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Old 14-11-2017, 22:35   #1
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Case Study:Diesel AC Gen to DC Gen- Larger boat

I started this thread to theoretically work thru what an Owner should look at when evolving from Lead to LFP batteries and the potential benefits of changing generation at the same time
.
Im using my boat as a test study for boats over 50ft.

The Thread WHAT IS A GOOD GENERATOR ?? has been a real education on the diesel generator evolution for LFP Battery Banks.

I had made a lot of wrong assumptions about the DC Gen option!

My 20 year NL 12kw @ 50hz still works fine, but eventually as liveaboards we will switch over to LFP from AGM and that may be the time to redesign the whole 24v DC system with a new DC generation system to be located in my Engine Room if a smaller DC Gen can be matched to save space

My wish List and Concerns if switching to a presumably smaller DC Gen:
1.. I would like to shift LFP Batteries/2 x Victron 24v-300w-70amp Multi-Charger-Invertors to the more spacious engine room right beside the new DC Gen .Is heat a concern for the Multi-Charger-Invertors? (My ER is very well ventilated! )

2.The whole engine room is now very well soundproofed so no sound shield is needed with a new DC Gen.
It has been proven to me that on most diesel engines, the best operating RPM is between 1200 -1500 RPM for both noise and mean time between failures.
So I would prefer to gear DC Gen to operate at their optimum output in that speed range. I dislike belts because of the dust and dirt they slew off and contaminate the ER.

3..Presently I have 1040Ah @ 24v AGM. I only consume 10% of my SOC in 24hrs at anchor,
With my existing chargers and AC Gen, I can Bulk charge 120amps to go from 70% to 80% SOC in two hours.

What should be a reasonable output target for a DC Gen to replace a 12kw AC Generator?

What would that require in Diesel horsepower, assuming that the DC loads have increased because I am now inverting AC consumers (6000w) and adding a new 24vdc HP motor driving the water maker pump?

Photo and Existing Gen Specs and Dimensions show all the room I would have to play with:

Look forwards to your thoughts and guidance.
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Old Yesterday, 14:03   #2
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Re: Case Study:Diesel AC Gen to DC Gen- Larger boat

Great project!

You could look at a brushless DC alternator Like a Delco 55SI. That unit produces 275A @ 24VDC up to an operating temperature of 110 C or 230 F. It's about 80% efficient so if it was direct coupled to your engine I calculate you could drive it with 12HP.

Now the issue is what engine produces 12HP in your desired RPM range. If you were willing to up the RPM range to 1800 you would widen the range of acceptable diesels.
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Old Yesterday, 14:16   #3
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Re: Case Study:Diesel AC Gen to DC Gen- Larger boat

Another consideration is running an alternator at that low an rpm will drastically reduce it's output. You could stay in your RPM range if you either use belts and pulleys (not you choice) or some form of gear reduction.
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Old Yesterday, 15:12   #4
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Re: Case Study:Diesel AC Gen to DC Gen- Larger boat

Quote:
Originally Posted by kenbo View Post
Great project!

You could look at a brushless DC alternator Like a Delco 55SI. That unit produces 275A @ 24VDC up to an operating temperature of 110 C or 230 F. It's about 80% efficient so if it was direct coupled to your engine I calculate you could drive it with 12HP.

Now the issue is what engine produces 12HP in your desired RPM range. If you were willing to up the RPM range to 1800 you would widen the range of acceptable diesels.
Yes, upping the RPM to 1800 seems to be necessary.
On my existing NL LUGGER engine, (see specs photo) it produces:
19.5 HP at 1500 RPM
26.0 HP at 1800 RPM,

That is a huge difference for only 300 RPM.

I guess it is finding the sweet spot of balancing
Smallest Size
Least noise and Vibration
Best DC generation , with or without a geared coupling to provide maximum output

If we are looking at 1800 RPM, what engine types should I be researching for around 12 HP?
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Old Yesterday, 15:33   #5
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Case Study:Diesel AC Gen to DC Gen- Larger boat

DC or AC, a Watt, is a Watt.
Why do you think you can go so much smaller with a DC generator?

My opinion is once you get into even decently sized generators that AC or DC is irrelevant, they are so easily converted to each other with decent efficiency now that its not really an issue. Now what would be slick is if someone builds a larger inverter / generator that could automatically vary engine RPM to load like a Honda. For some reason I assume that just isnt scalable?
And to be even more argumentative its not RPM that determines engine life so much as piston speed, just as its piston speed that determines upper RPM limit of an engine too, short strokes mean higher RPM and longer, lower. It is that simple.
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Old Yesterday, 15:43   #6
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Re: Case Study:Diesel AC Gen to DC Gen- Larger boat

Hi,

as I mentioned over in the other thread, this is pretty much what I'm doing at the moment.

You might want to have a look at Some good info and a vid) - CE Niehoff, P/N N1602-3, 28 Volt DC, 400 amp Generator Alternator, 30 available, (Shipping included in price to most locations in the continental U.S)

I'm using-

Yanmar 2YM15 Generator motor Best TQ at 2,400 RPM 8.5kW/ 12HP @1.4l/h or 0.4G/h output Max HP 10.5kW/15HP @3,400 RPM Max RPM 3,600 104kg 0.6l/h or 0.2G/h at Idle. Paid $5,800 for new 'bobtail' motor.

I am also going to install a remote oil filter kit to place for ease of servicing.

28V 400A 11.2kW 3,500 (max 8,000) rpm 400A. 1,500 rpm 200A 4.8kW 150 lbs CE Niehoff Generator Brushless N1602-3 Regulator Alternator Military

I am talking to a gentleman at Hayes to do me a direct coupling, and bell housing arrangement. He is saying it will run me maybe $3,500 as it's a one off so lots of development time required. Not a cheap option but will be done nicely. If you or any others want to do this too we could get a better rate for more units.

Engine controller, is the only thing I haven't sourced yet, but these can be purchased.

My idea is to control it at around 2,400 rpm max for max load, and idle for least load.

How does this compare with you NL AC unit, for cost, weight, size and fuel usage wise?

If you need any other details let me know specifically what you want.

Good luck.
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