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Topic: Alternator off at full throttle?

in Forum: C3 Electrical


Alternator off at full throttle?

Posted: 10/3/05 9:56am Message 1 of 7
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.

I know many guys replace the engine-friven fan with an electric one to gain some HP.  My assumption is that, if drag racing, they would flip a switch to disable alternator charging during the race.  If not and the alternator happened to be charging, using the theory that no new energy is created in the universe, it would seem that it would take just as much extra HP to spin the charging alternator (that has the additional demands of the fan)  as it would be to spin the mechanical fan.  

Anyone have actual facts on this?

If guys do wire in a "alternator disable" switch, can anyone provide directions? 

Also, ever heard of anyone installing such a switch so that the throttle pedal or linkage would activate the switch at near full throttle, but not at any other time?  Just curious more than anything...  




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Alternator off at full throttle?

Posted: 10/3/05 9:58am Message 2 of 7
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.
Oops, I forgot to ask - is it possible that our cars are ALREADY designed to disable charging at full throttle?  Just seems like a cheap way to gain a few HP...


Alternator off at full throttle?

Posted: 10/3/05 2:30pm Message 3 of 7
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Vette(s): 1982 COLLECTOR EDITION

I'll start the conversation on this one chesh, although I don't know the history of using this method for racing. Since the alternator works from opposing magnetic fields, I would imagine shutting down the alternator would reduce engine load, however the longer the alternator is shut down, the lower system voltage would drop, eventually causing a weaker spark. I guess in a short (drag) race  it wouldn't matter much. As far as installing a switch, you would just have to interrupt the field wire (I believe the #1 wire on the two terminal plug) with a switch. If you didn't want to do it manually I guess you could mount a switch near the throttle somewhere, that broke the circuit only near full throttle. If our cars are already designed to do this, I am not aware of it.




Alternator off at full throttle?

Posted: 10/3/05 6:54pm Message 4 of 7
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
It can, and has been done. It's only effective if you've just GOT to have that last litle bit of power! It does take a little hp to spin the alt. & charge the batt., but it's really not a big gain. It's not exactly a turbo!
If the batt. is fully charged, the alt. is not going to be doing much, anyway, as far as 1/4 mile stuff goes.
If you disconnect the voltage going to the alt., it will not charge. An alt. has to have voltage to work. You would put a switch in the large red wire on the alt. to turn it on & off. Not recommended for a street car.
We always did this on our drag-cars, and even the dragboat we used to race. Off at the start line, on on the return. Sometimes forgot to do either, or got it backwards!


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Alternator off at full throttle?

Posted: 10/3/05 8:34pm Message 5 of 7
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
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Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

When you do this, if you chose to do so, remember you will need to do more than just cut the ignition power to the alternator.  With ignition power cut, the alternator will continue to charge, once it started.  Even with no ign power from start up, at enough RPM and with residual magnatisim, the alt will start charging on it's own in many cases.

You must either change to a special regulator or disconnect battery power to the alt batt terminal.  This can apply to both the internal and external regulator cars.

Cutting the power to the batt term will always stop it from charging.  Do not use a standard switch to do this.  It will fry from the amperage.  Instead, connect a relay in the power lead to the batt/alt terminal.  Use the switch to control the relay.  You may be tempted to use a ford starter relay for this, but that relay is a momentary contact relay.  Continued use for longer periods can ruin the relay.  Use a relay such as the ones used for controling snow plow equipment.  They may look the same externally, but the insides are different.  The continous use relay won't overheat and destroy itself.

Of course, feed the relay control circuit through you switch to choose when it operates, but feed the switch from the ignition.  That way you can't forget and leave it on.  That would not harm the alt or charging system, but the relay draw would kill the battery while it sits parked.

But unless you are worried about a few, or less, hundrends of a second on a drag strip, it probably is not worth it.

kstyer38628.8615393518


Alternator off at full throttle?

Posted: 10/4/05 5:00am Message 6 of 7
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.
THanks forthe feedback guys.  It sounds like more effort than its worth, by a long shot.  What had me curious were the ads for underdrive pulleys and a recent article  saw referring to an alternator that (used 1/2 the HP of standard).


Alternator off at full throttle?

Posted: 10/4/05 6:32pm Message 7 of 7
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CUYAHOGA FALLS, OH - USA
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Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
Its probably not a 1/2 saving, but it does cut drag and free up HP.  The only problem is if the car is idling, it may not charge well if at all.  Above idle it will charge okay.  If you are going to use the cars in slow speed operation, traffic, parades etc, avoid them.  If you will  have the engine rpm up a bit, they are a nice choice.


in Forum: C3 Electrical


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