Galvanic Isolators

laika

laika

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I've long been in need of a galvanic isolator and as it's looking like I'll be spending most of the time connected to shore power this winter it's time to get one. But there's a big range in price from cheapos on ebay through the basic sterling ones to fancy "failsafe" ones with all kinds of lights and monitoring. Any advice? Do these things often fail "unsafe"? And is there any point in me getting a 30amp one if I only have a 16 amp cable?
 
Certainly no point in going for a larger one unless there is a good possibility of upgrading your systems to 32a. I like (and have fitted quite a few) the Aquafax model, decent quality and easy to test with a 1.5v battery.
 
laika said:
I've long been in need of a galvanic isolator and as it's looking like I'll be spending most of the time connected to shore power this winter it's time to get one. But there's a big range in price from cheapos on ebay through the basic sterling ones to fancy "failsafe" ones with all kinds of lights and monitoring. Any advice? Do these things often fail "unsafe"? And is there any point in me getting a 30amp one if I only have a 16 amp cable?
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I bought one from Safeshore and am happy with it.

It connects to the Earth, so the aim is that no current will flow through it normally. In a failure scenario I doubt whether the current flowing through it will voluntarily limit itself to either 16A or 32A. If you've got a RCD or RCBO that should trip out pretty quickly (depends upon the spec) so the leakage current shouldn't flow for long. I would hope the marina supply would also trip. However very large currents could be flowing until that happens and it is quite possible that the diodes would burn out. You would have to test/rectify that before resuming normal operation. You could ask the manufacturers what theirs would take before blowing.
 
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Safeshore yet again - got one with the remote monitor as it seemed worth it for the extra £20. Easy to test and seems to be working judging by better condition of main pear anode when boat lifted out last week. Also as l'escargot says, it has very clear fitting instructions.
 
Thanks all. No mention of this "failsafe" malarkey and concentration on the middle ground gives me a good idea of where people think the value sweet spot lies. Does the safeshore one have a battery for the remote monitor? I don't seem to see any indication of how far from the unit the remote monitor can be placed. Franky I'm disturbed by and a bit scared of that web site's aesthetics.

Is the aquafax one david2452 refers to the one with the little meter on it?
 
laika said:
Thanks all. No mention of this "failsafe" malarkey and concentration on the middle ground gives me a good idea of where people think the value sweet spot lies. Does the safeshore one have a battery for the remote monitor? I don't seem to see any indication of how far from the unit the remote monitor can be placed. Franky I'm disturbed by and a bit scared of that web site's aesthetics.

Is the aquafax one david2452 refers to the one with the little meter on it?
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The remote does not need a battery - it lights up from the current generated in a fault condition. It can be placed wherever you want. Just extend the cable. Galvanic isolators are very simple bits of kit - sterling make them sound complicated to justify the high profit margin. Safeshore are a small company, maybe a one man band - dont let their site put you off, the product is first rate.

Their attention to detail is stunning - they supply a battery with the remote purely so you can do a one time test after installatio, using the battery current to simulate an isolation problem.

No connection, just a satisfied customer twice.

Aquafax stuff, imho, often attracts a "marine" premium.
 
laika said:
... Does the safeshore one have a battery for the remote monitor? I don't seem to see any indication of how far from the unit the remote monitor can be placed. Franky I'm disturbed by and a bit scared of that web site's aesthetics...
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The eBay listing is possibly worse, but does tell you this: "THE MONITOR DOES NOT REQUIRE EXTERNAL DC POWER CONNECTION & IS SUPPLIED WITH 4 METRES OF CABLE (Which can be extended if required)..."
Ref: http://www.ebay.co.uk/itm/181486286322

At least they found the Caps Lock key eventually :)
 
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Comrade Red said:
... they supply a battery with the remote purely so you can do a one time test after installatio, using the battery current to simulate an isolation problem.
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So you can do periodic testing, not just after installation, I think. See http://www.safeshoremarine.com/assetts/G170sm%20instructions%20brass%20terminal%20posts2010pdf.pdf which says "To ensure continued protection we recommend performing this quick test on a regular monthly basis together with checks on the shore power / vessel rccd test facility." But otherwise I agree with you as another satisfied customer.
 
I don't fully understand GI's. Am I right in thinking that they only work if you've bonded the mains earth to the ship's battery negative and have an anode connection from the battery negative? I have neither of those and advice and boat safety regs seem to swing between having mains earth bonded to battery negative and not. I can't see why I need an anode connection to battery negative because my prop shaft and rudder are all isolated from it and have their own anodes attached.
 
Lazy Kipper said:
I don't fully understand GI's. Am I right in thinking that they only work if you've bonded the mains earth to the ship's battery negative and have an anode connection from the battery negative? I have neither of those and advice and boat safety regs seem to swing between having mains earth bonded to battery negative and not. I can't see why I need an anode connection to battery negative because my prop shaft and rudder are all isolated from it and have their own anodes attached.
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If the shorepower earth is not bonded to DC negative , anodes etc then you do not need a GI.

The standard for AC shorepower wiring is ISO 13297. The old edition ( 2000 ???) allowed you not to bond provided there was a "whole craft" RCD.
A bit of an anomaly when compared with standards for most other things.

The current edition (2012) does not allow this.
 
One option when seeking to determine whether your new-to-you boat on the hard has AC ground bonded to DC ground: Have a heavily corroded shore power connecter full enough of water to bridge between two of the terminals. Grasp the p-bracket firmly.....
 
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