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From: Arild Jensen (no email)
Date: Wed Feb 01 2006 - 19:57:32 EST
Mike wrote in a private post:
-----Original Message-----
John Barnet told me that the problem with running the 230 volt stuff
on 50 or 60 has something to do with voltage regulation. In other
words, as I understood it, the 50 hz units were susceptible to low or
high voltage and the 60 hz units were also. I did not get it clear as
to whether it was low with 50 and high voltage with 60 or vice versa.
But I think you get the idea.The units were built for 230 vac and
won't reliably bridge the gap from say 210 v to 240 v which is a
common problem in shore power connections. By the way this tends to
explain why most bigger yachts have voltage regulation on shore power
connections, via adjustable transformers.
You are welcome to post this email along with any clarification you
care to make, to the forum.
Mike
REPLY
The facts as reported are correct. The reasons for the failure are less
obvious.
In North America we have two kinds of 220V service.
The house hold variety is a single phase, center tapped transformer. The
center tap is the grounded neutral and each leg is 120V relative to this
center tap. The other winding is phased 180 from the first winding
resulting in a 240V output as measured from L1 to L2 but each leg
measures 120V relative to the center tap.
Unfortunately when you get into larger installations the efficient power
feed is a three phase transformer. You still get 120V from any one phase
to ground. But you only get 208V from phase to phase. In many cases this
is what is fed to the 50amp 4 wire outlets and euphemistically called
220V - Yeah sure! At best this is misrepresentation at worst it is
fraud and negligence.
Regrettably manufacturers rarely mass produce 208V motors for consumer
goods.
A 220V rated motor can barely run at 208V but it will run; although it
runs hot because it draws more current than it would at 220V.
However that 208V is based on getting the right input voltage to the
primary of the transformer.
Most power utilities face a daily peak load demand that causes the
utility supply voltage to nosedive. At that point the 208V output at the
marina also nosedives. Guess what, that when your 220V motors also
suffer and frequently die from burnt windings.
Unknowing or unscrupulous marina owners cause untold damage each year to
their customers equipment due to this practice. The repair cost is in
the hundred of thousands if not millions of dollars nation wide.
A big part of the problem is our nations huge demand for electrical
power. Another part of the e problem is the Greenies demand to shut down
dirty power generators, forbid the building of new power generators and
absolutely ban the development of more nuclear power generation.
A lesser part of the problem is that people for the most part refuse to
consider doing anything proactive in the way of energy saving on a
personal level.
And finally we come to the technical problem of voltage drop in the
individual branch circuits feeding the power post at each slip. As more
current is drawn the voltage sags.
Inductive motors tend to draw more current as the voltage drops. It's a
vicious cycle.
And it all leads to burnt windings in electric motors. Most often in air
conditioners and fridges.
Two solutions. Use a step up transformer to boost the 208 to an honest
220V or even 230V or get special low voltage winding motors that can run
at 200 - 208 V without over heating.
However both solutions cost $$$ and people will insist on always buying
the cheaper priced product and ignoring the specifications.
Cheers
Arild
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