To reduce amps from Alternator
 

I am having a Mitsubishi 4DR5 Alternator 12V 50A. I want to reduce the output around 30 Amps.

It doesn't put out it's rated output all the time, only if there's enough of a load on it. It tries to maintain a steady voltage, up to when it hits it's limit.

Your options are:
Reduce your electrical load as much as you can.
Replace the alt with a smaller alternator.
Rewind your alternator to reduce output.
Change the alternator pulley to potentially reduce output.
Trick your alt in to lowering it's output voltage.
Add some "fancy" current-limiting circuitry.
Remove the alternator altogether.

Or any combination of the above.

I slowed mine way down. It has to draw less HP but I can't prove it. Works great. Hardly cost anything to do.

http://ecomodder.com/forum/showthrea...ork-20558.html

P.S. F U Botophucket! :mad:

As Stubby says, if there's no load it should have very little resistance. I'm not sure what benefits there would be to lowering its RPM, unless perhaps it's more efficient at one RPM than another.

id just invest in a bigger pulley so your alt turns slower.

It's output is limited at lower RPMs. It will try to make up for it by boosting the field voltage, but it will hit a wall/limit and not be able to output any more without spinning faster. (as shown by cars with small alternators that can barely keep the voltage up at idle with a decent load put on)

Rather like an engine, it will have maximum efficiency when kept close to it's peak output. Peak output for a given RPM will always be better than partial at a higher RPM.

Plus, hey, they usually have fans build on/in them, so there will be a tiny bit less power "wasted" by the fan spinning slower.

Too true.
When I modded my Datsun to have a really tall overdrive, I didn't take into account the reduced engine rpm also meant reduced alternator rpm.
At 60kph, (with only 40A to start with), it couldn't keep the battery charged with lights, wipers and demister all going.:o

Changing Pulley and warranty
 

and
Changing pulley will be plain sailing for me. I think I should go for it. Does it have any impact on warranty status?

I had an idea years ago of a cvt drive for accessories. Engine speed changes yet the accessory drive stays at a consistent rpm.

You mean, electric driven accessories? :D