Alternator upgrade

[Graham_Wright]

It depends what you do with the spare power. My boat has 70A and 130A alternators. The 70A is dedicated to the starter battery the 130A to the domestic batteries (although they can be switched differently). Having two alternators offers redundancy which is always good but a large alternator permits the running of a high power inverter for instance allowing the use of mains voltage devices without flattening the batteries. Think microwave e.g.

 

[LadyInBed]

What the batteries will 'accept' is a function of the volts across them.
Get a bit more voltage across them, by upping the alternator voltage or reducing losses and the current will increase.

That would also be my inclination.

 

[pjsgsy]

Something you might want to take a look at, rather than replace the alternator. I added a sterling alternator charger to my setup. It is frightening (I mean it!) how much more current it can dump into the batteries now. It also does proper stage charging, so you are filling your batteries better anyway. Required I solder a sense wire into my alternator. I've had it fitted a few years now. Seems great.

 

[yotter]

You will NOT drive an alternator bigger than 90Amps on a single V belt, end of.

I have a 100Amp Atlernator on a single V belt, nae probs. But seriously, the other issue of a bigger alternator is heat, I have a fan blowing outside cold air onto the rear of the alternator. It will deliver around 60A+ for quite a long time when batteries have room. A sterling AB130 helps with this. Also agree Solar is good and use this also.

 

[Jim@sea]

Presently running a Thorneycroft T80 with a 70A A127 Lucas alternator supplying 4 x 110Ah batteries. The system has a Stirling regulator and a FET charge splitter.

I was looking at a 120A alternator upgrade with a view to less engine running time to recharge batteries heavily discharged after a long sail.

Is this a viable solution, there seems to be conflicting advice online. Some say that an alternator only supplies the current demanded by the resistance in the discharged batteries; others that heavily discharged batteries will recharge with less engine time with an alternator with a higher nominal output.

Thanks in advance

Mike

Dont Bother. I made a mistake when I bought a 1986 boat with the Thornycroft Diesel (50 bhp BMC 2500 Diesel.) The alternator was working fine but I needed to spend money so I bought a new alternator with an internal regulator. Unfortunately the wiring was entirely different and even though the dashboard of the Thornycroft was basically an MBG panel, Smiths Rev Counter, Water Temperature, Oil Pressure etc, like what I was used to in 1986 when I had a garage, to wire this new alternator up was completely different as on a car you have Positive and the Negative is Earth, on a boat you have 3, Positive, Negative and Earth, So I spent £120 on having an auto-electrician wire it up I wish I had not bothered,
PS I still have the Lucas Alternator & Regulator for sale. ?

 

[pvb]

Something you might want to take a look at, rather than replace the alternator. I added a sterling alternator charger to my setup. It is frightening (I mean it!) how much more current it can dump into the batteries now. It also does proper stage charging, so you are filling your batteries better anyway. Required I solder a sense wire into my alternator. I've had it fitted a few years now. Seems great.

He already has one, according to post 1.

 

[pvb]

Get a bit more voltage across them, by upping the alternator voltage or reducing losses and the current will increase.

The OP has a Sterling regulator fitted. If properly wired, this senses voltage at the battery terminals and regulates it at 14.1, 14.4 or 14.8v, depending on which battery type has been selected on the regulator.