whitepointer 33 Posted May 16, 2022 Share Posted May 16, 2022 I noticed the charge light is illuminated on my yanmar 3ym instrument panel, though the volt/amp meter is still showing current going to batteries, I had the alternator rebuilt about 30 hrs ago, anybody know what might be the cause Quote Link to post Share on other sites
aardvarkash10 943 Posted May 16, 2022 Share Posted May 16, 2022 How bright? A failed exciter diode (inside hte alternator) would cause the light to illuminate, but not a full brightness. The alternator will still charge, just to to spec output. Quote Link to post Share on other sites
whitepointer 33 Posted May 16, 2022 Author Share Posted May 16, 2022 Yes, it doesn’t seem that bright, that could be the cause alright, I will get it checked by an Auto electrician Quote Link to post Share on other sites
aardvarkash10 943 Posted May 16, 2022 Share Posted May 16, 2022 It will also glow dimly if there is a large voltage drop in the circuit between the bulb and the alternator. Either way, it's probably a auto sparkie thing. Quote Link to post Share on other sites
ballystick 72 Posted May 16, 2022 Share Posted May 16, 2022 This may help you 1 Quote Link to post Share on other sites
wheels 543 Posted May 16, 2022 Share Posted May 16, 2022 Two small things to check first. Any chance the belt could be slipping? I know you will likely hear a slipping belt, but there can be times when it slips and it does not squeal. Which brings me to the next thing to check. A slipping belt means that under high load, the ALT may not be spinning fast enough to produce full output. The same thing happens if the engine is idling too low. Does the light go out if you raise the Revs? High Load will be if the batteries are very low in charge state when you begin Charging. So also check that the Batteries are in OK condition. If they are not accepting charge, or are taking a very high current from the ALT, then the ALT light might also light up. Failing that, go with the great advice above. Quote Link to post Share on other sites
whitepointer 33 Posted May 17, 2022 Author Share Posted May 17, 2022 Batteries were at 90%, and belt tension is good, couple of days before the tachometer threw a wobbly briefly, I turned motor off and restarted and it came right again, maybe a sign off a bad connection somewhere, thanks for all advice, I will do some checks when next on boat Quote Link to post Share on other sites
wheels 543 Posted May 17, 2022 Share Posted May 17, 2022 Poor electrical connections tend to be the most common cause of such problems. Internal issues with an ALT is less likely, especially on a newly rebuilt unit. Not impossible, but the least likely. Do you know how to use a multi meter in both Voltage and Ohm's mode?? There could be a clue to a problem in what you have decsribed with the Tacho and turning engine off and on again. The ignistion Key may have a faulty/dirty/worn connection internally. That internal switch is sending a "sense" voltage to the ALT. If that switch has become "noisy" as in a poor connection, the ALT will be getting a poor and no constant voltage. That can result in the Tacho giving a non consistant reading. If you have a Voltage or current metre on the switch panel, you may see those readings vary in a constantly up and down way as well. Also check the power to the Ign switch and from ign switch to ALT. If you don't have monitoring metres on the switch panel, then use the Multi meter to view the voltage into the battery. It should remain a calm reading of around 13.8V upto 14.4V, depending on the setup. Quote Link to post Share on other sites
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