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Discussion Starter #1
Hello guys,

After a lot of testing I decided to write a post and hope to get some help here as I just can‘t figure out what the problem is, why my bike is not charging.
Bike: Yamaha TW125 - 1999 (I know this is a TW200 forum, but this should not matter I hope)

Problem: Not charging while riding the bike, I have to manually charge the battery every few days
What works: Starting the bike, lights and everything else

What I tried:
1.) Tested stator voltage: 47,5V and 47,7V on 1,2 and on 1,3 (white cables) - see picture below, same as for resistance test
2.) Tested stator coil resistance: 0,8 and 0,9 Ohms at 25 Celsius. (should be between 0.48 and 0.72 at 20 Celsius)
3.) Changed regulator, didn‘t fix the problem
4.) Fuse is working

Can anyone help me fix the problem? This is driving me crazy!

Thank you so much in advance!

Best,
Arian from Austria
 

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Since you have tested all the other stuff I would replace the battery.
 

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Remove the battery. Charge it on the bench with your manual charger. Disconnect from charger and measure voltage for the next couple days. My bet is you have a shorted cell and need a new battery. Most factory and many after market batteries have very thin plates that can short out due to vibration and bouncing.
I got tired of replacing batteries and bought a Lithium battery. It's held up for over 5 years and never needs charging. Even after sitting all winter, the battery will still easily start my bike.
Don't forget to post your results! We care how this ends up.
 

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Discussion Starter #6
Remove the battery. Charge it on the bench with your manual charger. Disconnect from charger and measure voltage for the next couple days. My bet is you have a shorted cell and need a new battery. Most factory and many after market batteries have very thin plates that can short out due to vibration and bouncing.
I got tired of replacing batteries and bought a Lithium battery. It's held up for over 5 years and never needs charging. Even after sitting all winter, the battery will still easily start my bike.
Don't forget to post your results! We care how this ends up.
Thank you very much for your detailed reply!
I did that already.
Voltage starts with 13,8V when charged to max.
After I fire the bike up it quickly drops to about 12,5 and loses a few .x volts every day while riding. With lights on the battery is dead very quickly and the lights will go completely dark which for me sounds more like a regulator or stator problem.

Would you mind checking your stator voltage, if you got time? I read somewhere, that it should be between 50-70 volts, where mine is just below 50V.

I will definitely post what fixed the problem once done - Love this forum, so many great and helpful people!
 

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Discussion Starter #7
Also: What voltage should I read with no battery attached and the bike running on the battery leads while idle and at about 5000rpm?
Thank you guys in advance!
 

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You should read around 12.8 volts on a fully charged battery while at idle. Mine normally doesn't go above 13.8 volts at 5K rpm.
 

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Discussion Starter #9
You should read around 12.8 volts on a fully charged battery while at idle. Mine normally doesn't go above 13.8 volts at 5K rpm.
Is this with a battery connected or disconnected? I would like to cancel out the battery as beeing a problem by knowing what voltage i should read without it. Thank you!
 

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Is this with a battery connected or disconnected? I would like to cancel out the battery as beeing a problem by knowing what voltage i should read without it. Thank you!
That is with battery installed. Measured at the battery posts on a fully charged battery with the motor running at idle and 5Krpm
 

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Discussion Starter #11
That is with battery installed. Measured at the battery posts on a fully charged battery with the motor running at idle and 5Krpm
changing the battery didn‘t help
so i bought another regulator and now with the motor at idle i climb to about 12,8V and at 5000rpm I climb to about 13,7V

looks like I got a bad regulator

thank you for your help!
 

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Thanks for the followup! Glad to hear it wasn't anything more expensive. I don't recall anyone having a regulator problem prior to yours.
 
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