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Old 12-09-2004, 08:45 PM   #1
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Default Alternator Shut Off Switch...worth it? Negative Effects?

Well, towards the end of the school year last year, in my automotive technology class, we were discussing alternators and voltage regulators, etc... Well, my friend and I were thinking that you could put a switch on the power to the voltage regulator and turn off the alternator for a few extra horsepower. We weren't sure how well it worked, so my friend went home and bought a switch and some wire.

The test: 1993 3.1L Chevy Lumina Sedan, 4T60 Auto.

He wired the switch in and put it under his dash. Beforehand, the car would chirp one tire off the line about 2-3 times if you brake-torqued it. After he put the switch on, we went out and tested it, from a brake torque with the alt off it smoked the **** out of the front tires, left like a 10ft. patch, which isn't a lot, but keep in mind the car would only chirp the tires before. Just to make sure it wasn't a fluke or something, he turned the switch back on and tried it, and sure enough he only got a few chirps. Turned it back off, and again, a ~10ft. patch. Got up to speed and the thing really pulled hard. Anyways, he left this switch on the car. When he turns it off, the volt gauge does drop to ~12 volts. He ran my friends '94 Buick Skylark 3100 (which is a lighter car, and the 3100 has an additional 25hp over the 3.1), and the Skylark was at the Luminas rear fender, yeah you heard right, the Lumina pulled on the Skylark. Did I mention the Lumina has 190k on it? The Skylark has 120k on it. With the switch on, the outcome is opposit, the Lumina at the Skylark'* rear door.

So anyways, basically we figured out we could shut off the alternator so there was no load on the engine (obviously temporarily, when you want the power, when you let off or don't need the extra power you turn the switch back on for normal use) for increased power. Well, I can't see any way that this would be bad on any of the parts other than the battery if it is run with no alternator for long periods of time. But, I'm wondering what do you guys think. I'm sure someone has heard of this before. I had never heard of it before, but since my friend and I thought it up so easily, there has to have been other people that have thought it up in the past.

But anyways, for the price of the mod, >$5 it is good "bang for the buck." But do you see any downsides to doing this? It would be nice to do for a track only thing or something like that. But does it seem like its a worthwhile mod?

Shawn
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Old 12-09-2004, 08:50 PM   #2
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Sounds good to me but Im sure you'll get some upsetting responses.
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Old 12-09-2004, 09:10 PM   #3
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i donno... mine is ready to go and causes a rough idle because of it. Every time I turn the car off the alternator clunks. I'd say keep it on always. Maybe during cruising have it off but at idle you want it on.
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Old 12-09-2004, 09:47 PM   #4
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with all my *cough.... lighting..... cough* I would need to run the alt all the time. But If i was to run the car at the track or a quick race on the street. that would be an awesome mod to do
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Old 12-09-2004, 09:49 PM   #5
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hey Shawn you need to try this on the GP and get us some track times with the Alt on and off

maybe someone here can also do this tha has there car at the track and convert this mod in to tenths of a second
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Old 12-09-2004, 11:00 PM   #6
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Well its not always gonna be the same gain because of accessories running and all that, but I will probably be dong this to my STE in the near future. If I do bring my STE back to the track next year, I will make sure to do a few runs with it on and a few runs with it off. But, honestly, if you turn it off for like 15 seconds and turn it back on, even if you have a big system, and neons and all that stuff, you still would be fine. I'm not talking about having the thing off most the time, just like to run someone from a stoplight or at the track. Even at the track you can have it running most of the time, just flip it off when you pull up to the tree, and turn it off at the end of your run. That way its off for a minute or less, then you can let it charge for a minute or two afterwards (or longer if you want to let the car run). Seeing that I already have the wire, and all I need is to buy the $3 switch, I'll be doing the mod on the STE i just don't know when. I'm just wondering if there are any negative effects that could result, although I really can't think of any.

Quote:
i donno... mine is ready to go and causes a rough idle because of it. Every time I turn the car off the alternator clunks. I'd say keep it on always. Maybe during cruising have it off but at idle you want it on.
I'm not talking about turning it off al the time. I mean, just for like less than a minute. If you need to merge on to the freeway or into traffic, or you want to run someone from a stoplight, or at the dragstrip, when you need all the power you can get. Not when you're crusing, thats when you want it on. I can't imagine it would make a noticable gas mileage difference, espeically since you really couldn't have it off long, so I don't see the point of it other than WOT runs. I was thinking maybe have a switch under the gas so it turns off automatically at WOT and then back on when you let up.

Shawn
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Old 12-09-2004, 11:09 PM   #7
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Interesting. Might be worth the low cost, and automating the system would be a good idea. It would really suck to leave it off... Maybe a 5A or so "Momentary ON" switch under the pedal controlling a... Wait. The alt is like 100A, How ya switching it? 30A okay? Just a little 30A relay to do the switching....that would be sweet.
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Old 12-09-2004, 11:12 PM   #8
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If the switch would be under the pedal, and when you gave WOT the alt would turn off, then I guess I wouldn't have much alternator use, huh? I think that would be a good idea, but have an arming switch before that. This way it will only turn on with WOT, when YOU want it to, not all the time. That sounds better to me.


-justin
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Old 12-09-2004, 11:15 PM   #9
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Quote:
Originally Posted by Damemorder
Interesting. Might be worth the low cost, and automating the system would be a good idea. It would really suck to leave it off... Maybe a 5A or so "Momentary ON" switch under the pedal controlling a... Wait. The alt is like 100A, How ya switching it? 30A okay? Just a little 30A relay to do the switching....that would be sweet.
You're switching the voltage regulator, or the input power to it, not the output. So, your basically telling the alternator the battery is fully charged. The line you shut off is like 5-10A. Its the little wire, not the big one. Its the plug that clips in, not that is held on with a nut. I will take pics to show you what i mean, since I can't think of the actual terms off the top of my head.

However, you could switch the output and use a relay if you wanted, it would get a little more pricey that way, and is more work, but it would work. Actually, the alternator would still be getting a signal from the voltage regulator to charge the batter, so it might not work, it might just not be charging anything, I could be wrong though.

Shawn
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Old 12-09-2004, 11:17 PM   #10
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Quote:
Originally Posted by opensourceguy
If the switch would be under the pedal, and when you gave WOT the alt would turn off, then I guess I wouldn't have much alternator use, huh? I think that would be a good idea, but have an arming switch before that. This way it will only turn on with WOT, when YOU want it to, not all the time. That sounds better to me.


-justin
That is an excellent idea. Its not always that you want that extra power. An arming swtich would definatley be good for a setup like that, espeically for people like us with a lead foot.

Shawn
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