Comparing DC alternators efficiency vs. RPMs.

[Dualfuel]

12v, the 'Rule-of-thumb' has been 1HP for each 100A produced when using a 12v alternator.  Or approx 1HP for 1.4KW?

1HP is 745 watts...so this is a second law violation. You can't put in 745 watts and get 1400 watts out.
I am sorry it took me so many years to catch this...
BTW what are the results from the Denso? Mine locked up and I replaced it with a 55 amp Delco 20SI.

DF

[mobile_bob]

i have never seen a reference to 1hp for every 100amps output from an alternator

about everything i have read over the last few decades, going back to the 70's was to figure 25amps for every hp available to drive the alternator as it applies to the use of a typical 12volt nominal system.

so that works out to be about 350 watts output for each 1hp input or ~750watts input for 350watts output or ~47% efficiency, which was probably about typical for the 10si units that guys were using back in the 70's.

and probably a good rule of thumb for a 12volt nominal system today, even though a well designed system with a modern alternator using a well designed serpentine drive belt, might do a bit better and get into the low 50's % efficiency.

fwiw
bob g

[Dualfuel]

Thanks Bob!
The over unity quote came from further up this thread (Thomasonw)
I am surprised it's as high as 47% but that's great.
I was admiring the chart with comparison between rpm and amps. It's very interesting.

Before, I had barrels full of 10si parts. Now 15 years have gone by and I am more interested in 48v. I very grateful to have enough resources to actually be picky about the next alternator.
After all your experiences, what do you recommend for 48vdc?

[mobile_bob]

what would i recommend for 48 volts?

that depends on what your needs  are to some extent.

if you aren't overly concerned with squeezing the system for maximum efficiency
then i would lean toward a custom wound stator in one of the large frame alternators, and upgrading the diodes to 200piv rated units.  i think one could get something in the mid to upper 50's % range with a little work.

if you want maximum efficiency?

this based on research from now nearly 15 years ago

i would go with two of the modified 555 units, connected in series, and controlled with a single balmar controller.
i think one could get into the mid 70's % with a little effort.

another option  that might well show promise is splitting the dual stators of the niehoff alternator, maybe one of the 24 volt units, and combining the two outputs in series,  they are even larger framed units, and might well prove to be quite efficient 
charging a 48volt system, especially given the quite low rpm's needed to get to somewhere around 75-100 amps output.
this option i have not tried, so i am not sure, but they sure look like a unit worth doing some research on.

bob g

[Dualfuel]

Sorry if I sound a bit incoherent. I just got out of surgery, and none is parsing my writing.

I use a mmpt charge controller to take 120vdcsolar panels down to 48vdc.
Perhaps instead of panels a DC motor of some sort could be substituted? I have a 3hp 120vdc treadmill motor...
Of course efficiency is not everything sometimes. Just the fact that the batteries could be recharged in a blizzard.
Any how I am just being chatty. And I appreciate the good work you did 15 years ago. It's still relivant.