- Joined
- Aug 19, 2001
- Messages
- 10,749
- Reaction score
- 580
- Points
- 113
- Location
- So. Calif (SFV)
- Vehicle Year
- 1990
- Make / Model
- Bronco II
- Engine Type
- 2.9 V6
- Engine Size
- 2.9L V6
- Transmission
- Manual
- 2WD / 4WD
- 4WD
- Tire Size
- 35x12.50R15
This is correct.As long as the alternator is putting out juice, even if the battery has to help it out, it flips something in the regulator and turns the light off. If the alternator is putting out nothing because of a failure or the belt came off, then the light comes on.
If the engine is getting ready to stall, it's turning so slow the alternator is putting out virtual nothing, I have seen the light flicker. But as long as the alternator is trying to keep up and has output, I have never seen the light come on.
The voltage regulator (VR) switches on the battery light when it sees there is no voltage output coming from the stator winding in the alternator.
When the key is first turned on, the VR is initially fed a small current through the battery lamp circuit (bulb & resistor in parallel). This causes the lamp to illuminate, and also activates the VR which in turn applies a current through the alternator's field coil (activating the alt's ability to generate power, so to speak). When the alt (field coil) begins to spin (starting of the engine), the spinning (energized) field coil induces an AC voltage/current in the stator winding, which is then rectified to DC (via six diodes) and fed straight out to the battery for charging and running of electrical loads. It is this voltage from the stator winding that, if present, will cause the VR to switch off all current going through the battery lamp circuit (causing the light to go off).
If you pull so many amps that the alternator can't keep up and you're now also drawing off the battery, the light still does not come on because there will still be ~12.5-13V at the stator since the alt is still putting out current, it's just not enough to overcome whatever electrical loads you have added and to be able to charge the battery.
At no point should the battery ever be at a higher voltage than that of a properly-functioning alternator (your accessory loads should be connected to your battery, not the back of your alt).
To the OP,
One or two LED lightbars, an E-fan, and two stereo amps the size you mentioned should be fine with a 130A alt. Most "500 watt" car amps for example are in reality closer to around 80-100 actual (or RMS) watts, since watt ratings on 12V car amps are not regulated the way home stereo equipment ratings are (you'll often see things like "Max watts" or "P.M.P.O." (Peak Maximum Power Output) touted prominently, which are nothing more than instantaneous power measurements taken at a specific point such as at the very peak of a sinusoidal waveform, which results in a highly-inflated number relative to the amp's actual power output capability before distortion (clipping) occurs).
If you do find that your truck's voltage fluctuates with the beat of the music (which is not unusual to have happen), like said above, adding a capacitor across the power leads to the amps should solve the issue (a one or two farad cap should do it). Capacitors are available at most places that specialize in mobile audio.