Motorcycle Repair: How to Check a 3 Phase Bridge Rectifier on a 2009 Kawasaki KLR 650

Motorcycle Repair: How to Check a 3 Phase Bridge Rectifier on a 2009 Kawasaki KLR 650

**Always follow the instructions in your repair manual when doing repair or maintenance work on a motorcycle. Manuals can be found at the dealer and online.**

Motorcycle alternators produce alternating current (AC) and voltage, and this type of electrical signal can’t be used to charge a battery. A rectifier is the part largely responsible for changing the AC signal to direct current, which can be used to charge the battery and run other components of the motorcycle. There are several different rectifier designs, but the rectifier circuit used on most modern motorcycles and automobiles is call a 3 phase bridge rectifier. The circuit is made up of 6 diodes and the diodes are responsible for flipping the negative portion of a AC signal to positive.

The diodes in the rectifier can be checked using a multimeter with a diode function. The meter I use in this video is a Cen-Tech, and can be purchased at Harbor Freight for under . When the positive lead of the multimeter is placed on the diode anode, and the negative lead is placed on the cathode, the meter should display the amount of voltage dropped across the diode in millivolts. When the negative lead is placed on the anode and the positive is placed on the cathode, than a 1 should be displaced on the meter, and it means the diode is open and won’t allow current to flow. If you get the same response from the diode no matter how the leads are placed on the diode, than the diode is defective and a new regulator/rectifier needs to be purchased for the motorcycle. We are not looking for a specific voltage drop value when the positive meter lead is on the anode and the negative lead is on the cathode, we are only concerned that there is a voltage drop.

Thank you for watching!

40 thoughts on “Motorcycle Repair: How to Check a 3 Phase Bridge Rectifier on a 2009 Kawasaki KLR 650

  1. This video clears my mind in understanding the rectifiers, i do have a question and hope you can answer it to my email., this is my bro account, anyways.. i see that youve selected threw a b c d e diodes, though you have 6 diodes inside the rectifier, do you just ignore the middle top one? or how do you know wich one, is A, b c d and e? i hope you can answer, nice video..

  2. Great video man!! I can say I actually learned something today. Everything you presented was well understood. I’m in the middle of testing my rectifier off my 05 gsxr 600. My diodes are opposite reading of what you’re doing. I have the same HF multimeter, and have the red/black leads hooked up exactly how you do. However, when I put the positive on (A), and touch C D and E I get a reading of around .45V. When I switch the leads around as you did, I get a 1v showing. From what you said, its good

  3. if you only show a drop one way which is what I got from my results. Is the gsxr rectifier just built differently? I tested exactly how the FSM said to, which is exactly how you were doing it. I’m just baffled how I have the reading reversed. I’m showing 1v when it should be .4-.7v according to my FSM and what you said. But to reiterate, the voltage drops only happen one way, and not both. Any insight?

  4. Good tutorial. That covers the rectifier part of the RR. What about the regulator? I know that the closed circuit voltage should be about 14.5V across the battery. What should the open circuit voltage be across the battery?

  5. hey man…when your explainin the load that the rectifier sends to…..could that load possibly my fuel pump relay..mine keep fring like fuel pump still works but my start button wont work so when i use the starter soleniod it cranks over but no spark…my bike is a yzf600r…ive change everything except my rectifier..alil project bike ive been working on…i forgot about the rectifier and i see alil burn on one of da pins on da harness..thanks in advance

  6. the top half has no reading does that mean that the top half is no good and it will not charge the battery

  7. thank you, i try to check the regulator rectifier but i didn’t know how, this video save me, thanks again

  8. Wow I had been confused on how to test my rectifier after view a number if video’s but after watching this, not only did I know how to test it, I was educated of how the system worked. Thx very much for taking the time to exp it all. Craig x

  9. thanks a lot for this video. i learned more in 15 mins of watching then I did in my entire semester of Intro-elec at school.

  10. how do you determine which “prong” is pos; neg; vs the diodes? trial and error? pos is always top left?

  11. hi, will there be a motorcycle rectifier that has single phase rectifier as oppose to three phase rectifier,?.

  12. I think it’s about time to get wrenches and begin to fix my motorcycle electrical problem.Thank you! Thank you

  13. Perfect explanation! My rectifier sends 17.4 volts to my f650 BMW batterie. If I wan’t open the lights, my bike makes power interruptions after 2000 rpms and I can not acclerate. It should send about 14 volts. I’ve allready changed it once and I do not want to pay again. Any idea what happens?

  14. Thanks brother! You helped me allot to understand wether or not my 08 KLR 650 rectifier is bad. Its not. Plus I learned allot using my multimeter by listening to you. Thank you!

  15. What wire would go from the alternator to the rectifier/regulator and what other wire could be used for accessories. Iam restoring a wheel horse 252h and the wiring was butchered any help would be appreiciated.

  16. Thanks so much for this excellent explanation of the workings of a regulator rectifier. Your video is easier to understand than my bikes manual which contradicts the perfect sense you make regarding the flow of electricity through the diodes. The readings I’m getting from mine are the same as yours yet my manual tells me I should be getting a reading between all combinations of wires on the reg/rec as opposed to readings on some and nothing on others. Have I missed something or would that be possible on some reg/recs? Thanks again.

  17. Very good video my rectifier test out fine but i also get a reading between red & green and only in one direction a & b in video is this fine or what

  18. This is a first-rate tutorial. Well done. On my bike I am running a PMA, through the regulator rectifier to a capacitor (no battery). Ran fine then hit a problem of running poorly. I followed your tutorial to test the regulator rectifier – all the diodes had voltage drop close to each other 595 to 620 one way, and reading 1 the other. Trouble is, my Chinese digital voltmeter is showing a reading 14.7v to 15.4v (wired between ignition switch and fuses).  I checked on my second Chinese digital voltmeter, and the same readings (the voltmeters were recommended by YouTube reviews). As far as I can tell, then, the regulator rectifier is working, but it is allowing to much DC voltage through. Is there anything else I could check, or must I replace the unit? By the way, I removed my new battery because the standing reading dropped quickly from 12.8 to 10.6v indicating a bad cell – the high voltage over 14.4v might have caused that. 

  19. good video.
    One thing you may want to mention is that the rectifier that you are diagnosing is a full-wave one as opposed to a half-wave rectifier.

  20. Thanks for this upload. It really explained alot in my particular situation. I tested my rectifier and I am getting a reading of around 432 one way but when reversing polarity, I am still getting a reading, this time 1218 across, not “1” like it should read. I hope this proves a bad rectifier because I really don’t feel like replacing the stator…

  21. I’ve been wounding how to check my voltage regulator/rectifier As my battery is not charging
    Your video is just what I’ve been looking for and the detail is perfect as other videos tell you very little in regards to component functionality thanks mate 🙂

  22. Thanks for an excellent video!
    My scooter has a rectifier/regulator with 6 cables. I.e. one more than yours. The 6:th cable (black) seems to be connected to the lights. The thing is, the scooter is dead. Ignition key in On position but no light, no start, nothing. (+) in your scheme, red cable on mine, and gets +12 when key=on. (-) is green. The black reads 0 V and I don’t measure any connection (ohm) to any other cable when unit is totally disconnected from the scooter. Any idea what the black is?
    Btw, the rectifier is OK. Thanks again for the VERY pedagogic instruction!

  23. thank you.. I was totally confused since when I test my stator it was fine but my rectifier giving me a bad reading if i follow the manual.. After watching your video I’m 100% confirm that my rectifier are dead since both side showing reading on lower part.. Thank you..

  24. I have a klr 650 and the cdi box went bad so i got a new one put in bike hit starter button spark plug had lots of spark for 30 sec then no spark put another cdi box and same thing the stator is a/c and bike is 12v dc if the rectifier is bad does the a/c go to cdi ??

  25. Great tutorial. I recently couldn’t start my 08 Kawi Versus 650 due to a low battery charge after riding slow around a city a few hours. I had to get a jump start to get home. I’m wondering if this is normal since I rode a long time around the city with the RPM’s low. I have about 35k miles on the bike and I checked the fairly new battery @ 12.8v after charging it up with the bike off. I then pulled the rectifier and tested exactly as you did. My question is if the tested voltage drops are supposed to be consistent or is it ok if they are different? My readings look like this + to white blue 1,1,1. Then — to white blue 511, 515, 517, Then + to brown 1,1,1 — to brown 1,1,1. Then + to black/yellow 506, 514, 484. Finally — to black/yellow 1,1,1. I’m looking at replacing the rectifier with a new FH020AA MOSFET replacement found on Ebay. When I ran the bike the volts were 12.8-14.5 while revving the bike to around 3~4k rpm. I’m trying to do more tests to determine if I need to replace my battery, stator, or upgrade my rectifier.

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