Voltage drop over time

[jawn101]

So over the last few months my car has developed a new little foible. When you first start the car up, it reads right at 14.5v on the dash gauge. Over time during a drive, the voltage steadily drops little by little until it reaches right around 13. This is even with all accessories off - fans, radio, a/c, lights, etc.

All the grounds have been recently cleaned and shored up. I have Hervey's fancy double ground cables run to the transmission. Alternator is a <2 year old Hervey D110. Battery is a couple years old but I have had it load tested (though not in the last few months I guess) and it always came back OK. The battery light does illuminate at key-on and the battery is charging. Belt is tight (could it be over-tight?)

Also, I don't know if it's related - but there is an electrical "whine" in my cabin. It is only present when the car is above idle (when the microswitch disengages) and seems most prevalent at around 1800-2000 RPM, though that may just be where the engine noise starts to drown it out. It isn't present only under load - you can hear it revving in the garage even in neutral. Can't hear it from the engine compartment, only inside the car. But I have tried and tried to find something obvious in the relay compartment and can't. Also the whine is not coming from interference with the stereo - it can be heard even with the stereo turned completely off.

[Michael]

Alternators do tend to charge at a higher rate when cold, so I would not worry too much about it especially considering how inaccurate the voltage gauge can be. You should use a voltmeter and verify the charge rate when the Alternator is cold, then again when warm. Do not count the battery out either, I had an Optima yellowtop fail after 2 years on mine. As far as the whine, depending on how the components are wired up, interference can come through the speakers even if the radio is off.

[jawn101]

Intersting. I figured heat probably had something to do with it, but this didn't seem to happen before recently. The alternator charge rate can be determined by just hitting the pickup post and grounding to the engine block with a DVM, right?

I hadn't considered that the speakers could still be producing noise with the stereo off. I don't know why that would have started suddenly either but I will listen more carefully and see if the speakers are in fact the culprit.

[DMCMW Dave]

Intersting. I figured heat probably had something to do with it, but this didn't seem to happen before recently. The alternator charge rate can be determined by just hitting the pickup post and grounding to the engine block with a DVM, right?

I hadn't considered that the speakers could still be producing noise with the stereo off. I don't know why that would have started suddenly either but I will listen more carefully and see if the speakers are in fact the culprit.

IMO your alternator is starting to fail, probably lost one diode in the bridge so far causing the poor performance and whine in radio.

On many radios the power amp section is powered as long as the car is powered. Turning off the radio only turns off the radio part. If you want to kill it completely as a test, disconnect both power wires to the radio (i.e. pull both inline fuses).

Measuring like you mention is a reasonable test. With everything turned off and the engine running you should get in the neighborhood of 14.2 volts. If you turn everything on (lights, A/C, blower fan on 4) it may drop to 13.5 at idle but should come back up over 14 when you rev the engine. If it is not doing this the alternator is weak or you have some bad connections at the alternator (rare). If the alternator bracket on the engine block was not cleaned when the alternator was replaced, that can cause issues. The sides of the bracket where it contacts the alternator, and where the bracket contacts the engine (3 8mm bolts) should be clean.

[jawn101]

IMO your alternator is starting to fail, probably lost one diode in the bridge so far causing the poor performance and whine in radio.

On many radios the power amp section is powered as long as the car is powered. Turning off the radio only turns off the radio part. If you want to kill it completely as a test, disconnect both power wires to the radio (i.e. pull both inline fuses).

Measuring like you mention is a reasonable test. With everything turned off and the engine running you should get in the neighborhood of 14.2 volts. If you turn everything on (lights, A/C, blower fan on 4) it may drop to 13.5 at idle but should come back up over 14 when you rev the engine. If it is not doing this the alternator is weak or you have some bad connections at the alternator (rare). If the alternator bracket on the engine block was not cleaned when the alternator was replaced, that can cause issues. The sides of the bracket where it contacts the alternator, and where the bracket contacts the engine (3 8mm bolts) should be clean.

Hmm. So the two symptoms could be related. I did clean the ever loving #@(+ out of the brackets that the alternator bolts to, as we had the engine out all last month and I got bored waiting for a clutch to show up. So that's not the issue.

Could be the regulator. I've had problems with it in the past. Is there any (easy, within reason) way to test the regulator? I can pull the alternator off in about 5 minutes, should I have a parts store test it? Something I can do myself with a DVM?

Also, Dave - by inline fuses, do you mean the glass ones behind the center console? Those are a nightmare to get at. Can I just pull fuses #8 and #11 out of the block for the test?

Edit: Barring that, it's actually fairly easy to reach behind the head unit and just disconnect the wiring harness to it. Much easier than accessing those glass fuses, at least in my car.

[Bitsyncmaster]

I have to agree that it sounds like the alternator is dying. As stated, the alternator voltage should be higher when cold and drop when hot. That is the design of alternators to do the best charging for the battery. It would be better if it measured the battery temp but most cars have the battery near the alternator.

Check the three bolts holding the alternator together. Mine had one work loose.

[jawn101]

I have to agree that it sounds like the alternator is dying. As stated, the alternator voltage should be higher when cold and drop when hot. That is the design of alternators to do the best charging for the battery. It would be better if it measured the battery temp but most cars have the battery near the alternator.

Check the three bolts holding the alternator together. Mine had one work loose.

You mean the long ones holding the actual body of the alternator together? I can check that too, no problem. Do they serve an electrical purpose?

[Bitsyncmaster]

You mean the long ones holding the actual body of the alternator together? I can check that too, no problem. Do they serve an electrical purpose?

Yes the long ones. You need a reverse torex socket. The keep the parts aligned properly.

[David T]

The drop in output voltage does not necessarily mean the alternator is going bad. Once it replaces the power used to start the motor and the battery is fully charged, the regulator reduces the amount of power the alternator produces so it doesn't overcharge the battery. If you suspect the alternator is going bad it is easy to test it. Many places will check it and your battery for free. If you see sticky black goo dripping out of the alternator on the bottom it is done, replace it. If the battery is over 5 years old, just replace it.
David Teitelbaum

[Bitsyncmaster]

The drop in output voltage does not necessarily mean the alternator is going bad. Once it replaces the power used to start the motor and the battery is fully charged, the regulator reduces the amount of power the alternator produces so it doesn't overcharge the battery. If you suspect the alternator is going bad it is easy to test it. Many places will check it and your battery for free. If you see sticky black goo dripping out of the alternator on the bottom it is done, replace it. If the battery is over 5 years old, just replace it.
David Teitelbaum

The regulator on lead acid batteries is just a voltage regulator. It does not know if the battery is fully charged or dead. Typical cold temps the voltage is 14.5 to 15 volts. When the alternator (regulator) is hot typical voltage is 14 to 14.5 volts. You really would not get much charging if your only getting 13 volts. That would be about what a trickle charger would use.

[Rich]

When you first start the car up, it reads right at 14.5v on the dash gauge. Over time during a drive, the voltage steadily drops little by little until it reaches right around 13.

All good postings from the community about these symptoms so far.

By now you know that the D's dash voltmeter, like most other car voltmeters, isn't necessarily accurate. Try calibrating the dash gauge using a VOM to the battery or similar points so you'll have a good feel for what the dash gauge is telling you when it says "13".

Example: On our car a VOM reading from the jump start terminal to the engine reads 13.5V when the dash VM reads "13V", engine idling and with enough load to drop it to "13". Here I assume that my VOM is itself accurate or as accurate as a $60 VOM should be.

Not denying that there could be a problem, only recommending that the data accuracy is worth checking. Put your VOM/DVM to work, at least to verify that the dash gauge isn't lying to you. Much.

[DMC5180]

Also, I don't know if it's related - but there is an electrical "whine" in my cabin. It is only present when the car is above idle (when the microswitch disengages) and seems most prevalent at around 1800-2000 RPM, though that may just be where the engine noise starts to drown it out. It isn't present only under load - you can hear it revving in the garage even in neutral. Can't hear it from the engine compartment, only inside the car. But I have tried and tried to find something obvious in the relay compartment and can't. Also the whine is not coming from interference with the stereo - it can be heard even with the stereo turned completely off.

I have a similar issue like you are describing. I still run the Motorola though. The mysterious WHINE is present with the (Craig) radio off and sounds like it is coming from the Right rear corner of the back wall.

The other issue I've had seemingly forever is substantial voltage drop. With Minimal load I get 13.9 (DVM) @ fast idle (85-0 rpm) the Gauge shows 2 Needles above the 13 mark. Then with A/C on MAX, FAN 4, OEM COOLING FANS running continuos and Lights ON H BEAM the voltage on DVM drops to (12.01) If I bump the RPM up to 2000 the voltage will come up to 12.75 (DVM) The gauge will be reading 2 needles below 13 mark. Does this just mean the old Motorola is just tired or simply under rated powered? Just Lights ON only pulls it down to 13.2.

[David T]

The voltage regulator senses voltage from the ignition switch through the charging light. That is how it knows when to excite the field coil. It also measures the voltage and if it is low it puts more voltage on the field coil causing the alternator to make more electric. As the voltage increases it reduces the alternator's output. It is also sensitive to temperature. The hotter it gets the lower (less) output it allows. If you see the black sticky goo on the bottom of the alternator it has overheated and the potting compound has melted and run out of the regulator. It gets on the brushes and they lose contact with the slip rings on the rotor. The alternator can be rebuilt but it is usually cheaper and faster to replace it. If you see the alternator light light on or on dimly the alternator is not working. Do not give the voltmeter too much credit. It is not all that accurate but if it is usually in one spot and now it is significantly lower you can assume something is not right. A really quick and "dirty" method to see if the alternator is making electric is done this way:
Get something metallic that is attracted by magnetism (a pocketknife or a screwdriver)
Put it close to the end of the rotor, the end AWAY from the pulley.
If the alternator is making electric it will have a magnetic field and you will feel the attraction of the pocketknife to the case of the alternator. This can't tell you how much it is making, only that it is working. Another way, if you have a voltmeter, is to see the voltage increase above battery voltage when the motor is running. Flip to the AC scale and see how much ripple you have. If it is above a volt or so you probably have 1 or more bad diodes.
David Teitelbaum

[Ron]

Actually, the knife test will not show that the alternator is working. It is a "one sided" test and should only be used to show that an alternator is NOT working -- Big difference!

[jawn101]

I have a similar issue like you are describing. I still run the Motorola though. The mysterious WHINE is present with the (Craig) radio off and sounds like it is coming from the Right rear corner of the back wall.

The other issue I've had seemingly forever is substantial voltage drop. With Minimal load I get 13.9 (DVM) @ fast idle (85-0 rpm) the Gauge shows 2 Needles above the 13 mark. Then with A/C on MAX, FAN 4, OEM COOLING FANS running continuos and Lights ON H BEAM the voltage on DVM drops to (12.01) If I bump the RPM up to 2000 the voltage will come up to 12.75 (DVM) The gauge will be reading 2 needles below 13 mark. Does this just mean the old Motorola is just tired or simply under rated powered? Just Lights ON only pulls it down to 13.2.

Glad it's not just me then. Have you had any luck tracking the noise down? Tried disconnecting the stereo to see if it goes away? I will probably try that this week sometime.

Thanks to David T and Ron for the input as well. The alternator isn't leaking goo and the battery light is not on, dim or flashing or otherwise.

[DMC5180]

No. I have not tried disabling the radio yet. For whatever reason I did not notice it during my last start up and drive. That said, I suffer from Tinnitus (ringing/buzzing in the ear) right now it is quit intense. It may have masked the WHINE. I will say the Whine is RPM sensitive, the frequency increases with RPM.

[jawn101]

Ah, OK Dennis. Thanks for the feedback though, I will try the radio disconnection this week and report back. Maybe we can help each other out with this one. I'm glad someone else is having the same problem, it makes me feel less crazy... :)

[DMC5180]

I did do a ripple check with my DVM set to the AC 20V scale I got 0.01V I guess that means my diodes check out good.

[jawn101]

I did do a ripple check with my DVM set to the AC 20V scale I got 0.01V I guess that means my diodes check out good.

..how do you do that?

[DMC5180]

..how do you do that?

" Another way, if you have a voltmeter, is to see the voltage increase above battery voltage when the motor is running. Flip to the AC scale and see how much ripple you have. If it is above a volt or so you probably have 1 or more bad diodes."
David Teitelbaum

I assume it is the same as checking your running voltage with a DVM except you set it to the AC scale. I used the the 20V AC scale. FWIW: my running idle No load voltage is 13.87

[jawn101]

" Another way, if you have a voltmeter, is to see the voltage increase above battery voltage when the motor is running. Flip to the AC scale and see how much ripple you have. If it is above a volt or so you probably have 1 or more bad diodes."
David Teitelbaum

I assume it is the same as checking your running voltage with a DVM except you set it to the AC scale. I used the the 20V AC scale. FWIW: my running idle No load voltage is 13.87

Oh, OK! I didn't notice that little bit when he first posted, it might have been an addition. Thanks, I will give few of these things a try this evening.

[DMC5180]

FWIW: my battery voltage is 12.81V (typical for Optima Red top) I went for short drive this morning, the WHINE is present with the radio OFF and ON (with volume turned down Silent).No change detected. Makes me wonder if is being generated from a some other component. The weird thing is that the car has 4 speakers but the sound radiates from the back Right corner. At least that's what my right ear thinks. I'm going to try the disable power to the radio this morning and see what I get. Note: this spring I replaced the rear speakers and the WHINE was present before the change.

[stevedmc]

All hail Earl Hickey!

[jawn101]

OK, so here's what I found this afternoon. Disconnecting the stereo made no difference. I unhooked the harness to it completely and the whine is still present in the right rear corner of the car. You're not crazy, Dennis - that's definitely where the noise is.

Measured the battery with the car off, pick up post to block - 12.5v. Turned the car on and it dropped slightly to 12.3, and the dash gauge read about a needle's width below 13. Close-ish.

Started the car up and was getting 14.45v with no accessories running. The dash gauge read about 1.5 needle widths above 13, so that's also close-ish. Revving the motor produced no change in voltage reading on either the DVM or the dash gauge. I then turned on all the accessories - Max A/C, blower to 4, headlights, brights, and the stereo. On the dash the voltage dropped to just a hair's width above 13, but was still reading around 14.2 on the DVM. So it seems the dash gauge is more inaccurate under load? Weird because I don't remember it doing that before.

I then also switched my DVM to the AC scale (mine only goes down to 200v though) and the reading slowly fluctuated between 27 and 31. I don't really know what that means but I did it because Dennis and David said to.

Next test I suppose would be to take a cold idling measurement of the battery voltage, take a drive long enough to produce the visible voltage drop on the dash gauge, then take another idling measurement of the voltage and see if there actually was a drop or if the gauge is just being wonky at higher temperatures/over time.

[Cory W]

But I've never looked too far into it. Never affects how the car drives, and my jaunts are short these days...

Whine at the right rear corner of the car? You sure it isn't the alternator itself?

[jawn101]

But I've never looked too far into it. Never affects how the car drives, and my jaunts are short these days...

Whine at the right rear corner of the car? You sure it isn't the alternator itself?

Nope, not sure of that at all. But you can only hear the noise from inside, if I put my head right at the alternator while the motor is running it isn't obvious. But the noise could just be drowned out by the engine racket.

Dave M - could it be the RPM relay for any reason? I know Dennis and I both have your improved one, and that's something in the relay compartment who's function is directly impacted by/dependent on changes in engine revolutions, just like the noise. Grasping at straws here :)

[Bitsyncmaster]

Nope, not sure of that at all. But you can only hear the noise from inside, if I put my head right at the alternator while the motor is running it isn't obvious. But the noise could just be drowned out by the engine racket.

Dave M - could it be the RPM relay for any reason? I know Dennis and I both have your improved one, and that's something in the relay compartment who's function is directly impacted by/dependent on changes in engine revolutions, just like the noise. Grasping at straws here :)

You might have a buzzing mechanical relay but that would be a rare failure. Put a screw driver on the alternator and hold that handle to your ear when the engine is running.

[jawn101]

You might have a buzzing mechanical relay but that would be a rare failure. Put a screw driver on the alternator and hold that handle to your ear when the engine is running.

OK forgive me if this is a dumb question, but I have a more than healthy respect for electricity. Is that safe?

[Bitsyncmaster]

OK forgive me if this is a dumb question, but I have a more than healthy respect for electricity. Is that safe?


Your just putting the screw driver on the case of the alternator. But even touching 12 volts you won't feel unless you touch it to your tongue.
Be careful of the rotating parts.

[jawn101]

Your just putting the screw driver on the case of the alternator. But even touching 12 volts you won't feel unless you touch it to your tongue.
Be careful of the rotating parts.

OK. I nearly melted a wrench accidentally shorting across my battery terminals once and I've been very cautious ever since.

[DMC5180]

I did pull fuse 11 (radio power) and 17 (memory) No change was detected.

[David T]

Using a screwdriver and putting it to your head behind your ear is an old mechanic's trick to try to isolate a mechanical noise. You can buy a mechanic's stethoscope which is safer. You touch it to the case, you do NOT touch it to any terminals where there may be electric. If anyone EVER offers any advice, either on the Internet or anywhere else, that you do not feel comfortable with, it is up to YOU to decide what to do. If you do not know how to do a particular procedure ask dumb questions (there are no dumb questions except the ones you don't ask) till you are confident you know what you are doing. Safety is paramount, no one wants to get hurt enjoying their hobby. Getting hurt takes all of the fun out of this. If you think the high pitched whine is from your alternator, take the belt off and run the motor. You can run it without the belt for a short period, long enough to know if it is the alternator or not. If the noise goes away it could also be the water pump, same belt. Melting a wrench on a battery will get your attention quick! I bet he won't do that again soon!
David Teitelbaum

[Dangermouse]

Here's an out of the box idea that may work. Or it may not.

Download a "noise meter" APP for your phone, one with a needle display. When you are looking for the sound, move the phone around the passenger compartment and see if the needle spikes anywhere.

I have used a couple of them just for fun, but never for any real diagnostics. May be worthless with the overall engine noise, but you never know.

[jawn101]

Here's an out of the box idea that may work. Or it may not.

Download a "noise meter" APP for your phone, one with a needle display. When you are looking for the sound, move the phone around the passenger compartment and see if the needle spikes anywhere.

I have used a couple of them just for fun, but never for any real diagnostics. May be worthless with the overall engine noise, but you never know.

Not a bad idea. I have a real dB meter as well somewhere but this is a pretty faint noise. If I thought there was any chance of picking it up with my phone's microphone I would have posted a video of it for you guys already :)

[DMC5180]

Try unplugging the Frequency Valve.

[jawn101]

Try unplugging the Frequency Valve.

Also not a bad idea. It's in the right bit of real estate and would adjust based on engine RPM. But it has a pretty distinct sound that I think I'd recognize. Worth a shot since it's so easy.

Edit: OK, tried the FV and the screwdriver-turned-stethoscope. Unplugging the FV made it run for crap of course, the motor was stumbling all over itself and it was tough to even get it to 1800 RPM, but the noise was still present. The alternator makes a whirring noise that I could hear clearly through the screwdriver, but no electrical whine that I could discern.

It's got to be something in that relay compartment. I just need to get a second set of hands to rev the motor for me while I touch and listen to every relay and CB back there.

[vwdmc16]

Have you tried disabling the alt for a test? take the belt off and go for a drive around the block, any whine then?

[jawn101]

Have you tried disabling the alt for a test? take the belt off and go for a drive around the block, any whine then?

I just tried this. With no alternator belt, the whine is still present. And boy does the voltmeter read low ;-)

Tonight I'll try and bribe my wife to hold the throttle around 1800 for me and I'll listen really carefully in the relay compartment.

[Michael]

Have you tried disabling the alt for a test? take the belt off and go for a drive around the block, any whine then?

I don't know if I would go around the block with no waterpump.

[jawn101]

I don't know if I would go around the block with no waterpump.

Yeah, I didn't leave the garage. The whine is in evidence when sitting still at about 1800-2000 RPM, so I just started the motor up (dead cold from sitting overnight), revved up until I heard the noise, then killed it again. Test over, no need for more than that.

[jawn101]

Well, it's not in the relay compartment either. Just verified it with my wife holding the RPMs steady and my head buried in the relay compartment. It's not in there, nor is it the battery or anywhere in that general area.

I guess since it's not electrical the thread might need to be moved. But what else could it be? Vacuum leak? I don't have any obvious economy/driveability symptoms of that.

[vwdmc16]

the sound was coming from the center of the engine to my ears when i heard it, still thinking it could be a whistle of air in the ISC.

[jawn101]

the sound was coming from the center of the engine to my ears when i heard it, still thinking it could be a whistle of air in the ISC.

Could be that. I might not have properly sealed the idle air pipe last time I put the mixture unit back in.