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Old 22-01-2011, 18:17   #1
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Isolation Transformer to also Provide Dual Voltage Shore Power ?

I'd like to make sure I'm understanding the possibility correctly.

An isolation transformer in and by itself has a lot of advantages. What I am wondering is if a 110/220 volt isolation transformer like ISO-G2 Isolation Transformer would not only provide the isolation but also the opportunity to wire a dual voltage shore power connection ?

IOW, have two shore power connections, one for 110 and one for 220. Wire the two connections into the isolation transformer and run the output into the single voltage 110 charger circuit.

Am I missing something ?

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Old 22-01-2011, 19:50   #2
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Am I missing something ?
You are correct, an isolation transformer with dual primary windings can utilize either 120v or 240v shore power and deliver 120v to the boat. The unit you are referring to also has dual secondary windings and can deliver 120v and/or 240v to the boat with either primary voltage.

Remember, switching the shore from 120v to 240v is NOT 'automatic', you have to re-strap the primary windings accordingly. When using 240v shore power, the 2 windings must be connected in series. When using 120v shore power, the 2 windings must be connected in parallel. This switching could be done via a 4-pole 1-off-2 transfer switch, making it *almost* automatic.

I had a toroid custom built (6250va) and assembled my own isolation transformer and saved some $$. They are not a very sophisticated device.

What you want to watch for is the transformer is actually a toroid and not an old E iron core. Toroids are much more efficient and quiet.
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Old 23-01-2011, 07:55   #3
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Remember, also, that the the ISO G2 cited is rated at 3.8 kW; or 16 A @ 240 VAC not the 50A generally associated with 240 VACsplit phase power seen in many US marinas.

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Old 23-01-2011, 11:43   #4
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Toroids are much more efficient and quiet.
yes but they exhibit very high inrush currents, they really need soft start circuitry

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Old 23-01-2011, 13:43   #5
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yes but they exhibit very high inrush currents, they really need soft start circuitry

dave
I measured the inrush on mine ~30-32a @ 240v with a Fluke, not enough to require soft start for my 50a shorepower. I would like to think both a 30a 120v and 16a 220v would handle the measured inrush (twice their rating for a cycle). I have a 30a ELCI between the primary windings & shorepower and it doesn't blow. I have the resistor & relay, but didn't install it.
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Old 23-01-2011, 14:08   #6
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Sven - just adding my agreement with DotDun here... that is the model I have, and for that reason.

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Old 23-01-2011, 17:07   #7
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Steve,

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that is the model I have, and for that reason.
Sorry, think I missed what model you were referring to ?

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Old 23-01-2011, 17:09   #8
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I have the ISO-G2 also, and chose it for the dual-voltage capability....
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Old 23-01-2011, 17:11   #9
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I have the ISO-G2 also, and chose it for the dual-voltage capability....
Aha, good to know !

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Old 23-01-2011, 18:08   #10
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I was thinking of installing a 3000 watt ferro-resonant style transformer, that I have, in a hull I am working on. But after what DotDun said and the fact that it is very noisy and gives of a lot of heat (98% efficient), I am reconsidering my plan. It is great at boosting voltage in a brownout though. How noisy and what is the efficiency of the Toroid type transformer?

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Old 23-01-2011, 19:08   #11
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Originally Posted by Bruce Bevan View Post
I was thinking of installing a 3000 watt ferro-resonant style transformer, that I have, in a hull I am working on. But after what DotDun said and the fact that it is very noisy and gives of a lot of heat (98% efficient), I am reconsidering my plan. It is great at boosting voltage in a brownout though. How noisy and what is the efficiency of the Toroid type transformer?

Thanks BB

Why would it run hot if its 98% efficient??? Noisy?? that all depends on how they are manufactured. Anyway, the so called constant voltage transformer requires a resonant capacitor to make the pair ferroresonant. I doubt you require a constant voltage for any application that I know of found on a boat.

It could however help in a brown out BUT!!! THEY ARE VERY FREQUENCY DEPENDENT! If the frequency is off by just a few cycles or hertz if you want to use modern terminology, the output voltage will change significantly.


JFYI-- a toroid by itself cannot provide regulation. Personally I think a toroid is a poor choice for a transformer. They are difficult to wind and cannot be gapped to help hysteresis conditions for inrush. The old stamped grain oriented laminated steel is hard to beat. Lamination noise is very well understood and can be controlled by good transformer manufacturers. First they vacuum impregnate them in a tar like substance and many resort to running a bead of weld on the lamination edges to minimize noise. Further, pushing the flux limitations during design to minimize cost and weight usually will increase lamination noise.

Foggy

EDIT: A good application for power toroid is where high voltage isolation is required. But this is a special case for the transformer. They look like two links of chain or donuts interlocked with each other. They are commonly found at the base of radio and TV towers for the tower lights. The space between the primary and secondary is large to minimize lighten getting back to the transformer primary.
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Old 23-01-2011, 20:54   #12
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Foggy......I assumed the 98% efficiency related to the fact that the remaining 2% was wasted as heat and noise in the regulating process. It sure is a heavy chunk of iron.

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Old 23-01-2011, 21:13   #13
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As with everything there are trade-offs.

I use my transformer for isolation from dock power, not voltage regulation. As I stated, I found the inrush on my toroid is acceptable for my application, and one can add a slow start circuit to limit inrush current.

I have a slow rpm 80mm cooling fan (18db) on the unit that makes more noise than the transformer under normal loads.

Another advantage to toroid is weight, my transformer has dual windings both primary and secondary (dual windings = more copper = more weight), rated/tested at 6250va, and weighs in at 84lbs. Total with cabinet/parts is ~100lbs. The 6kva Charles basic model has single windings for both primary and secondary and weighs 200lbs, I'd bet it's not a toroid.
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Old 23-01-2011, 21:13   #14
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Bruce-- 98% efficiency is very high for a transformer. And your right, the other 2% loss is core & wire heating but that thing will run cool. Been a long time since I dealt with transformers but a 3KW, 60Hz job is as you again correctly note, big and heavy.

My point was that 60 watts dissipated over a large surface area will not be very hot. That is a good transformer, no a VERY good transformer if it has that high efficiency.

In order for a ferro to work, part of the transformer needs to enter into saturation. When that happens the core loss gets to be high. But the amount of core that gets saturated is a small section so the total core loss can easily be minimized. This getting too far than need be into magnetic design.

I was just trying to give you some idea on what to expect with a ferro job, a common stamped laminate transformer and a toroid. Toroids do have their applications but they are a bitch to wind and a large one is usually a special application transformer such as the type I explained for TV tower lights.

Think about it. If a winding uses say 40 feet of wire for example. That wire needs to be threaded around the core, one loop at a time. The first loop needs to pass the full 40 feet of wire.

The C core and the stamped laminate cores have their wire wrapped on a bobbin turned by a machine similar to a lathe. the bobbin just rotates and the wire is taken from a roll above the bobbin. The winding process is simple and fast. Not so with the toroid. They do manufacture special shuttles for winding them but the entire process is time consuming and expensive. Hope this helps you a little.

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Old 23-01-2011, 21:28   #15
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Originally Posted by DotDun View Post
As with everything there are trade-offs.

I use my transformer for isolation from dock power, not voltage regulation. As I stated, I found the inrush on my toroid is acceptable for my application, and one can add a slow start circuit to limit inrush current.

I have a slow rpm 80mm cooling fan (18db) on the unit that makes more noise than the transformer under normal loads.

Another advantage to toroid is weight, my transformer has dual windings both primary and secondary (dual windings = more copper = more weight), rated/tested at 6250va, and weighs in at 84lbs. Total with cabinet/parts is ~100lbs. The 6kva Charles basic model has single windings for both primary and secondary and weighs 200lbs, I'd bet it's not a toroid.

If your happy with your transformer, I'm happy. But you are incorrect as far as sizes are concerned. Transformers have what is know as an energy product that determines their sizes. It matters not if the core is square or toridal. Finally, the correct way to measure the inrush is with an oscilloscope and a current transformer, not a meter.

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