I noticed today whie cruising my gauge was reading under 12V. I droive about 15 minutes / 10 miles and parked her at the store. After 90 minutes I went back home and my gauge still reading under 12v. I tested the battery and got a 12.20 reading. I tested the battery under load and no load @ 2000 rpms and got readings of 11.46 & 11.50. I went back later (about 30 minutes to test her again and she cranked twice and died. I charged her up and gott he slightly lower readings. I then parked her in the garage and got a reading of 11.95 on the battery. Note: Battery is 6 1/2 yrs old and the alternator is 10yrs old. Also, I always disconnect the neg. cable to the battery after every drive to avoid any unneccassry drains and as she only gets driven once a week. Any insight? Gonna take her to Pep Boys for a true battery test on Weds.
Age old question...Bad Battery or Bad Alternator???
- Thread starter ZooKypr
- Start date
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6 1/2 years on a battery is a little longer than I usually get. I would check the battery.
BillGrissom
Well-Known Member
What car do you have that has a voltmeter and what type?
It could take more than a 10 mi drive to recharge a battery. Put it on a charger until full. Autozone and others won't test a battery unless it is fully charged.
You should see >13 V at the cigarette lighter with the engine running, especially on the highway.
I have a Black & Decker 10A smart charger with built-in "alternator test" function. I understand it simply looks for a sinusoidal fluctuation, indicating a live alternator. Got it cheap at Big Lots. For a better measurement, I use a clamp-on DC ammeter probe (F.W. Bell, $15 used on ebay).
It could take more than a 10 mi drive to recharge a battery. Put it on a charger until full. Autozone and others won't test a battery unless it is fully charged.
You should see >13 V at the cigarette lighter with the engine running, especially on the highway.
I have a Black & Decker 10A smart charger with built-in "alternator test" function. I understand it simply looks for a sinusoidal fluctuation, indicating a live alternator. Got it cheap at Big Lots. For a better measurement, I use a clamp-on DC ammeter probe (F.W. Bell, $15 used on ebay).
Start the car and then remove the negative battery cable. If the car dies, then the alternator is not putting out enough charge.
To test the battery, check the voltage with the engine off, a fully charged battery should read over 12.5 volts. Then disconnect the center coil wire from the distributor so you can crank the engine without starting it. Crank it for 10 - 20 seconds, If the voltage drops below 10 Volts while cranking your engine over, then your battery is bad and not holding enough charge...
To test the battery, check the voltage with the engine off, a fully charged battery should read over 12.5 volts. Then disconnect the center coil wire from the distributor so you can crank the engine without starting it. Crank it for 10 - 20 seconds, If the voltage drops below 10 Volts while cranking your engine over, then your battery is bad and not holding enough charge...
Do this
Chances are if you have had a weak charge for a while the battery may be getting close to its death.I would bet it's the alternator if it's reading under 12 volts while running.
Yes, a good charging system will put out between 13.3 and 15 volts when the engine is running. If over 15 volts, your regulator is not doing its job.
67Dart273
Well-Known Member
PLEASE can we bury this old wives tale. NEVER unhook a battery cable on a running car. Yes, yes, YES you might get by with this 10, 100, 1000 times Hell you might even get by with it 10000 times without damaging something.
It is a flawed test and proves nothing, here's why
IF the system is working OK, but the engine and loads (headlights or even just ignition) is below the otuput of the low speed idle, it might die and be working perfectly fine
On the other hand, the alternator might have all but two diodes blown clear out of the housing, and still put out enough to run the ignition. In this case, you would pull the cable, it would keep running, and you would (incorrectly) think it's fine
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To the OP. The voltages you got while running indicate one thing. It is not charging
Battery readings "stopped" at this point are meaningless because the battery is likely somewhat discharged.
So you need a couple of "quick checks" to separate the problem
1.......Is it the alternator?
(What are we working on?????????? year, make, model??? What type of alternator? is this the pre---70 Mopar charging system?)
Remove the green field wire, and use a clip lead to jumper from the battery (starting relay large stud) over to the now exposed alternator field terminal. If you are in subdued light, you should see a small spark
Start the car and watch the voltmeter / ammeter. Bring up RPM, it should show some increase.
If not hook your multimeter directly to the alternator output stud. Repeat the test. If the voltage stays below 13V it is not charging. The alternator is bad
If the voltage goes way high, 16V or higher at the alternator, but stays low at the battery depending on RPM, then you have an open in the alternator charge line
If the meter does show a charge, showing the alternator is OK, hook the field wire back up
2.....Disconnect the two regulator wires and jumper them together. Repeat the above test If it again shows a charge, this shows the field wiring as well as the alternator is OK. -------
3......If the above test is OK, first try cleaning and re-grounding the regulator. If no improvement, replace the regulator. MAKE CERTAIN the regulator is grounded.
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Once you get the problem "fixed," post back. You are NOT done. You need to do at least two other things
1........Once you get the charging system operational, and the battery back up, you need to find someone to properly load test the battery. A battery that old is likely on it's last rodeo
2........Post back here, and do a search. You want to look for how to check for voltage drop in the harness which actually causes OVER charging (over voltage) on an otherwise working system
Its a '66 Barra. Form S. 273 Commando , stock replacement Alternator 60 amp, which is about 10 yrs old it self. I'll try your troubleshooting in a couple of days, busy work schedule . I'll post back my findings.
Had some time today to work on her and the battery was dead...reading 11.50 v . I had the battery tested and she would hold more than a 25% charge. Sooo I bought a new battery and as we all know that wasn't the issue. She fired right up and I was only getting around 12.15 under load / no load @ 2000 rpms. All contacts to alternator / voltage reg. are fine and were also cleand with some steel wool. I will update tomorrow with some additional test.
This is where we are at now...
1, bench tested alternator diodes and it tested bad
2. had the store bench test it, also read bad
3. bought reman. alt. (bench tested good) and my readings are as follows:
14.90v idle no load
15.15v idle w/ load
15.35v @ 2000 rpms no load
14.94v @ 2000 rpms w/ load
I've been told between 13.5 - 15v is the range...My portable cigarette lighter tester still says I'm overcharging when cruising but if 15v is the max for a good reading...is my $10.00 tester so sensitive it will give me an overcharging reading for .35v ?
Also, I discovered I have 2.20v draw from the voltage regulator testing it with the ignition turn on but engine off.
Where my at now fellas? I think I'm good except for the volt. reg. draw which I think is a different issue but I'll let you guys decide. My knowledge in electrical repair is very novice but I am gaining knowledge from you guys with the hands on approach which is the best way!
1, bench tested alternator diodes and it tested bad
2. had the store bench test it, also read bad
3. bought reman. alt. (bench tested good) and my readings are as follows:
14.90v idle no load
15.15v idle w/ load
15.35v @ 2000 rpms no load
14.94v @ 2000 rpms w/ load
I've been told between 13.5 - 15v is the range...My portable cigarette lighter tester still says I'm overcharging when cruising but if 15v is the max for a good reading...is my $10.00 tester so sensitive it will give me an overcharging reading for .35v ?
Also, I discovered I have 2.20v draw from the voltage regulator testing it with the ignition turn on but engine off.
Where my at now fellas? I think I'm good except for the volt. reg. draw which I think is a different issue but I'll let you guys decide. My knowledge in electrical repair is very novice but I am gaining knowledge from you guys with the hands on approach which is the best way!
67Dart273
Well-Known Member
OK NOW you've got it charging, NOW you have a different problem, most likely "harness voltage drop"
There are several possible causes for over voltage
MOST LIKELY
1....Voltage drop in the wiring harness
2....Poor grounding between VR and battery negative post
3...In a few cases a battery going bad
4...In a few cases, a VR out of calibration
Start by assuming it's either 1 or 2. You need to make some tests
A........With key in 'run' but with engine off, access the "switched ignition" or "ignition run" (IGN 1) coming out of the bulkhead and feeding the ballast resistor
Depending on the year of the car, the ign run feeds
the ignition system
the voltage regulator
On 70 / later, also feeds the alternator field (blue)
and some smog doo dads if used, and electric choke
SO get to the highest reading on the ballast resistor. Hook one probe of your meter to that post, and hook the other probe to battery POSitive.
You are hoping for a very very low reading, the lower the better. If the reading is more than .3V (three tenths of one volt) that is at least part of and probably most of the problem
B.....VR ground. This time, run the engine at a fast clip to simulate "medium cruise" RPM. Make this test first with all accessories off, and again with lights, heater turned on
One probe to battery NEG post. The other stab into the VR mounting flange. Stab through any paint or rust. Again, a low reading is what you want, and zero is perfect.
If you have harness drop the top suspects are bad bulkhead connections, bad connections at the ignition switch connector, or the switch itself. More rare is problems at the ammeter, and last, most rare, is a failure of the factory welded splice
Now it's time to go read the MAD article............
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
and
http://www.madelectrical.com/electricaltech/howitworks.shtml
There are several possible causes for over voltage
MOST LIKELY
1....Voltage drop in the wiring harness
2....Poor grounding between VR and battery negative post
3...In a few cases a battery going bad
4...In a few cases, a VR out of calibration
Start by assuming it's either 1 or 2. You need to make some tests
A........With key in 'run' but with engine off, access the "switched ignition" or "ignition run" (IGN 1) coming out of the bulkhead and feeding the ballast resistor
Depending on the year of the car, the ign run feeds
the ignition system
the voltage regulator
On 70 / later, also feeds the alternator field (blue)
and some smog doo dads if used, and electric choke
SO get to the highest reading on the ballast resistor. Hook one probe of your meter to that post, and hook the other probe to battery POSitive.
You are hoping for a very very low reading, the lower the better. If the reading is more than .3V (three tenths of one volt) that is at least part of and probably most of the problem
B.....VR ground. This time, run the engine at a fast clip to simulate "medium cruise" RPM. Make this test first with all accessories off, and again with lights, heater turned on
One probe to battery NEG post. The other stab into the VR mounting flange. Stab through any paint or rust. Again, a low reading is what you want, and zero is perfect.
If you have harness drop the top suspects are bad bulkhead connections, bad connections at the ignition switch connector, or the switch itself. More rare is problems at the ammeter, and last, most rare, is a failure of the factory welded splice
Now it's time to go read the MAD article............
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
and
http://www.madelectrical.com/electricaltech/howitworks.shtml
I will complete the testing you listed tomorrow....One question in regards to the Volt. Reg., the right bolt connecting to the firewall appears stripped. It will not tighten only loosely snug then spin and resnug. The VR is tighly mounted due to the left bolt being very tight to the firewall. Could this be my culprit? Any ideas how to fix the stripped hole in the firewall. I doubt I could drill the VR mounting larger w/o cracking it in order to use a larger bolt.
67Dart273
Well-Known Member
I'm not sure "the best way." You might be able to get by with a larger body bolt. These are sort of "self tapping" Some are tapered, some have a split part way almost like a tap. If you cannot do anything else, bend up part of the flange so you can "get to it" and drill and put something like a 10-32 screw and nut through there, with a pigtail wire. Run that to a known tight good ground.
By the way, if you run Mopar ECU (ignition) that box is another MUST ground item.
By the way, if you run Mopar ECU (ignition) that box is another MUST ground item.
"SO get to the highest reading on the ballast resistor. Hook one probe of your meter to that post, and hook the other probe to battery POSitive.
You are hoping for a very very low reading, the lower the better. If the reading is more than .3V (three tenths of one volt) that is at least part of and probably most of the problem
I was unsure which post to measure but I obtained the below readings:
1. engine cold - no start since last night - engine off
top post (blue wire) measured 7.04v - bottom post 1.67v
2. engine warm after 30 minute cruise - engine off - 12.83 top & bottom
3. engine warm & off - 0v measuring bolt and white ballast area.
B.....VR ground. This time, run the engine at a fast clip to simulate "medium cruise" RPM. Make this test first with all accessories off, and again with lights, heater turned on
One probe to battery NEG post. The other stab into the VR mounting flange. Stab through any paint or rust. Again, a low reading is what you want, and zero is perfect.
This VR Ground test produced readings of .13v and .55v with accessories on.
You are hoping for a very very low reading, the lower the better. If the reading is more than .3V (three tenths of one volt) that is at least part of and probably most of the problem
I was unsure which post to measure but I obtained the below readings:
1. engine cold - no start since last night - engine off
top post (blue wire) measured 7.04v - bottom post 1.67v
2. engine warm after 30 minute cruise - engine off - 12.83 top & bottom
3. engine warm & off - 0v measuring bolt and white ballast area.
B.....VR ground. This time, run the engine at a fast clip to simulate "medium cruise" RPM. Make this test first with all accessories off, and again with lights, heater turned on
One probe to battery NEG post. The other stab into the VR mounting flange. Stab through any paint or rust. Again, a low reading is what you want, and zero is perfect.
This VR Ground test produced readings of .13v and .55v with accessories on.
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