Lee:

Yes, they are pricey, heavy, and hot. Transformers are typically
around 95% efficient, so pay attention to heat generation -- they do
get hot.

I found a bunch of Topaz 5kw ultra isolation transformers when we were
outfitting Swee****er in 1995 and bought them at US$100. I still have
two. Surplus sales of Nebraska has them new for $1395:
http://www.surplusales.com/Transform...tionXmers.html

However, the good news is that any transformer is an isolation
transformer for our purposes -- it won't do quite as good a job on
keeping out unwanted frequencies, but we're primarily interested in
1) keeping out DC and
2)establishing an ungrounded AC system.
So take a look at things like
https://www.surpluscenter.com/item.a...tname=electric

It will do 5KW. You can put in 240 and take out 120/240 three wire
just like your house, or put in 120 and take out 120.
(240x480 means you can put in either 240 or 480)
(120/240 means you can take out 120, 240, or both)
(You do 120120 by hooking it up like 240240)

BTW, you do not want an autotransformer -- which will change voltage
but does not isolate.

If you feel more comfortable with a "real" isolation transformer, I
ran into a guy at the Maine BoatBuilders' show that was having them
made.
WesTran Power
5160 NW Five Oaks Drive
Hillsboro, OR 97124

(no web site)

He was selling a "marine grade" (whatever that means) 6KW unit with
pretty good specs for $900.

As far as ground fault alarms go, the typical big ship installation is
a light in series with a push button wired from one of the hot wires
to the hull, and then the same thing on the other hot wire. The two
push buttons are on the same actuator (a dpst). The bulbs are
typically rated for the system voltage, so when you push the buttons,
both come on at half voltage. If there's a fault on either side, that
light is shorted out and stays dark, while the other light is getting
full voltage, so it's brighter than usual.

Like this (sometimes ASCII graphics actually work, maybe):

hot1---pb---light---hull---light---pb---hot2

(with the two pb on one frame).

Jim Woodward
www.mvFintry.com





(Lee Huddleston) wrote in message . ..
On 10 Oct 2003 07:54:37 -0700, (Jim Woodward)
wrote:

That was the Royal Navy's choice when they specified Fintry thirty
years ago and we will continue this with her new electrical system.
The only electrical connections to the hull will be green safety
ground and radio ground for the SSB (which is isolated from electrical
ground).

We will have ground fault alarms on both the DC and the AC systems so
that if either gets shorted to the hull we'll know about it early.
Shore power will come aboard through isolation transformers.

Jim Woodward

Jim,

Would you have a recommendation for an isolation transformer? The
only one that I have found so far ate up a lot of the power before it
could get into the boat. That seemed strange to me, but maybe I was
reading the specs incorrectly. Also the price seemed to be very high.
Of course, protecting my beloved boat from galvanic corrosion is
probably worth a lot if that is what is necessary.

By the way, you mentioned DC and AC ground fault alarms. Who makes
them and are they available to private individuals?

Thanks in advance for your help.

Lee