I had the same, or a very similar experience two weeks ago. I was sure that I had a parasitic drain somewhere. The alternator would bring the battery up to 14.7 volts, but the next day, it would drop down to 12.2 volts. Anything less than 12.6 volts and the battery would not crank the engine over. In the end, the battery needed to be replaced.
Alternator or??
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Originally Posted By: Merkava_4
I had the same, or a very similar experience two weeks ago. I was sure that I had a parasitic drain somewhere. The alternator would bring the battery up to 14.7 volts, but the next day, it would drop down to 12.2 volts. Anything less than 12.6 volts and the battery would not crank the engine over. In the end, the battery needed to be replaced.
Please see above... It's not the battery.
I had the same, or a very similar experience two weeks ago. I was sure that I had a parasitic drain somewhere. The alternator would bring the battery up to 14.7 volts, but the next day, it would drop down to 12.2 volts. Anything less than 12.6 volts and the battery would not crank the engine over. In the end, the battery needed to be replaced.
Please see above... It's not the battery.
To me it sounds like there is a short somewhere, hence the voltage stays in the 14 range. Is it still in the 14's with the battery fully charged? It would explain the surface charge, but little actually goes into the battery. With the battery fully charged, the voltage at the terminals should stabilize at mid 13 volts.
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Originally Posted By: StevieC
Please see above... It's not the battery.
The battery is at 14.5 volts with the engine running; the alternator is working fine.
Please see above... It's not the battery.
The battery is at 14.5 volts with the engine running; the alternator is working fine.
Originally Posted By: Merkava_4
Originally Posted By: StevieC
Please see above... It's not the battery.
The battery is at 14.5 volts with the engine running; the alternator is working fine.
Can you please read the whole thread. Thanks. IT'S NOT FINE!
Originally Posted By: StevieC
Please see above... It's not the battery.
The battery is at 14.5 volts with the engine running; the alternator is working fine.
Can you please read the whole thread. Thanks. IT'S NOT FINE!
The only thing that don't make sense is the 31.2 volts reading with the engine running. If that was really the case, the battery would blow up.
Originally Posted By: StevieC
Voltage with vehicle running. (At Battery)
A/C Volts read at the battery while the vehicle is running. (Charging)
Voltage immediately after shut-down. (At Battery)
Voltage showing that it is creeping down from above voltage toward the 11.5 (Takes too long so I just snapped this here but it's less than 12.6v (flooded) / 12.8v (AGM) where it should be at the minimum for a fully charged battery)
That's a bad rectifier/shorted diode. 31VAC? Ya, get that aalternator/regulator off and tested ASAP. Also, I would fully charge the battery with an external charger and load test it with a carbon pile load tester. With a pure lead agm, the 11.x volts could be 5 fully charged cells and one shorted cell. But, there definitely should never be 32v ac anytime at all.
Voltage with vehicle running. (At Battery)
A/C Volts read at the battery while the vehicle is running. (Charging)
Voltage immediately after shut-down. (At Battery)
Voltage showing that it is creeping down from above voltage toward the 11.5 (Takes too long so I just snapped this here but it's less than 12.6v (flooded) / 12.8v (AGM) where it should be at the minimum for a fully charged battery)
That's a bad rectifier/shorted diode. 31VAC? Ya, get that aalternator/regulator off and tested ASAP. Also, I would fully charge the battery with an external charger and load test it with a carbon pile load tester. With a pure lead agm, the 11.x volts could be 5 fully charged cells and one shorted cell. But, there definitely should never be 32v ac anytime at all.
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Doing more research I found out that you need a True RMS multi-meter to do this test otherwise you get a funky reading like this. Now this matches other folks on Youtube with healthy alternators but I will use my dad's true RMS multi-meter (Fluke) so the reading is accurate. Didn't realize there would be a difference between cheap multi-meters like the one shown and a true RMS in this regard reading AC Ripple.
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When you got that 31.2 volts reading, you weren't measuring alternator output were you? Didn't you just have the leads hooked up across the battery terminals?
check this out battery university.com
battery university.com
battery university.com
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Check all the grounds . I have read of people that had to run additional grounds .
Check all your positive connections and cables .
Checking voltages on something not under load , only tells you so much . A very poor connection may show full voltage under no load . Under full load , is when problems occur .
Best of luck ,
Check all your positive connections and cables .
Checking voltages on something not under load , only tells you so much . A very poor connection may show full voltage under no load . Under full load , is when problems occur .
Best of luck ,
Originally Posted By: StevieC
A/C Volts read at the battery while the vehicle is running. (Charging)
Why are you trying to measure AC voltage on a DC side of the system? What am I missing here?
A/C Volts read at the battery while the vehicle is running. (Charging)
Why are you trying to measure AC voltage on a DC side of the system? What am I missing here?
that free harbor freight meter is not very accurate.good enough for simple stuff.
if the alt was really putting out 31.2vac you would be seeing smoke signals and have a VERY hot battery.soon to be a destroyed battery.
the battery should be a dead short to that level of ac.
now is when a scope would be nice to have.
yes you may have lost a diode and one phase is now putting out ac.
and leaking to the stator while off discharging the battery.
but more likely something else is causing a parasitic load like some module not "going to sleep" after shutdown.
even a amplifier not shutting down.
lots of stuff is live at all times.and a failure in any such item gets you to where you are now.
this is a "divide and conquer" job.
if the alt was really putting out 31.2vac you would be seeing smoke signals and have a VERY hot battery.soon to be a destroyed battery.
the battery should be a dead short to that level of ac.
now is when a scope would be nice to have.
yes you may have lost a diode and one phase is now putting out ac.
and leaking to the stator while off discharging the battery.
but more likely something else is causing a parasitic load like some module not "going to sleep" after shutdown.
even a amplifier not shutting down.
lots of stuff is live at all times.and a failure in any such item gets you to where you are now.
this is a "divide and conquer" job.
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a good meter can show excessive ac ripple from bad diodes in the alt.
that $5 meter is obviously not up to the task.that reading should be ignored as it is not possible.
the current it takes from an ac source to show 31.2v into a few milliohms is not going to be produced even if all phases have shorted diodes.
Originally Posted By: Quattro Pete
Originally Posted By: StevieC
A/C Volts read at the battery while the vehicle is running. (Charging)
Why are you trying to measure AC voltage on a DC side of the system? What am I missing here?
that $5 meter is obviously not up to the task.that reading should be ignored as it is not possible.
the current it takes from an ac source to show 31.2v into a few milliohms is not going to be produced even if all phases have shorted diodes.
Originally Posted By: Quattro Pete
Originally Posted By: StevieC
A/C Volts read at the battery while the vehicle is running. (Charging)
Why are you trying to measure AC voltage on a DC side of the system? What am I missing here?
Originally Posted By: StevieC
Doing more research I found out that you need a True RMS multi-meter to do this test otherwise you get a funky reading like this. Now this matches other folks on Youtube with healthy alternators but I will use my dad's true RMS multi-meter (Fluke) so the reading is accurate. Didn't realize there would be a difference between cheap multi-meters like the one shown and a true RMS in this regard reading AC Ripple.
Doing more research I found out that you need a True RMS multi-meter to do this test otherwise you get a funky reading like this. Now this matches other folks on Youtube with healthy alternators but I will use my dad's true RMS multi-meter (Fluke) so the reading is accurate. Didn't realize there would be a difference between cheap multi-meters like the one shown and a true RMS in this regard reading AC Ripple.
Originally Posted By: WyrTwister
Check all the grounds . I have read of people that had to run additional grounds .
Check all your positive connections and cables .
Checking voltages on something not under load , only tells you so much . A very poor connection may show full voltage under no load . Under full load , is when problems occur .
Best of luck ,
Did all this.
Check all the grounds . I have read of people that had to run additional grounds .
Check all your positive connections and cables .
Checking voltages on something not under load , only tells you so much . A very poor connection may show full voltage under no load . Under full load , is when problems occur .
Best of luck ,
Did all this.
Things left to try:
-AC Ripple test with a true RMS multi-meter.
-Thermistor temperature / resistance test on the Battery Temperature Sensor located on the battery that feeds back to the ECU to determine charge rate. (Both hot & cold)
-Voltage sense wire from the Alternator traced back the ECU
-Taking the alternator off and having it tested off the vehicle with proper loading.
-AC Ripple test with a true RMS multi-meter.
-Thermistor temperature / resistance test on the Battery Temperature Sensor located on the battery that feeds back to the ECU to determine charge rate. (Both hot & cold)
-Voltage sense wire from the Alternator traced back the ECU
-Taking the alternator off and having it tested off the vehicle with proper loading.
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Are you expecting wet cell voltage levels from an AGM battery? Then you don't understand AGM batteries. Did your vehicle originally have an OEM AGM battery? If not, that's your problem. Put a wet cell in there and get on with life.
I worked at a place that replaced all their wet cell batteries with AGM's, real high end quality stuff. Tried every brand. They installed zero, none, nada charge limiters. After 2 years we had 3 pallets full of dead AGM batteries. All warranty refused, overcharging. When I left they were still sitting in the corner.
AGM batteries have very specific temperature and charge requirements. If your vehicle is not made, or modified to honor that, you'll have problems.
I worked at a place that replaced all their wet cell batteries with AGM's, real high end quality stuff. Tried every brand. They installed zero, none, nada charge limiters. After 2 years we had 3 pallets full of dead AGM batteries. All warranty refused, overcharging. When I left they were still sitting in the corner.
AGM batteries have very specific temperature and charge requirements. If your vehicle is not made, or modified to honor that, you'll have problems.
Read above... 11.5 volts it not normal for Wet or AGM.
Originally Posted By: StevieC
Things left to try:
-AC Ripple test with a true RMS multi-meter.
-Thermistor temperature / resistance test on the Battery Temperature Sensor located on the battery that feeds back to the ECU to determine charge rate. (Both hot & cold)
-Voltage sense wire from the Alternator traced back the ECU
-Taking the alternator off and having it tested off the vehicle with proper loading.
definitely sounds like a good plan! It definitely sounds like the alternator, even if it's producing the voltage (when you check it), it doesn't sound like it's producing the correct amps to actually charge it. Sure, it's enough to float charge it, but not enough to deep charge it where that surface charge doesn't dissipate once you turn the alternator/car off.
Things left to try:
-AC Ripple test with a true RMS multi-meter.
-Thermistor temperature / resistance test on the Battery Temperature Sensor located on the battery that feeds back to the ECU to determine charge rate. (Both hot & cold)
-Voltage sense wire from the Alternator traced back the ECU
-Taking the alternator off and having it tested off the vehicle with proper loading.
definitely sounds like a good plan! It definitely sounds like the alternator, even if it's producing the voltage (when you check it), it doesn't sound like it's producing the correct amps to actually charge it. Sure, it's enough to float charge it, but not enough to deep charge it where that surface charge doesn't dissipate once you turn the alternator/car off.
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