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Old 26-08-2013, 06:19   #16
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Re: 12vdc generators - any good ones out there?

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Originally Posted by tom1263 View Post
There are also DC Gensets from portable to built-in generators. But not a lot...
Portable DC genset, that's what I'm looking for. I don't need a lot, just 1.
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Old 26-08-2013, 06:45   #17
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Re: 12vdc generators - any good ones out there?

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That was actually the first thing that I considered, but I figured that I would look to see if I could just buy one first. I'm not really finding what I want on the open market, so building my own is looking more likely. I have access to a machine shop, so the fabrication end of it is not a problem. Finding the right motor is looking to be the toughest part. I want something around 1-1.5 hp, small & lite. Maybe like a Wisconsin Robin aluminum block pull start. I would prefer diesel, but 1hp diesel engines are like hen's teeth to find. They seem more rare than sub fractional hp 3-phase motors.
I think the Robin DY23 is about the lightest diesel engine you'll find.

But you don't want to undersize it anyway -- you most definitely do not want to run these light-duty engines anywhere near their maximum power.

The Robins are really nice units with balance shafts, pressure lube systems, etc. I think you could make a very nice little generator matched to a 140 amp (or so) large-frame alternator. The Robin ought to be able to run such an alternator at full capacity at about 2500 RPM -- just what you want. Then you just throttle back when you need less than full output from the alternator. At 2000 RPM it's still producing about 2kW of (mechanical) power (enough to make probably 1.5kW of electrical power, I guess), so I guess you would be running it at 2000 RPM or less most of the time.

The only engineering you will have to do is to properly size the pullies to get the right maximum mechanical power draw from the alternator at the right engine horsepower.

The only concern I would have is how to get the heat out of the boat? Air cooled engines produce a lot of hot air, and require a whole lot of cold air to work properly. Or do you plan to run it on deck?

If you're going to run it on deck, then you don't necessarily need a diesel one. You can save yourself a lot of trouble and just buy a little Honda portable. They make a 1kW one (I own one!) which is extremely light and compact. Just use it with a simple battery charger matched to the generator's maximum output and you'll be in business.
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Old 26-08-2013, 13:34   #18
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Re: 12vdc generators - any good ones out there?

I had one years ago made out of a Briggs & Stratton lawn mower engine with an 85 amp Bosch alternator hanging underneath it, noisy but worked well to put a bulk charge into the house battery and was also handy for boosting volts when I used the anchor winch and the cranking battery was low.

I now have a 2.2kw AC genset and use an inverter welder for emergency cranking or house battery bulk charging, it works but will blow the excitation capacitor if I get too enthusiastic.

When the AC unit gives up the ghost I am going to build another DC unit using a Honda vertical shaft engine on a flange in the deck and hang an alternator underneath it inside the boat. This will keep the noisy, hot air generating engine outside and the salt water sensitive electricals inside I will be upgrading the inverter to handle the AC requirement.
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Old 26-08-2013, 13:37   #19
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Re: 12vdc generators - any good ones out there?

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No motor.
I'm old school.
You lucky duck.

Some outboards have small 12V alternators. But I understand maybe you do not use an outboard either.

You may think of solar panels or small wind gen or else a fuel cell (nice because you can use it anytime BUT expensivish they are).

Or else pick a car stock alt and find a small engine (you can use one from a lawn mower or one used in gas-driven emergency water pumps. And bild your own rig. Easy and inexpensive. BUT noisy.

barnakiel
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Old 26-08-2013, 13:48   #20
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Re: 12vdc generators - any good ones out there?

To build your own DC Genset it's good to have a water cooled engine. This is a 1 Cyl. water cooled Farymann incl. Bosch Alternator....
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Old 26-08-2013, 14:01   #21
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Re: 12vdc generators - any good ones out there?

These guys sell both gas and diesel models. http://www.alten-dc.com/gasoline-pow...enerators.html

Steve
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Old 26-08-2013, 16:50   #22
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Re: 12vdc generators - any good ones out there?

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These guys sell both gas and diesel models. http://www.alten-dc.com/gasoline-pow...enerators.html

Steve

That's the size that I want, but over a grand for that little thing seems a tad steep. This will be a great plan B if I don't find a more cost effective alternative. Thank you for telling me about it. It's the best off-the-shelf option I have so far.

Also, thanks to all the other people who have posted plausible options. A lot of good information is piling up here.

I can get that same Honda GXH-50 motor out of the genset for $400 - http://engines.honda.com/models/model-detail/gxh50

Hmmm.

Funny, that place will sell me a 5hp Honda engine for about $200, but a 1hp costs more.
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Old 26-08-2013, 16:55   #23
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Re: 12vdc generators - any good ones out there?

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Some outboards have small 12V alternators. But I understand maybe you do not use an outboard either.
Small outboards often have optional charging loops of varying capacities. I've seen them from 2.5 amps up to around 15 amps on the sub-10hp motors. Within a given engine size, they vary a lot from brand to brand. Even the "big" 15 amp charging system seems a bit small to me. Also, your second assumption is correct. I don't use an outboard either.

I'm basically looking for a small lite 50+ amp unit that I can easily row out in a dingy & hook up for an hour or two every now & then on a boat that gets only occasional use. It would double as an emergency back up plan for when a starting motor on a friend's boat gets drained down too far.
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Old 26-08-2013, 19:11   #24
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Re: 12vdc generators - any good ones out there?

Here's an article on a home-built 12v generator. It seems to fit your requirements.

Last year I picked up a "defective" gas 2hp waterpump for $30 from Canada's answer to Harbor Freight. The engine fix turned out to be a simple tweak to the throttle mechanism , so I hope to remove the pump and mount an alternator instead. Maybe. Some year...
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Old 26-08-2013, 20:45   #25
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Re: 12vdc generators - any good ones out there?

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These guys sell both gas and diesel models. http://www.alten-dc.com/gasoline-pow...enerators.html

Steve
That's an interesting source, Steve. If you see us anchored out during the festival next week, stop by and say hello.
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Old 26-08-2013, 21:05   #26
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Re: 12vdc generators - any good ones out there?

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That's an interesting source, Steve. If you see us anchored out during the festival next week, stop by and say hello.
I just might be zooming around during the festival in the playboy (pictured). Not exactly "show" quality but at least it is made of wood. My father built it back in '67 so it is sorta old too.

I will keep an eye out for Delfin and stop by if I see signs of life aboard.

Steve
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Old 26-08-2013, 21:35   #27
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Re: 12vdc generators - any good ones out there?

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I just might be zooming around during the festival in the playboy (pictured). Not exactly "show" quality but at least it is made of wood. My father built it back in '67 so it is sorta old too.

I will keep an eye out for Delfin and stop by if I see signs of life aboard.

Steve
That would be great. Your project has been executed with such tremendous innovation and skill it would be a great pleasure to meet you.
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Old 29-08-2013, 01:31   #28
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Re: 12vdc generators - any good ones out there?

It looks like I will probably go the DIY route to keep the costs down. I'll probably go with about a 1.5hp motor & an alternator in the 50-75 amp range. Does anyone have any suggestions on what alternator to use? Right now, I'm thinking of using a Bosch AL513X. They seem to litter the earth. They are rated for 60 amps & I can find them for less than $50. Does anyone have other suggestions?

Thanks,
Jim

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Old 29-08-2013, 03:46   #29
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Re: 12vdc generators - any good ones out there?

Jim, the homebrew I built had a Bosch Universal 85 amp alternator under a 3.5hp Briggs and Stratton 4 stroke lawn mower engine and about the best I could get out of it was around 50 amps at 12v before it stalled down.

Auto alternators are designed for fairly high RPM's and at low revs it takes a fair bit of torque to spin them. Depending on how many amps you want to be able to pull that size motor may not have enough grunt.

If you could get hold of torque/power/RPM curves for both the engine and alternator you might be able to better match things.
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Old 29-08-2013, 05:19   #30
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Re: 12vdc generators - any good ones out there?

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Originally Posted by pbiJim View Post
It looks like I will probably go the DIY route to keep the costs down. I'll probably go with about a 1.5hp motor & an alternator in the 50-75 amp range. Does anyone have any suggestions on what alternator to use? Right now, I'm thinking of using a Bosch AL513X. They seem to litter the earth. They are rated for 60 amps & I can find them for less than $50. Does anyone have other suggestions?

Thanks,
Jim
That will work ok, but a large-frame alternator (like a schoolbus alternator) works better than a regular alternator when called to put out constant high current.


You might find that a used suitcase generator from Honda or Yamaha is not that much more expensive than your home-brew. It will be a lot less hassle and will work better, store easier, etc., etc. You might want to check Fleabay and Craigs List.

Good luck.
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