Replaced alternator, charging light flickers when revved.

[m3456y]

I swapped out the alternator in my '92 and it looks to be charging fine- based on the gauge, but when I rev the engine the charging light flickers a bit. It did not do this before. Any suggestions?

 

[Old Guy]

The charging light is connected between the battery (switched through the ignition switch) and a connection on the regulator on the alternator that effectively represents the internal voltage of the alternator when it is running. If the battery voltage is higher than the internal voltage of the alternator, current flows through the light causing it to light up (this is why it lights up bright when you turn the key to the run position but haven't engaged the starter yet). Once the engine starts and the alternator starts producing voltage, the internal voltage of the alternator should be slightly higher than the battery voltage and the light goes out or is too dim to see - depends on the design of the regulator. Three possible causes (NOT THE ONLY CAUSES - but I will focus on the ones that could be tied directly to the replacement of the regulator) for the charging light flickering is that 1) there is an intermittent ground on the wire between the charging light and the voltage regulator connection (current is flowing from the battery, through the light to ground). Make sure that the 4 terminal plug regulator connection on the alternator is properly seated and that the wires leading into the plug are not chaffed. 2) the internal voltage of the alternator is dropping below the battery voltage in which case the battery is not getting charged and will eventually die (internal voltage of the alternator has to be slightly higher than the battery voltage). The voltmeter on the dash reads the battery voltage, not directly what the alternator is doing. The alternator and regulator can be faulty or underperforming and it make take minutes or days (depends on how underperforming) before the battery voltage deteriorates. The dash voltmeter should normally read around 14v or a little higher. If the battery voltage starts dropping over time (and the charging light is flickering) you have an alternator / regulator problem. If this is the case, check to make sure that the frame of the alternator is solidly grounded (no dirt) at its mounting point and that the 4 terminal plug on the regulator is seated and wiring undamaged. The regulator need +12 v from the battery to energize the field coli on the alternator. If the connections in that plug are bad, this could cause a charging problem. There are two +12v supplies to the regulator that are fused; however, if those fuses were blown I suspect the charge light would be on all the time. 3) The internal voltage of the regulator is too high. This one is a little iffy as I am unsure of the circuit arrangement in the NSX voltage regulator and whether the charging light would light up for this condition. With the engine turning about 2000 rpm, if the voltage goes above 15v you have an over performing regulator and you will overcharge the battery and ultimately destroy it. So the short answer is check the connections at the alternator and mounting of the alternator. If that does not provide an obvious fix, the service manual in the wiki section of Prime provides an excellent test procedure; however, it does require some test equipment. A final comment, if this is a rebuilt alternator, it does not necessarily guarantee that the regulator and alternator are up to spec!

 

[m3456y]

I love this community!!

I contacted the place that rebuilt the alternator and they said it was a voltage regulator issue. They are sending me another unit. Thanks for the response....it was very useful!!