Isolation Transformer???

[Richard10002]

My Newmar Heavy Duty marine Battery Charger says the following:

"These are some of the more important features....


....

Isolation Transformer - The worry of dockline electrolysis through the charger is eliminated, Corrosion of metal parts on the boat due to stray DC currents travelling through your AC line to charger cannot occur, as the transformer utilized in the charger maintains complete isolation between input and output"

I thought you only got this in the very expensive, (and large?), chargers?

or am I missing something.

I think my shorepower goes to the electric panel, from where it feeds the battery charger, the 3 pin AC sockets, and the water heater.

I guess I am wondering if the charger provides full protection, or should I still have a galvanic isolator.

Hope that makes sense and, if it does, why might my latest anode have depleted by 75% in about 10 months, whereas the previous one lasted almost 2 years?

Richard

 

[Bilgediver]

It would only give full protection if you only used the power from the batteries and the charger was the sole source.

You no doubt have the charger AND a mains source to ring mains Your charger will not protect this but a second isolating trnasformer would!

 

[absit_omen]

An Isolation Transformer transfers electrical energy (from shore power) into magnetic energy and back into electrical energy on board. There is therefore no electrical connection with terra firma. Don't ask me how it does it.

My IT is pretty big, hums and gets hot. It also cost a fortune.

I am puzzled that a Battery Charger can incorporate such a system.

 

[Bilgediver]

I am puzzled that a Battery Charger can incorporate such a system
***************************************************

Both are in fact identical !

An isolation transformer has two independant coils wound on one steel armature and the mains in one coil generates a magnetic flux in the core/armature. This magnet flux generates an electric supply in the second coil.

If the two coils are identical then the input voltage and output voltage are the same . However in a battery charger the secondary coil has fewer turns in fact about 1/20th the turns in the primary so this gives it only 12 Volts but higher current.

The building site transformers in B and Q are not usually isolating transformers and only have one coil which has a tapping at the ends and a tapping in the middle. This is an auto transformer and would need a galvanic isolator on a boat as no isolation as both circuits share a common neutral.

 

[VicS]

If your shorepower earth is connected to the 12volt negative and anodes etc as is required by ABYC standards and I understand CE standards the claims made about the battery charger are a bit of a red herring and you will still need a galvanic isolator to protect your anodes (and other vulnerable under water bits and pieces) from galvanic corrosion. Without one your anodes could be protecting the steel piling of the marina or the steel boat in the next berth.

A GI blocks the currents from low voltage galvanic sources but allows current from high voltage sources to pass thereby maintaining the safety aspects of the earth connection.

 

[William_H]

I think it is quite normal for a battery charger to have an isolation transformer inside. This can be the transformer that reduces the 240V to about 18V AC for battery charging (via rectifier and regulator) or in many modern devices the 240V AC is rectified converted to high frequency 100Khz and transformed to a lower voltage. The high freq transformer also isolates the mains from the DC output. One side of which goes to engine and ship negative. So your battery charger is not giving problems.

However it is most likely that your AC installation. Particularly your water heater has the mains earth connected to the metal parts of the tank hence plumbing and eventually ships earth. It is important thtat the ourside of the heating element be earthed as a common failure mode is from corrosion the water gets into the element shorting the mains to the body. Hence the body is connected to mains. If it is earthed properly this will take out the fuse or RCD if it is not is waiting for you to touch it (and die)

For similar reasons with various appliances the mains earth should be connected to the ships earth. However when using just an extension cord and single appliance it is acceptable to not have the mains earth connected to the ships earth. This especially so with so called double insulated appliances. ie plastic jug or space heater. But not a hot water tank.

The Galvanic Isolator is a barrier for small voltages ie electrolysis currents/voltages but will pass the high voltages and currents of a mains appliance defect.
It does require however that you remove any existing connections of mains earth to ships earth then make the only connection via the GI.

I would suggest you try just the charger on the cord with all else disconnected when you leave the boat. This will have you completely isolated frrom mains earth and may reduce anode loss. olewill

Note an isolation trnasformer is rated for a specific max mains current. A battery charger does not use a lot of current compared to heaters water or space so an Isolation trnasformer for a whole of boat supply is huge but one specifically for small appliances can be quite small.

 

[Richard10002]

"Red Herring" seems to be correct - I already knew that battery chargers have 2 sets of windings which convert the power magnetically, (schoolboy physics?), and am not sure why I asked the question /forums/images/graemlins/frown.gif

I've got a GI in a box somewhere, buy have never got round to fitting it.

Last time I left the boat, I disconnected the shore power, turned everything off, including the battery charger, knowing that the automatic bilge pump is connected directly to the batteries.

I'm guessing tha for he odd 6 weeks here and there, self discharge shouldnt be too much of an issue?

Thanks for telling me what I should already have known!!!

Cheers

Richard