My father brought his 1989 TRX300 to me last weekend with a dead battery. After confirming the battery was indeed faulty, I replaced it and the bike starts - no problem. I then started checking the charging system and found an odd charging pattern. At higher RPM ranges, I see the charge current drop dramatically. Let me explain in more detail.
I connected an ammeter in series with the battery to check the charging system. At idle, there is approx. 200mA current draw from the battery (no charge). Once I increase the throttle ever so slightly, current flow reverses and charging starts - it jumps up to about 3A of charge current. After reviewing the article on charging systems, I now understand this to be the break-even RPM ( https://atvconnection.com/D...ing-Systems-Page-2.cfm ). If I continue to increase the throttle, the charge current then drops down to a few hundred milliamps. I would expect the charge current to remain consistent at 3 or 4 amps.
I repeated the same test with the headlights on - same results (with different current readings).
Charge voltage is good - varies between 13.9V and 14.1V. For this reason, I do not suspect the regulator to be faulty.
Any thoughts on what would cause this?
Your help is appreciated. Thanks.

 

they sell a aftermarket voltage regulator for racing that does just what u say,charges at low rpm but shutsdown charging to reduce power draw from motor for racing at hi rpm. Just a suggestion search for it on ebay i think

 

Thanks for your response. The regulator in this TRX300 is a standard stock unit. I am starting to wonder if it is faulty. Does anyone have a recommended set of tests for the regulator? Thanks.