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Old 26-11-2008, 21:01   #1
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Isolation Transformers

I am in need of an isolation transformer for my boat where can I find one
and which brand works the best , Where is the best place to buy one

Thanks Buck I need a 120v 30 amp
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Old 26-11-2008, 21:26   #2
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There is this wonderful search engine called Google

marine isolation transformer - Google Search
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Old 27-11-2008, 10:35   #3
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Old 27-11-2008, 12:22   #4
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Thanks for info

Thanks for info this is what I was wanting, not somebody telling me how to use google THANK YOU Buck
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Old 27-11-2008, 13:16   #5
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Well it certainly answers the question concerning where you can find one and how to do comparison shopping. You need not buy a dedicated marine isolation transformer, although you should order one with epoxy insulated coils, copper shielding and a powder-coated case. Many isolation transformers can also be used as a step-down transformer which will enable you to step down from European 240V to North American 120V - handy not only in Europe, but also in some areas of the Caribbean (albeit you will still be at 50 instead of 60 cycles). If you are having one built, ask them to include the wiring diagram for use as a step-down transformer on the exterior of the case.

For 30 amps at 120 volts you will, of course, need a 3600Kv unit.

Brad
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Old 27-11-2008, 14:00   #6
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isolation Xfmr

Quote:
Originally Posted by Southern Star View Post

For 30 amps at 120 volts you will, of course, need a 3600Kv unit.

Brad
SS - small correction .... Buck needs 3600VA or 3.6kVA. However, I would suggest slightly bigger unit 4kVA at least.

Cheers,

Chris
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Old 27-11-2008, 14:13   #7
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Thanks Crhis - you are of course correct, the 'K' stands for 1000. Doh!

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Old 28-11-2008, 11:12   #8
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Buck, why do you want an Iso Tranny?? they are expensive, heavy, bulky and give off heat. A Galvanic Isolator will do the same thing at a fraction of the price. You can even make one if you wish. They are simple and effective and you still have an Earth should a mains fault occur.
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Old 13-12-2008, 20:22   #9
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Quote:
Originally Posted by Alan Wheeler View Post
Buck, why do you want an Iso Tranny?? they are expensive, heavy, bulky and give off heat. A Galvanic Isolator will do the same thing at a fraction of the price. You can even make one if you wish. They are simple and effective and you still have an Earth should a mains fault occur.
Are there no benefits over a Galvanic Isolator?
Has anyone used the one in the link? CHARLES 3.8KVA 30 AMP 120/240VAC 50/60HZ ISO-GUAR
It's only 60 bucks more than the Galvanic Isolator I bought. Weighs 70 lbs.
Anyone used it?
If so is it any good?

Thanks,
Extemp.
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Old 01-02-2009, 00:21   #10
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Quote:
Originally Posted by Alan Wheeler View Post
Buck, why do you want an Iso Tranny?? they are expensive, heavy, bulky and give off heat. A Galvanic Isolator will do the same thing at a fraction of the price. You can even make one if you wish. They are simple and effective and you still have an Earth should a mains fault occur.
Alan, I certainly don't know enough to confirm this but it seams to make some sense. Have a read and let me know what you think.
SmartGauge Electronics - Isolation Transformers or Galvanic Isolator? 1/2

Extemp.
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Old 02-02-2009, 11:58   #11
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Buck

you might wish to read Nigel Calder's "Big Smart Book"
(i.e. "Boatowners Mechanical...") on this matter.

What is "120v 30 amp" ? I mean, do you include inrush current (s)
in this amperage ?
if this is just a nominal of your AC loads, you might want to double the IT power capacity
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Old 02-02-2009, 12:44   #12
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Quote:
Originally Posted by vacendak View Post
Buck
you might wish to read Nigel Calder's "Big Smart Book"
(i.e. "Boatowners Mechanical...") on this matter.
What is "120v 30 amp" ? I mean, do you include inrush current (s) ..
In my recollection, Nigel is not clear on this matter.

30 Amp @ 120 Volt = 3,600 Volt-Amps (VA). This is a DC or Resitive AC figure, in practice (on boats) nearly analogous to Power (in Watts).
Watts = V x A x P.F.
(where PF = Power Factor - an inductive or capacitive reactancee component)

Inrush currents will NOT normally be a significant factor in sizing transformers for boats.

Transformers exhibit inrush currents upon initial energizing, where these higher currents occur to energize the transformer core. The steady-state magnetizing current (sealed VA) for a transformer is very low, but the momentary current, when it is first energized, can be quite high (10 - 20 times sealed VA, for about 5-20 ms).

These inrush currents are typically the same as with motor starting, except for one important difference — besides being a high current magnitude, the transformer energizing current is full of harmonics. Both even and odd harmonic components occur when a transformer is energized, and they can excite system resonances, resulting in dynamic overvoltages; but the most significant problem associated with inrush currents is the resulting short-term voltage sag.

See also: Watts, VA and Power Factor:

SmartGauge Electronics - Watts, VA and Power Factor 1/5

Quote:
Originally Posted by Extemporaneous View Post
There’s lots of good technical stuff on the Smart Gage site; but the Galvanic Isolator (Vs Iso’ Xfmr) tutorial, to which Extemporaneous linked, is a little out of date. Current standards require that Galvanic Isolators be self-testing or “fail-safe”, so that particular disadvantage may not apply. Notwithstanding, it’s a good article.
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Old 02-02-2009, 14:24   #13
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I believe that Nigel Calder's article in "Professional Boatbuilder" has some good information on Isolation Transformers and Galvanic Isolators.

http://www.proboat-digital.com/proboat/200604/
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Old 02-02-2009, 14:58   #14
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Buck: In 2006 when we outfitted Vingilot for the Med I put in 2 Charles Iso trans. 3.8kVa. They are branded as International models e.g., they take 240 vac and step down to 115 vac. They are inter. because they accept 50/60 Hz., though they do not change the freq to 60 Hz. They weigh about 30 lbs each and give off heat. However, this was the only way I could plug a 115vac boat into the Euro. 240vac shorepower. BTW, it also provides gavanic isolation as well. We have had no problems in 3 years and zincs last a whole summer!
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Old 03-02-2009, 07:18   #15
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Gord May,
Quote:
Inrush currents will NOT normally be a significant factor in sizing transformers for boats.
you mean that, if you have e.g. a 2000 Watt washing machine onboard,
a 2500 Watt IT will be enough ?
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