how big an alternator can you install? and what horn sounds the best?

[greenmeanie]

If you have a 3 wire system you can run as big an alternator as you can imagine. It will only put out the amps on demand so as long as it is rated to meet your max load (Sit down and calculate this rather than guessing at teh biggest unit you can fit) you'll be just fine. Note that you usually have to run the engine at a minimum rpm for the alternator to be producing any output so, unless you are lucky, or have played with the pulleys to get the correct rpm, it won't be doing much at idle. A hand throttle helps here.

Of more importance to your original question is the gauge and condition of the wire in your charging system. Its been a long time since I looked at an original Rover wiring loom but IIRC the charge wire is 12AWG which should be good for about 25.5A. Someone can correct me on that. I would want a minimum of 10AWG (Preferably 8AWG) and probably double it up to the main load point if I was running a winch. I'd also install a Maxi fuse in the line to protect the truck if the alt control goes wrong.

[JimCT]

Large output alternators

Output drops off dramatically as the case heats up, so do not be too hung up on output. That is why alternators for ambulances for example are large cases for cooling. Also if the fuse blows on the alt. output it fries the alt, sending it to full field.

[greenmeanie]

Output drops off dramatically as the case heats up, so do not be too hung up on output. That is why alternators for ambulances for example are large cases for cooling. Also if the fuse blows on the alt. output it fries the alt, sending it to full field.

Not that I know anything but case temperature may be what you look at but it is the resistance in the magnetic wire and to a small degree a loss of magnetism that affects output due to heat. The fan and the design of the casing to allow for airflow both over and through the unit are of more importance than casing size. The casing, after all, only conducts heat from the stator and does very little for the rotor.

You can only push so many amps through a given cross section of wire or obtain so much magnetic field from a given size of magnet unless you go with something fancy. Bigger units for a given rating merely have larger copper and magnets which gives them a greater margin when it comes to generating heat. Heat is energy loss so the bigger the unit for a given rating the more efficient it will be in broad terms. As you move to bigger units you also tend to see less PM alternators and more wound field units which, again allow for increases in efficiency and thermal resilience.

The fan and the design of the casing to allow for airflow both over and through the unit are of more importance than casing size. The casing, after all, only conducts heat from the stator magnets.

I'll admit I'm used to bigger units that include a thermal switch as an added protection against overload which you probably don't get on a cheapy automotive unit. If you install the correct fuse its failure point should be greater than the rated output of the generator but less than the wiring harness. If the fuse blows it is indicative that the alternator is already overloaded so you have a failure in your charge system. I'd rather slag the alternator than have it melt the harness with associated fire risk.

[JimCT]

Alternators

All true, just wanted to make sure folks knew they need a nice buss fuse in the output and not a small inline automotive type

[amcordo]

I used this horn:

http://www.sherco-auto.com/Merchant2/merchant.mvc?Session_ID=fcbb9d09fb102abb61ddb6f56f3e8a61&Screen=PROD&Product_Code=HN-1

It's very loud and it has a nice higher-pitched european sound to it. It seems right inside the rover.

[xsbowes]

Output drops off dramatically as the case heats up, so do not be too hung up on output.

you could install an alternator cooling system similar to what BMWs use. Quikcool for example.