Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

[oldtamiyaphile]

Most cars and all diesels sold in Europe today already have smart alternators.

They disengage when you accelerate, ramp up when you coast, and some ramp up further when you brake.

As such, it's not really necessary to do anything other than charge the battery when parked. On a charged battery my Fiat will go over 100 miles before the alternator starts to cut back in.

If there was any real gain to adding a clutch to the alternator I have to believe that the OEM's would already be doing it as it's simple and proven off the shelf tech that's been on A/C compressors for decades.

[teoman]

How did you measure the alternator cutback?

I have the same "feeling". However, the car manufactureres have been known to be very stingy with stuff like this. A while back the topted not to invest 18 usd in parts for an alternator that would be more efficient. The game may have changed since then.

[oil pan 4]

I have seen the oem's claim that alternator cut out increases fuel economy by up to 5%.
When someone just cuts power to the alternator and charges with external power the improvement is more like 3% if you are lucky but usually it's not even noticeable. Because the alternator is still using engine power to spin.

[bandit86]

Originally Posted by oldtamiyaphile

Most cars and all diesels sold in Europe today already have smart alternators.

They disengage when you accelerate, ramp up when you coast, and some ramp up further when you brake.

As such, it's not really necessary to do anything other than charge the battery when parked. On a charged battery my Fiat will go over 100 miles before the alternator starts to cut back in.

If there was any real gain to adding a clutch to the alternator I have to believe that the OEM's would already be doing it as it's simple and proven off the shelf tech that's been on A/C compressors for decades.

Most people don't Eco-mod and drive. They get in, crank the heat, the air, the lights and radio, and drive for a few minutes. The poor alternator can barely keep up on short drives. I Canada there is such a thing as daytime driving lights, meaning the headlights are always on. Always need to work the alternator a littlest why disengage it? Fuel pumps, computer, it all sucks some juice.

[teoman]

I found this while searching for the power consumption of a modern vehicle.
http://www.autohausaz.com/volkswagen...l-systems.html

It says a modern VW but they have failed to indicate how modern.

It says that the ignition consumes 6A. I am assuming that is the car ecu and the injectors and other stuff just to make the engine run.

When everything is on full blast, it consumes 77A which would be difficult to manage with deep cycle batteries.

[bandit86]

It is on eliminating alternator tha you Eco guys start to loose me. Battery voltage is 12.5 or less. Running voltage is 14-14.5. Electronics work better on higher voltage. If you're that concerned about alternators, get a tiny little 30 amp alternator and put it on a large pulley. Spin it at half the speed. Or Install an under drive pulley, that will reduce your water pump losses too.

[MetroMPG]

Regardless of the lower operating voltage, it works.

I saw significant savings on my car (which probably has relatively low electric overhead vs. newer cars).

Of course the problem of repeatedly deep cycling the battery remains.

[oil pan 4]

Yes the main problem is deep cycling a battery that is not a deep cycle type battery.

[Stubby79]

PITA to get set up, but 4 LiFePO4 cells hold a steady voltage of around 13 volts...and will get you plenty of deep cycles.
Of course, at this time of year, you'll discover they don't much like cold temperatures...

[teoman]

If you have a fixed daily route, and have charging ability (i.e have a garage or close to a plug at work) then completely removing the alternator is a very good option. But then you have to trat your car as a electrical vehicle.

%10 improvement is really significant.

You have to measure how many W your car consumes and then calculate the size of your battery.

A 2 battery system (or capacitors + battery) can be used to keep the car at whatever voltage is needed.