charging system nfg ; battery takes charge but dies after

[Steve Munyon]

This sounds like the problem I had last summer where my SV would start
missing after 1/2 hour of riding.  Here's a write up of what I did to find
the problem....

I got out the voltage meter and recorded the initial states of battery
condition.   I also checked primary and secondary resistance in the coils,
etc., which were in-spec.  The battery with the ignition switched off was
12.47v.  Anyway with the headlight (low beam) as a load, the battery voltage
dropped to 11.8v after 5-10 seconds.  So I know the battery is marginal.  I
started the bike and the voltage went to 13.1v.
I checked the primary side of both coils with my scope and I was seeing
400v.  The shop manuals states 150v & up, but a scope is a lot more
responsive the just a peak and hold meter that the factory manual suggests.
To me, that explains the higher voltage.
I took the bike for a 20 minute ride and the idle voltage was still 13.1v,
so I revved it to about 5K and the voltage was 13.3v, when I revved the
engine higher the voltage dropped back to 13.1v.  I’ve been searching around
the ‘net for similar problems.  One interesting find, was a bad solder joint
on the signal generator pickup, but my solder joints looked good.  Another
find, was that most Suzuki’s have weak regulator/rectifier based on ‘SCR’s”
while other bike have an R/R based on ‘MOSFET’s’.  Google them if you’re
interested.  As a band-aid for the weaker R/R the author used 12 gauge wire
with a 30 amp fuse to provide a more substantial current path then the
standard Suzuki wiring which looks like a 14-16 gauge with lots of
connectors.  Whenever I see an electrical connector I always figure on a .1
v drop at each connector.  So I ran a 12 gauge wire from the R/R output
connector directly to the positive battery terminal and took some
measurements.  Key off battery voltage is 12.44;  key on and headlight on
battery voltage is 11.9,  started bike and voltage jumped to 13.6v, after a
minute the idle voltage was up to 14.2v and when rev’d the voltage was 13.8.
So I removed the wire, went back and cleaned all the connections, check the
voltage and the voltages were back to where they were before.  At this
point, I soldered in the additional 12 gauge wire and the 30 amp fuse ending
with a terminal lug so I can screw the lug to the positive battery terminal.
Checked the battery voltages again and they were back up to the jumper wire
voltage levels and sometimes a little above.  I also clipped a ½ inch off
the spark plug wire just to make sure the connection to the coil is good.
So that wiring fix combined with a new Yuasa battery I ordered and the
problem hasn't been back.  Right now I don’t think it was the batteries
fault at all, just the small wiring for the charge circuit.