Discharging - not charging?

This morning I rolled the 82 KZ1000 LTD out, started the bike and let her warm up about a minute. I then shut it off to go in the house to retrieve something I had forgotten. Came back out, turned the key, hit the button and got that classic "dead Battery" groan for the starter. Being in a hurry I rolled it back in the garage and got the 550 out. I was gone about three hours. Came back and for the heck of it stuck the key in the 1000 and she fired right up. Let her run about a minute, shut it off. Tried to restart - "dead battery" groan. I'm not sure, but I thought it worked like, when the bike is running, it charges the battery not while it sits idle. I haven't had time to look closely at anything and thought I'd throw this out to see if the electrical guru's had any tips on good places to start. The bike is all stock and the battery was new the beginning of last summer. I've had no other electrical gremlins.

My understanding on the charging systems, is that at low rpm the battery is barely being charged. www.electrosport.com sells overwound stators that address this problem. How's the condition of the battery? Had it load tested lately? All battery cables including the ones on the starter solenoid clean and tight?

The following requires the battery to be fully charged as it will be the power source during this test.

Warm up the engine to operating temperature and then shut it down.

Disconnect the plug going to the regulator/rectifier. and put the multimeter across the three yellow wires. You'll need a friends help doing this as the engine needs 4000 rpm to be able to check the alternator output.(1-3,2-3,and 1-2) all should read about 50 volts A.C.

Use a multimeter set on A.C. range of 250. If any of the three legs of the three phase system check low the alternator may have a short or open winding in it.

The website www.electrosport.com has a good trouble shooting page to help diagnose these problems.

Battery fluid levels okay?

Good Luck!

MFolks, nice link, thanks! Info looks very handy.
I took the battery out and put it on the bench and charged it up. Put it back in the bike and read 12.8 volts across the terminals. Started the bike and the voltage across the terminals dropped to 11.4 volts. At 4,000RPM the voltage varried about .1 volt in either direction. I guess I got some work to do...

It might be dirty electrical connections,failing regulator/rectifier, marginal stator output, or a draining condition. I'd clean and check the older glass tubed fuses for problems. They develop internal failures from vibration and age. Also check the fuse clips for corrosion and tightness.

I installed new horns last week and I wonder if I may have futzed something up. I'll go through all the connections and clean them and double check all the wiring.

I've been through all the connectors on the bike and cleaned them again. I read the FSM and then followed the troubleshooting instructions for the charging system. It appears the rectifier portion of the regulator/rectifier is shot. I know the bike is 27 years old but is there something that might have caused it to go? I'm wondering if the increased current draw from the new dual horns could have done it? I've been through everything on the bike and all seems to be working fine. The bike starts and runs great, it just does not charge the battery. I hate to put a new R/R in it just to cook it because I didn't fix what caused the first one to go. Any opinions, suggestions are greatly appreciated.

Heat,age,vibration, and current surges can all cause the reg/rect. to fail. In your case the original one might have been marginal, and all it took to die would be a high current demand. How many amps does the new horns pull,and are they wired through a relay?

I replaced my dead horns with a set of Stebel Magnum horns. Man those suckers are loud! 139db. Current draw for both horns combined is 12 amps according to the packaging. They are also wired through a 30 amp relay and have a 10 amp inline fuse.

I don't think your new horns caused the reg/rect to fail.As I recently posted, It probably failed from age,vibration and heat. I'd ask at electrosport what they think.