Isolation Transformers

[jose r vigil]

Dear gregroves

I'm making a similar conversion to my boat. Did you have any problems with the frequency 50 Hz/60 Hz on the AC and fridge becuse the freq difference?.

Are you just using a step up transformer?

jose

Originally Posted by gegroves

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!

[goboatingnow]

The article mentioned is very inaccurate and downright misleading

lets look at some definitions

earth, ground neutrals etc get thrown around in that article

the green wire in an appliance is not a conductior in the true sense. it is more correctly called a protecive earth, it only carries current in a fault and then is only deisgned to carry that current for a very short time. its primary role is to provide a lower resistance path to earth ( or the generator return) for fault currents then hopefully your body to earth.

Contary to what that articles says electronics are not designed with internal AC feeds to "earth" to minimise RFI, earth is purely a protective connection to typically the box or metal case, why , soley to protect you the human. it plays no part in the electrical circuit of the device.

Yes RF currents get impressed onto earth lines, as they get impressed onto all power lines , but the currents and voltages are tiny ( if you know how to use a scope then you can measure them. Most designs contary to that articles try and minimise power line rf noise as its a effective antenna. The articels suggests opposite and is wrong. Major RF emitters will then to have a seprate RF ground buts thats another altogether

The article also misrepresents what an galvanic isolator is for. Becuase modern safety codes on boats requires that the protective earth is connected around the boat to many electrical devices and usually DC negative, and in a marina many boats are effectvely plugged into the same earth line, there now exists a circuit ( or a possible circuit) between underwater metals on one boat and another ( this is one of the main reasons that bonding is sometimes ommitted on GRP boats). Hence DC currents generated by galvanic action can flow between boats, using the earth wire as a return path. This is what a galvanic isolator attempts to stop. It is not a device to stop external currents that might exist on an earth line.


So impressed RFI will never ( in normal conditions) cause an isolator to conduct.

secondly "hot earths", the article is compleatly misleading here. HOT earths are earth with high impedence somewhere, and hence the earth rises in potenial to "real earth" or teh generator return ( usually neutral). Its normally measured with respect to neutral in neutral ground system or to local earth. All devices on the earth line are raised to that potential, both sides of the diodes in the isolator will be at the raised voltage so again they will not be conducting. ( everything connected the earth is also raised by that potenial, ie every AC connected device with an earth connection. In very bad cases this can cause a shock hazard that may not be protected by any fault trip. A full on hot earth is a very dangerous thing. note that a hot earth need a high impedance path to real earth to exist so a hot earth is not providing any protection anyway. ( this is the hot earth to neutral case I'm talking about.)


Galvanic isolators as not a cheaper version of IT;s they really do different things. IT's provide protection from impressed galvanic currents , ie from other DC sources as well as from underwater dissimilar metals. more importantly they provide complete onboard shock protection from live ( or neutral) to earth( ie real earth) faults. even if the protective ground inside the boat has failed or is disconnected the user cannot get a shock. The only way is to insert yourself into the live and neutral circuit. ( aka as a light bulb).

Finally comments about failure of the GI results in a break in the earth, while technically correct it is misleading, GI's are rated to carry full fault currents for 24 hours, Fault current anyway can only exist for very short periods, as the whole idea of a protective earth is a device to trigger a protection device.

Finally ABYC standards in teh US though not so in europe require a monitor circuit to verify the correct operation and the new standards also allow "fail safe " isolators to be installed without needing a monitor.

The fact is that protective earth connection to teh marina shorepower are two edged swords in the marine enviroment. GI are an attemp to mitigate that problem, ITS are a further attempt.

PS: Midland, teh breaker are not in parallel. The circuits are.

ALso Victron and matervolt are two very reputable brands in the marine electronics business.

[chala]

Quote from s/v JEDY post 42
“But is does break the ground wire”
“I find it amazing that these devices are allowed at all!”
goboatingnow
I would never take the responsibility to recommend or install a galvanic isolator.

[s/v Jedi]

Chala: I don't understand your post but see that I made a typo ;-) It should have read "but it does break the ground wire".

In my post I tried explaining that Galvanic Isolators are not a better priced alternative for Isolation Transformers. In my opinion, GI's reduce the safety of AC aboard, the older models more so than the newer designs. I would outlaw the older designs completely. An IT increases AC safety aboard, does the job that a GI tries to do in a perfect way, plus give the step-up & step-down features you need when you sail to other nations.

Cheers,
Nick.

[goboatingnow]

“But is does break the ground wire”
“I find it amazing that these devices are allowed at all!”
goboatingnow
I would never take the responsibility to recommend or install a galvanic isolator.

Safety on board is a multi-sided thing. Its a layered approach. Bets of all is a RCD interrupter as this works irrespective of ground wires or not, especially the 5ma trip versions. ( they do nuisance trip).

Protecive earth wires , only play a part in the scheme of things, They primarily exist from the time of fues and were used to blow fuses before you touched the "hot" item, ie they caused excessive fault currents to flow to blow the fuse as many fused would quite happily shock you to death ( in a 230 VAC system) before blowing. Protective earth has less role to play in a RCD system.

In practice in modern devices, most are double isolated , so earth wires play less of a role.

Yes a GI breaks the earth line, but only for small voltages. The modern ones Fail Safe as well.

[chala]

Originally Posted by goboatingnow

Protecive earth wires , only play a part in the scheme of things, They primarily exist from the time of fues and were used to blow fuses before you touched the "hot" item, ie they caused excessive fault currents to flow to blow the fuse as many fused would quite happily shock you to death ( in a 230 VAC system) before blowing. Protective earth has less role to play in a RCD system.

In practice in modern devices, most are double isolated , so earth wires play less of a role.

Earth wires are the primary line of defence against electrocution.
Earth wires are essential for the safe flow of residual currents to earth.
RCD are mechanical devices and can fail.
Earth wires should not be degraded by the introduction of doubtful gadgets and extra terminations.
A proper electrical wiring installation should not “quite happily shock you to death ( in a 230 VAC system)” and this applies for any system.

It could also be said that if, due to double insulation, earth wires are no longer required then also there will be no requirement for installing a Galvanic Isolator.

The following threads and links are informative readings.

Originally Posted by DeepFrz

I believe that Nigel Calder's article in "Professional Boatbuilder" has some good information on Isolation Transformers and Galvanic Isolators.

Professional BoatBuilder - April 2006/May 2006

This good article is an eye opener in regard to earthing. It shows that some countries are not able to maintain an effective segregation between AC and DC electrical circuits. It is unthinkable that AC could wander into DC wiring and definitely should never happen.

http://www.cruisersforum.com/forums/...rina-8445.html

http://www.cruisersforum.com/forums/...ats-24394.html

Originally Posted by NorthwestDragon

Could I get a few educated comments on this article?

SmartGauge Electronics - Isolation Transformers or Galvanic Isolator? 1/2

Originally Posted by Extemporaneous

Comments on the information in the attached link and its approach?

West Marine: West Advisor

Thanks,
Extemp.

All the above readings point to the fact that an isolation transformer will be a far better choice than a Galvanic Isolator.

[Microship]

I'm in the process of choosing an isolation transformer for my steel boat; good timing as I'm already doing major power surgery (changing old Prosine 2.0 to Outback FX2012, adding solar, etc). I already know I want an IT and not a GI, and this thread has been helpful.

My default choice is the Charles ISO-G2 with stepdown, but I am wondering if anyone has hands-on experience with the Mastervolt "Mass GI" product. It's switch-mode, which scares me a bit; much lighter, of course, but strong EMI potential and more to go wrong at this critical choke-point. Despite my geek nature, this is one area where I'm inclined to keep it simple...

But I'd love to hear any reports from users of the Mastervolt, favorable or otherwise...

Thanks 'n cheers,
Steve

[GordMay]

I don't know how a switch-mode power supply could provide true isolation without a core & coil isolating transformer.
I'd expect Mastervolt to explain how that's accomplished, if they claim it's so.

[vacendak]

Gord May

I spoke recently with Ari Bragge (of Mastervolt Finland)
ari@mastervolt.fi
on the subject; her confirmed that switch-mode IT's (MassGI)
provide excellent isolation, higher reliability, and save much weight/space
when compared to classical ones.

Microship

some info on switch-mode units:

http://en.wikipedia.org/wiki/Switched-mode_power_supply

[chala]

The following may give you an indication.

Originally Posted by EngNate

Switchmode chargers use very small transformers that operate at high efficiency because of the high frequency. The incoming AC is rectified to DC at full line voltage, then switched on and off to feed the transformer with around 20K Hz.
NEA

It will be also wise to check compatibility with RCDs, and the amount of interference they produce.

[Microship]

HI... thanks for the comments. I know how switch-mode supplies work, and have used them on a much smaller scale for years. What I don't know is how much noise this particular product generates; the potential for quite a lot is huge given the currents involved.

Square-wave edges, which have to be as steep as possible to maximize efficiency (minimum time in the "active region") contain energy well into the hundreds of megahertz... a sum of odd harmonics, to be precise. This can be hard to filter in the best of cases, like little DC-DC converters, and is what makes power supply design hard these days.

My concern here, with lots of comm gear aboard, that I'd find this a problem. The Prosine is already a problem for exactly the same reason, but it is going away.

I'll almost certainly go with the Charles, and weight is not a HUGE issue, though even in an 18-ton monohull my old bicycling-inspired "Roberts Law of Applied Mobile Gizmology" applies: If you take an infinite number of very light things and add them together, they become infinitely heavy."

Cheers and thanks,
Steve

[chala]

Originally Posted by Microship

Applied Mobile Gizmology" applies: If you take an infinite number of very light things and add them together, they become infinitely heavy."

Cheers and thanks,
Steve

and curiously removing them does not seems to make the boat lighter.

[gosstyla]

Originally Posted by chala

and curiously removing them does not seems to make the boat lighter.

Of course, since it takes an infinite amount of time to remove them all and if you stop before removing all an infinite number still remain to be removed.

[Microship]

Hmm, you know, you're right... I thought that waterline creep was an osmotic process that causes the bootstripe to slowly migrate toward daylight, but perhaps it's my impaired tonnage-reduction ability.

[s/v Jedi]

Mastervolt and Victron are both solid Dutch products. However, if you would ever want to listen to the SSB while on shore-power, I would advise not to go for the switching Mastervolt unit. The nice thing about a switching version is that it will probably support any input voltage without changing jumpers etc.

You should really check out the Victron unit as it's much smaller and lighter than my Charles (I think it's a Charles) unit. Actually, I just received a Victron unit and will be swapping it soon as the Charles model I have isn't really an IT.

cheers,
Nick.