Topic: over charging 19v please help?

[scottdolsen]

1978 cb750k voltage measured at the battery is about 12.4 volts engine running with the rectifier unplugged (AC generator disabled). I plug in the rectifier and measure voltage at the battery and it jumps to 16v and climbs to 19v after about 30 seconds. And the rectifier gets very hot! It began to melt the ground connector. Anny suggestions will be appreciated.

[michael schneider]

I believe you have an issue with your regulator. The regulator tells the bike when to stop charging. Get your manual out and there is a screw under the regulator cover you need to adjust!

[scottdolsen]

Is 19v normal? the battery boils.

[dave500]

no not normal at all!!when the correct voltage is reached a relay diverts the field feed voltage through a resistor,either its not switching or the resistor is cactus,if you cant adjust it and dont care for originality you can use a combined electronic rec/reg,i used one from a boldor.,dont ride the bike as it is!youll blow globes aswell as boil the battery which will buckle plates etc.

[scottly]

14.5 volts is tops. Your regulator is not working, and, as dave500 said, will do damage to your battery and lamps if you run it that way.

[dave500]

down load the shop manual here somewhere and it shows the correct way to set the air gaps in the regulator,dont just turn screws willy nilly!these dont work like car high output alternators.

[asom]

there's a screw that limits the volt output.  at least on my f.  take the housing off the regulator you'll see a screw that adjust a plate. Check your manual for direction. I did that today.  hope that helps.  I am not an expert.

[dave500]

it dosent so much limit the voltage output as much as switch in the resistor to lessen the field energy,its not like a variable screw that will lower or raise the voltage produced as its wound in or out ,its not adjusting the voltage,but the voltage at which the resistor will become part of the circuit,still a bit hit and miss although effective.

[asom]

gotcha!  well, I was close.  sorta.

[scottdolsen]

OK, New battery, new regulator, new rectifier, still same problem. bike is charging at 19 volts dc. Is it normal for the ac generator to produce 19V?

[GammaFlat]

Can you verify the voltage with a second source?  Try another meter.  btw - the rectifier is supposed to get hot - it lets flow go one way and then stops it in the other direction - thereby "rectifying" AC to DC. 

On an almost related topic: I just learned that my Harbor Freight air gauge was reading about 15lbs low.  Yikes!  

[Spanner 1]

New fangled reg./rect. or NOS electromechanical reg. and NOS rect.?

[scottly]

I'm guessing a wiring problem going to the reg: same symptoms with new reg. Need to measure the volts at the three reg terminals (assuming a stock type reg)

[scottdolsen]

used parts from our local wrecking yard.

multimeter reads 12.6 volts at battery engine off, 19 volts with engine running.

Is it possible that the ac generator is malfunctioning?

The rectifier and the connector gets very hot after about 30 seconds of running. If I manually push on the points in the regulator to turn off the field coil the voltage returns to 12.6v and the green thing wound with small wire (resistor?) on the bottom of the regulator gets very hot.

[GammaFlat]

Meter sounds good. 

Yes, the resistor (green coil) is supposed to get hot when the voltage regulator is reducing the voltage going into the phase windings.  It is bleeding off energy in the form of heat to make your alternator work less hard. 

It is as if you've now had 2 bad regulators...?  But 19 seems high regardless.  I'm sure others (like Spanner 1) would know.  I've never had an "overcharge" situation.  Everyone seems to have low voltage and undercharging if anything. 

[scottly]

The AC alternator isn't malfunctioning, your regulator is. For some reason, it is sending full voltage to the field of the alternator, making it put out all the voltage/power it can.

[Spanner 1]

' Stuck ' regulator.... if stock one.... still don't know... don't run the bike unless you want a more exp. repair... IMHO.

[scottly]

Just a guess: maybe the green wire ground-reference to the reg is bad. Test the voltage at the green terminal on the reg with the ignition on (motor off). It should read 0V. 

[dave500]

err,?maybe you have bought a second bad reg,or,they both have been wired up incorrectly?dont run the engine untill its sorted,you might cause over heating within the loom elsewhere,if it tests high again shut it straight down dont rev and run it,umm,have you downloaded a wiring diagram?has the po done any home wiring with wrong colours?have you had the bike running with normal charging before?your getting no regulation,the more voltage to the field will make more voltage to the field will make more voltage to the field which will make more voltage!to a point where its reached its full potential,heavy duty car alternaters in this conditon can make a hundred volts or more!destroying themselves.,try and check the correct colour wires are present.the factory reg has white/black and green markings next to the appropiate connection,maybe the feild has been wired bypassing the reg?

[faux fiddy]

Here's a couple regulator threads, the  first is testing and the second is substituting for something readily available for cheap.



http://forums.sohc4.net/index.php?topic=68357

http://forums.sohc4.net/index.php?topic=12465.0

[Bodi]

The alternator makes power by using a magnetic field created in the field coil (the small coil inside the alternator rotor whan the cover is on). The regulator switches the power to the field coil on and off to control the bike's electrical system voltage.
The stock regulator has 3 stages of control:
1- full on when system voltage is below about 13 volts.
2- low when system voltage is 13 to 14.5 volts or so, this reduces field coil power using the resistor on the back of the regulator housing.
3- off when system voltage gets above 14.5 volts or so. No field coil power at all.

I think there's something wrong with your wiring somewhere. Disconnect the white wire from the regulator. Switch the ignition on, no need to start the engine. (I generally remove the HEAD fuse and switch the kill switch to STOP when doing this stuff to avoid discharging the battery) Measure DC voltage from the white wire terminal on the regulator to ground (the green terminal and wire next to the white one). You should see full battery voltage here.
Measure from the (disconnected) white wire to ground. You MUST have 0V (zero) here. If there's voltage then somehow the regulator is being bypassed in the wiring harness and you have to correct that.
It's possible that the field coil ground wire is somehow connected to +12V too, but this would have odd consequences. The field would be turned on full with system voltage over 14.5V but at lower voltage would be turned off. Your symptoms would be very unlikely, there's no probability that the voltage would get high enough to switch the regulator into "off" mode (which would be "full on" for this mis-wiring). Measuring ohms from the white wire to ground with ignition off should read about 4 ohms more or less. Zero or infinity ohms suggests strangeness indeed.
If the whole shebang measures out as perfectly correct, you have to remove the alternator cover and look for trouble in there. Maybe somebody swapped alternators and you have a permanent magnet rotor in there - this requires a different type of regulator completely. Maybe the wiring is completely fubared.
I have seen some truly impressive wiring disasters where an utterly incompetent owner has tried to improve Honda's harness. The imagination and deviousness (combined with ignorance and plain stupidity) shown in some of these jobs was amazing.
Use the correct year and model Honda factory wiring diagram as your reference. Any factory diagram for the same production year of any SOHC4 will be very close to correct. Other years may be close as well. Clymer or Haynes (or the generic ones on certain websites) wiring diagrams are pretty to look at (ooooh! colors!) but they are incomplete and, when looking for oddball troubles, much worse than no diagram at all. With no diagram you have to trace out the wires - a total ba$tard pain in the a$$ - but at least you'll trace reality and not think the colorized spaghetti barf diagram from Clymer depicts the actual harness.

[scottdolsen]

FIXED!!!!!!

Thanks guys for all your help!
Well almost fixed, there were two problems, first the previous owner of my new (used) regulator had the adjusting screw turned ALL the way in! Second, the green ground wire appears to have a bad ground. I can use it as a ground to measure voltage, but when I set the multimeter to the continuity setting that makes at audible tone there is no continuity to ground. So I used an alternate ground wire at the "e" terminal and reset the adjusting screw and now the system appears to be working correctly.

Thanks again for all the good advise!

[scottly]

We all love to hear success stories!!!

[dave500]

just out of interest the alternators with a permanent magnet have a regulator that more or less just dumps any excess voltage to earth.

[asom]

Sweet, now go ride!