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

[oil pan 4]

I recommend unbelting it and cutting off its power so you can still use it when you need it. Such as cold wet winter days and extended trips.

[teoman]

On modern cars with the tight engine compartments, that would be quite a pain. But on older cars that is an excellent option.

[Stubby79]

Originally Posted by teoman

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

Or the use of a voltage booster circuit.

[teoman]

That is what i intended to describe. But you need the 2 batteries (capacitive elements) so you do not need a very high amp booster circuit.

[RedDevil]

I tested a small DC voltage buck converter to find that it draws 15 to 18 mA on both the output side with no input connected and vice versa. So that unit in a '12V' twin pack would continuously dissipate about 400 mW (assuming it draws on both ends).
On higher currents it was up to 95% effective though.

A capacitor bank/small battery split by a DC-DC converter is possible and clever but the converter is yet another parasitic load.

[teoman]

ThAnk you for sharing that.

[oldtamiyaphile]

Originally Posted by 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.

When PB batteries approach full charge, they become very inefficient. At their worst, the charge/discharge efficiency can fall to 50%. Newer cars may run lower voltages because of this. My Fiat runs at 12.8v, the Renault holds closer to 14v more of the time, but often you'll see it sitting at around 12.8 as well.

[California98Civic]

I estimated about 3mpg from putting my alternator on an on/off switch. Over time, I have learned to make the switch into a kind of ultralight regen braking. On long hills or on almost any stop light or stop sign I can see well in advance, I shift into gear for DFCO and turn the alternator on to charge. The on/off switch is the best. I can do my daily trips without the alternator. Whenever I am in a longer drive, or night driving, I can run the alt more.

[bandit86]

Originally Posted by oldtamiyaphile

When PB batteries approach full charge, they become very inefficient. At their worst, the charge/discharge efficiency can fall to 50%. Newer cars may run lower voltages because of this. My Fiat runs at 12.8v, the Renault holds closer to 14v more of the time, but often you'll see it sitting at around 12.8 as well.

I got 13 years out of my OEM dodge ram battery at 14.5'volts. My friend got 10 years out of his Interstate at whatever an ML320 charges at.

Battery inefficiency will be offset by electronics inefficiency at lower voltage. I had 24 volt machines that at 23.9 volts got right stupid. If your mileage varies, go with wha works for you. It's is just a good advice. Fuel pumps won't like lower voltage either.

[oldtamiyaphile]

Originally Posted by bandit86

I got 13 years out of my OEM dodge ram battery at 14.5'volts. My friend got 10 years out of his Interstate at whatever an ML320 charges at.

Battery inefficiency will be offset by electronics inefficiency at lower voltage. I had 24 volt machines that at 23.9 volts got right stupid. If your mileage varies, go with wha works for you. It's is just a good advice. Fuel pumps won't like lower voltage either.

It's not a case of what works for you. It's proven fact.

Old cars ran plain lead acid batteries at 14+ volts. Reason for the higher voltages was to improve battery life at the expense of fuel economy.

New cars use AGM batteries and run at under 13 volts, battery life is shorter but fuel consumption improves.

It doesn't make a lot of sense to prolong the life of a $100 battery to ten years ($10 a year), if it costs you significantly more than $10 a year in fuel to do so, even if part of the rationale is to make the car look good on the official cycle, and not to save the owner any actual money (AGM batteries are expensive).

Car electronics are designed to run as low as 10v, ie while cranking in cold weather. Lab equipment or whatever might be unstable at lower voltages, but auto systems have to be tolerant of a much less stable voltage supply.

You can buy 16v automotive batteries intended for race applications and that would be the best of both worlds, assuming of course you didn't damage some expensive components in the process.