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I am having an overcharging issue with my 2000 F350 diesel. It first started when I had a garage check the batteries due to poor starting this winter. They found one reading 6V and I had them replace it. After that the battery light came on. So I had them check it out again and they replaced the other battery. I can't remember if it started before or after the second battery but it started overcharging 16-17 volts according to the dash. I replaced the alternator still overcharging. Since then I have run a 4ga ground from one battery to the alternator and a 4ga ground wire from the other battery to the cab. I also checked most of the stock ground wires which all seem fine. Lastly, I also bought a ford alternator pigtail because one of the wires had cracked insulation and some corrosion. Currently it overcharges unless the battery light comes on which once it does the voltmeter in dash reads normal. Any help would be greatly appreciated.
Did the shop load test the batteries or just measure the voltage? My experience has been to always load test each individually and if one is bad replace both at the same time. How old were the old batteries?
A good starting point would to have a shop load test each battery and go from there. Most tire - battery places will do it for free as they want your business.
Rev up the engine to 2000 RPM. If the charge indicator light gets brighter, re-examine the batteries. If the charge indicator lights gets dimmer, re-examine the alternator.
"One of the batteries was pretty old and the other maybe a few years newer."
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Just an FYI you should always replace batteries in pairs/sets. An older and/or tired battery will drag the new one down quickly.
By the charge indicator light do you mean the battery light?
Yes.
Other than the lamp test at every ignition start cycle, the battery light, or charge indicator light, illuminates by virtue of a DIFFERENCE in voltage sensed between the batteries and the alternator's voltage regulator.
If that difference (in voltage, or potential) is large enough, current will begin flowing across the lamp filament, which we see as light. A difference as small as one volt can be enough to make the lamp glow dimly. Larger differences, such as 3 volts, can make the lamp glow brighter.
Since we cannot control the power output of the batteries with our foot, but we can somewhat control the power output of a working alternator with our foot (at least between idle and some reasonable semblance of road speed), the 2,000 RPM test is a quick, non invasive, no hands get dirty way to determine where to cast one's suspicions.
I had the batteries load tested and they came back fine. The charge light did get slightly brighter when revved to 2000 rpms. They tested the alternator on the truck and it tested as having a bad regulator. I removed it and when they tested it on the bench it tested fine. They gave me a new alternator anyways and it is doing the same thing. I am thinking it might be one of the wires going to the alternator field or the other one maybe.
Measured my alternator today for some reference specs.
1. Engine started, glow plugs OFF.
2. Battery Voltage = 14.53 volts.
3. A Terminal on alternator = 14.47 Volts.
4. I Terminal on alternator = 14.20 volts
Where A terminal is passenger side alternator plug wire. This is the battery voltage sense terminal and should be close to actual battery voltage. A few tenths of a volt off is OK, like mine.
Where I terminal is drivers side alternator plug wire. This is the wire that controls the battery light in instrument cluster. It should also be about the same as battery but is usually a bit lower due to the bulb filament, ignition switch and fuse resistances. The lower the voltage on this terminal the brighter the light will be ON.
Suspect A terminal abnormality, probably a few volts low. If that's the case it's a wire / connection problem from A terminal on the alternator towards the fuse box. The fuse is under-hood #6, 10 Amp. The fuse is probably OK but might have some corroded blades / socket, just a guess at this point.
This is from my E99. Except for wire color codes the alternator should be the same and is why I didn't indicated those wire color codes.
I believe the voltage measured at the I terminal will also have passed through a diode designed to protect electrical system components like the PCM.
To see this for yourself, take a voltage measurement at the 12v pin of the DLC, or easier still, albeit with less of a voltage difference, take a voltage measurement at the cigarette lighter or power point. It will invariably be one to two tenths of a volt lower than voltage taken directly at the battery, or directly at the A and B terminals of the alternator.
I don't think 2 tenths, or even 4 tenths, is enough of a voltage difference to illuminate the battery light. I think it takes at least a half of a volt difference.
The IC cluster printed circuit membrane contains the 470 ohm resistor for the I circuit to the alternator, in line with the battery light aka charge indicator lamp. See green circle and notation added to the photo below.
Originally Posted by gardenman
"I had the batteries load tested and they came back fine"
How were they "load" tested? A capacitance tester? (Small hand held newer type of electronic device) Or a resistance tester? (Larger, heavier, hotter operating device that generally appears older).
I had the batteries load tested and they came back fine.
How were they "load" tested? A capacitance tester? (Small hand held newer type of electronic device) Or a resistance tester? (Larger, heavier, hotter operating device that generally appears older).
I had the batteries load tested and they came back fine.[/QUOTE]
I would guess a resistance tester as it had 3 or 4 coils that were open to the air that were pretty heavy gauge wire. They looked like they were meant to carry some amps and dissipate some heat.
Measured my alternator today for some reference specs.
1. Engine started, glow plugs OFF.
2. Battery Voltage = 14.53 volts.
3. A Terminal on alternator = 14.47 Volts.
4. I Terminal on alternator = 14.20 volts
Where A terminal is passenger side alternator plug wire. This is the battery voltage sense terminal and should be close to actual battery voltage. A few tenths of a volt off is OK, like mine.
Where I terminal is drivers side alternator plug wire. This is the wire that controls the battery light in instrument cluster. It should also be about the same as battery but is usually a bit lower due to the bulb filament, ignition switch and fuse resistances. The lower the voltage on this terminal the brighter the light will be ON.
Suspect A terminal abnormality, probably a few volts low. If that's the case it's a wire / connection problem from A terminal on the alternator towards the fuse box. The fuse is under-hood #6, 10 Amp. The fuse is probably OK but might have some corroded blades / socket, just a guess at this point.
This is from my E99. Except for wire color codes the alternator should be the same and is why I didn't indicated those wire color codes.
This is some great info. I will have to check this tomorrow.
There's a fuse in the under hood panel for the alternator. 2 fuses if it has dual alternators. I believe if this fuse is blown, the alternator does not see "sense" voltage and the regulator will run wide-open. Like yours is doing.
04-13-2017, 09:04 AM
