Galvanic Isolator -- When to Use

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dread

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When I am attached to shore power, do I always want the galvanic isolator on? When I am at sea, I assume that it doesn't function, just as the charger doesn't, right?
 
Many of them are passive, just a box with 4 diodes inside that won't let current through until the voltage differential is over some amount (i.e. ground fault).

There's a fail safe type that will short the input to the output if the diodes fail. The non-fail safe types are supposed to have a remote display that indicates if it's operational.

None of them should have any effect while not on shore power, since they are only connected to the ground between the inlet and the AC panel, and even under normal conditions while on shore power, there shouldn't be any current through the ground. That's why there's no switches.
 
For those of you with C-Dory 25's, each one ( as far as I know ) come with a galvanic isolator. This is a passive box, that in Journey On sits in back of the AC Panel. As ferrit30 said, it's there to block stray currents fed through the green wire, whilst allowing ground faults through. I think it's just another example of the general level of quality in a C-Dory. I've had more expensive boats without that feature, which I installed myself. And several cheaper boats that didn't.

Remember, a C-Dory is basically a trailerable boat with an outboard which can be lifted out of the water so that there isn't a sure path for stray DC currents. I always wondered how they operated. The unit in Journey On is large enough that I thought it contained a transformer that allowed AC (60 Hz) to go through, but blocked DC. A diode bridge would pass AC in a fault but would have to be large enough to withstand the fault current. If a diode blew, there's no fault protection. They do come in different sizes and prices. C-Dory doesn't use the cheapest one.

Anyone have a schematic or take one apart?

Boris
 
journey on":11dhgcgv said:
a C-Dory is basically a trailerable boat with an outboard which can be lifted out of the water so that there isn't a sure path for stray DC currents .... A diode bridge would pass AC in a fault but would have to be large enough to withstand the fault current. If a diode blew, there's no fault protection.
Click to expand...

At least on our 22, even with the motor up, the part of the motor that mounts to the transom is still in the water, so we'll always be susceptible to stray current.

Also, as I mentioned before, the "Fail Safe" models will actually short the two connections together in case the isolator fails. At that point your inlet ground is directly connected to the panel ground.
 
On my 4-month old (for me) 2006, the 110v switch panel has a switch for the charger and a switch for the isolator. I turned the charger switch on yesterday, but the little green "on" light did not come on. I looked at the charger itself, and its indicators showed that it was functioning. I have never turned the isolator switch on, but I wonder when I should. Your comments suggest that, since I keep it in the water, I should always turn it on to prevent damage. Right?
 
I have no idea why the isolator would be switched. It should really be wired near the inlet, between the inlet ground and the panel ground bus. What model is your panel and isolator?

Maybe the isolator switch on the panel turns on the 'monitoring' panel and self test functionality? Non-fail safe isolators (I think according to ABYC) are supposed to have an easily viewable status indicator, and/or self test feature.

The really cheap isolators do not have status indicators or fail safe, and are just the 4 diodes. If anything goes wrong with those, your DC system could be floating and you could potentially send AC into the water (via a shorted charger, for example).
 
Captain's Cat/Charlie;

Thanks for the schematic(s). After looking through some, but not all, there appears to several ways to isolate the green/chassis ground. Several had series diodes, 2 in each direction as ferrit30 mentioned above, several had transformers and West Marine had a capacitor. Others which were called galvanic isolators were really complex with active circuits. You pays your money and takes your choice.

However, all were passive, i.e., not switched. Accept that. I like the ones which had no solid state devices to fail.

I found the Guest isolator which is on Journey On, but no schematic. I missed it.

Boris
 
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