Battery light on-1999 ranger 4 cylinder

[kburley]

Hi everyone, i have searched the forum for threads on this topic and have not found any,so forgive me if this topic has been covered already.

I recently noticed that when my engine goes above 3000 rpm, the battery light would flicker. Eventually, it started staying on (solid light as opposed to flickering). And just today, it started coming on at idle as well. Battery voltage at idle is ~14.5v and at 3000 rpm it is ~12.2v and drops swiftly when it is held there. I popped the hood and noticed the battery was quite warm and that there was battery acid all over my engine bay. When running, there is no smell or sound indicating a bad alternator, but i still wouldnt rule it out.

I should note that the vehicle runs and drives fine but the dash lights dim slightly when the battery light comes on.

Does anyone have an idea what is wrong? The battery is 5 months old, so im thinking either the regulator or the alternator. Any help is greatly appreciated. Thanks

 

[scotts90ranger]

your alternator is fried, and it sounds like it probably took out the battery, or is on the way to

 

[RonD]

'99 with have voltage regulator in the alternator, and while you can swap out just the regulator it is often best just to replace the whole alternator.

The battery light is a simple circuit.
A light bulb will only light up when power passes THRU it.
If you connect 12volts to one terminal of a light bulb, and 12volts to the other terminal, what happens?
Nothing, light bulb will stay off, there is voltage but it isn't flowing, passing THRU the bulb.
If you connect 12volts to one terminal and 0volts(ground) to the other, THEN the light bulb will light up, because there is voltage flowing THRU the bulb.

Battery light is connected to key switch, when you turn key on the battery light gets 12volts on one terminal, the other terminal is connected to the alternator(voltage regulator) and if engine is off the alternator is 0volts, so bulb is on.
When you start the engine the alternator generates 14volts and the whole electrical system now has 14volts, so battery light has 14volts on each terminal, bulb is off.

So what is happening in your case is that at higher RPMs the alternator is shutting off, the 12.2 volts is Battery voltage, the alternator voltage is below that, so...........battery light comes on as voltage passes THRU it.


And yes, your battery has been overcharged, overflowing battery chemicals is the sign of that, so replace both alternator and battery, then check system for proper voltage.
12.4 to 12.8 volts at battery with key off
14.5-14.9volts just after starting(recharging battery from starter motor drain).
13.5-13.8volts after a few minutes(keeps battery charged without over charging it)

Turn on lights, heater fan, radio, ect..........voltage should stay between 13.5 and 13.8volts, this means voltage regulator is working.