Marine alternator

[Dipper]

Hello and welcome to the forum. You seem to have dug up a very old thread!

I had a Volvo marine alternator rebuilt by Chris Putt (Starters and Alternators) Ltd, 2 Stanley St, Weymouth 01305 774084 about 10 years ago and it's been working ever since. He is still in the phone book so he might be worth a call.

 

[davey]

Marine Alternator myths

Whilst it is true that there are some special marine alternators that have Insulated Return this is pointless unless the starter motor also has it. OK it might be argued that a better paint job and anti-corrosion treatment is applied but most alternators have this anyway as on transverse engined cars the alternator pretty much gets blasted by rain and road salt driven through the radiator grille at 70 mph. By the way not all breakers yards are filthy and reeking of hypoid oil that smells like cat-pee as the Environment Agency clamped down on that years ago. Nowadays the parts are taken off for you and labelled. My favourite alternators are the Bosch Compact type but beware as some of these use a special plug with special features such as "inhibit charging during kickdown". Unless the donor vehicle is heavily into drive-by-wire you are unlikely to get snared by this one. The previous series of Bosch alternators with the external fan are also excellent but watch out for the fan as these can cut-open batteries and spray acid everywhere. By the way most alternators use a 6202-2RS front bearing and these are quite cheap. Less than £5 for a premium quality Made in Europe bearing but only about 50p for a perfectly adequate Chinese bearing. Watch out for the "W" terminal as this is unrectified AC meant for driving rev counters or occasionally used to heat an element in an electric choke. Usually it is there but not connected. Good luck!

 

[davey]

Aternator Repairs

"The alternator is unecconomical to repair." Try for another opinion. Unless it is obviously corroded to pieces I can't see it being possible. If it has an insulated negative then you may be able to retain the body and rectifier plates while replacing the rotor. The most common fault in alternators is a worn slip rings. These can be turned down but if they are too far gone then a new rotor is indicated. I think you will find the rotor is common to many vehicle alternators of the same manufacturer. So it is likely an alternator of similar manufacture from a wreckers yard (we call them) will provide a suitable rotor for your old alternator. In any case pull the old one apart and see for yourself. "don't let the [--word removed--] get your money"

olewill

It IS possible to obtain slip rings for alternators at fairly modest cost and I have replaced a few myself. My problem alternators used to be the Lucas/Marelli AC127 72amp fitted on the Rover 800 turbo-diesels. As these cars have 240 watts of main beam and 100 amps worth of glowplugs to heat before pulling 300 amps of cold cranking they are not so good on "granny cycle" (short trips to the supermarket). Diode assemblies would last about two years sometimes less especially if the alternator was used to drive a 1KW inverter (It would drive a 1000 watt "dumb" circular saw OK and non variable speed power tools. As a test I used it briefly to power a 1 bar electric fire) For variable speed power tools a Redi-Line rotary converter was used instead - excellent! The petrol Rover 800s all had 100 amp alternators which are trouble free possibly because petrol engines are so easy to start. Some French alternators have "sealed brushes" but this is not such a good idea as experience shows that copper dust and carbon get trapped in the housing and work like grinding paste - back to the drawing board!

Please don't get suckered by chandlers.

 

[charles_reed]

Where is the best place to get an "Isolated Lucas Marine Alternator" rebuilt or purchase a rebuilt one?
Do they still sell these new? If so where can I get one?

I've had my alternator(s) rebuilt in Telford, Archachon, Fiumicino and Camborne.

In every case it's been done by the local auto electrician for sums between £8-£25 (the most expensive was Arcachon, but he did it while I waited).
Since the 35-amp Hitachi (which dies the most frequently) I've had a marinised Lucas 70 amp and now have a bog-standard Magnetti-Marelli 100amp which (touch wood) in 2000 hrs of motoring (on 2 engines) has not needed any attention.

The 2 points I'm making are:-
1. You don't need to spend the earth on a repair, if you avoid the marine mumbo-jumboist "experts".
2. The larger the rated output of the alternator, the less likely it is to require repair.

PS I've only once bought an electrical unit from a breaker and their price was nearly as much as trade-price from an auto-electrical wholesaler - the MM 100amp (chosen for its very high low-rpm output as it was fitted to Fiat cast diesels) was, from memory £124.

 

[Playtime]

This is an old thread but, surprisingly, no-one has mentioned saildrives as the reason for insulated return engine set-ups.

I have an MD22L coupled to a saildrive. As has been stated previously, the MD22 is insulated return and I often wondered why until I started thinking about the saildrive. If the engine is isolated from the DC negative ('earth') then so will be the (aluminium) saildrive.

If the saildrive is not isolated (i.e. it is earthed via the engine block) and there are any stray currents around then electrolysis or galvanic action could start to attack it - there is certainly plenty of electrolyte present! Maybe better to keep the saildrive isolated?

It is worth noting that the glowplugs do use earth return through the block but this is achieved by a relay that connects the block to DC negative only when the glow plugs are operated. All other engine related items and functions (mounts?) are isolated.

Are there any saildrives out there that are permanently 'earthed'? If so, how do they overcome this (potential) problem?

 

[solent_hazard]

I have replaced the Alternator on my Yanmar 4JH with one from Exeter Rd Alternators, Plymouth. They sell loads on Ebay

I did have a faulty one first time but the replacement works a treat with insulated neg.

 

[Playtime]

Are there any saildrives out there that are permanently 'earthed'? If so, how do they overcome this (potential) problem?

Forgive me for quoting/bumping my own post but I would like to hear other thoughts on this subject.

The question is also relevant to AC/DC ground bonding and the use of galvanic isolators.

 

[lw395]

Don't know anything about saildrives, but if the drive leg were earthed (to DC -ve), it ought to be ok if no other immersed metal was connected to DC -ve. Essentially you need a circuit for the DC return to cause any electrolysis, grounding say a bronze seacock nearby would create that circuit.
Grounding your DC -ve to the steel frame of the pontoon or shore power earth would be equally bad.
It's not hard to bush the alternator mounts with GRP tube and isolate the fasteners but there may be some risk of the belt acting as a van deGraaf generator, I suspect the pulleys should really be earthed!

(using the term 'earth' in the loosest possible way that only IEE members are allowed!)