Why won't the battery charge after installing a new alternator?

Answer 1

A couple of things come to mind on this problem.

First, just because you purchased a new alternator does not guarantee that it will work properly. I have purchased several in my lifetime that I've had to take back to the parts house and have them checked...only to have them give me another because their "new or rebuilt" alternator was faulty. Most auto parts stores have the capability of checking the alternator (always a good idea to have them do before walking out the door with the "new" alternator...will save you a trip and much frustration).

Secondly, your battery may have a partially shorted cell. Your car battery is actually comprised of 6 cells, each producing approximately 2 volts. When a battery ages, some of the material on the lead plates will sluff off of the plates and settle in the bottom of the battery. If this material builds up to the point where it touches the cell plates, it will short out those plates. Sometimes it's just enough to prevent the battery from coming to a full charge (but not enough to give indications of a bad battery when checking unloaded voltage.) Take your battery to an auto parts place and they will check it for free for this condition.

The cause for your check engine light can be determined with an ODB-II scanner. This scanner plugs into a special plug underneath your stearing column. It then collects error information from your Astro's computer. It will also allow you to clear your Check Engine light. Many auto parts stores have tool rental/loaner programs. The one I use simply has you pay the full amount for the scanner and then you can bring it back at anytime for a full refund. By the way, ODB-II scanners are generic to all vehicles sold in the US (after 1997...not absolutely sure on the date). Anyway, if you rent the tool, it would be a good time to check all of your vehicles...often they will have error codes that will give indication of a pending problem..could save you a hassle by taking care of the problem before a component completely fails).

AnswerCheck the thick wire that runs from the Altenator to the Starter Motor. It should then travel from the Starter back the the +ve Battery Terminal. This is the flow for the Altenator to charge the battery. Disconnect the cable at the Starter to isolate its output charge from the Altenator. Connect a Voltmeter from the wire to earth and you have the Altenator output. The battery needs 13.6 to about 14.4 to sustain itself given the heavy load from the Altenator. Although the car battery is 12v it wont sustain itself against load if it isn't charged at 13.6v.

You may have a current drain. You need to trace this through each system.

To do this reconnect the alternator & put your volt meter in series with the battery +ve terminal while on amps mode( remove the lead and insert your multimeter leads to the post and lead end. You should have .03 amps leakage. If the reading is higher start taking your fuses out one by one until the reading goes down to this level. You have now discovered in which circuit you have the current drain(a device left on or pulling power before source, short circuit). A common one is the boot interior light switch being left on. Because you don't hide in the boot if it stays on it kills the battery, but goes indetected because you don't see it Worthwhile doing this before doing anything else. Push the switch that the boot causes to put the light out to see if it goes out.

Hope this helps

Michael