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Discussion Starter #1
Car: 2003 Ford Focus zx5 Zetec Vortech Supercharged.

Hi, I recently bought a new alternator and pigtail connector.
I installed everything and my alternator was working charging my battery to 15V.
Until I threw the ignition off and back on, my alternator didn't charge my battery like before and battery light came on.
Every time I unhook one of the battery terminals and I hook them back, my alternator charge my battery like it is supposed to do, until I throw the igniton off and starting my car back on, my alternator doesn't charge.[rant]

Battery tested good at local part shop.
All my grounds are good, all my connection to the alternator are good and I even tested all my fuses in the hood compartment.
I tested the alternator to the positive battery terminal and it gave me under 0.05 Ohms which is good.
I tested the alternator connector and it was all fine.

Don't know what to do except go change my alternator again since it's guarantee.

Thanks for your help, regards, Kevin.
 

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Many are bad right out of the box and common. Have the store test it.
 

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Your alternator does not charge the whole time the car is running, and the voltage will kick up and down while you drive. When your car is idling, it also go into a low or nil charge state and run mostly on batt power until you give it gas.

A great demo to yourself of what I'm talking about is to hop in your ride and hold the odometer reset button while you start the car. Keep holding it until the instrument cluster goes into diagnostic mode. When it does (you'll know when it does), lift off the button and make 16 presses. You have to watch the screen while you press the button and count because the button is a cheap lil plastic thing and doesn't always change with every single press, so it needs to change 16 times from button presses. If you press say, the fourth time and the display doesn't change to something else, then don't count that press. 16 presses will give you a display of the batt voltage. (b 12.8)
 

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Start your car with the ac ON. You wi see the voltage climb to 13.9 or somthing maybe 14 something when your car is running. Eventually (after the engine is full operating temp) it will settle to 12.9-13.1. Anyway on with the test part....

While it's running and the voltage is steady, give your car a little throttle. (Just a moderate amount, nothing crazy). You will notice the voltage drop when you press the gas. That's good and normal. Then let off the throttle and stare at the voltage meter. After the car has been back at idle for 15 seconds or so, you will see the voltage slowly climbing .1V at a time. Hit the gas, boom voltage drops again. That means your alt n regulator are working fine if it behaves exactly as described.

A fun little trick I use for bass contests is, while the car is still running, go ahead and shut off the ac. Notice what your voltage is with the ac on (~12.6-13.1), then after you have shut the ac off wait 60 seconds and you will see the car raise a whole 'nother volt! :) I use that extra volt to combat voltage drop at the bass contests. Many other competitors have to rev up their 'high output alternators' while competing, but since I knew our cars behave this way at idle, I had Mechman build my alt to have the highest current I possibly could, at idle, so I compete at idle while most everyone is revving their cars up. Makes our little cars look more amazing at the competitions when you hit big numbers at idle and no extra batteries. ?

Sorry for the long read. If your car behaves the ways I described, your alt n regulator should be good.
 

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Other things you could check are
check whether it stops charging when the ac compressor kicks on. If the belt is slipping too much it will not charge. Ac can make the belt slip when it kicks in if it is running low on lube, or if the belt is cheap, stretched, too long or if any pulley bearing on the engine is failing.

I mentioned a 'cheap' belt because I literally bought a new acc belt from az a couple of months ago when my ps pump blew a leak. I had to clean the whole side of the motor and engine bay (was a 4.5 hr messy job!). AZ don't sell Gates belts for our cars, so I put a no-name on it. Fkn sqealed like a pig every start up and when the ac kicked on OR IF MY ALT was trying to charge heavily to recover from heavy bass use. It must've been an inch too long. I dealt with it for a week thinking I must have not cleaned all the pulleys well enough. I finally went and bought a Gates and boom..... All good. So don't trust a brand new cheapo belt.
 

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Oh yeah and check your tensioner. It may just need to be persuaded a little tighter against the belt. Sometimes that spring action gets bound and doesn't push it's max against the belt. Without making the belt come off, exercise the tensioner back and forth a few times to break up whatever crud could be holding it from max tension.

Ok I'm done lol. Each of those things I wrote about have been seperate problems I've had to figure out and fix, and each time my alt wasn't charging.
 

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15 volts would be bad as well, shouldn't charge that high.
 

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Discussion Starter #9
Thanks for all your replies.
The rebuilt alternator was the problem.
I installed it and everything works fine.
But still goes to 15V on idle, is it OK?

Regards, Kevin.
 

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That's too high to see as a consistent number, battery would be overcharged & damaged.
 

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If it is charging that high you have a bad ground brotha. That new batt will be toast quickly. Add a new, thicker ground wire from the neg to the frame.
 

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Pure overcharging is generally caused by a bad regulator.
 

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It could also be an issue with the PCM to alternator interface / wiring which disrupts the smart charging system. In other words, the alternator will function as a conventional generator and its output will no longer be controlled by the PCM.

Bear in mind also that the high output voltage is not being delivered only to the battery but to other components directly connected to the power rail.
 

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Again, you're talking regulator there.
 

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It's regulated to avoid differences with speed, otherwise it'd be constantly changing with rpm.
 
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