Chuck,
I have been down the route of automatic inrush control. The circuit I
designed was keyed off of secondary voltage in that when secondary voltage
was developed, would the relay short the lamp. This worked very well, but I
like the manual switch better. It is cheap clean and bulletproof. On the
switched transformers the problem is efficiency, reliability and noise. I do
use however a modified UPS for minor AC use and it works a treat. It is a
1400 KVA Smart UPS by APC, but instead of using it off internal batteries,
I run it off ship's batteries (24V). Normally it will not fire up without an
external AC source, but if you use the undocumented cold start procedure, it
will. It has an additional utility as well. When pluged into shore power and
is powered up, it will act as an intelligent battery charger, keeping the
ships batteries fresh.
Steve

"chuck" wrote in message
hlink.net...
Thanks for the info. I was not aware of the product and as you can
imagine, I have no experience with it. My comments are therefore
necessarily abstract.

The two primary advantages of a switch-mode device are lower weight (less
iron) and a built-in capability to regulate output voltage (and perhaps
adjust for different input voltages) automatically.

Potential disadvantages, however, are numerous. The standard isolation
transformer is perhaps the most reliable electrical component we have.
Switch-mode circuits tend to involve many electronic components, some of
which operate under life-shortening stresses. While an isolation
transformer could easily outlast a boat, I doubt the same could be said of
the vastly more complex switch-mode devices.

Without examining the actual circuit, it is impossible to discuss the
degree of isolation achieved or the potential isolation fault modes of the
device.

No mention is made in the specifications about the purity of the sine wave
output. For some appliances, this may not be critical; for others, it is
very important. Possible electronic noise from the switching circuits
could also be troublesome. While modern switch-mode circuits can be
designed to deal acceptably with these issues, it is difficult to evaluate
the product to which you refer since no mention of them is made on the
website.

Other considerations are susceptibility to noise and voltage transients
(e.g., lightning) on the shore power line and radio frequency interference
from onboard radios, battery chargers, fluorescent lamps, and radar.

It is unclear how the ABYC and various EU standards will view such a
device.

Sorry I can't offer anything more specific. Perhaps others have had some
experience with switch-mode isolation devices.

Good luck.

Chuck



Daniele Fua wrote:
chuck wrote:
...snip


A short on either primary or secondary would trip the breaker, of
course, provided it has been sized properly.

...snip

Chuck


I am following your discussion with much interest as I am planning to
install very soon an isolation transformer in my boat.
I add a further question: I have just learnt that a firm is going to
commercialize a Switch-Mode Isolation Transformer (they claim is the
first in the world!) and, if you are interested, just make a Google
search. My question is: is it indeed equivalent to the ol' faithful and
massive isolation transformers?

Thanks for your help
Daniel