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Old 08-19-2008, 07:52 PM   #21 (permalink)
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The ignition key on a car turns off the electrical power, to stop a magneto it must be grounded. The Magneto is a self-contained system, a DC generator complete with permanent magnets and a distributor. A typical 30's, 40's, 50's INDY 500 car had no battery or electrical system except for the magneto. see http://www.taylorvertex.com/Vertex/p...structions.pdf

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Old 08-19-2008, 07:54 PM   #22 (permalink)
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cobraBall...

My Amp Meter is not an in-dash pass through. I have a 100 amp shunt and a panel meter to monitor. The Shunt is connected between the alternator and 70amp fuse input to the fuse box.

...Do a search, find the other thread where we were talking about this.
My method, giving up some efficiencies, is to use a deep cycle battery, to an inverter, to a charger to the house battery, and kill the alternator field/ or use a Normally Closed selenoid or relay to disconnect the charge line to the alternator.

The reason for this inverter/charger setup --- mantains proper 13.8 voltage to the car. And 2..... I have yet to find a DC-DC converter that can do 12v-13.8 40amps (not for less than $50 anyway)


.... if you will notice, not many here have large stereos.. THEY WEIGH TOO MUCH!

Not all of us are 16 years old.



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Old 08-19-2008, 08:31 PM   #23 (permalink)
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Quote:
Originally Posted by dcb View Post
but, dude, it is trivial, I mean trivial, to set up a magneto to turn off with the ignition key! Don't play the safety card on that!
a mag on a street car makes your car easy to steal... VERY DANGEROUS <reaching a long, long way LOL>

When I was a teen, there were a few street hot-rods running around sparked by a magneto, usually supercharged V8's. I knew one guy who ran a mag, who installed a quick release steering wheel, so he could keep his ride safe from theives.

On a more serious note, can we agree that on balance, the horsepower required to generate that spark is equal?

I mean to say that weather you charge the battery with an alternator and draw energy from it to spark the spark plugs, or generate electricity with a magneto to spark, they both take power, no free electricity.

If so, trading one power draw for a different one doesn't help. Again, good discussion point, though.
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Old 08-19-2008, 09:44 PM   #24 (permalink)
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A magneto might have been a tiny bit more efficient. Especially if you could get rid of the alternator and battery altogether, like a dragster. But even the fuel delivery on most of our cars needs electricity to work, so...
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Old 08-20-2008, 12:20 PM   #25 (permalink)
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is there any benifit to be had from P&G'ing the alternator? seems to me that when you switch it back on it will take the same energy charging as if you had left it on all along?

the only benifit of the alternator cut out switch is if you install a deep cycle battery and run the ignition off that right and charge at home? thats when you get the +10% FE right?
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Old 08-20-2008, 12:31 PM   #26 (permalink)
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There is no advantage to P&Ging an alternator unless you pulse it while braking like BMWs new system (I forget what they called it). If you are already driving for FE, you use the brakes so little already that I don't think this would provide enough charging time. So, you'd still have to have a way to turn it on for normal charging should voltage drop too low.
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Old 08-20-2008, 12:41 PM   #27 (permalink)
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Noel.

"DC-DC converter"

Convert DC what to DC what?

CB
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Old 08-20-2008, 04:20 PM   #28 (permalink)
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Can I answer my own question?

Quote:
Originally Posted by whitevette View Post
For those of us out here who are "electrically challenged" ( I know not to stick anything into a wall socket ... except a plug) , would you elaborate a bit on the specifics of this "load switch"? I am in fear of burning up a very expensive alternator. It sounds great to me! The battery gets lots of charge time, anyhow....My Scangauge shows me great numbers of (downhill) "charge times" but who needs alternator drag while pulling a steep grade? -whitevette
Last night, I was talking to a EE friend of mine...and the subject of turning off the field of the alternator ( to reduce the charging drag ) came up. His rather quick response was "Don't!" Then he remarked "How many HP in, say, 1300 watts?" I said "Less than 2." He then said " And you're gonna save how many MPG? You can't even measure this." He then said "You'll be sorry, later, when your charging system electrics go sour." He was referring to the pulses in the system when this "switch" was cycled ( off, on, off, on again...). Poor alternator! Poor relays, poor diodes, etc.
So ... I guess I'll leave well enough alone.
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Old 08-20-2008, 04:23 PM   #29 (permalink)
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What to watt?

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Originally Posted by CobraBall View Post
Noel.

"DC-DC converter"

Convert DC what to DC what?

CB
No, DC what to watts.
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Old 08-20-2008, 04:29 PM   #30 (permalink)
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Uhh... your diodes are CONSTANTLY cycled while the alternator is putting out juice. I don't think your friend thinking correctly if he doesn't think a couple horsepower wouldn't make a noticeable impact on mpg. Given that a beetle takes 12 hp to maintain 55mph, 2 hp is HUGE!!!

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