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Old 01-24-2009, 02:52 PM   #31 (permalink)
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Pwm?

I'm wondering what if we use a PWM at the alternator rotor coil...

Hmmmm... Any ideas??

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Old 01-26-2009, 10:20 PM   #32 (permalink)
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Quote:
Originally Posted by Katmandu View Post
Come on now. Get a grip. You guys are "SPLITTING HAIRS" worrying about alternator drag and it's effects on MPG.

These alternators are so small to begin with that they do enough just keeping your battery charged.

If you're willing to risk a DEAD battery (out in the middle of nowhere) for the sake of increasing MPGs. Knock yourself out.

Medication for OCD is cheaper than AAA and a new battery. Just think of all the time/energy/$$ you'll spend just to save (1) MPG.
"Knock yourself out.."

You might find it interesting that one of the european manufacturers, BMW or MB, I don't remember which, is installing a slightly larger battery and only allowing the alternator to go into charge mode during coastdown or braking periods. Except if the battery charge begins to get "too" low.
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Old 01-26-2009, 10:25 PM   #33 (permalink)
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Originally Posted by afdhalatifftan View Post
I'm wondering what if we use a PWM at the alternator rotor coil...

Hmmmm... Any ideas??
Modern day solid state alternator voltage regulators are already of the PWM "switching" type, just as were their forebears, the old mechanical relay type regulators.

Apply full battery voltage to the rotor winding, wait the few milliseconds for the battery voltage to rise to setpoint, open the circuit, wait for the voltage to decay, repeat as needed.
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Old 01-26-2009, 10:57 PM   #34 (permalink)
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I much like the idea of a switching alternator... although I believe it should be accompanied by a mechanical continuously variable pulley as well, which would be designed to keep it at its most efficient RPM, regardless of engine RPM.

Also, it should work when the engine is at idle speed, since during idle, you're burning fuel for nothing anyway. (Unless you're coasting with the engine on, but the engine still isn't DOING anything for the fuel it's consuming.)

For an electronic controller, "Idle speed" is defined as "particular idle speed while at 0 load and 0 TPS reading." (For automatic vehicles, change "0 load" to "limited braking load" due to it being in gear.)
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Last edited by Christ; 01-26-2009 at 11:04 PM..
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Old 01-26-2009, 11:42 PM   #35 (permalink)
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I have a 75 Amp alternator. If I currently EOC 30% of the time, with lights, ecm, and radio on, draw must be like 40A or less since I've never had a charging issue. I'm curious as to how much exactly it draws, though. Time to find an ammeter that can handle 60+Amps, or try a few fusible links.
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Old 01-27-2009, 02:29 AM   #36 (permalink)
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Something to note.... the AD244 alternator GM uses in several fullsize rigs puts out around 200A at idle, and slopes off to 145A around 1900rpm. I have no idea why it does that, but I plan to swap to it on my truck to support all the offroad aux lighting.

Anybody understand the principles better than I?
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Old 01-27-2009, 12:32 PM   #37 (permalink)
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That's odd... normally, alternators increase their amperage output while accelerating.

I figured out that I have over-charge protection on my Honda's new alternator, simply b/c when I rev it to 6500RPM, the alternator light comes on. It stops charging so that it doesn't overdo itself. I think that's LOL-able.
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Old 01-29-2009, 02:37 PM   #38 (permalink)
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Quote:
Originally Posted by wwest40 View Post
Modern day solid state alternator voltage regulators are already of the PWM "switching" type, just as were their forebears, the old mechanical relay type regulators.

Apply full battery voltage to the rotor winding, wait the few milliseconds for the battery voltage to rise to setpoint, open the circuit, wait for the voltage to decay, repeat as needed.


No no no, not the voltage regulator...

I mean the rotor coil. The one that spinning in the alternator...

Any thoughts??
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Old 06-07-2009, 01:49 AM   #39 (permalink)
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Quote:
Originally Posted by sdpflag View Post
what if you put an air conditioning compressor clutch on the alternator and hooked that up to an openguage or something that tracks instant MPG's and had it engage only when the MPG were above a certain amount. this would disengage the clutch whenever we accelerate or drive up hills or such when any extra load on the engine hurts us the most.
I was wondering about this myself.
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Old 06-07-2009, 10:57 AM   #40 (permalink)
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Quote:
Originally Posted by 1GCRXHF View Post
The "friction" in the alternator actually charging is the magnetic resistance the active circuit is supplying. The resistance is the current voltage the battery sitting at in the circuit. Generators (like your alternator) and electric motors are the same thing, the difference is the polarity of the circuit. If you hook up your alternator straight to your battery it will run; The engine has to overcome this force in order for the alternator to charge the battery, because it actually has to spin the alternator the OTHER way, in order put the battery in a charging state. I think the only way you could get less resistance from the alternator running would be to go with a low amperage unit. Adding a larger output alternator would be the exact same as installing a larger electric motor for your engine to fight. If you did your wiring right and went minimalist on your electrical goodies, you could easily get away doing this. Take a good look at anything that uses electricity in your car, and remember that every single milliwatt you is energy derived from your gasoline. Use less power, use less gasoline.
There seems to be a flaw to this logic. An alternator is NOT a generator. It has no permanent magnets. It is very similar to an induction motor, such as what you would find on a vacuum cleaner. But when there is no power going to the field coil, there is no magnetic resistance, only frictional resistance. And the alternator only draws its max output when the field coil is strengthened by the regulator.

Instead of alternator mods, worry more about reducing the electric load, as he pointed out. An alternator is designed by manufaturers to be very efficient, but the electric loads are not entirely efficient.

If you want to reduce the alternator load, put in a bunch of solar panels on the roof and dashboard.

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Quote:
Originally Posted by jamesqf View Post
I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.

Last edited by ShadeTreeMech; 06-07-2009 at 11:08 AM..
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