DeWolf

I'm sure this is a stupid question and I'm sure I already know the answer but: does a 150Amp alternator require any more power to run than a 90Amp without a load as such?

joejoe

Mmmmm......no.

928NOOBIE

I love that picture every time I get to see it lol..

DeWolf

I knew it was stoopid!!!. lol

joejoe

Absolutely not a bad question. My answer is from when I asked same question years ago lol.. Newby that is one of my favorite pictures of 'Dutchess'. She (and Barney on left) were dumped off here. She could not outrun a semi twice so no longer here. Now I have a 3 legged husky who my cousin gave me when I was real sick and kinda learning to walk again. Became a real pain when he realized he could easily keep away from me.

jpitman2

Once had an LR Disco (normally an 80A alternator) that got a hot climate upgrade to a 120A alternator, and a free-er flowing grille. Minor issue - they had to bypass the original 80A master fuse. Do we have such a master fuse anywhere ?

jp 83 Euro S AT 57k

DeWolf

The reason I asked this question was there is a guy locally who can rebuild my original alternator and upgrade it to 150Amp for $200.00

Alan

Without a load they are both 0 Amp alternators - the only losses are friction - hardly different.

Alan

Alan

No fuses at all for the alternator!

jpitman2

There used to be a guy in Oz who could rewind alternators for serious off-road use, and fit a heavy blade switch that could throw the output to external connections that could do welding repairs. Several guys I knew in Saudi had them.
Sounds like a good deal Scott. Let us know how you get on, might send him some business.
jp 83 Euro S AT 57k

Carl Fausett

There is more to a modern 150 AMP alternator than the number of windings. The modern diodes are more stable, and less prone to damage. Also, our alternators have two fans, not one.
Finally, our modern 150 AMP alternator will charge at 928 idle speeds, and I do not know (but I doubt) that just an old alternator with more winding's will do that. Its about the electronics inside and the efficiency of the unit.
Modern alternators are more efficient, take less to excite. .

The Forgotten On

Alternators behave like an eddy current brake when under load. The higher the amps demanded of them the more strain they put on the engine. They will put the same load amp for amp regardless of the rating if the alt is the same.

I would however stick with the lower amp alt as it will put out a lot more power at idle and under hot conditions. It's a trade off when going to a higher amp rating in the same alt.

Alan

Generally agree with Blake - for a stock alternator rewinding for more current is a trade off - you will get the opposite of what you want. More max current at high RPMs gets you less current at low RPMs. There is only a given fixed space for the windings. If you go with heavier windings you also get less turns - so less sensitivity...

Larger case alternators can have a slightly different trade off. 6 phases instead of 3 can help too (if there is sufficient space) Better regulators can also help - but it is still always a trade off. Don't select more max amps than you actually need or you will hurt low RPM generation. If 150A is enough use that rather than 200A (or less even).

Some newer high current alternators generate better at idle than the stock units but some (many?) definitely do not (so verify)

Alan