1GM10 earth/insulated return

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co256

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Evening all,

I have the 1gm10 and it's earth return wired.

I'd like to change to insulated return as recommended by any source I've found (t-b training, Calder).

Anyone had any experience of this?

Any problems to look out for?

Basically (because I am), I want to remove the engine earth bonding and take it all to a "common earth point" where it can then go back to the battery negative. As I understand it (?!) any earth leak then finds its way back to the batteries rather than out of the prop shaft and therefore contributing to galvanic corrosion.

Many thanks,

Guy.
 
The normal wat is to use a point on the engine as a ground and run a heavy wire from there to a bus. All negatives should lead to that bus. Your engine has to be grounded anyway. As well all grounds should go to the same point to be sure they are all at the same potential.
 
If I understand you correctly you will need an insulated starter motor (or perhaps you can get around that with an earthing relay that earths the engine while starting only) an insulated negative alternator and "twin wire" sensors for oil pressure and temperature.

But if you have a flexible coupling the stern gear is probably isolated by that.

But why not fit a Galvanic isolator in your shorepower earth ... that'll achieve want you want wont it

How serious is your galvanic corrosion. What anodes do you have. How are they connected?
 
Last edited:
mitiempo said:
The normal wat is to use a point on the engine as a ground and run a heavy wire from there to a bus. All negatives should lead to that bus. Your engine has to be grounded anyway. As well all grounds should go to the same point to be sure they are all at the same potential.
Click to expand...

the alternator would have both pos & neg wires therefore not using the engine body as the neg / return
 
I never could understand electricity. OK, so instead of taking the earth from your generator to the engine you take it directly to the battery. But the engine has to be earthed anyway, as the starter motor (and several other things) wouldn't work otherwise. So what difference does it make, knowing that electricity can go seven times around the world in a second? (one of the few things I know about it)
 
mitiempo said:
The normal wat is to use a point on the engine as a ground and run a heavy wire from there to a bus. All negatives should lead to that bus. Your engine has to be grounded anyway. As well all grounds should go to the same point to be sure they are all at the same potential.
Click to expand...

The "Normal way" is what I have and that's earth return, not what Nigel Calder and others recommend.
 
VicS said:
If I understand you correctly you will need an insulated starter motor (or perhaps you can get around that with an earthing relay that earths the engine while starting only) an insulated negative alternator and "twin wire" sensors for oil pressure and temperature.

But if you have a flexible coupling the stern gear is probably isolated by that.

But why not fit a Galvanic isolator in your shorepower earth ... that'll achieve want you want wont it

How serious is your galvanic corrosion. What anodes do you have. How are they connected?
Click to expand...

Hello VicS,

yes you are right, I do really need to insulate the starter motor and the alternator to fully achieve this but Nigel Calder says.... for the short amount of time the Starter motor is working it's not worth worrying about as the alternator is running it's all heading to the batteries anyway.

I'm not sure I have a flexible coupling, I'll have to check that.

I don't have any shore power.

I don't have galvanic corrosion, or non that is noticeable.

Guy.
 
vyv_cox said:
I never could understand electricity. OK, so instead of taking the earth from your generator to the engine you take it directly to the battery. But the engine has to be earthed anyway, as the starter motor (and several other things) wouldn't work otherwise. So what difference does it make, knowing that electricity can go seven times around the world in a second? (one of the few things I know about it)
Click to expand...

Hello vyv,

Doesn't taking the earth for the starter and alternator to the batteries create the earth you are refering to when you say "the engine has to be earth anyway"???

Cheers,

Guy.
 
mitiempo said:
If my memory serves, Nigel Calder has not said that except when referring to a metal boat. Can you quote the relevant passage please?
Click to expand...

"it is not easy to electrically isolate a non-insulated alternator and still ensure a sufficiently rigid installation. A good compromise is to connect a heavy ground cable from the alternator case to the boat's common ground point. This will provide a direct electrical path to the battery that bypasses the engine block, discouraging leakage currents."

There you go.....
 
The way my, aluminium boat is wired is to have the senders and alternator insulated from the block with a 2 wire conection. To start the motor the block is momentary grounded to the battery negative with a relay. As soon as it starts the battery negative is no longer conected to the engine block.
This sort of connection is essential for a metal boat and the corrosion gurus also recomend this for all boats. Few manufacurers do it this way beacuse its more expensive.
 
co256 said:
Hello VicS,

yes you are right, I do really need to insulate the starter motor and the alternator to fully achieve this but Nigel Calder says.... for the short amount of time the Starter motor is working it's not worth worrying about as the alternator is running it's all heading to the batteries anyway.

I'm not sure I have a flexible coupling, I'll have to check that.

I don't have any shore power.

I don't have galvanic corrosion, or non that is noticeable.

Guy.
Click to expand...
Can't see any need for this complication. Just removed a 1GM with a standard earth return after 17 years use and never any problem - even when I had it bonded to the stern gear and a hull anode.

Would be unusual for a 1GM not to have a flexible coupling - otherwise you spend a lot of time in the dentist having your fillings replaced (it is posssible to have a completely flexible installation with a solid coupling but unusual).

If don't have any problem with galvanic corrosion what are you trying to achieve anyway?
 
Hello Tranona

I am re-wiring the boat entirely.

So whilst I am at it I figured I may as well follow the best advice I can find and that means doing it the way Nigel Calder recommends.

The present wiring is a mess and the main battery cut off switch doesn't???!!!

Another good reason to re-wire in my opinion.

Cheers,

Guy.
 
But there is no need to do what you intend doing. Might I suggest you get a quote from Merlin Power for a complete system? If you are replacing everything then suggest you use a BEP Marine switch cluster with VSR for charging and battery control and then completely separate engine and service system. I did this on my boat and Merlin designed it, provided the wiring diagrams, hardware (bus bars, fuses, cables etc.). I had my own distribution and switch panel custom made (bit of an indulgence) but you can make your own or buy standard panels in modular format.

No connection with Merlin other than a satisfied customer. I used them after doing a lot of research and deciding that I would get the best job going that route rather than trying to do it all myself. Well worth the effort, and probably little different (apart from my panel) in price than trying to design and source it all myself.
 
Thanks Tranona

I have been in touch with James already, I have bought a couple of items from him but cannot afford the whole kit for sure.

I'm trying to simplify the electrics entirely so that I have a hope in hell of fixing things when it all goes wrong, which one day (all things being equal) it will!

Guy.
 
Tranona said:
Can't see any need for this complication. Just removed a 1GM with a standard earth return after 17 years use and never any problem - even when I had it bonded to the stern gear and a hull anode.

Would be unusual for a 1GM not to have a flexible coupling - otherwise you spend a lot of time in the dentist having your fillings replaced (it is posssible to have a completely flexible installation with a solid coupling but unusual).

If don't have any problem with galvanic corrosion what are you trying to achieve anyway?
Click to expand...

I agree with the principle of "if it ain't broke dont fix it", but corrosion issues can show up in old boats following for example a change to a new marina. If its wired correcly you have less chance of problems and isolating the engine has no drawbacks, from a corrosion point of view, unlike other suggestions like bonding which has both advantages and disadvantages.
A flexible coupling does not isotate the engine (and therefore battery negative) completly . The seawater cooing provides a possible path for conduction and therfore corrosion of other metal structures such as the rudder stock.
 
If you move to a marina and have corrosion issues and zincs not lasting long, it is either the marina's wiring or the ac on another boat. Not the dc on yours. Through hulls in my opinion should not be bonded.
Nigel Calder must have changed his mind because that certainly is not in my copy.
 
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