gdog Posted October 8, 2015 Report Share Posted October 8, 2015 Could not find a definitive answer online so far (as to whether the lamp is actually in the field circuit w/o a shunt, or not). I "think" on early alternators (say in the '70s maybe?) it was, but engineers figured out that that is not a very robust design and started wiring it differently. On one engr site saw this discussion where someone claimed there's a resistor in parallel but did not see any schematics to back that up. This link below seems to explain modern automotive charging systems pretty well IMO.http://www.carparts.com/classroom/charging.htmThe only fault I would find with it is that they say the most common alt fault is one of the six rectifier diodes going out (either going open circuit or shorting out) but I would say that's the 2nd most common failure; first is the brushes wearing out.. Link to comment Share on other sites More sharing options...
gdog Posted October 11, 2015 Report Share Posted October 11, 2015 @B850: no update? Link to comment Share on other sites More sharing options...
Brad850 Posted October 11, 2015 Author Report Share Posted October 11, 2015 I will when i feel like fixing it. Link to comment Share on other sites More sharing options...
erikv11 Posted October 12, 2015 Report Share Posted October 12, 2015 OP: does either cable and/or cable end get hot in the twenty minutes you can run it, as happens when a crimp connection is failing internally? It's very common, usually the positive cable. Link to comment Share on other sites More sharing options...
Brad850 Posted October 14, 2015 Author Report Share Posted October 14, 2015 17.5-18 volts at the alternator… 13.7-14 volts at the battery. Are the numbers supposed to fluctuate on the meter?Erik as far as i can tell the cables aren't overheating. Link to comment Share on other sites More sharing options...
Oreo931 Posted October 14, 2015 Report Share Posted October 14, 2015 Alternator is bad and frying your battery. Alternator voltage should be around 13.8-14.2 volts, with approx. same voltage going to battery. Sounds like the voltage regulator in the alternator is bad. Link to comment Share on other sites More sharing options...
Brad850 Posted October 14, 2015 Author Report Share Posted October 14, 2015 Wasn't using the meter correctly. Here are my actual numbers when engine is cold. 13.89 at alternator - 13.82 at battery. When I turn my hid's on, voltage at battery and alt drops down to ~12.5 and i can hear the beginning stages of the funky idle. Voltage at battery climbs back to 13.81 when the lights are shut off, idle comes back smooth.Basically any time there is an additional load from the lights or fan, it drops down to 12.5 at both alt and batt, and continues to drop at a slow rate. I let it go to 12.2 before shutting off the lights to let it charge back up.Guess the answer is still bad alternator Link to comment Share on other sites More sharing options...
BEJinFBK Posted October 15, 2015 Report Share Posted October 15, 2015 May be bad cabling and/or connections.Are you using the alternator case as a groundpoint when you measure alternator voltage,or some other point in the engine bay? Link to comment Share on other sites More sharing options...
H0lD mY d6InK Posted October 15, 2015 Report Share Posted October 15, 2015 Oh yeah, definitely your alternator is starting to let go.Should not be charging that low at all. Link to comment Share on other sites More sharing options...
Brad850 Posted October 15, 2015 Author Report Share Posted October 15, 2015 May be bad cabling and/or connections.Are you using the alternator case as a groundpoint when you measure alternator voltage,or some other point in the engine bay?My only doubt about bad cables is the fact that there isn't much of a voltage drop when it's idling with the lights and fan off. To my knowledge 13.89 alt to 13.82 battery isn't too bad. Unless that's wrong. I've been using different grounding points just to confirm I'm doing it correctly. Is using the case the best way to do it?Oh yeah, definitely your alternator is starting to let go.Should not be charging that low at all. That's what I'm thinking. Link to comment Share on other sites More sharing options...
H0lD mY d6InK Posted October 15, 2015 Report Share Posted October 15, 2015 A battery is needed to only start a car when the alternator is not running. After the car starts, the alternator handles all power supply for however long the car is on. The 13.89v you got when checking the battery while the car was running, was actually what your alternator was recharging your car. A good battery would just sit at 12.5v forever. Anything less wont supply the car properly to start and anything over 12.5v would indicate an overcharge( which is actually just as bad). Link to comment Share on other sites More sharing options...
Glenn Posted October 16, 2015 Report Share Posted October 16, 2015 you should be able to turn every cotton picking thing "on" in your car and the alternator should maintain 14 volts... including rear defroster, emergency flashers.. wipers on high.. heater blower on high... AC on... headlights on... stereo on... loud! Link to comment Share on other sites More sharing options...
Brad850 Posted October 16, 2015 Author Report Share Posted October 16, 2015 I'm going to get it tested before I purchase a new one out of curiosity. Hope she's enjoying her last moments in the car. Link to comment Share on other sites More sharing options...
BEJinFBK Posted October 16, 2015 Report Share Posted October 16, 2015 When you're looking at alternator voltage, use the alternator case as a ground reference.This eliminates all positive and ground cables and connections as potential voltage drop points.And if the voltage at the battery continues to drop the longer the engine is running, failingcables and/or connections may be heating up and increasing in resistance. Heck yeah - Get it checked out. It may well be the alternator.But remember that a lot of "rebuilt" alternators are cheap crap.A new regulator in an OEM alternator is cheaper, and more likely better. Link to comment Share on other sites More sharing options...
H0lD mY d6InK Posted October 16, 2015 Report Share Posted October 16, 2015 Yes, replacing the regulator might fix it.Just whatever you do, don't get any aftermarket alternator. Link to comment Share on other sites More sharing options...
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