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Bulletin Board >> Discussion Forum >> Electrical System (posted on behalf of Arild Jensen) |
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> -----Original Message-----
> From: Ken Williams
> Arlid:
>
> The electrical system was designed by Mickey Smith, as you suspected.
> Mickey and I have a funny history together. Decades ago, when I
ran a
> computer game company (Sierra On-Line), Mickey was our representative
> from Intel.
REPLY
Yes I remember Sierra On-Line.
My fouir year eold daughter learned how to use computers while playing the Mother Goose game.
> Here's a question for you: I had always thought there was a direct
> correlation between horsepower and fuel. Aren't the hydraulic
> alternators consuming exactly the same amount of fuel that an
> equivalent generator would?
REPLY
You are correct!
In addition most hydraulic systems have an additional 5% loss compared to a purely mechanical drive.
However taking an additional 5 - 10 HP from your main engine does not shift it far along the power curve relatively to wher it is just driving the boat.
The little extra fuel burned is not as much as would be consumed in a genset delivering the same electrical power as single phase 120 or 220V AC at 60HZ.
1800 RPM is not the optimum RPM for the engine blocks used for gensets.
I'm not aware of anyone doing detailed studies complete with a lot to data comparing the two methods.
Alternators actually produce 3 phase power which is then rectified to DC. A technical argument can be made that this is actually more efficient per unit of fuel burned that the single phase AC output used in smaller gensets.
Nordhavn owners usually speak of their output as "free electricity", but I'm not sure it is. In my case, I'm happy to have a little extra load on the engines. With twins, I'll be consuming only about 90hp per engine much of the time. I'm not sure constant under-loading is good for an engine.
REPLY
Here again you are quite correct. All engines have only a narrow range of RPM in which is it most efficient.
Therefore the close you come to running the engine at that RPM and loaded appropriately the better.
Deriving your electrical power from the propulsion engine in a manner which is essentially independent of the exact RPM is th ebest solution to cruising power.
> As to the house battery bank: . we'll have 1,530 24v amp hours.
> That should be enough for our use. 99% of the time it will just be
> Roberta and I on the boat, and we're pretty conservative on using
> power. On Sans
Souci, our 62,
> the primary power consumer at night, while at anchor, was the sat TV
> positioning unit. I always had to power it off, and the Fleet 77,
> before going to bed.
REPLY
Being conservative with using power is the key. In your case I am suer the systemwil perform nicely and meet your expectations.
I have run into some people that want a similar system but expect to use power in a profligate manner as if they were ashore in a luxury condo. They expect to air condition the entire vessel day or night.
> "...How do you split the load between the genset and the inverters
> when you have central air using chillers?...
>
> It has been a few weeks since I looked at the electric panel. I need
> to do some investigating to answer this question. I'll look this afternoon...
>
REPLY
I will look forward to hearign from you later.
Very best regards
Arild
| Williams, Ken |
2006-11-19 14:40:59
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Arlid:
The electrical system was designed by Mickey Smith, as you suspected. Mickey and I have a funny history together. Decades ago, when I ran a computer game company (Sierra On-Line), Mickey was our representative from Intel. We were located at Yosemite, and he once brought his family along for a tour of our studio. I never would have suspected we would wind up someday linked in a completely different way. It's a very small world. Mickey also had a 62, and is likely someday to be an owner again.
Our cruising alternators were Electrodyne on the 62, and I'm fairly certain that's what we will have on the 68. I'm not sure of the exact model. I didn't know that Dashew had them on his boat. That's quite an endorsement. Here's a question for you: I had always thought there was a direct correlation between horsepower and fuel. Aren't the hydraulic alternators consuming exactly the same amount of fuel that an equivalent generator would? Nordhavn owners usually speak of their output as "free electricity", but I'm not sure it is. In my case, I'm happy to have a little extra load on the engines. With twins, I'll be consuming only about 90hp per engine much of the time. I'm not sure constant under-loading is good for an engine.
As to the house battery bank: . we'll have 1,530 24v amp hours. That should be enough for our use. 99% of the time it will just be Roberta and I on the boat, and we're pretty conservative on using power. On Sans Souci, our 62, the primary power consumer at night, while at anchor, was the sat TV positioning unit. I always had to power it off, and the Fleet 77, before going to bed.
"...How do you split the load between the genset and the inverters when you have central air using chillers?...
It has been a few weeks since I looked at the electric panel. I need to do some investigating to answer this question. I'll look this afternoon...
...Well if you get stuck feel free to send me an email..
Thank you!!!
-Ken W
| Williams, Ken |
2006-11-19 09:59:18
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Hi Ken, I appreciate the prompt reply.
AS you may have noticed from my posts on the Trawler list; I am quite involved in electrical design so I am always intrigued by unusual designs.
> -----Original Message-----
> From: Ken Williams >
> Arild:
>
> As you've noticed, the electrical system on my boat is unusual. Most
> of the system is fairly standard for a Nordhavn, but there are some unique
> aspects to the boat, particularly the inverters.
REPLY
That is what caught my eye. I have used similar approaches but not at that level of power application.
Is Mikey Smith doing the design, or someone else?
> Let's start by talking about the cruising alternators. These are
> hydraulically powered by a PTO from the main engines. It's the same
> ABT hydraulic system that powers the stabilizers and the thrusters.
> Each of the two cruising alternators puts out 250 amps of 24 volt power.
>This gives the equivalent of a 14kw 220v generator, without powering a generator on. For
> long passages, this comes in handy.
Steve Dashew uses Electrodyne, I know of one Leece-Neville model also capable of such an output.
In fact I have one sitting on my shop bench. What brand /model are you using?
> There are four 3.5kw Outback (not Victron) inverters that will be
> installed. This will provide 14kw of 220v power. This allows me to
> meet most ordinary
> loads on the boat without firing a generator.
REPLY
I was mis-informed they were Victron but Outback are just as good, perhaps better.
I have only installed one Outback system but was impressed by their quality.
How big a bank of batteries are you installing to support such a large inverter capacity?
I would think that it has to be at least 2400 Amp -Hours or the batteries will not last any reasonable lenght of time.
> The honest reason we did this was to avoid having to start up a
> generator while at anchor. If I have a boat of sleeping guests, and
> want to fire up the expresso machine, this allows me plenty of power
> in short bursts without turning on the generator. If also allows the
> full output of the cruising alternators to be tapped while underway.
REPLY
I did a similar thing on a Michael Kasten design I did last year.
Sure reduces fuel burn if you don't have to run a genset while under way.
> Theoretically, the inverter output is sufficient to run a portion of
> the air conditioning. My hope is that I have sufficient battery capacity to cool
> JUST the master stateroom, while at anchor overnight. On paper we have
> enough amp hours in the house battery bank, so - maybe.
REPLY
How do you split the load between the genset and the inverters when you have central air using chillers.
I noted in your write up that you have four chillers to lessen the start surge. Good plan!
> I have thought many times about simplifying the electrical system.
> Sans Souci will be traveling around the world, and it will be up to me
> to fix things when they break. I'm a software engineer, not an
> electrician. I've been reading books on marine electrical systems, but
> most of this is still over my head. The right answer was probably to
> dump the cruising alternators, all but one inverter and perhaps even
> one of the generators -- just to reduce complexity, and free up space
> in the engine room
> -- but, I've convinced myself I can handle it, and hopefully I'm right!
REPLY
Well if you get stuck feel free to send me an email. Many other trawler list members do, even when they are cruising on vacation.
| Williams, Ken |
2006-11-19 09:36:39
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Arild:
As you've noticed, the electrical system on my boat is unusual. Most of the system is fairly standard for a Nordhavn, but there are some unique aspects to the boat, particularly the inverters.
Let's start by talking about the cruising alternators. These are hydraulically powered by a PTO from the main engines. It's the same ABT hydraulic system that powers the stabilizers and the thrusters. Each of the two cruising alternators puts out 250 amps of 24 volt power. This gives the equivalent of a 14kw 220v generator, without powering a generator on. For long passages, this comes in handy.
There are four 3.5kw Outback (not Victron) inverters that will be installed. This will provide 14kw of 220v power. This allows me to meet most ordinary loads on the boat without firing a generator.
The honest reason we did this was to avoid having to start up a generator while at anchor. If I have a boat of sleeping guests, and want to fire up the expresso machine, this allows me plenty of power in short bursts without turning on the generator. If also allows the full output of the cruising alternators to be tapped while underway.
Theoretically, the inverter output is sufficient to run a portion of the air conditioning. My hope is that I have sufficient battery capacity to cool JUST the master stateroom, while at anchor overnight. On paper we have enough amp hours in the house battery bank, so - maybe.
I have thought many times about simplifying the electrical system. Sans Souci will be traveling around the world, and it will be up to me to fix things when they break. I'm a software engineer, not an electrician. I've been reading books on marine electrical systems, but most of this is still over my head. The right answer was probably to dump the cruising alternators, all but one inverter and perhaps even one of the generators -- just to reduce complexity, and free up space in the engine room -- but, I've convinced myself I can handle it, and hopefully I'm right!
-Ken W
| Williams, Ken |
2006-11-18 09:07:59
|
Hello Ken,
I have been following your NH68 building progress on your website with interest.
I'm wondering about the three Victron inverters grouped together in the picture of your engine room. I also noted some alternators which appear to be driven hydraulically.
Can you tell me how that has worked out in practice? Exactly what are the three inverters intended for? Is it for three phase power for the air conditioning?
best regards
Arild
| Williams, Ken |
2006-11-18 08:49:18
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