Case Study:Diesel AC Gen to DC Gen- Larger boat

[Pelagic]

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
.
I’m using my boat as a test study for boats over 50ft.

The Thread http://www.cruisersforum.com/forums/...or-193270.html 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 ¾ 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.

[kenbo]

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.

[kenbo]

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.

[Pelagic]

Originally Posted by kenbo

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?

[a64pilot]

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 it’s 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 isn’t scalable?
And to be even more argumentative it’s not RPM that determines engine life so much as piston speed, just as it’s piston speed that determines upper RPM limit of an engine too, short strokes mean higher RPM and longer, lower. It is that simple.

[Q Xopa]

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.

[kenbo]

Originally Posted by Q Xopa

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.

That is an outstanding generator. But I'm not quite understanding your need for an engine controller. What would be it's purpose? Are you looking to achieve some variable output automatically?

[Q Xopa]

Good question.

I'm sure you are aware of the fact that most Generators are 'governed'. Mostly we are talking AC Generators, of which the aim here is to maintain a fixed RPM to keep the output frequency stable, ie 110VAC 60 Htz in the US and 220VAC 50 Htz for most other places.

So essentially with a light load this keeps the engine throttle is mostly closed. Then as load is placed on the generator the engine throttle will be opened to keep the engine RPM constant as much as possible.

This was done originally using mechanical means like flyweights and 'speeder' springs, or an engine driven fan pushing on a vane attached to the throttle linkage.

These days this is all done with electronics.

DC generators have slightly different needs to operate efficiently. They are not restricted to keep a constant RPM. Generally they will try to vary the RPMs slow/ idle (quiet and low fuel use) for light loads and higher (usually optimum TQ and Fuel efficiency etc) RPMs for heavy loads.

This is how the new generation (pardon the pun) 'Inverter' technology Generators like the Honda 2000i or the Westinghouse iGen2000. I know some people dont want me mentioning Inverters, but that's what the 'i' in those little generators name stands for. It's kinda the secret to their operation, as they use the Inverter to maintain a constant AC output Frequency. It's how they can make them so small and efficient.

So the engine control on the Honda i2000 etc is done electronically. Ie the system that makes it speed up and get noisier when a greater load is placed on, eg your air cond compressor kicks on.

So the only difference (ok it's bigger too) with what I'm trying to do is using a diesel motor instead of a gas motor. Same principle of operation though using an Inverter to electronically keep the output frequency stable and using the battery bank to average out load surges etc.

So expanding a little on an electronic speed controller, you can also do a number of other things to like-
• Auto start when a low batt voltage is sensed, (someone previously suggested I use one)
• Auto stop when batt voltage is reaches a certain point,
• Auto warm up at idle before a load is placed on it
• And much more (only really limited by our imagination)

I have asked permission of an article writer, to post a link to his well written description on this subject.

Of course we don’t have to do this, this could all be done manually by simply setting, and readjusting a throttle as required. Me personally, if we are going to this trouble to build something like this I cant see why we wouldn’t want this capability. Commercial units are capable and in the scheme of things not that much money, say $300ish.

Cheers All.

[kenbo]

Q Xopa

Great explanation, thanks. I would be very interested in the commercial controllers that you have sourced.

I was disposed to manual control but for not much money why not.

[Q Xopa]

Why DC Generators or ‘Inverter Technology’ (to use the modern marketing term) can be smaller.

Yes agreed that a Watt is a watt.

It’s a question of usage patterns. A DC Gen can be sized for ‘Average’ Watt useage for a given period.
Where as an AC Gen must be sized for maximum load.

Sometimes there isn’t much of an advantage or size difference that can be utilized.

For example most of us get Generators to run our Water makers and or Air Conditioners. Air conditioners are good example. As we know they cycle their compressors on and off to regulate a set temperature. So the total ON time might be say 50%, sometimes called ‘Duty cycle’.

For an AC Gen it would running at it’s same speed whether our Air cond is ON or OFF. A DC Generator could use a Battery pack to average out those loads by charging the batts when the the Air cond compressor is cycled Off and use the Batts to make up a temporary deficit when the Compressor is cycled ON.

Or the DC Gen can reduce speed when the Compressor is cycled off, saving some fuel.

This isnt always the case, for example if the Generator was used predominately to run a water maker. They don’t cycle, so in this example the advantage of a DC Gen would be far less.

However there is still an advantage of not having to maintain a constant RPM to maintain a constant output Frequency. Think of sitting at the traffic lights in your car with your engine reving at Highway speed RPMs, but with no load. Doesn’t sound too efficient. It is definitely going to ‘sound’ loud though. This is how AC Gens operate.

The new Honda 2000i (Inverter) Generators which are DC Generators work more like your car and speed up when they are loaded and Idle when the load is Off.

So continuing the car analogy, for city driving usage patterns a smaller car will be more efficient. However for more Highway usage a larger car is going to be more efficient. Obviously I’m being quite vague here trying to illustrate the concept.

Have a look at a fellow poster’s web page that explains all this very eloquently- mv.VikingStar: Kubota DC Generator and Arduino based Alternator Regulator and Small Engine Control

Apart from the above Speed controller another commercial example is- https://www.controllers4generators.c...tuator_output/
Cheers All.

[Dockhead]

Originally Posted by Q Xopa

Why DC Generators or ‘Inverter Technology’ (to use the modern marketing term) can be smaller.

Yes agreed that a Watt is a watt.

It’s a question of usage patterns. A DC Gen can be sized for ‘Average’ Watt useage for a given period.
Where as an AC Gen must be sized for maximum load.

. .

Why is that? What difference does it make whether it's an AC or DC generator? I think the difference is only whether you have an inverter/charger (or gang of them) which is capable of "peak shaving" -- that's what utilities call it -- using "power boost" to use inverted power to cover deficits when you have peak loads greater than the generator's capacity. With LiFePo batteries, you don't need to reduce the output of the generator (by reducing revs on a DC generator) -- just pump in power. Unlike with lead acid batteries.

Pelagic, why do you want to change the generator at all? Your generator will be fantastic with LiFePo batteries. It's large and powerful and will pump power into the batteries in short, efficient generator runs. If it's in good condition, I would leave it, and save a lot of money!

My suggestion would be to use a GANG of charger/inverters. The Victron Multiplus ones can be put together two or three at a time. It will be cheaper to rectify those 12kW (or whatever part of the whole capacity you want to use for charging), than changing out the generator, by far. And then you have failure-proof redundancy in this critical item of gear and you will have tons of inverting capacity to match the qualities of the LiFePo bank.


These things don't like heat. I have mine in my engine room and it's OK at my latitudes and with good blowers, but you should measure your engine room temperature before making the decision about where to put them. If it's more than ambient + 10C, you might consider a different place.


As to generating capacity -- I would leave the NL but maybe put on a mongo Ecotec alternator on the main engine. Not too expensive, and then you have fully redundant high capacity charging. It will load your main engine enough, and will allow you to do short enough charging runs, that you could use the main engine for this even when you're not underway, without hurting it, I would think.

[CarstenWL]

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! )

You are talking about the 24V-3000-70 Amp Victron, right?
What temperature do you have in your engine room after a longer run?

Generally I don't think it is a good idea to put the inverter/chargers there, the unit will get quite warm itself when running.

Regards,

Carsten

[Q Xopa]

If you’re looking for an argument from me, sorry to disappoint but couldn’t agree with you more.
It doesn’t matter to me, you by the sound of it, or in practice if it’s AC or DC output.
It only really matters, is if you want an AC output how we produce it. I would suggest better to do that in a DC first using a VARIABLE RPM motor, then electronically invert it.
Much preferable to the ‘traditional’ generator way of running the motor at constant RPM to get a stable AC output Frequency.
Having our AC gens just spinning at high speed when they’re unloaded just seems wasteful and unnecessary when we know there is a better way.
The crux of the issue is using our Generator motor as efficiently as we can, ie slow speed, for no load, and in it’s fuel efficient RPM range for higher load running.
If it’s DC we want, go crazy, regulate it and put in your batts or straight on your DC bus bar. This is the same (usually bigger) as any Alternator set up on our main engines, or cars.
Again fully agree, with LiFePO4s. Just run our DC, or AC (whatever we want our setup to be) Generator at optimum RPM and loading. So it spends most of it’s running life at it’s most efficient operating range.
We cant do this with Lead acids, with absorption and especially Float stages not being as ‘Loaded’ as Bulk stage. The trouble with Lead batts they will only accept Charge at a certain reducing rate. So we are using our Generator to try and charge Lead batts, it is a slower process with load decreasing as we progress.
So of course we have to size our Gen for our initial ‘Bulk’ stage high current, but then we end up end up having our Gen running lightly loaded (under optimum). If it’s an AC Gen it is still running at the same higher RPM range, but ‘under’ loaded. Of course this is obviously not the best engine wear or fuel usage profile for our Generator engine. It also takes longer, because Leads only accept charge at a slower and slower rate so our Gen runs at this sub optimal range for longer.
In contrast if we are charging Lithium batts, we can just go hard and have them charged in a shorter time. So our run times can be substantially shorter, and proportionaly more of that run time in a closer to optimum RPM and load band. This of course uses our fuel most efficiently and wear on the engine is lower. Overall Generator engine run time is less.
Even trying to charge Lead batts with a DC Gen is going to be more efficient than using an AC Gen. As the charge acceptance rate decreases the because it will decrease it’s RPM as the load decreases. Not ideal, but better than still spinning the motor quickly unloaded.
Most of us wouldn’t treat our main motors this way. It would be the same as having a too small prop. So basically we in agreement so far.
Victron Inverters ganged together. Yes again I have 2 x 3000W. If/when I need more I will just add more. I love em, all my AC power is clean and Stable. The only thing any dirty shore power runs on my boat is a battery charger.
Also agree that the logical place to start is bigger and or 2nd Alternators on the main engine. Seeing we got to have a main engine, why not have it being utilized as fully as possible producing as much as we can. As you say as big a case as we can fit. Yes Ecotechs are nice, but not cheap. But if you can afford, and fit them, why wouldn’t you. They are not always ideal but still cheaper than and easier to find space for than a Genset.
A Genset is going to be better for a big elec demand, long time at anchor scenario. Not so worthwhile for plugged in at a dock or if you can squeeze some motoring into your schedule.
As the OP stated, the smaller the boat, or the load the less practical this becomes.
Sorry to be so boring and agree so much. We’re apparently drinking the same ‘Coolaide’.
And oops sorry to mention Inverters: Peace.

[Dockhead]

Originally Posted by Q Xopa

If you’re looking for an argument from me, sorry to disappoint but couldn’t agree with you more.
It doesn’t matter to me, you by the sound of it, or in practice if it’s AC or DC output.
It only really matters, is if you want an AC output how we produce it. I would suggest better to do that in a DC first using a VARIABLE RPM motor, then electronically invert it.
Much preferable to the ‘traditional’ generator way of running the motor at constant RPM to get a stable AC output Frequency.
Having our AC gens just spinning at high speed when they’re unloaded just seems wasteful and unnecessary when we know there is a better way.
The crux of the issue is using our Generator motor as efficiently as we can, ie slow speed, for no load, and in it’s fuel efficient RPM range for higher load running.
If it’s DC we want, go crazy, regulate it and put in your batts or straight on your DC bus bar. This is the same (usually bigger) as any Alternator set up on our main engines, or cars.
Again fully agree, with LiFePO4s. Just run our DC, or AC (whatever we want our setup to be) Generator at optimum RPM and loading. So it spends most of it’s running life at it’s most efficient operating range.
We cant do this with Lead acids, with absorption and especially Float stages not being as ‘Loaded’ as Bulk stage. The trouble with Lead batts they will only accept Charge at a certain reducing rate. So we are using our Generator to try and charge Lead batts, it is a slower process with load decreasing as we progress.
So of course we have to size our Gen for our initial ‘Bulk’ stage high current, but then we end up end up having our Gen running lightly loaded (under optimum). If it’s an AC Gen it is still running at the same higher RPM range, but ‘under’ loaded. Of course this is obviously not the best engine wear or fuel usage profile for our Generator engine. It also takes longer, because Leads only accept charge at a slower and slower rate so our Gen runs at this sub optimal range for longer.
In contrast if we are charging Lithium batts, we can just go hard and have them charged in a shorter time. So our run times can be substantially shorter, and proportionaly more of that run time in a closer to optimum RPM and load band. This of course uses our fuel most efficiently and wear on the engine is lower. Overall Generator engine run time is less.
Even trying to charge Lead batts with a DC Gen is going to be more efficient than using an AC Gen. As the charge acceptance rate decreases the because it will decrease it’s RPM as the load decreases. Not ideal, but better than still spinning the motor quickly unloaded.
Most of us wouldn’t treat our main motors this way. It would be the same as having a too small prop. So basically we in agreement so far.
Victron Inverters ganged together. Yes again I have 2 x 3000W. If/when I need more I will just add more. I love em, all my AC power is clean and Stable. The only thing any dirty shore power runs on my boat is a battery charger.
Also agree that the logical place to start is bigger and or 2nd Alternators on the main engine. Seeing we got to have a main engine, why not have it being utilized as fully as possible producing as much as we can. As you say as big a case as we can fit. Yes Ecotechs are nice, but not cheap. But if you can afford, and fit them, why wouldn’t you. They are not always ideal but still cheaper than and easier to find space for than a Genset.
A Genset is going to be better for a big elec demand, long time at anchor scenario. Not so worthwhile for plugged in at a dock or if you can squeeze some motoring into your schedule.
As the OP stated, the smaller the boat, or the load the less practical this becomes.
Sorry to be so boring and agree so much. We’re apparently drinking the same ‘Coolaide’.
And oops sorry to mention Inverters: Peace.

If that's addressed to me -- I was certainly not looking for an argument I was just trying to understand one minor part of what you were saying.

I certainly agree with everything here.

As to Ecotec vs. alternatives --

This is a good question without an obvious right answer. Ecotec is obviously superior. It should be reasonably easy to repair if necessary -- alternators are not all that complicated. But this is expensive and not as easy to understand for third world auto electric shops as a normal truck alternator like Leece Neville etc.

It might be reasonable to trade some of the advantages of Ecotec for being cheap and easier to repair. For Pelagic especially so, since he's cruising in third world part of the world.

I can report from experience -- I've had a 2.5kW Leece Neville alternator on my boat which was fitted when the boat was originally built. I wonder how many megawatt/hours I've produced with it over 8 years -- lots. I did manage to melt it down, however, by forgetting to take off big inverter loads while operating a 10 hp bow thruster while the engine was at idle. I guess an Ecotec would have survived this kind of abuse. On the other hand, it takes 20 minutes to pop off the alternator, and it cost less than $200 to completely rebuild it. So there's something to think about there.

[Dockhead]

Originally Posted by CarstenWL

You are talking about the 24V-3000-70 Amp Victron, right?
What temperature do you have in your engine room after a longer run?

Generally I don't think it is a good idea to put the inverter/chargers there, the unit will get quite warm itself when running.

Regards,

Carsten

That's the exact unit I have, and I have it in my engine room.

I monitor engine room temp, and on my boat it doesn't get over 40C. But then again, I don't sail South of 50N, so YMMV. At 40C, this Victron does not put out its nominal output. Practical sustained inverter output is a bit over 2kW. So I think it's very good to gang them and don't push maximum inverter output. More and more important, the warmer the operating environment. And if the engine room gets much over 40C, I would look for a different place.