does a negative on the 'slap' test mean my rotor is definitely bad?

[fullercameron]

Had the bike up and running for about 600 miles and the other day it died at a stop light. My starter doesn't work so the bike is kick only right now and I could not get it to start. It didn't even sound like it was trying so I pulled the voltmeter out of my bag to see what was in the battery.

I had 9 volts in the battery. I was lucky and near an auto supply store and they hooked the battery up on their charger for five minutes or so and I got the bike to fire and got it home.

I looked through some of the threads on testing the charging system and did a couple of the tests. when I place a wrench near the alternator cover (within a 1/2") and turn the key, it doesn't move. The battery is fully charged now - AGM battery that was reading just over 13V. If it fails this test, does this automatically indicate that my rotor is toast?

Second, I started the bike up and tried to see what kind of voltage I was getting at the battery if I revved the engine to 3000+ rpm. The voltage was dancing all over the place and I couldn't seem to get a steady reading (it is a digital meter). It was fluctuating from what looked like 18V to -? to 13V and I could not get a fix on what the hell it was putting out at full speed. Does this little voltage dance indicate that some other component has failed or does it just demonstrate that I don't know how to perform this test properly?

I see where the thread talks about how to bypass the regulator to test its function, but can I just test the voltage at the battery to see if I am charging?

I'd like to eventually do a PMA swap, but I can't really afford to do it now and would like to keep the bike on the road for at least the next month or so without having to charge the battery every night.

Also, when I charge the battery, it reads full and shuts off, but if I disconnect it and reconnect it to the charger, it seems like it will read less than full and begin charging again. The battery is only 3-4 months old. Is there a quick way to load test a battery just to double check that this isn't also an issue?

Thanks. I know that this is a lot of questions wrapped up into a big ball of I don't have a clue right now, but any assistance would be greatly appreciated. I certainly wouldn't have gotten this far without your help.

 

[visimpact]

What does it read at idle? I believe it should be about 13 or so. Rev it up and around 14-14.5 or somewhere in that range. If the readings arent somewhere in that range and the slap test is a flop, you can also test between the rings on the rotor and see if it comes in around 5 ohms. If you dont know how to do that just youtube it. Simple to do. Sounds like rotor issue

 

[Grinder]

Check your brushes first to make sure they are minimum length and while you have them out check the rotor with an ohm meter to make sure it's in spec. Lots of info on chargings systems on the forum.

 

[fullercameron]

Thanks for the quick response. I'll do the test between the slip rings ASAP, but like I said in the previous post, the voltage readings with the bike running seemed to be all over the place.

I was wondering if the reason my voltage was jumping around so much when it was running might be due to a rectifier problem. I don't know much about electricity, but my understanding is that the alternator produces AC current which moves in waves and the rectifier changes this to DC which is stable (I'll admit I could be totally misinformed). I thought maybe the voltage moving around could be a result of the pulsing of un-rectified AC power going to the battery.

I'll do some more tests. Thanks again.

 

[fullercameron]

Missed that last one. I took out the brushes earlier today and they were both around 1/2" long. In looking at the charging troubleshooting stuff, it seems like that is within spec. They definitely make contact with the rotor.

 

[gggGary]

While you had the brushes out did you ohm out the rotor? What did it read? Yes it could be a rectifier, you could have dirty points in your regulator, it could be a loose wire almost anywhere, it could be an intermittent short, it could be a bad stator, and it could be a bad battery. There have been a lot of bad AGM batteries sold in the last couple of years. This is where you have take a deep breath and start methodically testing and eliminating "could be's"

 

[gggGary]

On a stock early set up (pic shows a 72?) supply +12 to the outer brush, start it and check voltage at idle should be 14 or so. Don't run it like this as you have eliminated the regulator.

 

[XSLeo]

Your meter jumping around could be bad leads on the meter. I replaced what I thought was a bad meter and with the new meters leads the old meter worked fine. Try a different meter.
Have a Harbor Freight near by? They have a good meter for just a few bucks on sale. Right now they have a coupon in the magazines to get one free with a $9.99 purchase. And who can't spend $9.99 at HF?
I like mine. I might go buy a few things and get several.
Leo