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Old 08-17-2013, 11:10 AM   #1
jrblank
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Battery voltage drop

I have a 2006 focus with 103000 miles and just changed out the Alt and Bat but I'm still having a voltage drop when both the AC and Head lights are on ( starts at 13.0 and goes down below 12.4. When just lights are on is steady at 13.6 and when just AC is on steady at 13.8. I'm not sure where to go from here. I really need some suggestions, Thanks JR


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Old 08-17-2013, 11:35 AM   #2
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Have you considered changing out the grounds, and positive from alt to battery? Do your terminals look good? Any stripped wires anywhere?
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Old 08-17-2013, 12:17 PM   #3
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Whose alternator did you use?

If it was not OEM then there are reported failures of alternators , out of box from alternate suppliers. This is assuming that your battery connections are perfect
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Old 08-17-2013, 12:56 PM   #4
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rechecked the voltages and when the AC is on the voltage is dropping (I stopped at 12.3 so as not to hurt the system). Did not drop below 13.6 when just the lights are on. all connections look good and no frayed wires ( cleaned and lubed the Bat terminals when it was changed out). do not know why the change in the voltage test on the AC but checked it 5 times. Alt is a Duralast from Auto Zone
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Old 08-17-2013, 05:56 PM   #5
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Redo your ground under the air box. Remove the air box, remove the ground wire, sand down the contact areas to bare metal, reattach wires, cover with dielectric grease, reinstall air box.

Retest.
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Old 08-17-2013, 06:13 PM   #6
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@JR

Are these symptoms the same as BEFORE you replaced the Alt and Battery?
Did replacing the Alt and Bat fix anything or add any new symptoms? Did you do the work? Did you inspect your Alt pigtail wires and connector?

Like Gadabout said, you should disconnect/inspect/clean your connections at battery to-> frame; battery to-> engine block; battery to -> starter & starter to Alt.

I have learned here at FF that a healthy charge system should hover inside 14 to 14.4Vdc (this without heavy loads like AC and lights). When less than 14Vdc, you have an old/aging system that may soon fail. Running the AC, Lights, High Speed Fan (AC) will drop it maybe 1 volt. Your issue might sound like a bad Alt, but from what you have said and done, it now sounds like a bad electrical connection.

My charge system runs at 13.9Vdc (no load) and 13.3Vdc when fully loaded. I have a second-hand battery (bought the car like this). I have the original OEM Alt. My days are numbered, and expect to replace both soon.

Good Luck
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Old 08-17-2013, 09:25 PM   #7
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Thanks for the help, I'll clean all the contacts just to make sure. The Alt pig tail was in great shape. When I took the car over to Auto Zone this afternoon the Bat and Alt checked fine and when I put the AC load on it dropped to 12.3 but no lower. It appears that the drop does not start until the high speed fan comes on. When I first tested the voltage and did not have a drop the temp was cool and the high speed fan was not running. When I retested the temp had risen and the fan was running. after I clean all the connections I'll take the car out on the road and check the voltage while driving, if I don't have any drop I'll have a better idea of what to do.
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Old 07-28-2014, 07:21 PM   #8
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Did you figure out a solution to this problem? I'm having the same issue.

Voltage drop to 12 and below if I run the AC. Alternator changed twice (factory replaced in May, and then had to replace the replacement two weeks ago). Same voltage drop when sitting in traffic.

Smelled electrical burning with AC fan running at 4, shut off the ac. Voltage came back up. Tried to verify burning by turning the AC back on once safely out of traffic. Voltage drop with AC fan on at 2, 3 and 4 don't appear to increase the fan speed.

Just pulled heater blower motor and resistor, neither smell burnt
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