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So I was checking my alternator performance by checking the voltage at the battery, and at idle it measures 13.5 volts, but as I rev the engine up, the voltage goes down to about 12.5

Definately not normal, the manual says at 5000 rpm, output should be around 14 volts.

Why would voltage DROP as rpm's increase?


Jud
 

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Not enought output to supply what the engine needs to run.
Check the output from the stator, should be around 90VAC ±. If you're unsure how post back and myself or someone else will lead you thru it or do a search for stator.....Mike
 

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Discussion Starter #3
Ahh yes, makes sense. I was going to check the stator next, I believe the procedure is in my service manual. Thanks.
 

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My bike had the very same problem and after about 4-5 days of riding it wouldn't have enough juice to start the bike. (so on trips I brought along the battery tender and hooked it up overnight once in awhile). I limped it along like that for almost 2 years but it kept getting worse until I would be out of juice in a day. Using an AGM battery too, so it wasn't battery related.

Just last summer I bit the bullet and replaced the stator and rectifier with electrosport brand (the wire connector between the originals had long been removed and direct soldered so I figured it best to just dump both parts - pennywise pound foolish - besides - just try claiming warranty on the electrical parts when the two are from different manufacturers).

Works great now! Parts were about $265 for the stator and rr, and another $40 for gaskets and a shift shaft seal for the side cover. Not a bad DIY job.
 

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The battery is a source of instantaneous current and will in general drain relatively fast. The alternator on the other hand is a source of relatively continuous current and is designed to support the lions portion of the load during standard operation.

When your alternator isn’t covering for the load the voltage will drop. When the voltage is below optimal operating voltage you will not be charging the battery back from starting but worse you are driving the lights and spark plugs off your battery. It is just a matter of time because every time you ride you are slowly draining it more and more.

Not operating with a good alternator will also prematurely kill your battery life. It is bad practice to ride the bike under powered. That being said I love those ratbikes!!!
 
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