Alternator v. no alternator - 10% gain @ 70 km/h
 

FYI, other GS threads that talk about alternators are:

• Alterpower (shutting off alternator)
  
  
• Does the Civic VX have a unique alternator?
  
  
• Power (accessory type) consumption and FE
  
  
• Solar/plug-in 12V system, alternator optional

Anticipate any difficulties switching belts on the roadside? A-B-A testing is going to be a pain...good luck! Us yocals without instant mpg readouts really, really, REALLY appreciate the effort!

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*sigh* I'd love to, but I have far too many demands on my pocketbook already. I've got other repairs on the car that I should get done before I purchase a MID. I'm having a hard enough time scraping together the money for my exhaust.

Details man! Details! Post something in the daily updates thread.

No, it's away from the hot stuff, and I only need to adjust one bolt on the alternator to get the OEM belt on/off. The home made bypass belt is basically a big rubber band - pretty easy to get on/off. (v.2 has been in service for about 275 km / 170 miles now without self destructing.)

I agree. Driving without FE instrumentation is like drag racing without seeing your 1/4 mile time at the end of the run, or like lapping and not knowing your lap times... until a week or so later when they come in the mail or something.

Back when I was messing with my alternator, I measured the electrical loads of various things (using a shunt on the alternator output). Not a super-exact test, but it should give a ballpark for smaller cars.

I tested at both voltage settings of the alt, where 14.4 is typical alt voltage, and 12.7 is similar to a fully charged battery. The idle current is subtracted out of the other settings.

Idle: 128w @ 14.4v, 89w @ 12.7v
Rev up to 3500 rpm: +35w, (not tested)
Heater fan setting 1: 55w, 38w
Setting 2: 98, 67
Setting 3: 141, 99
Setting 4: 189, 135
Marker lights: 95, 71
Full lights: 240, 179
A/C (heater fan subtracted, but including condenser fan): 163, 114
Defroster: 104, 77
Wipers 1: 48, 38
Wipers 2: 76, 64
Radiator fan: 144, 83

Does that mean that a/c is less of a drag than full blast non-cooled air? Of course you need to add the fan to the a/c, but still, do you get me?

drag
 

The AC will drag the engine directly and not present an electrical load except for any clutch power on the pulley and the blower fan. Nice measurements on the car electrical loads!! How about the car computer, fuel pump and ignition loads??

I have some results.

But first: Randy, great data. Thanks for posting it. What car/engine is it from?

Preliminary results (I'll do a proper write up later with charts & margin of error etc. and post at the top of the thread):

Speed 70 km/h / 43.5 mph

A: alternator belt ON - 71.16 mpg (US) - avg of 3 bi-dir runs (6 one-way runs)

B: alternator belt OFF - 78.08 mpg (US) - avg of 3 bi-dir runs

A: alternator belt ON - 70.2 mpg (US) - avg of 2 bi-dir runs

Notes:

• the last A runs were made after reinstalling the belt and driving for 10 minutes to replace energy taken out of the batt from the B run (simply re-installing the belt and doing the runs would have skewed it as the alternator ran at a higher load recharging things).
• electrical loads, all runs: cruise control, parking lights
• for half of the last A runs: same, plus headlights on (ran out of daylight)

So! That's about double the effect I was guesstimating. I'm expecting a run on deep cycle batteries now...

I wonder if the effect will be different for larger engines, since the alternator is a proportionately smaller part of engine output at a given speed. Discuss. :)