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Old 01-09-2015, 16:30   #16
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Re: DC genset to power boat.

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Originally Posted by Sailor Doug View Post
Am I missing something? I thought every one uses alternators to produce DC voltage from AC.


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Your not missing anything, difference I believe is most AC sets use RPM to determine Hz rate, where an alt that uses diodes to convert AC to I believe pulsed DC, can be run at differing RPM as Hz rate isn't relevant, or pulse rate in this instance.
At least I think putting AC through diodes results in pulsed DC, and not "pure" DC?


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Old 01-09-2015, 16:36   #17
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Re: DC genset to power boat.

Why not use a Honda inverter generator? It will run my smart charger and run hotter heater at the same time, cheap simple unless you require large AC amperage.


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Old 01-09-2015, 17:03   #18
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Re: DC genset to power boat.

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Originally Posted by Sailor Doug View Post
Why not use a Honda inverter generator? It will run my smart charger and run hotter heater at the same time, cheap simple unless you require large AC amperage.


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That was my initial plan, I actually have two of them. I ran into two issues, OK three, well no several.
They aren't all that quiet in an anchorage, a built in gen is quieter to the neighbors, but if it's in the dinghy, it's almost silent inside of your boat, quieter than a built in.
No matter where I put the things, except in the dinghy, I got measurable amounts of CO in the boat, not deadly levels, but long term low exposure? I'd rather not have any CO.
They were a PIA to drag out of the Lazarette and set up, flipping a switch to fire up the built in is so much easier. I'm not getting any younger
I'd rather not have any gasoline in the Lazarette.
The ground on any portable generator is questionable.
A built in replaces shore power, I can pull 30 amps out of it, 13 out of one Honda, 26 out of two.
Difficult to use while underway like on passage
I'll most likely keep one as a back up though. I do see as to how the little Honda has really done a lot for many cruisers




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Old 01-09-2015, 17:16   #19
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Re: DC genset to power boat.

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I really think you need to take a hard listen to the gensets. Unless you can come up with really effective sound insulation, I think you might prefer to be hot.
Not only that, boats that run a generator should fly a flag that tells everybody else that they run their generator. If you have an on deck generator you should have 2 flags sames goes for a dive tank compressor.
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Old 01-09-2015, 17:24   #20
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Re: DC genset to power boat.

Why all the amps? My 2k Honda just purrs on Eco, all that is need for battery charging. Life is nice when you ditch high amp ac accessories.


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Old 01-09-2015, 17:45   #21
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Re: DC genset to power boat.

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Not only that, boats that run a generator should fly a flag that tells everybody else that they run their generator. If you have an on deck generator you should have 2 flags sames goes for a dive tank compressor.

You know that is not actually a bad idea, I've thought the same thing, but what flag?

So far I have only frequented either anchorages where I'm by myself, or there is so much jet-ski traffic etc. that I'm sure no one has noticed my generator


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Old 01-09-2015, 17:53   #22
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Re: DC genset to power boat.

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Originally Posted by Sailor Doug View Post
Why all the amps? My 2k Honda just purrs on Eco, all that is need for battery charging. Life is nice when you ditch high amp ac accessories.


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If things work out like I want them to , I won't need AC power at all, except when it comes time to make water, and if I'm running the thing anyway, why not use it for everything I can, like clothes washing, maybe heating water, making some extra ice, charging batteries, heck maybe even pressure washing something? I hope to run the thing twice a week, for maybe 4 hours at a time, so if I'm in a noise sensitive area, I'll wait or move.

Truth is, I'm hoping to be in a position to give water away, surely some would appreciate rafting up for a while and getting a little extra water?


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Old 01-09-2015, 18:42   #23
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Re: DC genset to power boat.

[QUOTE=a64pilot;1905252]

Truth is, I'm hoping to be in a position to give water away, surely some would appreciate rafting up for a while and getting a little extra water





You bet man, I will bring the beer. Hauling our 2 6gal jugs back and forth from shore onto the boat and back again sucks and we hold 80 gal. Are you going to be set up for a hose connection too? Having to up anchor and move the boat is a pain.
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Old 01-09-2015, 18:55   #24
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Re: DC genset to power boat.

I have built and used 3 Kubota based diesel DC generators. They work well. The big advantage I think is that they can be run at low and quiet rpm and a wet exhaust. After the initial 15-20 minutes of heavy amp output they can hardly be heard. Most marine ac generators run at 3600 rpm. That's screaming. Does that mean a DC gen set is "better"? Not really I don't think, but it's an option.
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Old 01-09-2015, 19:20   #25
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Re: DC genset to power boat.

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...It is loud in the aft cabin though as it shares a whole wall with the lazarette, where the generator is in.
I say feel as I believe a whole lot of noise is transmitted through structure, and if that's the case you can sound proof and it not do much good...
The bulkhead acts as a speaker diaphragm. To reduce this noise, optimize the generator's vibration isolation. And damp the bulkhead's oscillations. Insulate the generator side with sound foam.
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Old 01-09-2015, 19:55   #26
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Re: DC genset to power boat.

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One important variation in having a DC genset is that it can run at its optimum RPM and power output for most of the time that it's in operation. That's because, unlike an AC genset, it sees a full load as it charges the batteries. Where an AC generator is seldom run at full capacity, and has to deal with small nuisance loads on occasion, having a large bank of batteries in the circuit allows the DC generator to run flat-out, until the acceptance begins to taper on the battery bank (presuming no inverter loads). Running a diesel at it's intended power output will maximize engine life and fuel economy.

My problem with the solution is that most choices are small single cylinder engines that may not be as smooth has two- or three-cylinder engines on larger AC gensets. So I agree with the person who suggested you listen to it, under expected load.

Chuck
Good points Chuck but another point to consider with variable speed DC generation, is the danger of it falling into the critical RPM range... (Usually around 1,280 to 1,350 rpm), which can cause accelerated vibration damage and higher noise.

Marine AC gens primary mover's are fixed at either1,200 1,500 or 1,800 rpm as a function of desired Hz and purposely set outside the engines critical range.

Fixed1,500 rpm (50Hz) is considered to be the most stable rpm for diesels, which is why they are the most popular worldwide having the best longevity and MTBF of variable load generation.
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Old 02-09-2015, 06:47   #27
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Re: DC genset to power boat.

A64, your motivation for the genet revolves around water making, but you sat you've got the capacity for 1,250w of solar. I think you tackle it that way...I have 1,000w of solar (Kyocera) with 840amps worth of Lifeline Batteries running a Spectra Cape Horn Xtreme. We are able to make between 40-80 gallons/day with this combination along with supporting all other electrical needs. One of the keys is the Cape Horn can run with 1 pump making 8 gph while drawing less than 7amps. Around noon I start the 2nd pump which brings output up to 15gph. I'm certain if I had the new Northstar TPPL batteries and moved my boom over I could do even better.
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Old 02-09-2015, 07:00   #28
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Re: DC genset to power boat.

For the same power, a DC motor is heavier than an AC motor.
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Old 02-09-2015, 08:00   #29
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Re: DC genset to power boat.

I've got 660 amps at 12V of Lifeline batteries sitting on my loading dock right now, will take them down this weekend.
I've got the AC generator installed now, don't have a watermaker yet, but like the simplicity of the AC ones. Of course they are energy in-efficient, but I'm willing to give that up for simplicity / common parts sake, and besides I have the generator now.

What I assume this thread is about is do I go with a full DC electrical system, or a hybrid AC / DC system? Or saying it a different way, do I make AC power and convert it to DC to charge my batteries, or or do I make DC and charge them directly, but convert the DC to AC for other uses?
I went the AC generator route as it is conventional wisdom, but I can see as battery technology gets better, that maybe full DC will become more common place.
Going full Solar and DC was tempting, but to be truthful I want the option of running the airconditioner if necessary
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Old 02-09-2015, 08:20   #30
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Re: DC genset to power boat.

I looked at the DC-AC route a long time ago. The issue is efficiency. The best inverters are no more then 70-80% efficient. You will use more fuel to turn DC-AC then you will to run the gen as needed. I also would never trust a company that says "you can recharge a bank in an hour, then run for 10....
I went with a phasor 3.5 I can run my AC off of it, and charge batteries, make hot water, ECT.
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