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Old 08-07-2007, 05:03 PM   #1
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Regenerative Charging

What's anybody think of hooking a switch to the gas pedal that only switches on when the gas pedal is all the way up? This would be hooked to the field on the alternator so that unless you are slowing down or at idle there would be no work being done by the alternator. I guess you would need a deep cycle battery.

My calculations go like this with a 60 amp alternator 12V*60A/60Min=12WH per minute deceleration so if the car draws 100W you would have to decelerate 8Min/Hr
This would probably get you around all day around town. You would want to put a bypass switch for driving at night so it would work normally though. If you went with a RV type alternator you could double the amount of charge per minute on deceleration for about 10 Lbs extra. Maybe glue a thin film kind of solar panel to the roof.
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Old 08-07-2007, 11:01 PM   #2
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FritzR -

I have a 90 amp alternator. Would that mean I need to decelerate 12 min/Hr?

Sounds like a good city car mod.

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Old 08-08-2007, 06:09 AM   #3
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What's anybody think of hooking a switch to the gas pedal that only switches on when the gas pedal is all the way up? This would be hooked to the field on the alternator so that unless you are slowing down or at idle there would be no work being done by the alternator.
For one thing, that would tend to increase your idle level, as you don't really want the alternator to come on when the car is in neutral (or clutch in), as it will just increase your idle speed (wasting fuel).

I think a better idea (and one I've considered, but haven't yet acted on) is a relay that comes on if the brake lights are on AND your car is "in gear" (not clutch in, and not in Neutral, "in gear"). The way I figure it, you really are "SLOWING DOWN" if you pressing on the brakes (however lightly) and the car is "in gear".

And if you really want to cause the "alternator braking", without using much in the way of brake pads, it's pretty simple (with a setup like this) to just press the brake pedal just hard enough to trip the brake light switch (but without actually triggering the brakes themselves). So if you had a relay like this, triggering the "alternator braking" should be as simple as just pressing the brake pedal just a little (not enough to turn the brakes on, but hard enough to turn the brake lights, and therefor also the alternator relay on).

BTW: If you did do this, be sure to also put a switch on the dash, so that you can "revert to stock" behavior if/when needed, just by "flipping a switch"...
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Old 08-08-2007, 08:30 AM   #4
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BMW has something like this.
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BMW found that the on-demand generation of electrical energy helps to reduce fuel consumption in the EU homologation test by approximately 4%.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 08-08-2007, 08:54 AM   #5
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I think this makes good sense. Doesn't the vx use some type of alt control like this? I am usually coasting to stop with the engine off so that wouldn't utilize the system BMW has well.

I also like the idea of the thermoelectric waste heat recovery BMW is playing with.
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Old 08-08-2007, 09:26 AM   #6
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... Maybe glue a thin film kind of solar panel to the roof.
I think the rear trunk (for sedans that actually have a flat trunk) would prob be a better location. A ROOF install would mean more aero drag unless it was made to blend in seemlessly. Even then you now have a roof that 1" taller which STILL create more drag. This is where the trunk makes sense. Its where you prob have turbulence anyway. Something on the trunk would not get in the way of aero and might even hekp with aero by reducing the area of turbulence sedans are hit with.
This is my HYPOTHESIS. I could be WAY off on this. What do you guys think??

Oh and I just realized that Fritz said "thin film". I didnt see that and I just assumed regular 1" thick solar panel thats widely available. (BTW, cant wait till prices go down on those)
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Old 08-08-2007, 11:10 AM   #7
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For one thing, that would tend to increase your idle level, as you don't really want the alternator to come on when the car is in neutral (or clutch in), as it will just increase your idle speed (wasting fuel).
This probably depends on the car. The last car that I had with a bad alternator was an 87 corrolla which had a carb. It idled higher when the alternator was not working because of less load. If you went and smacked it with a wrench it would start working and the idle would drop. It got about 5% better mileage when the alternator was not working. Of course I got it fixed and the benefit went away.

With a fuel injected car this might be different. It might behave like when you turn the A/C on and increase the idle. I'll try pulling my alternator cable later and see what happens

"I have a 90 amp alternator. Would that mean I need to decelerate 12 min/Hr?"

That would depend on how much your car draws. If it was 100W then only 5 min/hr
with a 90 amp alternator. I think a lot of cars draw less than this. In my old corrolla I drove for 6 months with a weekly drive of 200 miles to LA on Sunday, 5 miles a day to and from work, 200 miles back to San Luis Obispo, then I'd pull the battery and charge it. This was using the radio and everything else except never the headlghts at . That car with a 60 amp alternator would only need to charge 4 min/hr at most
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Old 08-08-2007, 12:02 PM   #8
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Newb question here, but would a smaller amp on an alternator give better FE than a larger amp? Umm, provided your not drawing more current than you can produce.
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Old 08-08-2007, 12:31 PM   #9
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Newb question here, but would a smaller amp on an alternator give better FE than a larger amp? Umm, provided your not drawing more current than you can produce.
That's probably true. If you are doing any night driving though the alternator is probably sized by design to be able to run the headlights at idle and a smaller alternator than the one specified might make it less efficient. I would only think a larger alternator might be better for the mod here in certain cases.

Thanks for everyone's input. I think I'll play around with this once my CRX is done, the engine is broken in, and I have some benchmarks to compare it to. I'll post my results in a couple of months
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Old 08-08-2007, 01:30 PM   #10
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My Insight has regenerative braking, 'cause it's a hybrid. About a year after I got it , I rigged a parallel switch to the one on the brake pedal. Now when I regen, it's without hydraulic drag.
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