater to the generator.
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Old 03-08-2014, 07:47   #56
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Re: Are Marine Diesel Generators Pure Sinewave?

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Originally Posted by transmitterdan View Post
It is not likely that the alternator would be damaged.
This is an example most alternators are damaged because people overload their current rating. Not all self protect.

Quote:
Originally Posted by Rapanui View Post
and switch mode power supplies for virtually all electronics.
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Old 03-08-2014, 14:07   #57
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Re: Are Marine Diesel Generators Pure Sinewave?

All diesel generators should have a circuit breaker at the output to protect it. If your generator does not have this you should add it as soon as possible. All generators sold in the US are required to have this and I believe the same is true pretty much everywhere else.

DC alternators can overheat due to lack of cooling. Temperature sensors are available so external regulators can reduce the output and thus control temperature. If you have a big battery bank it's a good idea to use external regulation with temperature sensor on the alternator as well as the battery bank.

A well designed system will be self protecting.
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Old 04-08-2014, 00:23   #58
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Re: Are Marine Diesel Generators Pure Sinewave?

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A well designed system will be self protecting.
Do not trust protection devices to prevent damage. When they operate it is mainly because damage as been done. They just try to prevent further damage. To prevent damage just monitor a well-designed system this is the best self-protection that you can achieve.

Having said that do you have any low power factor appliances on board, soft mode charger, compact light?
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Old 04-08-2014, 09:56   #59
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Re: Are Marine Diesel Generators Pure Sinewave?

Self Protecting in an alternator/generator application is in reference to the machines ability to continue to provide current into a dead short. Also known as self limiting.

An AC alternator is not self protecting, that's why circuit breakers are required on the machine, ie load leads to the panel, or outlets.

An automotive style alternator is an AC machine, but it is self protecting. This is true because the machine uses a bridge rectifier, to convert the ac output into dc. This machine will blow the diodes in the bridge during a short circuit. Consequently it can't provide current into a dead short.

A DC Dynamo/Generator, as found on engines before the advent of the automotive alternator, is not self protecting. It can produce current into a dead short, and once excited and spinning can runaway. It is connected direct to battery. It thefore needs a fuse in the out put.

Lloyd
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Old 04-08-2014, 10:40   #60
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Re: Are Marine Diesel Generators Pure Sinewave?

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Originally Posted by FlyingCloud1937 View Post
Self Protecting in an alternator/generator application is in reference to the machines ability to continue to provide current into a dead short. Also known as self limiting.
A circuit breaker is a device that requires no operator help nor any source of power other than the load it is protecting. It is a form of self protection.

Beyond that all alternators have a fixed (or maximum) field current that sets an upper limit on the maximum current the alternator can produce. Thus all alternators are self limiting. The current limit is up to the designer. For most small alternators on boats the current is limited to about 2 times the maximum rated current so it can start motor loads. It is important not to put an oversize circuit breaker or one with the wrong timing curve on an alternator for this reason. An alternator operating into a crowbar short can damage the engine but it is unlikely it will damage the alternator itself. I have seen 1 megawatt generators stopped cold by a crowbar short but the alternator was undamaged. The crank shaft of the engine was bent though.

Quote:
Originally Posted by FlyingCloud1937 View Post
An automotive style alternator is an AC machine, but it is self protecting. This is true because the machine uses a bridge rectifier, to convert the ac output into dc. This machine will blow the diodes in the bridge during a short circuit. Consequently it can't provide current into a dead short.
There is no fundamental difference between an alternator with rectifiers and an alternator without rectifiers. The operating principle is exactly the same. A rotating field winding with DC current induces AC current in a non-rotating stator. In the case of a DC alternator the field current limiting is designed to prevent the diodes and stator windings from failing when a short circuit is on the output of the alternator. Were it not so an alternator would fail any time someone tried to charge a fully discharged battery bank.

Diodes fail when the load is open circuit not short circuit. The reason is the voltage output of the alternator goes too high and causes the diodes to avalanche and fail. This is why there are warnings about not disconnecting the battery from a running alternator.
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