Alternator battery drain
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From: Grottoes Va
Alternator battery drain
I have a 1991 ranger with 4.0. It has developed a draw on the battery. With the key switch off the alternator and power distribution box have power to them. The alternator will stay hot after the engine has cooled off. I have replaced key switch, ignition switch at bottom of steering column, starter solenoid switch, and alternator twice. Original alternator was bad. Second one was charging at idle 16.8. Any help would be great.
Welcome to the forum
Alternator always has power on 2 wires, key off, B+ terminal on the back, and the Yellow wire on the 3 wire plug, thats normal
The light green wire on the 3 wire plug is the on/off switch for alternator, also the Battery Light wire, it should only have 12v with key on, this turns ON the alternator, also lights up the Battery Light on the dash, Battery Light should go off after engine starts because alternator is making its own voltage now, so the light green wires 12v is no longer needed
Max voltage from an alternator would be 14.9volts, over that will RUIN the battery and possible vehicle electrical parts, period, so test your volt meter just to make sure its reading correctly
If you really got 16+volts then DO NOT run it, pull it and take alternator back, its BAD
After battery has sat overnight or 4+ hours, test its voltage
12.8volts is a new battery
12.5volts is a 3 year old battery
12.3volts is a 5/6 year old battery and time to shop for battery sale
12.2volts or under is a bad failing battery
If battery voltage drops while you are testing it then battery has an internal short and is self draining, truck electrics are fine
Start engine
Battery should now read 14.3-14.8 volts, thats alternator's voltage regulator working and doing a Quick recharge for battery
After idling or driving for 10 minutes test battery, at idle, should read 13.5-13.8volts, UNDER 14volts, this is maintenance charge, keeps battery topped up without "cooking it", voltage regulator is working well
Over 14volts will "cook" a 12volt battery long term........................which is why 16volts is VERY BAD
Alternator will be warm after working for awhile, that is normal, but not HOT that would mean 1 or 2 fields are bad or a bearing
When engine is running the alternator is powering ALL the vehicle electrics, which is why it gets warm, alternator generates a minimum of 13.5volts, and battery is maximum 12.8volts, so battery is not used at all, its lower voltage, its only purpose is to START the engine
Alternator always has power on 2 wires, key off, B+ terminal on the back, and the Yellow wire on the 3 wire plug, thats normal
The light green wire on the 3 wire plug is the on/off switch for alternator, also the Battery Light wire, it should only have 12v with key on, this turns ON the alternator, also lights up the Battery Light on the dash, Battery Light should go off after engine starts because alternator is making its own voltage now, so the light green wires 12v is no longer needed
Max voltage from an alternator would be 14.9volts, over that will RUIN the battery and possible vehicle electrical parts, period, so test your volt meter just to make sure its reading correctly
If you really got 16+volts then DO NOT run it, pull it and take alternator back, its BAD
After battery has sat overnight or 4+ hours, test its voltage
12.8volts is a new battery
12.5volts is a 3 year old battery
12.3volts is a 5/6 year old battery and time to shop for battery sale
12.2volts or under is a bad failing battery
If battery voltage drops while you are testing it then battery has an internal short and is self draining, truck electrics are fine
Start engine
Battery should now read 14.3-14.8 volts, thats alternator's voltage regulator working and doing a Quick recharge for battery
After idling or driving for 10 minutes test battery, at idle, should read 13.5-13.8volts, UNDER 14volts, this is maintenance charge, keeps battery topped up without "cooking it", voltage regulator is working well
Over 14volts will "cook" a 12volt battery long term........................which is why 16volts is VERY BAD
Alternator will be warm after working for awhile, that is normal, but not HOT that would mean 1 or 2 fields are bad or a bearing
When engine is running the alternator is powering ALL the vehicle electrics, which is why it gets warm, alternator generates a minimum of 13.5volts, and battery is maximum 12.8volts, so battery is not used at all, its lower voltage, its only purpose is to START the engine
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