My 2003 GS500 has chewed up 3 batteries since I got it about 8 years ago, although I think storage problems is part of the cause.  When I was doing diagnostics last year, I noticed that the voltage between the terminals was running low, so I replaced the stator coil and also switched up to a MotoBatt (I am sooo done with fillable batteries).

Here's my question: with the new coil in, I still think my voltages aren't correct.  I'm reading about 13.5V at idle, then it drops on throttle down to 12.8 or so, and back up to 13.5 at around 5000 rpm.  The test docs all say I should be reading around 13.5 to 15.5.  I've done all the tests here (http://bbburma.net/Documents/JohnBates_ChargingCircuitTests3.pdf) and everything seems okay, which is why I changed the coil.

Thoughts?


PS: I don't preclude my multimedia being wonky.  It's been dropped

when you say you "changed the coil", you mean you changed the stator, right?

Did you do the step 12-13 check?

Couple of things this procedure can't check. My guess is you have some corroded, melted, or both, parts/wires/connectors somewhere along the way between the stator and the battery. Could be melted bullet connectors at the stator, melted connector between the reg/rect and the pigtail wire, corroded wires between (pretty much no way to tell they are corroded until they burn or melt the insulation), corroded/bad battery wires, bad battery connectors, etc.

Try checking the voltage with the negative battery terminal disconnected. Check it between the ground cable (disconnected) and the positive battery terminal. If the DC voltages look good when you do this but are low when you connect the battery, then it's very likely corrosion in the system somewhere.

FWIW I have had to replace pretty much every inch of wire between my stator and battery including all connectors and the reg/rect itself due to corroded wiring, which eventually all melted.

Also have your battery load tested at an auto parts store. Don't rule out the chance of having more than one thing wrong. And a battery can go bad even if it's nearly new.

Anyway you should indeed have 14.4VDC or more at the battery terminals at 6K rpm. The voltage should go up from idle and flatten out somewhere above idle, but depending on the reg/rect it might just be flat 14.4V all the way... my MOSFET reg/rect produces 14.6V from 1100 rpm all the way to >6K with zero variation.

I could share my theory about why your voltage goes down when you rev it but nobody cares. It's either your battery is shot or there is one or more high-resistance wires or connector junctions in the circuit. That high-resistance junction may be inside the regulator-rectifier and may even be a bad diode in the r/r. That's why you disconnect and isolate parts to test.

I'll give the open negative test a try and see.  May have to re-do all the testing again...  I'm guessing it's the rectifier.

I JUST WANNA RIDE!!!

+1 mr72, chances are that there's a burnt / bad connector from the alternator, or maybe the rec/reg is stuffed.

Make sure you have a good quality meter, it's important for this type of thing. 13.5 at idle is OK and anything over 15 is too high anyway. 14.5 should be fine.

You can get a Fluke 101 for about 50 bucks it's very basic but it's reliable and well made and you know it's going to give you an accurate reading. So if you're using a cheap $15 one as I was I'd get the Fluke even if you don't need it now. After seeing the difference between a cheap and even a bottom of the range good one, I'm converted.

Check to see if there are any AC volts lurking around out of your charge regulator - you may have some, and even a small AC component present can kill your battery pretty quickly.  Your DC sounds good, but depending on the meter you may not see the telltale "noise" that you could have some AC sneaking through.

Equally - you mentioned storage.  What type of battery chemistry are we talking? wet/flooded cells are going to possibly only give you 2-3 years of service with reduced usage (especially cold climates).  AGMs are more tolerant of long term storage and generally recover charge quite well once put back into use. AGMs (Motobatt) are giving me at least 5 years trouble free performance.

@user - I have an HP multimedia that I "borrowed" a while ago.  But I think the leads are damaged so it picks up noise.

@kiwi - I'm using a MotoBatt now.  I keep the battery indoors during the winter and charge it up once a month with a smart charger.  My last Yuasa was charging fine for about 5 months over the winter, then all of a sudden just lost almost all the water in a month.  Suspect that there just happened to be crack somewhere in the battery and it just shorted it out.

But how do I check the AC leak?

one more thing SnowRider, unplug the connectors to the CDI black box which is held on with a rubber strap under the left side cover and spray the contacts with electrical contact cleaner and do that to any of the other plug in wires that connect to the rectifier.

Did more testing today (and learned about Diode-Testing with my multimeter).  I completed the John Bates testing.  Here are the results:

- Minimum voltage (2K rpm): Around 13.5V = Should be fine?
- Maximum voltage (2K rpm): Also around 13.5V = Should be fine?
- Battery cable tests: PASSED
- Stator Test - Continuity: PASSED
- Stator Test - Isolation: PASSED

- AC Output - 65V = NO GOOD?

- Rectifier/Regulator Test: PASSED

So this is with a brand new stator coil installed.  Which leaves me with the AC Generator Rotor left.  That seems like a very rare problem.  I might get a new multimeter just to make sure mine isn't faulty before spending 20% of what the bike is worth on a new part that may or may not fix the problem.

Thoughts?

If the factory manual says 65vac is too low then so be it. But I think 13.5vdc is too low and a good regulator rectifier should work with 65vac. A half wave rectifier with 65vac should produce about 23vdc by my math leaving the regulator over 8v headroom to work with. If it's only making 13.5v and you are absolutely sure the cables are 100% then in my opinion the r/r is bad. But believe the shop manual before you believe me.

My bike? I'd be retrofitting a MOSFET r/r. I did that with my GS and it was night and day better. Probably going to do the same with my triumph.

Not Sure if this helps but I also had a 65 volt result on my AC output with about 13.5 on the battery. I also had slowly dying batteries. For me, it turned out to be a loose rotor that was spinning on the end of the crank and not turning as fast as it should. Resecuring that made the bike work well again - same battery for 3 years now.

Also, note that the Haynes manual says this :

"Note: If the voltage   Is below 13.5  volts. then It is more likely that the alternator is faulty. If the voltage is above 15.5 volts. It's more likely that the regulator  is faulty."

HereNow,

Hmmm... May try tightening the rotor.  Gonna be messy (need to drain oil...  AGAIN), but at least this time I won't have to scrape gaskets.  I hate scraping gaskets.

Thanks!

Yeah, It's a pain as you have to lap the end of the crank and rotor with grinding paste to make sure the fit is good on the taper. At the time there were quite a few posts with similar problems so a search should throw up quite a bit of info on it.  +1 on checking all wiring before going there, but it seems you have done this and there's not much wiring to affect the 65 Volt reading. But maybe 20 bucks for a new (spare ) Reg/Reg as recently posted might be an easy troubleshooting step.

Sure the workshop manual says 75V AC but more important is that all three phases are the same, if they are 65 can't really be a problem because you're still throwing away excess supply in the form of heat!

FWIW, the workshop manual also says the PSI range for the cylinders is 195 - 142, but mine are 115 and 120 and she's purring along wonderfully. I've seen an almost brand new bike out of their range. (an S40)

Also the manual says 13.5V at 5000, rpm, is OK. Here's page 114 of the workshop manual