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

[Magician]

I drive about 12 miles a day round trip in my civic, so I'm seriously considering the alt delete using flexible solar panel attached to the roof... 1 deep cycle battery... or at minimum the on/off switch to a minimum drop it to the lower charge. First I'll be going to LED head lights and marker light, tail lights etc...

[Ni87]

Sorry I'm coming into this thread pretty late. But wouldn't you save from getting a smaller alternator? Like for instance my civic has an 80 amp alternator. And I also have an old 87 pickup (Nissan nothin major) that has a 40 amp alternator. And between the two nothing's really different. Neither of them have ac and it's very basic as far as options go. So wouldn't a smaller 40 amp alternator do the trick by Increasing mpgs and maintaining drivability?

[Formula413]

Originally Posted by Ni87

Sorry I'm coming into this thread pretty late. But wouldn't you save from getting a smaller alternator? Like for instance my civic has an 80 amp alternator. And I also have an old 87 pickup (Nissan nothin major) that has a 40 amp alternator. And between the two nothing's really different. Neither of them have ac and it's very basic as far as options go. So wouldn't a smaller 40 amp alternator do the trick by Increasing mpgs and maintaining drivability?

I believe you would see little if any improvement. The load from the alternator on the engine is mainly a function of the electrical load on the alternator, not its capacity.

[redpoint5]

The alternator delete or switch and deep cycle battery is a good idea. Replacing lights with LEDs will allow a smaller battery, or longer run times.

Originally Posted by Ni87

wouldn't a smaller 40 amp alternator do the trick by Increasing mpgs and maintaining drivability?

No, alternators are sized according the vehicles electrical needs. While a 40 amp alternator might be sufficient most of the time, it is likely to be insufficient in certain instances when the lights are on high, the windshield wipers are going, the blower motor is blowing, etc. The extra stress is likely to cause premature failure, and any MPG gains would be minuscule. An alternator attempts to deliver the electrical energy that is being consumed regardless of size, and it robs the engine of the power necessary to deliver that energy.

BTW, 1 horsepower is 746 watts. Since there are losses converting mechanical energy from the engine to electrical in the alternator, more power is sapped from the engine than is generated by the alternator.

[alexander.foti]

Has anybody any thoughts on "intelligent" alternator control? Modern cars control the exciter current through various feedbacks (EG Mercedes). They charge on the overrun, when slowing down in gear and under various situations, but don't charge the battery back up to full straight away.

The same could be achieved with a voltage switch/relay on the exiter wire to the alterntaor. EG turn on when voltage is below 11.9 volts (emergency) and turn off when above 13.9 volts. You could also wire the brake lights into the exiter wire so that the alternator charges at idle with the foot on the brakes.

Thoughts?

[Daox]

It sounds like you want to check out this thread.

http://ecomodder.com/forum/showthrea...xer-34919.html

[ASV]

it seems counterintuitive but the large alternator is more efficient than the small alternator. The closer to max capacity an alternator is the more it heats up.
Hot copper is less conductive than cold
if you want your alternator to be more efficient give it some nice cold air
and don't over size the pulley
at higher RPM it easier to produce the necessary power and is better able to cool itself

the only problem I can think of at the moment with the higher RPM is air resistance in the cooling fan

[Stubby79]

Originally Posted by ASV

it seems counterintuitive but the large alternator is more efficient than the small alternator. The closer to max capacity an alternator is the more it heats up.
Hot copper is less conductive than cold
if you want your alternator to be more efficient give it some nice cold air
and don't over size the pulley
at higher RPM it easier to produce the necessary power and is better able to cool itself

the only problem I can think of at the moment with the higher RPM is air resistance in the cooling fan

I would think having the "right" size alternator is the more effective way to go. You're probably right that you don't want to stress it to it's limit, but at the same time, I would expect efficiency to go to heck is you were only using a fraction of it's potential output. If it's anything like an electric motor (and it is), it would be most efficient at it's peak sustainable output. Any more and efficiency starts to drop off. Notably less and it very quickly drops off.

There are things other than the size of the wire inside that affect efficiency. This is A/C we're talking about...eddy currents and switching in the rectifier and whatnot.

Just a random alternator efficiency curve, showing that more RPM is less efficient. (Of course, it only shows full output, and partial loading will be less efficient)



Reminds me of the efficiency of an ICE. Or perhaps a TDI.

[Crashy]

I have managed to read the whole thread and would like to clear up some misconceptions. Then I will provide solutions to some of the issues raised.

1. Lead acid battery has a "safe dod of 50%"
False. The number of amp hours you can get from a lead battery is fixed. A cheap one will give around 5000. Average 10000. Really good one 20000. Let's use average 10000 as an example with 100Ah capacity. You can discharge 10ah 1000x, or 20ah 500x, or 50ah 200x, or 100ah 100x. In every instance the number of amp hours is 10,000. There is no magic line in the sand where one side is safe and the other side is risky. People seem to think that a 10% discharge and a 50% discharge will have the same effect on lifespan, but a 50% discharge is equal to 5 discharges of 10%

2. Alternator power is 5x more expensive than grid power
False. It is 20x more expensive depending on where you live and the car you drive

3. A smaller alternator is more efficient
False. Your loads are the same. If you undersize your alternator it will work hard, overheat and become very inefficient. If anything, you should oversize it for better fuel efficiency because it will run cooler

4. Deep cycle lead acid is a good suitable battery to use for this mod
False. It is terrible. The charge efficiency of a lead acid battery is 45% between 80 and 100% state of charge. Below 80% soc it is 90% efficient so if you must use lead batteries the ideal range is 60-80% but this may result in sulphation. The added weight of the batteries and poor input / output efficiency will cancel out any fuel savings. Unless they are grid charged

5. Supercapacitors are a good addition
False. They have high self discharge and adding losses to a system cannot possibly improve efficiency

6. Alternators don't waste much horsepower when unplugged
False. Bearing, belt and fan friction are still present and are significant. Self excitement of the rotor is still occurring unless you disconnect the main and rotor wires. Try spinning a removed alternator by hand for 2 minutes. Your arm will ache

[Magician]

I have to add to this thread. I installed 1 panel and then a month later a 2nd.
I have been solar charging 9 months of the year and the other 3 I simply put the belt back on and turn my added toggle switches to the wiring back on for those 3 months. I could charge with a car charger, but it's an added task that I don't feel like doing and only charge this way when I have rainy days.
I have a 13 watt and a 18 watt solar panel in parallel with a controller. It charges the battery much faster than what you'd think. Also, my Civic VX has very little draw on the battery when running. Especially since I EOC 1/3 of my driving distance. I can drive an hour before the battery drops to a level that would even remotely concern me. Most of my trips are 10-20 miles round trip, so the solar option works quite effectively. I don't know the exact fuel savings, but when I take the alternator belt off, I instantly see my tank fuel economy start rising. If I had to take a stab at it, I'd say easily 5-10% savings.