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| Bassfreak55 |
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Hmmm...
Just drove my car for the first time tonight, since i got my underdrive pullies fitted, to fill up petrol.. Noticed that the headlights dimmed a little on idle, but when i revved it, theyd brighten until the revs dropped, then the same thing.. And no, before anyone asks, i didnt have the music pumping or anything, lol.. Anyways, i also noticed that at idle, the voltage guage shows 12V, but jumps up to around 13.5 to 14V max when driving normally for a little.. This doesnt seem right to me... At all! If its not normal, can anyone tell me why its doing it? By the way, the car has a new extra heavy duty battery, installed 3 months ago. |
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| Daniel |
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Obviously its a trade off of the underdrives - if you dont want it to happen you will have to loose the pulleys i rekon.
Its possible you have a crook alt. or something, but if the problem is only present once the underdrives are fitted then i feel thats where it lies.
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| EDXR8 |
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That is normal, at idle the voltage will drop down to 12v (sometimes a bit lower), thats just what you will get with underdrives unfortunately. It won't be a problem unless you have headlights on, a loud stereo system and you idle it for ages. If you are worried you an upgrade the alternator wiring which does help charging rate but thats not absolutly needed.
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| ESP |
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Age: 54 Posts: 496 Joined: 11th Nov 2004 Ride: 06 Teritory,mod Capri,XE falcon Location: Coffs Harbour |
Underdrive pulleys are the prob.Most modern alternators will run at 13-13.5 volts at idle.Remove pulley or upgrade alternator.Sorry..............
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| Vic |
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Upgrade the alternator for a heavier duty one.
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| EDXR8 |
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I don't think you need to worry about upgrading the alternator or removing the pullies. When I had underdrives on my car, I had a similar problem with voltage but it never caused any problems with stalling or flat battery etc. at all.
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| Waggin |
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A bigger alternator wont help!
The fact is that the underdrives will cause the alternator to run alot slower at idle.. no matter how big ur damn alternator is, you'll find its out of its operating RPM to create any sort of charge. At idle, ur car is running entirely off your battery... which may vary from 11.5-12.5V... and once u get the rpm high enough for the alternator to kick in, it will push the voltage up to around 13.8-14.4. So of course the higher voltage will make the lights appear brighter, or dimmer under idle. If it bothers you, look at putting in a good battery. Im running an Optima Yellow Top. At idle with the underdrive pulleys, the sound system turned up, drawing around 150A (2000W+ RMS) my lights barely dim down. If you can put up with the diming, then you'll be fine. Just dont idle for 4 hours with your high beams on 
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| Bassfreak55 |
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Waggin wrote: A bigger alternator wont help!
The fact is that the underdrives will cause the alternator to run alot slower at idle.. no matter how big ur damn alternator is, you'll find its out of its operating RPM to create any sort of charge. At idle, ur car is running entirely off your battery... which may vary from 11.5-12.5V... and once u get the rpm high enough for the alternator to kick in, it will push the voltage up to around 13.8-14.4. So of course the higher voltage will make the lights appear brighter, or dimmer under idle. If it bothers you, look at putting in a good battery. Im running an Optima Yellow Top. At idle with the underdrive pulleys, the sound system turned up, drawing around 150A (2000W+ RMS) my lights barely dim down. If you can put up with the diming, then you'll be fine. Just dont idle for 4 hours with your high beams on Good stuff! I can eeeaasily put up with the dimming of the lights n stuff, lol, was just scared that it might eat my battery alive within a few mins! lol But yeh, if itll last a couple of hours during idle, then theres no prob there! Cheers guys! Ps. I dont regret putting the underdrives on ..whatsoever! Best mod for $$$, performace wise! Thanks Shane! 
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| AXR88U |
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Pretty obvious that your battery dont hold full charge very well, as when you are driving around there should be more than enough charging happening (especially during the day time) just that the battery wont hold it. Try a new battery. As for someone saying to get a heavy duty alternator, that defeats the purpose of an underdrive on the the alternator (although you would still have the advantage on the water pump).
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| Bassfreak55 |
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AXR88U wrote: Pretty obvious that your battery dont hold full charge very well, as when you are driving around there should be more than enough charging happening (especially during the day time) just that the battery wont hold it. Try a new battery. As for someone saying to get a heavy duty alternator, that defeats the purpose of an underdrive on the the alternator (although you would still have the advantage on the water pump).
Lol, i do have a new battery! Only a couple of months old.. Dont remember what brand, ill have to check, but i know its a pretty good one.. Also, im one of those people that drive around with their headlights on during the day, lol, is that a 'no no' now with underdrives? 
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| MrLandau |
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I checked a couple of cars I did and they all got full charge by 1600rpm. With an auto - this means so long as you are doing 60kms they are charging. With the manual you have more control of the revs (unlike the stall converted auto) and are more likely not to get full charge at low rpms in high gears. Check your own car with the multi meter and see what rpm gives you 14.6 V
Shane
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| Waggin |
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Bassfreak55 wrote: Also, im one of those people that drive around with their headlights on during the day, lol, is that a 'no no' now with underdrives?
I also drive with my headlights in the day time. Its fine, the same principal applies though.. you may have problems if you are stuck in a 4 hour traffic jam
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| smoke_ |
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i agree with waggins previous comment.
the alternator is turning too slow, hence the drop in voltage. the only way to fix this is to put the original pulley on. I don't think the underdrive pulleys will cause you any problems though. Just check you have 14v at the battery with a high idle.
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