Isolated Earth Alternators?

[powerabout]

Originally Posted by michael pierzga

How do you know that the current is negative ?

good point ( are we talking proton or electron flow)then I re phrase
what part of the circuit involves the earth via the alternator?

[powerabout]

Originally Posted by michael pierzga

Yes indeed..it is possible to deploy an impressed current corrosion protection system. I have used them...not cheap...and they must be constantly monitored.

MerCathode is an active impressed current system, I would call that a simple system?

[BertKu]

Originally Posted by powerabout

you dont need isolated earth to do that.

So whats the problem you are solving with isolated earth?

But it makes life easier if you want to connect 2 alternators in series to get 24 Volt. (28.8V) The casing is in that case isolated from the minus and plus of the second alternator. One can do that in any case with a normal alternator , but you need nylon washers to do that. But then there is a risk to shortening the casing of the second alternator to mass/ground/earth and have fireworks. Not with a isoltaed alternator as second unit.
Bert

[powerabout]

Originally Posted by BertKu

But it makes life easier if you want to connect 2 alternators in series to get 24 Volt. (28.8V) The casing is in that case isolated from the minus and plus of the second alternator. One can do that in any case with a normal alternator , but you need nylon washers to do that. But then there is a risk to shortening the casing of the second alternator to mass/ground/earth and have fireworks. Not with a isoltaed alternator as second unit.
Bert

yes, for sure on that one.
cheers

[goboatingnow]

Originally Posted by powerabout

good point ( are we talking proton or electron flow)then I re phrase
what part of the circuit involves the earth via the alternator?

surely you mean holes or electrons, protons play no part

Dave

[powerabout]

Originally Posted by goboatingnow

surely you mean holes or electrons, protons play no part

Dave

so electrons go one way , what goes the other way?

[powerabout]

I was hoping to learn what an isolated earth alternator is protecting you from?
I do notice that most marine engines that have these the earth from the alternator is still wired to the block! what gives here?
Never heard or seen any data that says "oh your heat exchanger ate out so change to isolated earth alternator"?

[michael pierzga]

Huh ? Isolated earth alternator wired to the block ????? Incorrect installation. The concept of isolation is to keep the complete electric system off the hull to avoid corrosion caused by stray electricity. Small craft that live of trailers, with limited electrical system installations and a limited projected service life may well get away with single pole electric systems. Best practice is always to keep the electric system off the hull of any boat the permanently lives in water..

Aside from stray current corrosion the isolated dc system protects you from fire. A chafed positive conductor , wire, that earths to the negative pole engine block will arc and burn up the wire bundle.

[powerabout]

Hi Michael

When you unpack a marine engine with isolated alt I would say in every case I can remember it has wiring straight to the block.
Have a look at any Volvo/Yanmar etc wiring diagram
Just looked at a new Perkins, also mentions to bond the block to the vessel bonding system
If you try to isolate the block I would think it will make a circuit via the sea water and then you are in big trouble
It would only take a small earth leak from any electrical device on the engine and ....

[michael pierzga]

Yes....block bonded. All equipment should be bonded to a connection to the sea to allow dangerous charges like lightning to exit the vessel.

The Negative pole of your electric system, on a floating , isolated system, is not on the engine block. To tell if an alternator is isolated simply take your multimeter and measure between the negative output terminal and the alternator chassis. If you measure conductivity between the neg and the chassis your alt is not isolated. As a visual inspection of an unknown engine simply look at the sensors...sending units...for oil pressure or temp. Two wires serviing the sender unit indicates isolated..one wire and its automotive style negative engine block.

[powerabout]

yes thats how most look BUT a wire does run from the isolated term to the common earth on the engine.
Show me a new engine thats not like that?
Makes me think someone has a rule about isolated earth alternators but no rule on how they are wired?