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Old 08-04-2014, 17:23   #1
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Compact Diesel DC Generator 3-5Kw?

I'm looking at different power systems to put in my next boat, and I'm leaning towards a small diesel DC generator to feed the batteries and output supply through a 240v inverter. An AC generator would be too big for a quality one, and since I have would have an inverter and lifpo4, AC generation just doesn't seem necessary.

I'm wondering if anyone has used a small one or two cylinder water cooled diesel engine and just combine a 300 watt alternator like a Balmar one?

I'm thinking it should be pretty light, compact and easy to repair if required. A speed controller shouldn't be too hard to build, or I could just use manual control.
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Old 08-04-2014, 17:50   #2
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Re: Compact diesel DC generator 3-5Kw?

well... I've built 3 smaller ones up to 150 amp. Direct drive might be best... not sure where you get a 300 amp alternator, but the other issue is your batteries cannot take high amperage very long.
An example: 6 h Kubota powered 100 amp alternator. 6 Golf cart batteries. At start up the alternator would put out about 85 amps maybe close to 90. This lasted 15-20 minutes before the batteries were not able to take power anymore at that rate. so the regulator backs off the output. Mine were controlled by an aircraft vernier cable infinite speed adjustment.
All in all, there are some small diesel AC gen sets out there, and if you are 240 volt, my vote is to go that way. (Personally I would avoid the Panda, and not that fond of the Westerbeke either.)
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Old 08-04-2014, 18:36   #3
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Re: Compact diesel DC generator 3-5Kw?

Balmar make a 310 amp 12 volt, and 220 amp 24 volt alternator 6-Series Alternators and Charging Packages

500Ah of lifpo4 batteries should soak up much of the 310 amp. My main load would be air conditioning ~ 140 amps, fridge and freezer as well as normal electronics.

I would like to have solar/wind to mostly keep up with the fridge and freezer, however I have yet to do any calculations for that. The generator is mostly for the air con really, and mainly when sleeping.

I don't want a panda, or other domestic generator. I want a solid generator which is easy to maintain, as well as compact. I plan on putting it on a 39 foot yacht, so most generators would be too big. The Balmar alternators seem to have a good reputation, but this installation would be pretty taxing on them I would assume.
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Old 08-04-2014, 18:42   #4
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Re: Compact diesel DC generator 3-5Kw?

As far as compact AC generators go this one seems to be the one folks choose when space is limited: NEXT-GEN - Marine Power Units
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Old 08-04-2014, 18:47   #5
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Re: Compact diesel DC generator 3-5Kw?

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Originally Posted by jostalli View Post
As far as compact AC generators go this one seems to be the one folks choose when space is limited: NEXT-GEN - Marine Power Units
Yes, I was origionally looking at the next gen, it definitely looks the goods, but now am thinking that DC might be better for me.
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Old 08-04-2014, 18:53   #6
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Re: Compact diesel DC generator 3-5Kw?

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Balmar make a 310 amp 12 volt, and 220 amp 24 volt alternator 6-Series Alternators and Charging Packages

500Ah of lifpo4 batteries should soak up much of the 310 amp. My main load would be air conditioning ~ 140 amps, fridge and freezer as well as normal electronics.

I would like to have solar/wind to mostly keep up with the fridge and freezer, however I have yet to do any calculations for that. The generator is mostly for the air con really, and mainly when sleeping.

I don't want a panda, or other domestic generator. I want a solid generator which is easy to maintain, as well as compact. I plan on putting it on a 39 foot yacht, so most generators would be too big. The Balmar alternators seem to have a good reputation, but this installation would be pretty taxing on them I would assume.
Well, what you're trying to do did work for me, although there was a learning curve! Remember, you are becoming your own Beta test site!
Problems I had: Machined V belt pulley broke in half from the stress, Aluminum frame welds cracked (aircraft certified welder), Belts, belts and more belts. (dual belts on the 150 amp version) and some other stuff. Based on that I would say diret drive the way to go. Someone used to make a direct drive diesel DC generator...? Anyone remember who it was?
As far as premade AC gen sets, there are good ones out there. Northern Lights being one. I had one, really wasnt that much bigger than my home built DC unit. I've heard good things about Kohler too.
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Old 08-04-2014, 19:05   #7
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Re: Compact diesel DC generator 3-5Kw?

I have traded emails with James, the owner of this company about real life experiences with the Polar Power DC generator. Reach out to him: Electroprop 5 KW DC Generator - Electroprop
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Old 08-04-2014, 19:06   #8
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Re: Compact diesel DC generator 3-5Kw?

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Well, what you're trying to do did work for me, although there was a learning curve! Remember, you are becoming your own Beta test site!
Problems I had: Machined V belt pulley broke in half from the stress, Aluminum frame welds cracked (aircraft certified welder), Belts, belts and more belts. (dual belts on the 150 amp version) and some other stuff. Based on that I would say diret drive the way to go. Someone used to make a direct drive diesel DC generator...? Anyone remember who it was?
As far as premade AC gen sets, there are good ones out there. Northern Lights being one. I had one, really wasnt that much bigger than my home built DC unit. I've heard good things about Kohler too.
So a cogged v belt with a Balmar belt load manager/regulator and all stainless frame should help.

I would prefer not direct drive as I want it easily removable and direct drive has more engineering work to do such as balancing, machining, etc.
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Old 08-04-2014, 19:09   #9
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Re: Compact diesel DC generator 3-5Kw?

There have been a number of threads on this exact subject during the last year or so. You can find the long conversations with the search function.

If I were you, I wouldn't be too fussed about AC versus DC. You'll be consuming both AC and DC power and a good charger/inverter makes it trivial to convert between the two. There are losses, of course, but if you use both types of power then you'll have losses in any case. The only really big advantage of DC generation I can think of is that DC generators need not be constant speed. So you could reduce the speed of a DC generator when the load is light, which will make it more efficient and save your ears. But I don't actually know of a good one. I would never touch a FP, myself.

Plenty of people on here have made DC generators using 1 cylinder Kubota engines and large-frame alternators. I think you would have to have tons and tons of time on your hands and a boredom problem to solve for this to be worthwhile.

If you want very compact and cheap, NexGen seems to be the popular choice around here. If you can afford a little more weight and cost, then Northern Lights makes a gorgeous 5kW heavy duty, continuous duty rated genset: Northern Lights, Inc. M673LD3

The difference between them is that the little one-cylinder Kubota powered gensets are extremely noisy, vibrate, run at high speed, and produce a harsh sound. These are rototiller engines -- and you can't plan on getting a lot of hours out of them.

Something like the Northern Lights, on the other hand, has a three-cylinder Lugger engine which just lopes along at 1800 RPM, quiet and smooth, and will go for thousands of hours.

Kohler also makes a 5kW heavy duty marine genset: Kohler Power: 5EFKOD: 5 kW: 5EFKOD: Diesel Generators: Marine Generators

I own a Kohler myself (a 6.5EFOZ), but I think the consensus is that the Northern Lights are better made and even more reliable.
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Old 08-04-2014, 20:49   #10
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Re: Compact diesel DC generator 3-5Kw?

I don't know any reason why you couldn't build your own DC genet as you describe with a 300A alternator belted to a small diesel. Kubota makes a nice 2 cylinder engine that Onan uses in their 4/5 kw models. It produces about 10 HP which is about right for 300A. I suggest that you use either a flat multi groove belt or a pair of size "B" V belts. As someone else said, one advantage of a DC alternator is that you can reduce engine RPM as the load decreases.
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Old 08-04-2014, 21:20   #11
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Re: Compact diesel DC generator 3-5Kw?

Phasor Marine Generators LP1-3.5KW

This is what we have now, when i purchased it, we started in on a truck tailgate, and loaded it with a heater. It was so quiet we were talking right nxt to it with it running.

I looked into the DC route. If you will be running an air con, go with AC, not DC. with DC you loose amps as the alternator heats up. 300amps will not be for long, you will end up with 200 amps, 2600 watts, then a loss in the inverter, 8-10% so only 2400 watts. far too small. Get the AC, let the inverter charge the batteries. The simple, 2800 RPM kabota will run for a long time. And the rebuild is easy!
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Old 09-04-2014, 04:14   #12
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Re: Compact diesel DC generator 3-5Kw?

Quote:
Originally Posted by Rick R View Post
I don't know any reason why you couldn't build your own DC genet as you describe with a 300A alternator belted to a small diesel. Kubota makes a nice 2 cylinder engine that Onan uses in their 4/5 kw models. It produces about 10 HP which is about right for 300A. I suggest that you use either a flat multi groove belt or a pair of size "B" V belts. As someone else said, one advantage of a DC alternator is that you can reduce engine RPM as the load decreases.


Have a look round reefer breakers yards. Lots of fridge units have kubota blocks.

Dave
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Old 09-04-2014, 04:31   #13
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Re: Compact diesel DC generator 3-5Kw?

Thanks Dockhead, lots of good info there.

Quote:
Originally Posted by Dan316 View Post
I looked into the DC route. If you will be running an air con, go with AC, not DC. with DC you loose amps as the alternator heats up. 300amps will not be for long, you will end up with 200 amps, 2600 watts, then a loss in the inverter, 8-10% so only 2400 watts. far too small. Get the AC, let the inverter charge the batteries. The simple, 2800 RPM kabota will run for a long time. And the rebuild is easy!
If I went the AC route, I was planning on using a Victron Quatro so I could run off the batteries and let the genny start up when the batteries get low. That is also more $$'s and more potential points of failure.

With DC I was just going to use a 3k continous, 6k peak inverter run off the batteries, and a couple of amp guages and twist hand throttle for speed control of the engine. Without looking at torque figures, it looks like a simple process to haver the motor under 2000rpm and supply enough power for the air con.

2800rpm seems like a good compromise to me. 2 cylinder would be better than one but that is more space.

But the heat could be the final straw. After further investigation the output of a Balmar alternator drops off 20% going from 122F to 190F. Considering it would be in an enclosed, sound proof enclosure I reckon it would be quite warm, and you would need an air blower on the alternator to keep it at a decent temp.

The temp issue might be a deal breaker.

I don't even have the boat yet, but I want to make sure the one I choose can fit a suitable generator in it, which is why i'm looking. 16000 btu Air con is a must have for me.

Has anyone fit a compact diesel generator in a Lazaret in a sub 40 foot mono before?
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Old 09-04-2014, 04:49   #14
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Re: Compact Diesel DC Generator 3-5Kw?

This is what I have done.

DC Generator - The Smart Way to Go

I changed the batteries from AGMs to 600ah LifePo4

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