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Discussion Starter · #1 ·
Hi everyone,

Drove out the other day after cleaning maple tree debris from car while it idled. Pulled the P-brake, so saw indicator off; no other dash lights. Mild and VERY humid morning.

Going up steep hill to intersection, battery light came on for up to 60 seconds. Then went off.

I have a multimeter, so here are voltage values taken from the battery posts:

Cold, engine off12.3 V
Start, cold idle, no load16.0 V
Idle warm, no load15.69 V
Idle warm, load15.75 down to 15.6 V
Engine off after idle test (15 minutes)12.68 V

Window switches used while glass up seemed to make headlights lights flick. (I did forget to turn on wipers and rear defrost for the test. Will have to redo.)

So why the battery light? Is my alternator running too high AND the battery dying? That 12.3 V after sitting for a day suggests an old battery.

This is a 2009 V6 XLT with about 138,000 km. Never had a light other than bad TPS and low tire pressure (both fixed). We've had heavy rains and cool, extremely humid weather for weeks.
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Thanks for advice!
 

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My OPINION is that the voltages are a bit higher than expected, but it could be meter differences. A fully charged battery is several tenths higher than 12.3. If you want, you can check a disconnected battery daily to see the voltage drop and graph to see if too severe. In-vehicle, you would have to put a meter in series to know the 'sleeping' battery consumption. It can be done without losing radio stations, etc, with a little planning.
As far as the alternator, you can also use a clamp-on meter around the feed from the alternator to determine amperage that is being produced.
I believe there have been some recent posts about alternator problems and in one of them is a link to a FoMoCo test procedure. For sure there's one about checking the connection from alternator to the ECM and also noting the pulsed commands from ECM to alternator.
My memory(nothing official) says that the limit on voltage should be around 14.7 at its max, but my memory is long, not deep.
tom
 

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Discussion Starter · #3 ·
My memory(nothing official) says that the limit on voltage should be around 14.7 at its max, but my memory is long, not deep.
tom
In my case here, we have a battery light on, 16 volts on a cold revving car engine at startup, and I just found radio and fan system don't like to work sometimes just as the engine is fired up.

I'm reading 15.7 V when the engine is at warm idle. This seems high.
 

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I recall the in-dash cd player making errors and refusing to play when the battery was getting old and its capacity and internal series resistance were not absorbing correctly the power spikes from the alt and the loads. When the battery capacity is too low, any fluctuation in current draw and direction reflects in the battery voltage. You see it with the headlights flashing. A battery tester would probably call it near death. How old is it? As your car may not be able to crank soon, I'd start with a new battery. Then read the voltages again, to make sure that the alt behaves correctly. If the battery still goes above 14.5 volts the alt might deserve more attention.
 

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Discussion Starter · #5 ·
If the battery still goes above 14.5 volts the alt might deserve more attention.
The factory alternator is approaching 90,000 miles and is putting out 15.7 volts now with the car at warm idle. Would I cook a new battery if a problematic alternator is overcharging?
 

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The factory alternator is approaching 90,000 miles and is putting out 15.7 volts now with the car at warm idle. Would I cook a new battery if a problematic alternator is overcharging?
If the battery capacity is too low, the lowest "charge" command may be enough to place the battery in overcharge state. Yes 15.7 is high, this is why you must monitor the voltages with a new battery to avoid frying it too. With a full capacity it accepts a higher trickle current without its voltage going so high. Just keep an eye on the voltage as soon as you have it installed. The "charged" voltage" should be lower, and the "cold car off" voltage should be higher than what you have (this also being the result of a lower internal resistance). A new battery is an easy job. A new alt is a different story. Replacing it is quite a pain. Even though it has a good mileage, it may still be good.
 

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you know, auto parts stores bench test all this crap for free… Why are you guessing?
 

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you know, auto parts stores bench test all this crap for free… Why are you guessing?
when the 12v battery goes out in my hybrid, the car stops. My guess is your battery is dying. my battery fully charged us 13 V about… Look at the date code on your battery, it should be replaced every five years.
 

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Discussion Starter · #9 · (Edited)
you know, auto parts stores bench test all this crap for free… Why are you guessing?
Just one place here does free battery tests. I gave them numbers and they said "alternator." As soon as they saw 16 volts on start-up and 15.7 at warm idle. Not guessing, really. The alternator is far older than the battery. The car also starts effortlessly.

Winter is coming and I'd rather just replace both. If the alternator is bad and overcharging, it's gonna cook a new battery while I have to swap the alt anyway. If the battery is going, the alternator is gonna fail anyway in six months, or nine, or twelve. Right now I have the chance to get the work done just up the street. Rather the expense now than a failure down the line.
 

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If you can talk someone into it, you could swap in a new battery and see what the charge voltage is. An alternate test would be one of the resistance testers that calculate the condition based upon amp hour capacity. They will also use CCA as a 'measuring' factor and come up with 'life' left. They are not expensive testers.
The idea of having part store test my alt, from an emt with a 3.0 is kind of something I will not do. too dang hard to R&R for testing only. battery voltage at rest, at idle, at road rpm, and loaded/unloaded will/should tell the tale.
tom
 

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Discussion Starter · #11 ·
battery voltage at rest, at idle, at road rpm, and loaded/unloaded will/should tell the tale.
tom
The thing I've found about alternators is how they fail typically while you're en route to someplace. I've seen three failures. They were aaaaaalways on the highway or in heavy urban traffic. How often does anyone test an alternator?
 

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Discussion Starter · #13 ·
At speed on rainy, slushy days.
Something else: my local Ford parts shop reports new and re-man Motorcraft alternators for '09 Escape are .... discontinued and/or on back-order.

A few here were saying "why bother," but my new GL951/9L8Z-10346A arrived today ...
 

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An alternator does not have a plethora of parts. An armature with bearings at either end. The bearings can fail, but they announce way ahead of time mostly. Two slip rings attached that connect to the armature windings. Generally last a long time, but can get grooved. Replacement time for me.
The diode array mounts inside the alternator, gets the juice from the slip ring via the brushes(another wear item) and rectify it. One or more can fail, but they are not hard to replace, except for the large soldering iron necessary.
The regulator, accepts the DC from the array, and pokes at the field windings(forgot) that surround the armature. More v to the field==more juice from the armature>slip rings>rectifier>regulator>battery/consumers.
Many rebuilt alternators are cleaned up, rings tuned and shined, bearings replaced(maybe) and the diode array washed and tested. Regulator re-used if it tests good. So a mish-mash of parts from how many 'dead' alternators are
poked together and sold... What are the odds you get a bunch of good parts vs the odds of one or more 'used' parts that will fail soonly?
I have replaced bearings, replaced brushes, and cleaned slip rings. I think should I need more, I will likely try to get parts from an online re-builder supply store. And do it myself. At least I know then what is what, where it came from, and how well it was inspected/cleaned/adjusted/shined/etc, cuz I will do it.
I do think the regulators are not replaced as often as needed by rebuilders, but that is just opinion. If it tests good, ship it. Takes no account for heat related problems, etc.
The windings in the armature and field mostly will be fine, unless they are smoke tested. Brushes are a visible check item. Bearings, by feel. Diode by measure resistance in both directions, and regulator? who knows.
tom
 
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