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mine does that to, but only slightly, if you think its a big deal, why not put in the mr2 alternator, there are 1 or 2 mr2 alternators that have a higher current then ours

remember, these cars are old now, so it is also very likely that the alternator could be dying, especially if you have an aftermarket stereo with amps and it draws a high current. My alternator in my old car died with my system putting to much of a load on it, and it was only a 1997.
 
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drjonez said:
heh....you have that a bit backwards.... ;)
ah, no, I don't.

It is one of two things, the battery is dead, or the regulator is not providing enough field current to generate the required output at low rpm.
 

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The regulator is bad. DISCONNECTING THE BATTERY WHILE THE CAR IS RUNNING IS A BAD IDEA. Sorry dude, hate to :uzi: but that is just WRONG. If the alternator wasnt producing enough current, that test would let you know - if you didnt jack up something in the process. But it IS producing enough current, its just not REGULATING the current. The voltage regulator is built into the alternator.
 
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I am confused as to who is talking to who now.

Pulling the cable while running is not a good idea cause the battery is the systems "shock absorber"

field current controls alternator output

regulator controls field current

regulator should read bus voltage

battery takes up slack for the alternator when it cant make enough output at low rpm because of lack of motion in the magnetic circuit

the post before me is right, the regulator could be stuck providing too much field strength.

It took me longer to type this than it would have taken for me to test it with a dmm and have the answer.
 
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XTC Dynamic Supra said:
dang dont jump on my back on this....im not telling the guy to drive the car around with the battery out. its a matter of disconnecting the battery and one rev. yes you can have a spike but tell me you guys have never tested someones or even your own alternator this way. shit this is the way to do a ghetto jump start.
I've done this a long time ago, on a friends car. Disconnecting the battery with the engine running was fine, once we reconnected it, we blew out majority of the lights, blew out the computer and fried the ignition.

DON'T DO IT, it's just not worth it. It's a dumb test, when just looking at the brightness of your lights can tell you if the alternator is charging fine.
 

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LISTEN-
He said it's a brand new alternator. And yes, you could have a bad brand new alternator/ regulator... but he ALSO said that his lights are only a BIT brighter when revving. Let's remember that these are 12 to 17 year old cars. What about their wiring? Before worrying about anything else, I would replace both the positive and negative battery leads, preferably with larger gauge units. Then check the obvious grounds around your engine bay. THEN I would look elsewhere...
 
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LISTEN-
He said it's a brand new alternator. And yes, you could have a bad brand new alternator/ regulator... but he ALSO said that his lights are only a BIT brighter when revving. Let's remember that these are 12 to 17 year old cars. What about their wiring? Before worrying about anything else, I would replace both the positive and negative battery leads, preferably with larger gauge units. Then check the obvious grounds around your engine bay. THEN I would look elsewhere...
YAH I bought one too and blew the voltage regulator on it (same day) .. it mabe my voltage gauge read out 30v! It nearly blew my whole car up. Take that flipping alternator back.
 
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the alternator is internally regulated, Think about the power difference at 1000 vs 4000 4x the power, without a regulator it would be up and down.

but you could be right i would start with the battery
 
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The battery is not just a primary load? it also acts as a pretty good capacitor, it will soak up any voltage spikes generated by motors switching off and heavy loads either being connected or disconnected.

The quality of the battery is also important, it's impedence to charge current is determined by how good the plates are, if a battery is more than 3 years old the plates start to sulfate up, to a greater extent it itself regulates the the voltage coming out of the alternator, it will take current but will not charge because of the sulfating the impedence to current goes up, so it's voltage regulating effect will deminish. This effect will cause the lights to brighten up.

Also spikes chaused by heavy loads will also increase, making it more likely of electronic damage, the first thing to suffer will be the ECU.

Which is why a mechanic will put a load test on a battery if it's suspect, A hydrometer may show a fully charged battery but if the cells are plated then the battery will give out reduced load current.

This is why manufacturers will only put a 3 year garantee on a battery, as a rule I fit a new battery when this garantee runs out.:)
 

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if the damn thing cranks ok, its not gonna be the battery...I have driven around on a completely discharged battery and a good alt, and vice versa-neither of which i experienced dim lighting. How much brighter are we talking about? Mine do that, it may not even be a problem. Check to see that you are pushing at least 11V at an idle. If its lower, it is prob. the alternator.
 

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Discussion Starter · #39 ·
Alright I got the alternator and battery both checked today. The alternator was fine and after charging the battery they said it was good. So i put the both back in, turn the key...nothing.
I bring out the jumper cables, jump it, turn the key...nothing.
turn the key...nothing. turn the key...nothing. WTF is my probnlem here?
 
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