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Author Topic: MD22L Alternator failure  (Read 2386 times)

sy_Anniina

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MD22L Alternator failure
« on: September 01 2022, 11:54 »
Last weekend I noticed dodgy tacho readings and finally charging warning light & beeper came off - strangely warning light came off only in "glow/preheat" key position - and in this position tacho was mostly working - "key up" normal running position no tacho - no warning light.

Spare alternator already ordered but I am planning to measure alternator (in-situ) wired directly to battery, and a separate wired warning light between battery + and alternator D+; effectively bypassing control panel & all other Volvo wiring totally.

If found faulty I have located some Youtube tutorials on how to measure alternator controller and rectifier using a multimeter.

Any other hints / experiences? I am reporting the progress here once I get to the boat the next time (hopefully in a couple of wks)

BR,
Tommi
s/y Anniina
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Yngmar

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Re: MD22L Alternator failure
« Reply #1 on: September 01 2022, 13:33 »
What was dodgy about the tacho readings? The signal for these comes off the "W" terminal, which is simply connected to one of the three stator windings, no diodes are involved at that point. I assume you checked the belt, dropping in and out could be belt slip. Could also just be a faulty electrical connection. Lastly, it won't produce a signal (or power) unless the field is energized, so it could be the regulator failing to do so. So check all of those first and the rectifier diodes last :)

Never a bad idea to have a spare alternator onboard though! :)
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(formerly) Sailing Songbird  ⛵️ Bavaria 40 Ocean (2001)

sy_Anniina

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Re: MD22L Alternator failure
« Reply #2 on: September 01 2022, 17:59 »
No proper charging voltage even on B+ terminal, regardless of start key position.

Dodge tacho = some 10-20sec or so delay on tacho reading  while preheat/Glow, but 'stuck' tacho needle when key in normal position.

Will check connections and measure more.... Governor or connections seem plausible suspects on addition to stator windings...

Tommi
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sy_Anniina

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Re: MD22L Alternator failure
« Reply #3 on: September 23 2022, 09:57 »
Replaced the alternator with a non-Volvo part that fit very well https://www.ebay.com/itm/184213118191 Even the pulley was included even though the description and photos suggested otherwise. Output at batteries 14.4V, yellow sense wire works as expected, since alternator output was closer to 15V (did not take notes..). Have not yet tested max amp output as only charged starting battery that does not accept huge amp rate. Even the dodgy tacho worked now as expected.

Still have to so some bench testing for the old alternator - will repot back on that one. First multimeter diode measurement across B+ and B- suggests that the diode rectifier bridge could be ok...

BR,

Tommi
s/y Anniina



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sy_Anniina

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Re: MD22L Alternator failure
« Reply #4 on: November 18 2022, 09:53 »
No bench testing yet for the old alternator (waiting among the pile of winter jobs), but...

Managed to test alternator max output (leisure batteries 70%, all 12V appliances on, bow thruster on) and the clamp meter was showing consistent 100A output as per spec. Next season is the time for long-term testing of this solution.

BR,

Tommi
s/y Anniina
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