Dim lights, battery light

[hell_raiser_1]

I own a 1990 accord, about a year ago i changed the alternator with a rebuilt one, bought a new battery, and change a faulty alternator pulley, now i have some problems, after driving for about 30 to 45 minutes the battery light starts flashing and dissapears with low or high RPM's, and when it flashes the dash and head lights go dim and the neddles bounce.They also do when a turning signal is on and no battery light. i've been reading and i think it might be a ground problem combined with a faulty alternator. But i post to read your comments not mine.

[inafogg]

hello,i would check charging system first sounds like another alt good luck

[jeffcoslacker]

About a year is typical life from a discount auto parts store alternator...that's why I don't use them if I have my choice...

Wouldn't surprise me if it was going bad if that's where you got it. Sounds like a weak diode problem...most parts stores can check the alternator on the car without removing it and the newer testers will tell if a diode problem exists....

Without going into a whole bunch of theory on rectifiers and AC to DC conversion (because I'm not that good with that stuff), here's what may be happening...

The diode bridge takes the output from the three phases of the alternator's AC output and rectifies it into a continuous DC output...each phase produces a third of the combined total. When a diode in the bridge fails, output from that phase is lost in certain conditions and total output drops to 2/3 of normal (so about 9v if normal is around 13.5v) and will pulse with rotation of the alternator...

This usually is more evident at certain rpm ranges, and most times the battery will still have a net positive charge assuming the engine runs mostly in the range where the fault isn't most severe...

The effect mimics a belt that slips in a certain rpm range, to some degree...