Can you tell if you have a galvanic isolator fitted?

[RIN]

We moved the boat this year to a marina where we have electricity so we are looking to leave the boat connected to shore power all through the winter so we can have a battery charger and heating/dehumidifier on timers.

Because of this, we wanted to ensure we had a galvanic isolator on the incoming supply.

We had a good look through the electrics on the boat to see if one had already been fitted, and couldn't find one, nor was there a manual for one with the boats documents

This was in the locker together with the battery charger

No manual for it. Would this provide galvanic isolation? or is it just a circuit breaker?

Also the boat puts on a warning light if the polarity of the supply is not correct would this mean there is something that provides galvanic isolation?

Is there anyway to test whether a galvanic isolator is already on a boat?

As ever, grateful for any advice

 

[fergie_mac66]

RCD

thats a RCD trip switch at its simplest its a fuse but does a lot more

 

[Skysail]

An RCD switch is not a galvanic isolator, nor is the polarity indicator.

You are looking for something like this on the input of the shore power:

http://www.marine-super-store.com/posit/shop/index.php?selectedpartno=99051587

or this:

http://www.echandlery.co.uk/galvanic-isolator-with-indicator-459-p.asp

or this
http://www.adverc.co.uk/products/6
.

 

[David2452]

"Is there anyway to test whether a galvanic isolator is already on a boat"

Yes, just in case it's hidden away:

Plug the shorepower lead to the boat but not the mains, take the lead inside and bridge the incoming earth connection on the RCD and the earth pin on the shorepower lead with a meter, there should be an open circuit if a Galvanic isolator is fitted and working OK. Unless there's an open circuit on the earth, but if there is it's good to find out now.

 

[kashurst]

following on from David2452 do as he describes using a multimeter with a diode testing function (-l>l- symbol). you should measure @ 1.2 to 1.4 V drop across the galvanic isolator. swap the tests leads over and you should get a similar reading. If you get an open circuit in either direction (or both directions) then something is amiss.

If you get 0 in either direction then you do not have a galvanic isolator. test again on resistance setting you should get a very low resistance reading (< 1 ohm) to check you have an earth connection.

PS make sure you disconnect the shorepower lead from the mains before measuring anything

 

[Ripster]

If you end up needing one have a look here too... http://www.sterling-power.com/products-galvanic-why.htm. I fitted one to mine last year. Fairly straight forward job. I got the one with the indicator lights on to show all is OK with the circuit and unit itself.

 

[jimmy_the_builder]

Make sure not to leave any switched-mode power supplies connected when you're leaving the boat for long periods, these will apparently defeat the galvanic isolator.

Cheers
Jimmy

 

[Powersalt]

Make sure not to leave any switched-mode power supplies connected when you're leaving the boat for long periods, these will apparently defeat the galvanic isolator.

Cheers
Jimmy

I leave the fridge and battery charger on all summer with a galvanic isolator. Are you saying that causes a problem?

 

[jimmy_the_builder]

I leave the fridge and battery charger on all summer with a galvanic isolator. Are you saying that causes a problem?

I guess it depends if the power supplies in them are switched-mode or not.

Cheers
Jimmy

 

[msimms]

Make sure not to leave any switched-mode power supplies connected when you're leaving the boat for long periods, these will apparently defeat the galvanic isolator.

Cheers
Jimmy

Do you know how switched mode manages to do this?

 

[jimmy_the_builder]

Do you know how switched mode manages to do this?

Stand by, I'll try and find the article. The gist of it was that if you've got switched-mode power supplies on the boat, then a galvanic isolator won't work, you need an isolation transformer instead.

Cheers
Jimmy

 

[jimmy_the_builder]

Do you know how switched mode manages to do this?

Here you go. In fact there's a lot about this on the web, all googleable, including some previous discussions on the forum. Here's the article that I was referring to:

http://www.smartgauge.co.uk/galv_tran.html

Cheers
Jimmy

 

[RIN]

Here you go. In fact there's a lot about this on the web, all googleable, including some previous discussions on the forum. Here's the article that I was referring to:

http://www.smartgauge.co.uk/galv_tran.html

Cheers
Jimmy

Jimmy, my head is beginning to hurt. What have I got on my boat that might have a Switched Mode Power Supply? Would it be likely that it is in a tube heater or an older style battery charger or in a dehumidifier?

 

[jimmy_the_builder]

Jimmy, my head is beginning to hurt. What have I got on my boat that might have a Switched Mode Power Supply? Would it be likely that it is in a tube heater or an older style battery charger or in a dehumidifier?

I'm not an expert on these, sorry - as I understand it, the most likely candidates are things like phone chargers, tv power supply units, that sort of thing.

Cheers
Jimmy

 

[msimms]

Thanks for the link.

I can see where they're coming from but don't believe the the small number of appliances that I have on board will generate enough noise to cause my homemade GI a problem. We're only connected to shore power whilst we're on board so not subjected to much of a risk.

I run a seperate extension lead to power the dehumidifier when we're away from the boat.

Cheers

Mark

 

[VicS]

I'm not an expert on these, sorry - as I understand it, the most likely candidates are things like phone chargers, tv power supply units, that sort of thing.

And modern battery chargers.

Things that ought to feel heavy due to a mains transformer but dont have switch mode power supplies.

 

[DAKA]

Only a skim read but it seams to be only an issue with boats that are based in fresh water.
seeing as fresh water is less corrosive anyway I dont suppose it is much of a concern to fresh water boats anyway.

Switch mode equipment affecting galvanic protection issue appears to be a theoretical problem only although I could do with Vic to confirm my understanding is correct.


The problem is that in order for this to happen, they can cause the galvanic isolator to conduct the RFI to ground, so the galvanic isolator is almost permanently conducting.

This almost certainly won't happen in saltwater as the parallel path of the water will conduct most of this AC to earth. However in freshwater it is a possibility.
http://www.smartgauge.co.uk/galv_tran.html

 

[RIN]

Thanks for all the replies everyone. Still not sure about the need for one but at quite a bit less than £100 and a very easy DIY, I will be going ahead with this. Next step is what to do with the battery charger as we will be making fewer trips to the boat in the winter. I'll have a think about this and put the problem and my intended solution in a new post. To have it shot down in flames of course.