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From: Norm of Bandersnatch (no email)
Date: Sat Jun 09 2007 - 15:02:31 EDT
Tony,
I am looking at the data on page 16, Figure 10, of the transformers manual
which is the most informative. It describes a transformer with a center
tapped primary. You can connect 240 vac across the entire primary H1 to
H3, or 120 vac across half of the primary using the center tap. The wire
of the primary is limited to 50 amps. So if you hook the whole winding up
to 240 you can push twice the power through the transformer as you can with
120 across half the winding.
The secondary is similar. Note the typo on the second line describing the
secondary - it should read "output between X1-X5", the "X" in "X1" is
missing.
The secondary winding is almost identical with the primary with the
exception of the two taps X4 and X3 which deliver a slightly lower voltage
(104/208) which apparently allows one to use 50 cycle power to operate 60
cycle equipment.
To use this transformer as an isolation transformer (remember you are
isolating DC to prevent electrolytic corrosion problems and transformers
will not pass DC) you connect the primary to the dock, using the entire
winding when hooked to 240 vac, and one half of the primary when hooked
into 120 vac. Put 50 amp breakers on H1 and H3 lines.
The secondary will produce 240 and 120, just like the juice in a house. If
you are hooked to 240 on the dock you be able to load it down to twice the
power before you trip one of the 50 amp breakers.
Hook the outputs up like you would to a house, half your 120 volt loads on
the X3 (neutral line) to X5 and the other half on the X3 to X1. Of course
your 240 volt loads go across X5 and X1.
SH and GND should go to your boats ground. No ground to the shore.
The choice of connection the neutral, X3 to ground or not is a good
question. Houses have these two points, called neutral and grounding
(white and green wires) grounded in the breaker box with a short length of
wire between their respective terminal strips. I believe the ABYC also
requires this connection.
Big ships sometimes use the "bathtub" system. They do not connect neutral
to ground. IF the system is intact and there is no leakage one can stand
in seawater in the bilge and touch either the hot or the neutral wires
without feeling a thing. Ground is not a part of the electrical system as
long as there is no leakage. Leakage is measured by meters and light bulbs
between neutral and hot and ground and there is a man on the ship whose
business it is to chase down ground faults as they appear. This system is
safer, IF there are not faults.
This is my take on the matter but I would like to see Arild and Andina
respond too, especially in the matter of grounding.
When installing the transformer be sure to have a downward loop in the
wires (drip loop) as they enter the transformer box to allow any moisture
travelling down the wires to drip off before entering the box. Don't just
rely on the "strain reliefs" (packing glands). It would be a good idea to
put some more paint on the box too.
You can also use this transformer to offer your genset a balanced load by
hooking up the 240 vac primary to the gensets 240 volt output and then
running all your 120 volt loads off one half of the secondary. I do this
thinking it will spread the heat in my genset generator end more evenly and
reduce heat related degeneration.
Norm
S/V Bandersnatch
Lying 30 40.427N 081 28.245W
Fernandina Beach FL
> [Original Message]
> From: Tony Lester <>
> To: <>
> Date: 6/7/2007 8:27:13 PM
> Subject: (T&T: & TWL2:) ISOLATION TRANSFORMER
>
>
> After everyone on this board - Correctly mentioned for me to install a
> Isolation transformer .... Thanks (aluminum 65' trawler)
> After purchasing it and dragging it half way around country...
> After hauling all 235lbs on Board... It felt like 500 lb...
> After waiting a year to figure out where to put it...
> After lifting it inch by inch into position...
>
> I don't know what to do with it...
>
> It seems simple, but there are several ways of connecting it.
> Also I thought the whole idea was to isolate ground. It seems the ground
> are attached to case which is going to be bolted to boat
>
> The piggy is Charles 12kw Iso Transfomer model 93-IXFMR12I-A
> Manual can be found at
> http://www.charlesindustries.com/marine_manual/12i%20kva.pdf
>
> Your help is once again needed and appreciated
>
> thanks
>
> tony
>
>
>
>
>
>
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