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Old 29-08-2013, 06:31   #31
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Re: 12vdc generators - any good ones out there?

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Originally Posted by RaymondR View Post
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.

That's very useful feedback. Thank you.

I was planning to undersize the motor a little so as not to overwork the little 60 amp alternator.

The motor that I'm looking at develops full HP in the 6,000-7,000 rpm range. I don't really have a feel for how fast an alternator is going to want to spin. I'm not sure where to look for data on how fast they want to be spun either. Do you have any suggestions where I might look?
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Old 29-08-2013, 06:34   #32
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Re: 12vdc generators - any good ones out there?

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You might find that a used suitcase generator from Honda or Yamaha is not that much more expensive than your home-brew.
I'm not sure what you mean by a suitcase generator. The portable generators that I see at auto parts stores & camping supply stores have 12vdc circuits with maybe 10-15 amp capacity, which is a little low for what I want to do. I was hoping for something more like to 50 amps. Do Honda or Yamaha make something like that?
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Old 29-08-2013, 06:41   #33
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Re: 12vdc generators - any good ones out there?

Take a look at the Ample Power Genie 12V/150A. US$5,400 plus options.
Bio-Diesel Battery Chargers - Manual Start/Stop
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Old 29-08-2013, 06:44   #34
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Re: 12vdc generators - any good ones out there?

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Originally Posted by pbiJim View Post
I'm not sure what you mean by a suitcase generator. The portable generators that I see at auto parts stores & camping supply stores have 12vdc circuits with maybe 10-15 amp capacity, which is a little low for what I want to do. I was hoping for something more like to 50 amps. Do Honda or Yamaha make something like that?
Every standard AC generator I've ever owned or checked the specs, the DC output was minimal. Like the Honda EU2000i at 8 amps DC. You'll do much better using the generator to run your regular battery charger.
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Old 29-08-2013, 06:45   #35
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Re: 12vdc generators - any good ones out there?

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The motor that I'm looking at develops full HP in the 6,000-7,000 rpm range. I don't really have a feel for how fast an alternator is going to want to spin. I'm not sure where to look for data on how fast they want to be spun either. Do you have any suggestions where I might look?
Gasoline 1:1,5
Diesel 1:2 to 1:3

The efficiency is between 50 to 70% and it takes up to 3.5 kW (approx. 5 hp) from the engine...
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Old 29-08-2013, 06:49   #36
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Re: 12vdc generators - any good ones out there?

The Balmar website has a lot of tech resources for figuring out your alternator setup.
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Old 29-08-2013, 07:04   #37
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Re: 12vdc generators - any good ones out there?

Quote:
Originally Posted by pbiJim View Post
I'm not sure what you mean by a suitcase generator. The portable generators that I see at auto parts stores & camping supply stores have 12vdc circuits with maybe 10-15 amp capacity, which is a little low for what I want to do. I was hoping for something more like to 50 amps. Do Honda or Yamaha make something like that?
Here you go:

Honda EU10i and EU20i suitcase portable generator specialists, sales, parts, repairs and service.

Yamaha makes the other really good one. Chinese ones like Kipor are much cheaper, but might not give such good service.

They produce AC power. You would charge your batts with your regular shore power battery charger.

DC power will work equally well, and so a DC generator is for sure what you want for a home-brew because it is so much simpler to build.

But AC power will also get the job done, and there are a lot of advantages to these suitcase gens compared to an open-frame DC generator:

1. They are much, much, much, much quieter.
2. They are much more compact and easier to store.
3. They have sealable, leak-proof fuel tanks, so you can store them inside the boat (a normal vented fuel tank is dangerous inside the boat).
4. They are versatile -- besides for charging batteries, you can use them for AC power as well (power tools, etc., etc., etc.).
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Old 29-08-2013, 07:12   #38
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Re: 12vdc generators - any good ones out there?

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Originally Posted by tom1263 View Post
Gasoline 1:1,5
Diesel 1:2 to 1:3

The efficiency is between 50 to 70% and it takes up to 3.5 kW (approx. 5 hp) from the engine...
If you do a home-brew, don't undersize the motor. You don't want to run air-cooled lawnmower type engines near redline for a long time, so want to derate the engine. Size it so maybe half output will give enough power for full alternator output (so probably, for a 1kW alternator, you need near 2kW from the engine, so a 4kW engine. For example.

Then size the sheaves so that the power curve of the alternator, keeping in mind the efficiency factor, will put an appropriate load on the engine, not overloading it at any RPM. Then you will not have to run the engine at full throttle.

The RPM ranges for every alternator are published as part of the technical spec. They run faster than the engines they are mounted to, so you need a smaller pulley on the alternator than you have on the engine, in whatever ratio you calculate after doing the power curves.
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Old 29-08-2013, 07:20   #39
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Re: 12vdc generators - any good ones out there?

Jim,
There is a diesel genset, the ROTO, available in Australia that fits your description.
Roto DC Marine Generator Genset Battery Charger
For export, the domestic GST included in their price would not apply to you.
At the very least the components list would be of use as a guide to DIY.
I have absolutely no connection with this company.
Cheers,
Mac
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Old 29-08-2013, 07:54   #40
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Re: 12vdc generators - any good ones out there?

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The RPM ranges for every alternator are published as part of the technical spec. They run faster than the engines they are mounted to, so you need a smaller pulley on the alternator than you have on the engine, in whatever ratio you calculate after doing the power curves.
Yes, 1:2 means Engine RPM: Alternator RPM.

Last year I wanted to build a DC generator with a higher power at 140A. The engine should be a Kubota EA300, which drives a water-cooled alternator from Bosch, with a speed ratio of 1:2.2 and automatic Start / Stop over Victron BMV 600S.

But in the end it was too expensive ....
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Old 29-08-2013, 08:18   #41
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Re: 12vdc generators - any good ones out there?

Quote:
Originally Posted by Dockhead View Post
Here you go:

Honda EU10i and EU20i suitcase portable generator specialists, sales, parts, repairs and service.

Yamaha makes the other really good one. Chinese ones like Kipor are much cheaper, but might not give such good service.

They produce AC power. You would charge your batts with your regular shore power battery charger.

DC power will work equally well, and so a DC generator is for sure what you want for a home-brew because it is so much simpler to build.

But AC power will also get the job done, and there are a lot of advantages to these suitcase gens compared to an open-frame DC generator:

1. They are much, much, much, much quieter.
2. They are much more compact and easier to store.
3. They have sealable, leak-proof fuel tanks, so you can store them inside the boat (a normal vented fuel tank is dangerous inside the boat).
4. They are versatile -- besides for charging batteries, you can use them for AC power as well (power tools, etc., etc., etc.).
All of the above which is why my current choice for this application will be an AC portable and specifically a Honda EU2000i (can't really use that funny European version with the wrong voltage and frequency).

If Honda would just make a mini-diesel version of the EU2000i it would be almost perfect.
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Old 29-08-2013, 10:17   #42
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Re: 12vdc generators - any good ones out there?

The big disadvantage of teh Hondas, is

(a) You have to carrying considerable amounts of petrol

(b) As you really have to run them out in the open, they are much louder then conventional marine gensets. They really annoy me in anchorages, especially when reving up from idle to take the load.

useful as an occasional standby, but that its in my view

dave
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Old 29-08-2013, 11:41   #43
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Re: 12vdc generators - any good ones out there?

All valid issues. My way to deal with them is:

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Originally Posted by goboatingnow View Post
The big disadvantage of teh Hondas, is

(a) You have to carrying considerable amounts of petrol

I keep a portable generator on my boats for backups, emergencies or very occasional use so generally will not use much gasoline (as far as I know one can't purchase petrol over here).

(b) As you really have to run them out in the open, they are much louder then conventional marine gensets. They really annoy me in anchorages, especially when reving up from idle to take the load.

As noted, my use would be occasional and would try to limit to daytime except in dire need. Also I do always try to anchor a good distance from other boats. If someone comes in later and drops a hook a bit too close for comfort I might be tempted to find some urgent reason to crank the Honda.

If forced to anchor in crowded and quiet anchorage I would definitely avoid any sort of unpleasant noises unless absolutely necessary.



useful as an occasional standby, but that its in my view

Mine as well.

dave
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Old 29-08-2013, 11:49   #44
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Re: 12vdc generators - any good ones out there?

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I keep a portable generator on my boats for backups, emergencies or very occasional use so generally will not use much gasoline (as far as I know one can't purchase petrol over here).

French (essence de) pétrole, (essence of) petroleum, gasoline, from Old French petrole, petroleum, from Medieval Latin petrleum

we go a little further back then the 1600s
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Old 29-08-2013, 11:53   #45
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Re: 12vdc generators - any good ones out there?

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A little bigger than what I'm looking for, but interesting.
Thank You.
The genie is really quite small. You could just put it in your lazarette! It's a simple Kubota diesel based unit.... and the real nice thing is you can run it at low rpm... very quiet down there.
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