Alternator - Insulated Return?

[Jonny_H]

We are looking to get a spare alternator to take with us. We have a Lucas A127 70amp alternator which I believe is quite common. I've contacted a few people who can sell me a brand new one for about £50 (at this price well worth carrying), but as soon as I double check the terminal layout they inform me that for an insulated return unit (which is what we currently have) they want £150 (not so much of a cheap spare anymore!).

I understand the basic difference with an insulated return alternator vs non-insulated return. However, as this is only being carried as a spare could I get away with a non-insulated return unit, and if so where would I connect the cable which currently goes to B- should I need to?

Additionally, anyone know of a good supplier of insulated return alternators who can do them at reasonable cost??

Thanks

Jonny

 

[halcyon]

Main differance between the two is that neg diodes on one is connected to a output terminal, the other is connected to the body. So if you sort a suitable bolt on the new one to connect the earth cable to on the body, you should be okay. Check for any external mod's to the regulator, i.e. earth connection on the current one, when you need it, trying to sort out what a spare cable is, is not the time.

Brian

 

[Jonny_H]

On the current one we have a sterling regulator with the cables soldered inside the alternator - however as the new one will purely be a spare I assume I can just run it without these connected?

So, basically if I get a non-insulated one - could I just get a big jubilee clip to attach the earth cable to case, or should I try to drill and tap the case to put a bolt to the case to attach the earth to?

Jonny

 

[VicS]

[ QUOTE ]
Main differance between the two

[/ QUOTE ] Some non insulated ones have a negative terminal as well. Pretty sure that the one in my car does. It just carries an earthing wire so that the mounting brackets are not relied upon for the connection.

 

[William_H]

You need to find out if and why you have an isolated negative alternator. The first question is, is the starter also negative isolated likewise the oil pressure and temperature switches.
Isolation is not common because of the automotive heritage of most electrics and engines. The isolation can be useful in combating electrolysis corrosion especially on steel boats.

If the engine is totally isolated for corrosion reasons connecting the negative of the system to the engine body for a limited period is not likely to cause problems. However if it is done for some other reason then there could be problems.
If it is only the alternator isolated then it may just have been a convenient model at the time or a tricky way of increasing charge voltage.
With your existing alternator in place check with a multimeter for any voltage difference between between the negative and the engine body. (both engine stopped and running) If there is no significant voltage difference then try connecting a wire from negative to body. Check the charging current if you can while doing this in case the isolation is used as a way of increasing the charge voltage via a diode. The charge current will fall with the negatived to body if that is what is happening.
So the answer may be simple or complex. Maybe someone else will know. olewill

 

[pampas]

IF you have an all insulated system then you will temporarly have to connect a negative from the engine to the battery when using the earthed return alternator. If your hull is of alloy construction dont do this, as it will start reactions which after use ,may cause ongoing problems with the hull, In other words dont use it all, only a fully insulated return alternator.

 

[Jonny_H]

We already have the engine battery -ve connected to the engine block. (GRP Hull) - does this mean we should be ok?

Jonny

 

[DAKA]

On my last boat Volvo penta I changed the isolated alternator for a standard car one.

There were issues that took a few trips to sort out.

The alternator disconnected at 1750 revs and the tacho stopped.

this was from a solenoid that closed the exhaust at start up and opened at 1750 revs.

I needed help to get it working but it did work and there was a massive saving.

Not for a carry on board spare IMHO.

 

[galeus]

Hi Jonny
I am presently replacing my 35amp insulated return Lucas alternator with a larger unit(with the Sterling regulator wire already attached) which like yours does not have the insulated return wire.The foreman at the boatyard has advised me that this thick black wire now becomes redundant as the earth return will be back through the engine block but I am watching your post with shared interest.

Galeus

 

[pampas]

Then go ahead by all means assume then hull is not metal. If its grp/ wood/Ferro will be ok if the starter or the alternator in use fails and new is required it will be ok to replace with Neg return as well .Cost(From new) for double insulated call premium prices, Insulated returns are usually supplied from new by engine maker so that its final application will fit all Sociecty uses eg llyods,and other insurance bods to conform with specified uses. Hope this settles your worrys.