What is wrong with my brand new alternator!? Please help!?

Question

Ok so i bought a brand new alternator for my vehicle, wired it up, then tested the wiring by turning on the ignition to see if the battery light came on. I then started the engine and the battery light went off, and the battery voltage increased on the dash.

I then put in a battery that was charged to about 10 volts and jump started the car. The battery light was now on, and I had to leave the jumper cable connected for the voltage to increase, turning the battery light off. I then drove about 2 miles and switched the car off, tried to start it again but it didnt start, showing a battery voltage of about 9 volts.

I then put in a good battery that was charged to 13 volts, and started the engine. The battery indicator came on and the battery stayed at 12 volts while the engine was running, and 13 volts with the engine switched off. Based on my observation, i noticed that my brand new alternator wasnt charging the battery. Why? Could it be that i need to charge the battery to 14 volts? Did i wire it incorrectly?

Answer 1

Make, model, and year would help because we don't know what the warning light means otherwise. In the 1980s and 1990s it was very common to wire the warning lamp in series with the excitation voltage, the regulator input. When the alternator was not charging the current through the regulator lit the light; when it was charging the alternator provided its own supply to the regulator and the warning light went out. This scheme had a problem, though - when the brushes wore out the current could not flow. The alternator would not work and the light stayed off. By about 2000 that scheme went out of style and later ones often actually measured charging voltage. It would be great to know what the vehicle thought of the voltage. It would also be good to know if the voltage regulator is in the alternator or external, as in some Fords, or in the ECU as in some some Dodge/Chrysler/Jeeps.



Otherwise, if the alternator is a rebuilt my suspicion goes to that first. An amazing number of rebuilt alternators do not work right out of the box or fail very early in life.

Answer 2

Well, you may have shorted out the alternator B+ output fuse or fusible link, or possibly the B+ alternator field flashing current to the internal alternator voltage regulator is dead. With the engine ignition turned on, but without starting the engine, make sure you have +12 VDC on the alternator regulator field flash module input wire with a test light or VOM.



Then, check the alternator output on a VOM and see if you get the same at the battery B+ and the alternator output post. There may be a fusible link in the alternator battery charging cable or if you have an oriental manufactured car, there may be a bolt in fuse in the main engine fuse block that burned out if you got the battery polarity wrong when installing the battery. Those damn jap type cars have batteries of the same size nomenclature with B+ and B- flopped if you get the wrong battery and don't pay attention to the battery terminal polarity markings.

Answer 3

How did you start the motor before you put the battery in? You say " I then put a battery in that was charged to about 10 volts". 10 volts is not a charged battery! A charged battery should be 12 to 13 volts. Check all of the big fuses (fusible links) in the engine compartment fuse box. You probably blew the one that protects the alternator and electrical system while either installing the alternator or jump starting the vehicle. I have no clue why you didn't put a good battery in to begin with. WTF do you mean "change the battery to a 14 volt one"? Cars take a 12 volt battery. They may read a higher or lower voltage depending on how much of a charge they have in them. When the motor is running you should have 13.7 volts or more at the battery posts with the motor running at 1,200 rpm.

Answer 4

*A brand new battery can only be charged to 12.6 volts after the charger has been disconnected for at least two hours to get rid of the residual - surface voltage. Normal battery / alternator voltage with the engine running for at least 30 minutes is 13.3 - 13.4 volts If the internal voltage regulator inside the alternator is allowing the alternator to charge more than 13.4 volts, the acid inside the battery will boil out.

Your alternator needs to be replaced again.

Answer 5

A battery with 10v is dead on arrival with a do not resuscitate label round it's neck. It may charge but probably has an internal short which causes the voltage to plummet as soon as you take it off charge. Get a good battery in your car, at idle it should show 12.5 volts. At a fast idle it should have 14.5 Volts. Use a proper meter. Those in the car are just to look sexy and not necessarily accurate.

Answer 6

It takes more than TWO miles of driving (about 5-10 minutes) to charge a weak battery. You'd be better off to use a battery charger to bring your weak battery up to full charge. If you insist on using your car's alternator to do it, then drive for not less than TWO HOURS before shutting your engine off.

Answer 7

Most auto shops like auto zone will test your alternator for free if you think its not charging, you may have it wired wrong or ether a loose connection that's pulling the battery. start with the alternator first and rule it out, then battery, then connection.

Answer 8

do the job right and fit a brand new battery with your new alternator...........................

Answer 9

do the job right and fit a brand new battery with your new alternator...........................

Answer 10

do the job right and fit a brand new battery with your new alternator...........................

Answer 11

Hi so what makes you think it is the alternator as this could be a variety of other issues besides. an auto electrician would be the best person to find the cause of the issue.

Answer 12

How on earth under any situation you can measure 12 v with the engine running and 13 v with it stopped is beyond me.

FlagMichael has given you the best answer.

Answer 13

Do the job right and fit a brand new battery with your new alternator.

Answer 14

do the job right and fit a brand new battery with your new alternator.........

Answer 15

over 45+ years working on my own cars, I have had two defective alternators right out of the box

yes, it sucks to do the same job twice in one day on your own car

Answer 16

I think your new alternator croaked

Answer 17

i think your new alternator croaked

Answer 18

do the job right and fit a brand new battery with your new alternator...........................