3rd gen charging problem

1991 750f with roughly 70k miles.

Last summer I suffered from r/r problems, first the original fried the battery, then a cheap replacement did the same to a new battery.
After the 2nd time I got a bulky r/r from a yamaha forgotwhatmodel with big cooling fins and plenty of surface area. I also got a gel battery to go with it.
I chucked the connector to the r/r and just connected the individual wires.
All went well for about 1000 miles but then, after a 6-month-winter, the damned thing died on me after the first couple of hundred miles due to drained battery.
After following a general charging system flow chart I came to the conclusion that the battery, r/r and stator along with the connections are all just fine. The problem is of course that something's wrong since it's not charging properly.
It seems to me that, when measured cold, it gives a nice 14-14.5 volts around 2k rpm but as the heat escalates and the fan is turned on it goes down to 12.5v, measured directly from the battery.
The voltage increases slightly with revs and always remains between 12.5 and 14.7 volts.

So, a new battery, a new r/r and a successful traverse through a flow chart. I maintained a good charge in the battery throughout the winter and it still holds a good 13v charge and only drops to 10.5-11v when starting the bike.

SOLVED:New r/r unit, properly mounted and a small fan on top of it. Measuring 14.0-14.1v cold or hot above 2k rpm.

What's next? More information?

EDIT: Tested battery voltage after thorough warming throughout the rev range. The heat was torturing me and the fan had been turned on a minute or two ago. Simulates a hot summer day stuck in traffic. The damned multimeter measured 12.4-12.5v from 1k to 12k rpm without so much as a hiccup one way or the other.

EDIT2: Took the r/r unit off again for remeasuring and alas the thing is dead. I didn't get any resistance readings at all. Last time I got weird readings(x100 more than expected) but I assumed it was due to my lack of knowledge of multimeters...

EDIT3: Replaced the r/r, it heated up to finger burning temp and began raising faint smoke from the wires(probably just glue from electric tape) in about 5 minutes. Charging dropped from 14.1v to 13.5v in those minutes. Turned it off at that point. The cooling of the unit wasn't up to scratch; I'm gonna try again after drilling a new hole to attach it with 2 bolts and after installing a small fan. Currently the bottom isn't actually touching the frame much so I wouldn't expect it to cool off very efficiently.

 

what is voltage at idle and at 5k rpm?

 

cold
approx. idle 13.5v, 5k 14.2v.

after 10 minutes of idling
approx. idle 12.5v, 5k 13.1v

 

Did you solder the three yellow wires from the stator to the wiring loom? You have to check AC voltage from these three yellow wires, if you soldered them, it makes it a little more difficult. What about your starter solenoid, is it in good shape? The plug that goes to this usually gets hot and melts, along with the solenoid. Check your grounds too. Keep us posted :thumbsup:

You have a manual for this make/model? Important stuff...Cheers

 

No, the wires aren't soldered and the voltage reads at almost exactly 73v for all 3 combinations at 5k rpm.
I haven't checked the solenoid, though it makes a huge racket when the starter's cranked at very cold temperatures or when the battery's low on charge.
I've got a good manual for the bike but I'm a little unsure where I'm supposed to find information concerning the issue.

 

that dc voltage is low after the 10 min warm up. measure the stator ac voltage after it is warmed up also

 

It's virtually unchanged. drops from 73 to 69.

 

Added an edit after trying out a new r/r unit. Could the unit be overheating due to a failure elsewhere in the system? Is it possible for the current that goes through to be above normal or can it only go down?

 

Nope. Stator output will never go above normal, but a bad r/r can feed excessive voltage into the system, damaging the battery and possibly the CDI box too.

 

ohm out stator when hot, they do breakdown then also