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Discussion Starter #21
Regardless, you still have a voltage to the alternator field that, in your case, is controlled by the car's computer. In older cars, the field voltage was controlled by a voltage regulator, that was internal to the alternator. If you can monitor that field voltage, while you are driving, that would be a big help.

Also, and unless you have a huge load on your system, a fully charged battery, will not immediately drop below 12 volts, even if the alternator shuts down.

Of note, if you monitor battery voltage while starting your car, the voltage shouldn't drop much below 9 volts. The starter is a very, very large short term load.

Also, the Torque app, for the Android phone, along with a Bluetooth OBDII adapter, total less than $20, can monitor and store alternator voltage while you drive.
Right now, I'm just monitoring voltage from a power outlet in the console. I'm generally doing so without any additional loads on that circuit, and when I have correlated the monitor with the battery directly (with a meter at the battery) they seem to be the same voltage. I believe the accessory plugs are disabled when starting the car-- I don't recall seeing any voltage shown AS I start the car.

I'm having no problems at all with the car starting-- not even slow starting. I'm having no problems with the car charging either, but I'm getting warnings, and I don't want some small problem to strand us hundreds of miles from home...

The Torque App sounds interesting but I'm an iPhone guy-- I'll have to see if there is an iPhone version or some similar solution I would love to be able to review a log of the voltage recorded through the OBDII

I'm not sure one can monitor that field voltage in a useful way-- the mechanic I talked to explained that this is a modulated signal-- switching on an off rapidly to control output voltage from the alternator.

Something I didn't post because it seemed unrelated-- my air conditioning went out right when all of this started. No direct correlation perhaps, but I stopped using it when the compressor started short cycling, and turned off all the accessories possible when the chiming started to happen as well.

I'm told that 12.5 - 12.7 volts is to be expected under low-draw situations when the car lightens the alternator load to save power, and the voltage will then cycle up and down to maintain a charge on the battery, or cycle up and stay up with sufficient load applied.

This is outside my experience, but for a couple of days, I've been test driving it-- the A/C has been fixed, so I'm back to being able to run it all the time-- basically I never turn it off under normal operation, so having it off was really unusual.

With the A/C back on, and the radio & navigation operating and no special consideration to reduce power loading, today, the car started up around 14 volts, then leveled off in the 13.5 to 13.7 volt range. Lowest noted voltage was 13.3 when idling in a carol line, in gear with the AC blasting... That's far from conclusive, but pretty interesting. With no accessories on, a few days ago in the same situation I had roughly 20 warning chimes and nearly sixty noted low voltage excursions within a single hour. Today, the same ambient conditions existed. Same car, same driver, same driving route, again for around an hour, and zero alarms, and zero low voltage excursions by the meter.

It is all quite confusing.

It all makes my head spin...
 

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Discussion Starter #23 (Edited)
Were the ac relays replaced ?
Yes. No change. After that failed to help, the A/C issue was found to be (per my mechanic) an overcharged system. It must have been that way for quite some time (it has not been touched in probably 5 years) but a simple servicing of the system and restoring the unit with the correct amount of freon seems to have restored it to proper operation.
 

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Plainsman, monitoring the field voltage will show something either on the DC range or on the meter's AC range. While the alternator is working, try it and see what you read. You don't have to understand the reading; you just have to know what is normal. Make an extension, and run the wire into the car so that you can monitor while driving.

If the meter normally reads, say a fluctuating 4 volts, and all of a sudden you get zero volts for a long time, you have a problem.
 

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Discussion Starter #26
I follow your general concept, marvinstockman. That idea is worth exploring.

The challenge is that (again, per what my mechanic explained) these alternators run in variable modes. I'm not even clear if there are variable states at fixed levels (sort of like a three-way bulb) or more like a light with a dimmer switch with nearly infinite output levels. So abrupt changes may or may not be meaningful.

I would be interested to see a reading when the information center chimes, but the voltage at that point is very close to when it doesn't chime while the voltage simply goes into the mid 12-volt range. This is all brand new to me. I was not aware that a charging system could be functioning properly when the voltage drops, but it actually makes sense, with the right computer controls.

For now, I'm running all the accessories again, and so far, the van has stopped the low voltage excursions entirely, as well as the chiming.

A week or so ago, the car drove for a total of 450 or 500 miles with only two observed low voltage excursions. I do know that I was running the air conditioner and navigation and stereo when that happened, and both of the excursions were associated with a chime, and both were white city driving. Both times, the car had driven 100+ miles on the interstate and then been parked-- once for two hours once for 4, then while on city streets, we had the chime, the car was parked and rested for a hour or so (both times) and then the car drove without incident on the freeway for 100 or more miles, again, without incident.

After these two chime events, the check charging system display lasted only a few seconds, so unless I had the meter on and ready at the moment it chimed and the right range selected, I suspect the problem would have cleared before I could get a reading.

I cannot remember what was on load-wise when the hour long voyage confusion started, but at the point where the voltage started on the roller coaster-- the first chime, I turned off every accessory.

Now coming to understand that the vast majority of what I have been seeing may be normal for low-load operation, I'm going to watch for a while and see if I can find a new trend under typical driving conditions. I still think somethings wrong... I'm just not certain what. I guess time will tell...
 

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Discussion Starter #27
I am curious if anyone else has monitored their Odyssey charging system voltage, and seen similar 12-volt-range readings when they turn off all possible accessories.

So far I continue to run in a reasonable charging voltage range (13.5 - 14.2) so long as I maintain a decent load on the alternator, but turn off everything and we're back to the voltage roller-coaster.
 

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Discussion Starter #29
I'm not sure how one is "sure" but the first replacement appeared to be correct, was installed (by myself) and worked without incident for two years. The second alternator was an exchange for the exact same model from the exact same parts house (under a lifetime warranty), was replaced by my mechanic because I didn't have time to do this myself, and when it was exchanged the unit basically did exactly what the first unit had done when in the (assumed) failure mode.

Note that the parts house said the first alternator tested fine, but agreed to exchange it once I showed them a video of my voltage readings while driving.

Changing nothing at all in the setup or what is installed, when running accessories at a typical level, so far I've had perhaps three warning chimes in around 1000 miles of driving. The battery has never gone dead or even low enough to be described as "slow starting."

With the first two (of the three initial post-alternator-change-) chimes, I had a brand new alternator, and nervously decided to ride things out and see what happened. I left the A/C and other accessories on, and so forth. With the third, it chimed several times in a row, but it was pleasant out, so I had the windows down and the A/C off from the start-- I was driving locally, so the navigation was off, and I turned off the stereo as well (as soon as it chimed) so I was running fewer accessories, and I turned off more. Following that, I had an hour of chimes and low-voltage readings intermixed with typical ones. All that was drawing power was the car ignition and cooling fan, and whatever computers and such were in use.

I drove it more after this and got tons of chimes and odd behavior, but ALL of those things happened with a bare minimum of accessory loading. With the accessories back on, at least so far, I cannot reproduce the low voltage response.

My local mechanic spent four hours trying to troubleshoot this, and gave me a detailed report of what happened, but refused to charge me anything because he could not reproduce things consistently enough to offer me a repair option that he could stand behind. He can't be scamming me-- he wasn't trying to charge me a cent. His only request was to let him know the cause if it was found in case he ever ran across it again. He checked with a local Honda specialty shop for a consultation as well-- they were unfamiliar with this problem on Odysseys but said it was something that happened on other Hondas. This cars have a replaceable voltage control module. Sounds like that module is built into one of the fuse boxes and is a costly replacement (as opposed to a $30 controller on other models). My mechanic said it could really be that module or one of a couple of computer models, or (less likely in this case) the alternator. He was highly confident that the battery was not at fault. He said mine is showing to be above specs for even a new battery.

All the wacky behavior-- the roller-coaster voltage swings have happened when I was turning off everything possible for fear that I was discharging the battery and likely to get stuck in traffic with a stalled van. That's exactly what happened two years ago. I got one warning chime and intended to drive straight home as soon as it happened. I got two or three miles and the car shuddered then stalled. Battery was super low. Alternator was toast. Changed the alternator (and battery-- that was due) and had zero incidents for two years.

Without the first (definite) alternator failure (two years ago), I wouldn't have been nearly so panicked at a single warning chime. I've monitored voltage on countless other vehicles, but never while driving an Odyssey like this. This response from the "modulated" charging system is brand new to me. I'm given to wonder if the reason they don't offer volt meters or any voltage monitor on these vans with an actual volt readout it because the voltage reading are atypical as compared with other kinds of cars, and especially older cars-- again, this mechanic (and he's good, but not a Honda specialist) said this is a fuel saving measure, and that makes sense. When you energize the field it does load the accessory belt more heavily. If unnecessary, that just adds heat, and burns extra fuel.

Hopefully someone will be able to plug a temporary volt meter in their own Odyssey and share their voltage readings with all accessories off as they drive for a while. I would find the results very helpful.
 

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Discussion Starter #31
Thanks. I'm watching it now.

I got one warning chime today. It was so fast that all I could do was see a 12 jump on the volt meter, and by the time I glanced at the information center display, the error was gone, and then glancing back to the meter, it was back to proper charging. The event was perhaps 1 to 2 seconds. Crazy stuff...
 

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Discussion Starter #32
New Observations

Temperatures have been milder with recent rain around here. I assume the A/C cycles off more because of that-- the charging system started chiming more, but setting the temp colder (uncomfortably cold) appeared to stop the problem. I turned off the A/C and frequent chiming and low voltage excursions returned.

I realized that I could not recall a chime or low voltage excursion after dark having happened-- not once. Turning accessories to a bare minimum, the chiming & low voltage excursions again returned. Anticipating this, I quickly turned on the headlights-- a reasonable power draw that is consistent, unlike the way the A/C clutch cycling and fan speed can vary.

Turning on the headlights appears to cause the alternator voltage to go back to around 13.5 and the clear warning every time. Leaving the headlights on (even with noting else on) seems to prevent the problem.

I haven't yet learned a definitive cause of the chime (precise voltage or other details which sound the chime), but this is the first time I have a repeatable action which appears to clear the warning and brings the voltage back up. I repeated this solution throughout the day yesterday, repeating this process perhaps 15 times, and preventing low voltage excursions as well, simply by leaving the headlights on for fairly lengthy timeframes. This correlation is consistent enough and happened enough times to begin to feel meaningful.

I don't love this "fix" but perhaps I'll be able to build enough information that a Honda shop (or somebody!) will be able to tell me what part is reasonable likely to cure this problem. I will continue to observe if the headlights stop/prevent the concerning behavior.

It seems to me like the circuit that controls the voltage is just slightly out of adjustment, as opposed to instrumentation giving a false alarm (though if the reaction voltage of the instrumentation is off, the result would be the same) but I don't believe there is a way to adjust anything involved, and replacing the voltage controlling part (that modulates the field voltage) stands to be costly-- I think the most likely cause is a $300-range fuse block, where other Hondas have a $30 replaceable module... I'm not certain which block it would be, but I wonder what the cost of a junkyard replacement block might be. It might be worth a swap for a reasonable cost to see it it helps...

Any clues?
 

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Discussion Starter #34
Thanks jkayca. I'm fairly good. I'd love to read what the manual has to say about this matter. Do you happen to know the exact name of the manual? I'm seeing drivetrain & wiring manuals-- is that what I'm after?
 

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Hey AtlantaOdyssey, did you figure out the problem? I'm having the exact issue on my 07 odyssey. New alternator, new battery and intermittent battery light on and off.
 

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A new alternator is the usual solution. Most of the time the parts house brand alternators are junk and won't put out enough power to run everything on the vehicle. Replacing it with a Denso reman will usually solve the issues.
 

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Old thread I know but I am in the exact same situation as the OP. Three new alternators and a charging system light intermittently still... Was there any resolution to this?
 

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What is your definition of a "new" alternator? What brand?
 
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