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Old 08-23-2008, 12:32 AM   #1 (permalink)
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Deceleration Alternator

I was thinking tonight about making my alternator kill, into a deceleration alternator. Would give me atleast a couple extra miles of run time that way.

I am using a Potter-Brumfield 70a relay to disconnect the output, and a Bosch 30a relay to kill the field wire. I was thinking of putting in a switch like this.
Nitrous Oxide Systems (NOS) 15640NOS - NOS Micro Throttle Switches - summitracing.com
on the throttle to be activated at idle position, but also connected to the clutch pedal through a set of relays as well, Basically only allowing it to run alternator when clutch is engaged and throttle is at idle. This way avoiding pretty much all conditions except for neutral idling, and deceleration.

I figure if the car is idling it might as well be doing something, and DFCO sounds like a good time to charge the battery to me.

Suggestions? If it sounds feasible I could possible get some diagrams started and a How-to. I have it stuck in my brain and need to get it out.

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Old 08-23-2008, 03:10 AM   #2 (permalink)
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Sounds like a good idea but if your clutch is engaged you won't be in dfco, your car will just be idling like in neutral. DFCO occurs when you coast in gear above a certain rpm range- in my car it kicks out of dfco at about 900 rpm.
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Old 08-23-2008, 09:49 AM   #3 (permalink)
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Clutch engaged while driving, dis-engaged while coasting, shifting.
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Old 08-24-2008, 11:15 AM   #4 (permalink)
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"Smart" alternator control is a valid approach - it's been used (and is being used) on many models. BMW comes to mind, with its "efficient dynamics" program.
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Old 10-12-2009, 08:30 AM   #5 (permalink)
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Originally Posted by Frank Lee View Post
Frank gave that link with relation to BMW's electric water pump, but I also noticed that BMW is going semi-alternatorless, i.e. using the alt only when braking. I'm wondering whether that is enough? Imagine cruising for hours, stereo blasting, it's hot plus A/C = high engine temps, so (electric!) water pump is spinning fast. Plus the engine is an I6 or V10, so the ignition is also wanting... All of that is using up a lot of juice, and you're not braking to replenish it. Even the beefed up battery will be weak after a few hours. Maybe there is an emergency mode that turns the alt on when the battery starts feeling bad? I doubt Beemers would have to be plugged in for the night.
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Old 10-12-2009, 09:15 AM   #6 (permalink)
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I am sure they thought of that eventuality and put in a low volt threshold for the alt cut in.

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Old 10-12-2009, 12:51 PM   #7 (permalink)
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OP -

Do you ever do any engine braking? You might try to figure in a circuit that allows the alternator to charge during engine braking as well.
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Old 10-30-2009, 05:34 PM   #8 (permalink)
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I posted something about a system I developed to do this that works on injector duty cycle (when in deceleration its at 0% so switches the alternator on at this level only) and also a battery voltage switch that prevents the battery becoming too discharged.

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Old 10-30-2009, 06:17 PM   #9 (permalink)
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Woudn't just one relay on the field circuit accomplish the same thing without the heavy duty relay which the output circuit would require? A simple circuit to disable this when the headlights are on would probably be enough to eliminate the dead battery worry.
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Old 10-30-2009, 10:53 PM   #10 (permalink)
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I found on my 4x4 that when crawling down a steep hill, that turning the AC on helps keep my speed under control. the ac is just enough to hold me back...
Makes sense it would work for the alternator...


If it has a motor its worth playing with.......
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