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Discussion Starter #21
Drove to local parts store, equipment said the alt is fine but the battery needed to be replaced.

Voltages also started randomly dropping to ~12v for about 30 seconds at a time and then returning to ~14v during the ten minute drive. The last drives never dropped below ~14v ever. The van did sit for 2 hours idling before this and never dropped below ~14v. Now being at home and idling in the driveway again, there's no drop. However I can make the drop to ~12v again sometimes by rolling all the windows down and holding the buttons down. When I let go it returns to ~14v, or if I hold them like that for ten secs or so it goes back up to ~14v while they're still down.

I guess I need both.
 

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Generally bench tests are more accurate than the tests with it all installed in the car.
 

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I want to make a clarification just in case it wasn't already clear. Just a terminology thing.

All the OEM alternators that came from these Odysseys from the factory were made by Denso. There are many companies (some of them terrible, some of them okay), that "re-manufacture" these alternators. The core of these re-mans are ALL Denso cores.

What you want is an alternator that was remanufactured BY Denso, the OEM supplier. You can walk into an Autozone or Advance Auto or NAPA or whatever store, and they may sell you a re-manufactured Denso alternator that was re-manufactured by Duralast or Pure Energy or some other brand. That's not what you want. You want a re-manufactured Denso alternator, re-manufactured by Denso.
 

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Ordered that bad boy this morning from RockAuto. Thanks for all the great advice, everyone.

Now looking at batteries.
Hope you made sure to order the right one for your trim level. You have an EX, so you'd want the one for non-VCM engines.
 

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Discussion Starter #26
Hope you made sure to order the right one for your trim level. You have an EX, so you'd want the one for non-VCM engines.
Oh my. There is only one Denso available for my year on RA. I went with that so fingers crossed?
 

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Oh my. There is only one Denso available for my year on RA. I went with that so fingers crossed?
This is what I see. A VCM and a non-VCM one
161263
 

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This is all I've got for 2009. Do I need to start cross referencing part numbers?

View attachment 161264
Never mind, I chose the wrong year. Interesting that 2009 doesn't seem to have the same VCM non-VCM split the other years have. I think you should be good.
 

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I don't know what you need or don't need, but when you hold a button down for a window or windows, you're in stall mode for the electric window motors, and you're using max current. Alternator voltage will normally drop under very heavy loads.

Also, Honda has a 'dual mode' charging system, which allows alt voltage to drop when the external loads are low. The controller is in the under hood fuse box. See article below:

 

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Sounds like root cause may be the battery. If a cell is going it certainly can load an alternator. I’d replace both as your planning but I’d replace the battery first.
 

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Discussion Starter #32
Good to know the alt is still strong enough to operate normally after overheating like that. The plan is to replace both at the same time, but I wonder if replacing the battery first would turn off the battery light.
 

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Sadly, Rock Auto doesn't have a new one, and I've been having a hard time finding a new one anywhere.

Is a remanned Denso better than no Denso?
YES. I replaced mine with reman Denso ($150 or so from Rockauto) & no problems. Or get unit from HONDA ($MuchMore).
 

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The battery light is turned on by the regulator in the alternator. When the voltage is missing the pin goes low to turn on the light. You saw 10 volts output which I think was caused by a shorted cell in the battery. You let it cool off and charged it possibly clearing the short. Now if everything seems ok and the light is still on the regulator is probably damaged. So you are on borrowed time. Changing the regulator might fix the light problem, but I would not trust the alternator not to fail in the future. The heat has stressed all the components in the alternator and diodes or even the brushes might fail. If the battery is 5 years old replace it, if not load test it to see if it still has capacity.
 

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?? You quoted geotex, but provided no new text.
 

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Discussion Starter #36
FedEx will have it here tomorrow. I'm still scratching my head over why the alt overheated. Was it just its time? I don't want to slap a new one in there if the problem is still there.

My headlight load resistors are 6 ohm at 50 hertz, but they barely get warm. After testing them I couldn't find anything wrong with them to relate them to the alt. They are the only recent addition, which is why I'm hung up on them.
 

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It could have been a shorted diode that is now open. These are 6 phase alternators, two three phase windings in parallel, so it will still run ok with a single open diode.
The burning smell is from the epoxy or silicon rubber that is used for potting the diode. It could also be melted varnish from the stator.
I was a former PE for alternators at one of the largest rebuilders in the country and we also rebuilt for Denso.
Denso is probably the best choice although you could get lucky with another rebuilder depending on what components they used and their process.
With cost being the only requirement it’s hard to know which brands are better with ANY aftermarket part.
 

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These are 6 phase alternators, two three phase windings in parallel, so it will still run ok with a single open diode.
Will you also, possibly, get a whining noise from an alternator with such a problem?

OF
 

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Yes, there will usually be a whining or growling noise when a phase is out (diode or stator). It might not be as pronounced on the six phase units as it would be on a three phase.
 

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Yes, there will usually be a whining or growling noise when a phase is out (diode or stator). It might not be as pronounced on the six phase units as it would be on a three phase.
T-500, thanks for that helpful information. On one of our vehicles (2005 Nissan Altima), that is happening.

That Nissan has surprisingly few grounds (like, only two by my counting), and I'm probably going to replace one and clean up the other before replacing the alternator. I may add one more. This may have contributed to the demise of its alternator, which is still working, but developed an audible whine.

The Odyssey, Accords and Acura TL in our household .... I work on them all, and am always grateful that Honda has a number of stout grounding points, cables and straps leading back to the engine or transmission (and, ergo, the alternator, which grounds via its case).

OF
 
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