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From: A Jensen (no email)
Date: Wed Aug 04 2004 - 22:36:09 EDT
Bill Cooke wrote:
I paraphrase that to There are ways to make the power system much more
efficient. Trouble is some
people are not interested in even looking into ways and means of doing that.
Its called NUCLEAR. And so that its boating related, "As in submarine and
aircraft carrier".
Bill
REPLY
You don't even have to go that far.
The new 87 foot USCG cutters are all powered by 3 phase AC. Not the more
conventional split single phase 120/240V
Power is generated by conventional Northern Light gensets buit the output is
3 phase.
All motor loads run better on 3 phase. Smoother starting, lower surge
current, better power factor and so on.
So why don't the big boat builders use this approach?
I asked this very question of the electricians at a major builder her in the
PNW
Answer: They said they had enough trouble understanding single phase 120V,
never mind going to 240 3 phase. DUH!
Secondly, trying to convince the old established design engineers to try
something different than what they had been doing for the past twenty years
would be a hard sell.
In othe rwords people are afraid of change. Any change i\enve if it is an
improvement.
The technical facts are: 3 phase motors are smaller and lighter for the same
horsepower.
There is no unbalanced neutral current to deal with.
At 240 V the current draw for the same load is half of what you need at 120V
so you don't need the big 50 amp shore cord.
And that translates into less weight of copper needed for your wiring
system.
If you look at the plugs at a marina chances are it is tio white wier pin
that is burnt or becoming brown.
Why? Because of unbalanced neutral currents. In other words this is a
significant source of electrical fires in the AC system.
Even if you only have a single phase fed, it is technically possible to
convert this into a 3 phase system on board.
But once again most people are to scared to even look into this option.
So I stand by my original claim.
There are ways to rerduce your power consumption, lessen the surge demands
on your genset and thus reduce th esize of generator you ned to buy to power
your air conditiners. In addition there are several options available to
lessen the heat load on any air conditioner system used on board a boat.
No one said yo uha dto do without air conditioning. I merely pointed out
that I sucessfully used the mitigation techniques to reduce the heat load
so much that in my case the designed for air conditioning system proved to
be not needed.
In hotter climates the required size would have been greatly reduced over
what conventional design thinking would call for.
And that reduces the amount of power I would have to purchase or generate in
orde to be comfortable.
regards
Arild
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