burning up batteries

[rlkarren]

Needless to say I'm a little frustrated after 3 batteries in 2 weeks.

Battery works great for a few hours but then it just quits charging... I can place the battery on a charger and it will charge, but it will no longer keep a charge. It seems as if one of the cells has gone bad.

My testing so far includes:

Magneto AC output on single coil - green wire (day operation)
Magneto AC output on dual coil - yellow wire (night operation)
AC input to the rectifier
DC output from the rectifier
input to battery, battery connected
input to battery, battery disconnected

All tests were consistent with an identical machine with a good charging system.

I've got new coils, replacement flywheel, checked and rechecked the air gap, checked and re-checked all my connections, even replaced a few that were even remotely suspect. Checked Ohm readings and the coils and verified they fall within spec, verified voltage ">6v @ 2500 rpm w/ 45w load" falls within spec. I'm beginning to suspect the rectifier... but it tests OK, (as far as one way voltage). And finally, I don't believe it's the Voltage Regulator since the problem presents itself in "Day" operation, (which means the "Night" operation to which the regulator is attached, isn't engaged), and because the regulator regulates the AC circuit and I'm having trouble with the DC circuit. Which again.. points to the rectifier.

Does this sound like a familiar problem to anyone? What was your solution? Does anyone have a method to pinpoint the problem any better than I have?

Thanks,

Roger

[BrianZ]

Does the battery go dead when the bike is not running? I'm wondering if there is any drain on the battery when the bike off.

Brian

[taber hodaka]

Will the battery keep a charge if it is on the bench? With everything turned off hook the charger in line instead of the battery, if current flows then you have a short. The only way you could burn up a battery is if you overcharged and boiled it dry unlikely. Let us know when you solve the mystery. Clarence

[rlkarren]

I think I found the problem... just as I suspected... it was the rectifier gone bad. 35 miles later and everything is purring right along...

Explanation follows for archival purposes:

I got a rectifier from Doug, (flyindg), and I tested them both before I installed the new one. I used a resistance test. (Multimeter probes are identified in the parentheses)

New rectifier showed 150+ Ohms white (+) to red (-) - expected behavior.
New rectifier showed infinity resistance red (+) to white (-) - expected behavior
Old rectifier showed 150+ Ohms at first, then immediately dropped to ~12 Ohms, white (+) to red (-). Not good
Old rectifier showed ~12 Ohms, red (+) to white (-). Not good

Tested multiple times just to make sure what I was seeing. Rectifier was bad.. If not for the drop in Ohms, at least because it was not blocking current in the reverse direction.

As I understand it... The rectifier used by Hodaka are half wave rectifiers, (per the manual). This means that its functions are to take incoming AC current and block half the sinewave of AC current thereby producing pulsating DC current. And... it blocks DC current from being "backwashed" back into the AC curcuit. A residual affect is that it also reduces the voltage by about half, since the sinewave was just cut in half. Also; If you pass AC current to charge a battery, it will not last very long and you've essentially destroyed it. So a rectifier is a one lane, one-way street as opposed to a four lane highway.

Diagnosis: My old rectifier was passing AC current to the battery and it was passing almost all of it since there was nearly no resistance. Also, the "one-way" feature of the rectifier wasn't working either so the DC current was being fed back into the system. When I was testing the rectifier input and output, I failed to notice the "lack" of voltage drop through the rectifier. That should have been my first clue. But.. now I know.

Lesson learned: When or if you overheat your motor to the point that solder joints in your stator melt, save yourself some time and money and just replace your entire charging circuit: Coil A, Points, Condenser, Rectifier, and battery, possibly Coil B too since it got cooked in there too).

Thank you! See you at HD14.

Roger

[dcooke007]

Roger, happy to hear you have your charging system sorted out.... but you have to tell us how you "over heat" your engine and melt the stator solder joints. Curious minds want to know.

Danny Cooke