How many amps should my Caddy's alternator be putting out at idle? The battery keeps going dead and I took to four diff auto parts places today to have it checked. Only the one autozone said the alternator was only putting out out 39 amps at idle and it should be well over 100. The rest of the parts stores said the alternator and battery check out fine. I did a voltage check and it seems okay.
alternator amperage at idle?
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I would say that 39 amps at idle is fine. I would look for something that is drawing too much power when the car is off
100amps at idle?? No way! The massive pull would shut your motor down at idle.
39amps at idle is a considerable amount as well. Did you have the a/c on? radio with subwoofers & amp? etc.. etc..
as accessories and electronics ask for power the alternator generates more to accomodate the load. at idle, you the alternator is only spinning fast enough for a basic amperage output. When too much load is requested and the alternator isn't spinning fast enough, the power then starts coming from the battery and now the altnernator tries to charge the battery and accomodate the electrical load. Unfortunately the battery usually gets nothing and you get an overheated alternator and failure begins.
the person at autozone is 100% wrong in the sense that an alternator needs put out more that 100amps. for your caddy the alternator is rated at like 105amps, but you would need a LOT of electrical accessories running for that number to show up.
their alternator tester is a pass/fail tester and usually errs on the side of fail so they can sell you a new one.
39 amps at idle tells me you're running a subwoofer/amplifier system, probably over 1500+ watts.
39amps at idle is a considerable amount as well. Did you have the a/c on? radio with subwoofers & amp? etc.. etc..
as accessories and electronics ask for power the alternator generates more to accomodate the load. at idle, you the alternator is only spinning fast enough for a basic amperage output. When too much load is requested and the alternator isn't spinning fast enough, the power then starts coming from the battery and now the altnernator tries to charge the battery and accomodate the electrical load. Unfortunately the battery usually gets nothing and you get an overheated alternator and failure begins.
the person at autozone is 100% wrong in the sense that an alternator needs put out more that 100amps. for your caddy the alternator is rated at like 105amps, but you would need a LOT of electrical accessories running for that number to show up.
their alternator tester is a pass/fail tester and usually errs on the side of fail so they can sell you a new one.
39 amps at idle tells me you're running a subwoofer/amplifier system, probably over 1500+ watts.
The radio may have been on when they tested it but I'm pretty sure it was off. I think it may have read 39 amps because the battery was slightly discharged. The stereo system is stock.
The only thing I can think of that may be pulling a current when the car is off is the suspension. On my older caddy when the airbags wore out the motor would constantly run to refill them. I don't hear the motor running on this car though.
I'm going to charge it up and take it out for dinner tonight. I'll check the voltage when I get back and if its dropped I know the alternator is not doing its job.
The only thing I can think of that may be pulling a current when the car is off is the suspension. On my older caddy when the airbags wore out the motor would constantly run to refill them. I don't hear the motor running on this car though.
I'm going to charge it up and take it out for dinner tonight. I'll check the voltage when I get back and if its dropped I know the alternator is not doing its job.
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Even basic electricity is often misunderstood by parts-monkeys. I would always take their advice with a grain of salt.
EricF has pretty much covered all bases, but I'll re-word some of it.
A 100-amp alternator is rated at its optimum RPM. Can't say exactly what that is, but it will be well above idle. So a 100-amp alternator will not be able to put out 100 amps at idle.
The amount that your alternator puts out at ANY RPM is a function of how much current is being drawn by assorted vehicle circuits, but will be no more than the maximum output of the alternator (whatever that happens to be). If current draw exceeds the capacity of the alternator at any RPM, the battery will take over temporarily, albeit at a slightly lower voltage- which will show up in the form of dimming lights and such.
When an alternator is tested ON the vehicle, you usually turn on the headlights, blower motor, a/c, rear defroster, etc. to load the alternator, then check the amperage output and the voltage. If the alternator is putting out quite a few amps (this will be a guestimate, but 39 is plenty), AND voltage is roughly between 13.5 and 14.7 or thereabouts (opinions will vary on exact voltage requirements), then you have a working alternator. Now, in MY opinion (and some will disagree with me here), the amperage check isn't really necessary (though it's good for verification). If you turn on all vehicle accessories and still have around 14 volts at the BATTERY, then you can pretty much assume that the alternator is doing its job.
So what's the symptom that we're trying to shoot down here? Just slow cranking/not starting in the morning? If that's the case, then you've pretty much eliminated the alternator as a problem. Parasitic (key-off) current draw is a possible cause... but in my experience, 90% of the time, starting problems can be traced to a bad battery and/or bad connections. That's where I'd start.
EricF has pretty much covered all bases, but I'll re-word some of it.
A 100-amp alternator is rated at its optimum RPM. Can't say exactly what that is, but it will be well above idle. So a 100-amp alternator will not be able to put out 100 amps at idle.
The amount that your alternator puts out at ANY RPM is a function of how much current is being drawn by assorted vehicle circuits, but will be no more than the maximum output of the alternator (whatever that happens to be). If current draw exceeds the capacity of the alternator at any RPM, the battery will take over temporarily, albeit at a slightly lower voltage- which will show up in the form of dimming lights and such.
When an alternator is tested ON the vehicle, you usually turn on the headlights, blower motor, a/c, rear defroster, etc. to load the alternator, then check the amperage output and the voltage. If the alternator is putting out quite a few amps (this will be a guestimate, but 39 is plenty), AND voltage is roughly between 13.5 and 14.7 or thereabouts (opinions will vary on exact voltage requirements), then you have a working alternator. Now, in MY opinion (and some will disagree with me here), the amperage check isn't really necessary (though it's good for verification). If you turn on all vehicle accessories and still have around 14 volts at the BATTERY, then you can pretty much assume that the alternator is doing its job.
So what's the symptom that we're trying to shoot down here? Just slow cranking/not starting in the morning? If that's the case, then you've pretty much eliminated the alternator as a problem. Parasitic (key-off) current draw is a possible cause... but in my experience, 90% of the time, starting problems can be traced to a bad battery and/or bad connections. That's where I'd start.
If indeed your battery and alt are fine, check for a parasitic draw I think you have to hook a multi-meter in series in place of the battery...anyone care to chime in?
Originally Posted By: eljefino
you want 14.5 VOLTS at just above idle or maybe idle too.. that means charging.
With few accessories no lights should get the 14.5 at idle.
Depends on the temp of the alternator..the only time I ever see 14.5 at idle is when it's 20 degrees out and the engine has just been started. Otherwise, 13.6-13.8 is more likely in summer.
you want 14.5 VOLTS at just above idle or maybe idle too.. that means charging.
With few accessories no lights should get the 14.5 at idle.
Depends on the temp of the alternator..the only time I ever see 14.5 at idle is when it's 20 degrees out and the engine has just been started. Otherwise, 13.6-13.8 is more likely in summer.
When my truck is idling in gear when fully warmed up with the A/C compressor engaded the volts will drop to 12.6V (650 RPM idle). If I put it in neutral it will idle at 800 RPM and the volts will shoot up to 13.9, rev it to 1,000 with the same conditions and it's 14.2 volts.
A/C not running, and no other accessories, and all RPM's read 14.3 volts.
A/C not running, and no other accessories, and all RPM's read 14.3 volts.
Originally Posted By: EricF
39 amps at idle tells me you're running a subwoofer/amplifier system, probably over 1500+ watts.
14.5 V x 39 A = 565.5 Watts
39 amps at idle tells me you're running a subwoofer/amplifier system, probably over 1500+ watts.
14.5 V x 39 A = 565.5 Watts
Originally Posted By: onion
So what's the symptom that we're trying to shoot down here? Just slow cranking/not starting in the morning? If that's the case, then you've pretty much eliminated the alternator as a problem. Parasitic (key-off) current draw is a possible cause... but in my experience, 90% of the time, starting problems can be traced to a bad battery and/or bad connections. That's where I'd start.
Basically their isn't enough juice to turn the car over after about three to four days. Sometimes a week.
I was thinking about what could be draining the battery and I remembered I have a bad power door lock switch on the passenger side. I'm wondering if this may be drawing current and draining the battery. I may pull it out tomorrow if I can figure out how to get the door panel off.
The battery is less than a year old and is a diehard platinum. It checked out fine at all the parts stores today. I checked the voltage earlier with the accessories on and its ok per the manual. Only thing funny about it was it did not drop much when the accessories were switched on. It made me think maybe something is up with the regulator.
So what's the symptom that we're trying to shoot down here? Just slow cranking/not starting in the morning? If that's the case, then you've pretty much eliminated the alternator as a problem. Parasitic (key-off) current draw is a possible cause... but in my experience, 90% of the time, starting problems can be traced to a bad battery and/or bad connections. That's where I'd start.
Basically their isn't enough juice to turn the car over after about three to four days. Sometimes a week.
I was thinking about what could be draining the battery and I remembered I have a bad power door lock switch on the passenger side. I'm wondering if this may be drawing current and draining the battery. I may pull it out tomorrow if I can figure out how to get the door panel off.
The battery is less than a year old and is a diehard platinum. It checked out fine at all the parts stores today. I checked the voltage earlier with the accessories on and its ok per the manual. Only thing funny about it was it did not drop much when the accessories were switched on. It made me think maybe something is up with the regulator.
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An easy way to tell if it's a faulty battery or a drain is to park the car, disconnect one of the battery leads and charge the battery using a charger until it says it is full.
Then leave parked for the time it would normally take for the battery to drain.
Hook the battery back up and attempt to start the car. If it starts then you have a drain or a charging problem.
The next step would be to disconnect the battery any time you leave the vehicle parked for a period of time. If it always starts up then the vehicle is charging and it is a drain causing the issue.
Then leave parked for the time it would normally take for the battery to drain.
Hook the battery back up and attempt to start the car. If it starts then you have a drain or a charging problem.
The next step would be to disconnect the battery any time you leave the vehicle parked for a period of time. If it always starts up then the vehicle is charging and it is a drain causing the issue.
I took some measurements from my Saab 93 with a clamp-on DC ammeter:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1238993#Post1238993
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1238993#Post1238993
Until a few years ago, I installed an ammeter in all the cars I've owned. A healthy battery and alternator show 10-20 amperes charging current after a start and lasts a minute or so at idle, then drops off to 5 amps or even less thereafter. Your 39 amps at idle is way too much, assuming that the reading is correct. I'm not sure about your particular model, bu most alternators can't even output 100 amperes CONTINUOUS current at whatever speed. Autozone is dead wrong on their advice. If your battery is continuously going dead, try a good loaner battery from a battery dealer. If things don't change then you know it's a problem with your car, not the battery you now have.
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Your 39 amps at idle is way too much
Not necessarily. Depends on how they ran their alternator test. If no accessories were turned on, then you would be correct. But if the headlights, blower motor, rear defrost, etc. were turned on, then 39 amps wouldn't be unusual at all.
Your 39 amps at idle is way too much
Not necessarily. Depends on how they ran their alternator test. If no accessories were turned on, then you would be correct. But if the headlights, blower motor, rear defrost, etc. were turned on, then 39 amps wouldn't be unusual at all.
I vote for a parasitic drain somewhere in the electrical system. Make sure you don't have something like a bad trunk light switch or glove box switch causing the lamps to keep running when the doors are closed. If you can rig in a multimeter to test for current draw from the battery, with the engine off, you can then start pulling fuses and watch the results on the meter. If no change, put the fuse back in and pull the next one. If there's a drain you'll be able to tell which circuit is doing it when the meter shows a noticable change when that fuse is pulled.
Ed B.
Ed B.
Originally Posted By: SuperEd73
I vote for a parasitic drain somewhere in the electrical system. Make sure you don't have something like a bad trunk light switch or glove box switch causing the lamps to keep running when the doors are closed. If you can rig in a multimeter to test for current draw from the battery, with the engine off, you can then start pulling fuses and watch the results on the meter. If no change, put the fuse back in and pull the next one. If there's a drain you'll be able to tell which circuit is doing it when the meter shows a noticable change when that fuse is pulled.
Ed B.
This sounds about like what I'll have to do. I replaced the battery today because the positive side post was loose and wiggling around. I also detached the faulty lock switch on passenger door and pulled a bad bulb out of the driver's door. Hopefully the problem is fixed. I'm keeping my fingers crossed.
I vote for a parasitic drain somewhere in the electrical system. Make sure you don't have something like a bad trunk light switch or glove box switch causing the lamps to keep running when the doors are closed. If you can rig in a multimeter to test for current draw from the battery, with the engine off, you can then start pulling fuses and watch the results on the meter. If no change, put the fuse back in and pull the next one. If there's a drain you'll be able to tell which circuit is doing it when the meter shows a noticable change when that fuse is pulled.
Ed B.
This sounds about like what I'll have to do. I replaced the battery today because the positive side post was loose and wiggling around. I also detached the faulty lock switch on passenger door and pulled a bad bulb out of the driver's door. Hopefully the problem is fixed. I'm keeping my fingers crossed.
Use a voltmeter, not an almost useless ammeter.
12.5 V at rest, and 14.4V maximum at 2,000 RPM or so.
12.5 V at rest, and 14.4V maximum at 2,000 RPM or so.
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