New Alternator for a Perkins 4108

[BigART]

I need to replace the misbehaving Hitachi alternator fitted to my venerable Perkins 4108. The Hitachi has four outputs, battery +, battery -, the tacho output and alternator light.

The Bosch 1285 which has been recommended only seems to have three outputs, one of which is 'W'. I think this may be a tacho output. Of the other two, one is a big stud (battery+ possibly?) the other a smaller stud (battery-?).

Any ideas on how I could wire up the alternator warning light - or alternatively a better replacement?

Angus

 

[lw395]

I suspect the small stud is 'alternator light'. A -ve terminal would be at least M6 I would have thought. The -ve may just be through the mountings. Is your current set up insulated from the engine?
I'm not aware of any car/truck alternators without a warning light connection, the warning light current helps start the alternator by providing a little current into the rotor.
I am standing by to be 'corrected'!

 

[ianj99]

I suspect the small stud is 'alternator light'. A -ve terminal would be at least M6 I would have thought. The -ve may just be through the mountings. Is your current set up insulated from the engine?
I'm not aware of any car/truck alternators without a warning light connection, the warning light current helps start the alternator by providing a little current into the rotor.
I am standing by to be 'corrected'!

Yes, it does sound as though this alternator does not have insulated return and the smaller stud is for the warning light.

My 4108 has insulated return on all engine electrics so the alternator (lucas) has 2 large studs for +ve & -ve outputs. (its a steel hull so important to avoid galvanic currents)

You need to replace like for like type or you will possibly see increased galvanic currents and more rapid corrosion of underwater metal work.

If you want to upgrade the alternator at the same time, Sterling Power supply some with a digital regulator and insulated return.

http://sterling-power.com

 

[BigART]

Thanks guys. As you may have guessed, alternators are not my specialty.

Yes, the non-insulated return would explain it. The smaller stud looked a bit small for the expected current. As we are a steel boat, I think I will look around further for an insulated return alternator. If no luck, see if I can fathom a method of insulating the mounts and providing a direct return. Not sure how important this is as the starter motor appears to be earthed via the case and not cause a problem, but at least that is a single point of connection to the hull.

Keep looking

Angus

 

[PCUK]

My steel boat is 26 years old with earth return alternators. The batteries are earthed to the hull to ensure electrical balance, but all equipment is earthed to the batteries with dedicated returns. No corrosion to date!

 

[oldvarnish]

I replaced an alternator last year on a 4108 and haven't got a great deal of expertise.

The people who make the ADVERC charging system had a very helpful lady who knew the answer to every question. I bought the alternator from them.

 

[Tranona]

You might also consider a Balmar high output alternator. They have a wide range and in the popular Volvo/Yanmar types are actually cheaper than OE. UK agents are Merlin www.power-store.com

 

[Billjratt]

I changed out the Lucas alternator on my 4108 (1978-ish) for a bosch taken from a VW in the local scrappy - £14. ( I had to insulate the neg feed from the frame)
Your setup is different, having a hitachi - have you checked/had it checked out properly before replacing?
The previous owner may have done the same as me with the hitachi), it involves rewiring, as the lucas had external relays and mechanical regulator.
Do you have a square panel just below and to the left of the alternator? has it got a black box on it and some smaller silver boxes/cans? (these are the old control devices)
The black box contains a fuse in the negative line from the alternator to the starter motor, and then on to the battery common neg.
I believe this fuse should be bypassed with heavy wire, for two reasons: 1 - the alternator you are putting in will have the ability to overload the old circuit. 2 - if the fuse blows, it will effectively disconnect the alt ( like turning the battery isolator sw) thus possibly injuring it. (originally the relays would have dropped out and protected it in the case of a blown fuse)
Remember to upgade the positive feed as well.
What I'm trying to say here is you should verify where the existing problem is, as there may be old wiring clouding the issue - for instance, my tacho is engine-driven from a sensor, not the alternator - that's another oddity.
If you google for lucas alternators on E-type jags, there's an american site that explains the upgrage process and provides original wiring diagrams - that will explain the redundant stuff (if any) that is lurking around you engine.

 

[BigART]

have you checked/had it checked out properly before replacing?

Ah. I knew someone would pick up on that.

I suspect the reason the alternator is misbehaving is the fact that I installed a Merlin 'Alternator Management System' (AMS) with upgraded wiring to help give it a boost. I wish I hadn't now as it set off a chain of problems.

It took a while to get it working (another story), but eventually I managed to persuade it to function. Unfortunately it worked so well, the harder working alternator ran so hot it melted the internal regulator potting compound which oozed out the bottom. It continued to work adequately but to my mind at too high a voltage ( I was seeing up to 14.8 volts). No problem for 10 minute "get you out of the anchorage" runs but I wasn't really comfortable with this so I would disable the AMS for longer passages to avoid cooking the batteries. I solved the excess voltage problem by setting the AMS to the gel battery setting which lowered the voltage to something I was more comfortable with.

As the internal regulator was looking rather sad, I replaced it with an external Bosch regulator. After a year of this, the Hitachi alternator stopped self exciting without the assistance of the AMS. I didn't want to have to rely on the AMS, so I added an external button and a light bulb to spark up the beastie.

The wiring round the back of the alternator was now looking a bit of a mess, so I took it to a man that understands these things who said it was not man enough for the job and I needed a bigger alternator. And here we are.

The Balmar seems bit expensive for my pockets so I thought I would go so the more conventional route but of a bigger size with better cooling.

The moral is beware of unintended consequences.

Angus