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Motorcycle Repair/83 Kawasaki Charging


QUESTION: Lazaros,
Iím having charging problems on my 1983 Kawasaki KZ550 LDT.  My battery went dead, but I was able to recharge it and the battery is fine.  I have gone through some of the tests from what I read, the best I could and here is what I found out.  Iíve checked the battery volts and they were at 12.6. When I took the RPM up to 4000, the battery voltage went down and not up to the 14.5 I read it should.  I uncooked the headlight and the test was the same.  I checked the alternator by unhooking the 3 yellow wires and checked the AC volts.  It was 24 Ė 25 volts.  The book said it should be 75 and the alternator is bad.  Last, I checked the stator resistance on 200 scales.  It showed 0.7.  On the highest setting it showed 000.  The book said it should be 0.3 Ė 0.5.  The book said if the stator test is ok, itís probably the rotor has become demagnetized.  Iím not sure what to replace.  Thank you.

ANSWER: Hello Robert,

Sorry for the delay. It seems there was a problem in the system...

First of all, in how many revolutions did you check the alternator output?
Was it at least 4000RPM?
Next, you should check resistance with the lowest range available on your tester.

The most common problem is the regulator-rectifier, next comes the stator, and a demagnetized rotor is a very rare possibility.

If you need more info, don't hesitate to get back to me any time.

Best Regards,

---------- FOLLOW-UP ----------

QUESTION: Lazoras,
No worries on delay. I checked the battery voltage at idle and 4000 RPM. I only checked the alternator at idle because my book didnít say to check it at 4000 RPM as well.  At idle it was 24-25 Volts.  I did check the resistance on my lowest reading, which was 200.  It showed 0.7 on all three wires.  Today, I pulled the alternator out and checked all three wires with one lead on the wire and one to ground and I got no reading on the ohm meter, which is good from what I read.  I did notice in the rotor area some crud/dirt in there.  I planned on cleaning it. I did not check the rectifier yet.  Is there an easy way? Thanks a bunch, Robert.

ANSWER: Hello Robert,

It seems your alternator is O.K. As long as it gives 24-25VAC at idle, almost certainly it will give more than 50VAC at 4000rpm, which is pretty adequate. No surprise if it pulls out 75-80VAC at 5000rpm.

As for the Regulator-Rectifier, there is no easy way to test it. You will need a high-quality analogue multimeter and a 0-40V variable power supply (40V is the lowest, it can be up to 100V)or three 12V batteries.
But as long as you test the alternator at 4000-5000rpm and it passes, then your problem is Reg/Rect for sure.

You can use almost ANY motorcycle three-phase regulator/rectifier, as a replacement, as long as it is designated for at least 400cc motorcycle.
Nevertheless, if you wish to test yours, and you have what I mentioned that's needed, let me know, and I'll guide you through the procedure.

Best Regards,

---------- FOLLOW-UP ----------

QUESTION: Lazaros,
Iím back again with issues and questions.  After the last discussion, I bought a Regulator-Rectifier and started the bike up with the old and had only 12.6 volts and it didnít increase when I brought the RPMís up, but instead went down.  I unplugged the old Regulator-Rectifier on the bike and plugged the new one in and laid it against the frame.  I started it and I had the same results as the old one.  One thing I tried this time was to see at what point I started losing voltage.  When I brought the RMP up to around 2000, my voltage started dropping and my headlight dimmed.  When I lowered the RPM down below 2000 to idle, it started charging slightly or maintaining voltage and the headlight brightened up.  Iím stumped.  I also noticed the new Regulator-Rectifier was getting hot, after a few minutes of running, if this helps.  I could not check if the old one was getting hot because itís under the battery case and I didnít remove it yet, until I confirmed it was bad.  Any ideas on my weird or at least weird to me issues.  Thanks again, Robert

Hi Robert,

I looked back to your first contact with me, and have some second thoughts about your battery.
Does your bike start on it's own ,or, it needs extra power from external source?
I'm asking this, because, it's not easy for a dead battery to come back to life and work properly. Especially in the charging phase, where it may not draw the current it should, thus drive the regulator "crazy".

I'm sorry I didn't pay the attention I should, on your description on the battery condition, and probably wasted some of your time.

At this point, you need a donor battery (don't haste buying a new one just yet) for testing.
It doesn't have to be exactly the same with yours. All we want is for it to be within 2Ah from
the capacity of yours. If my memory is correct, your battery is 12Ah, so you need a 10 to 14Ah
fully functional battery for testing.
Remove the bikes battery and connect the donor, temporarily (even hanging outside the battery case) and make all the tests from the beginning.

In addition, do NOT test with a second battery connected in parallel or with an overcharged one
or with a jump-starter connected.

Best Regards,

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Lazaros Ampatzidis


I can help you on EVERY issue involving POST-1980 Japanese Motorcycles plus KTM and Husaberg. My field of expertise includes Engine, Transmission, Fuel system (carburation & EFI),Electrics and Electronics. Maintenance, repair and tuning. Road and off-road suspension tuning. Please don't ask me about non-Japanese Motorcycle, especially American built on which I have low to zero experience.


I'm a rider and hobbyist since childhood. 25 years motorcycle workshop mechanic.15 years motorcycle racing mechanic. In order of experience high to low:Kawasaki,Suzuki,Honda,Yamaha,KTM,Husaberg.

Hellenic (Greek) Technical School.Internal Combustion Engines Engineer. Automotive Electronics.

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