weird electrical problem

[Mathh]

Since over a week I have an absurd problem with my girlfriends' 79 Special. During a trip of approx 10 miles the ignition fuse (10A) blows 2 - 5 times.
It always happens when I come to a stop or almost to a stop, in deceleration. I change the fuse and it runs again.
One time I switched the 10 A fuse for a 15A and nothing happened, but I am not happy with such a solution.

I do not recall what I have exactly done in total to the bikes electrics, but it is not much.
I moved and wiggled all cables with the bike on contact, nothing happens. I cleaned all connections with an electrical cleaner, no luck so far.

Yesterday instead of doing it the correct way and changing and testing part by part I dumped the reserve lighting unit, switched the rectifier / regulator and took of the ballast resistor. I rode 5 miles with no problems. Than I put the ballast resistor back in place and rode another 10 miles without a problem.
The ballast resistor measured the required 1.6 ohms, felt solid with nothing loose inside so I guess it is ok.
The reserve lighting unit also has no connection with the ignition fuse so that one is not guilty either in my opinion.

Leaves the rectifier / regulator as the guilty one.
Does that make any sense to any of you considering the problems I had?
Any other suggestions ?

[mro]

rectifier

While not on a bike, have seen rectifieres do strange things.
(Have repaired a lot of battery chargers and ac/dc electric motors)


mro

[Mathh]

Re: rectifier

Originally posted by mro
While not on a bike, have seen rectifieres do strange things.
(Have repaired a lot of battery chargers and ac/dc electric motors)
mro

Not sure what you mean exactly

[oldyam80sg]

The ballast resistor has nothing to do with blowing fuses.The fuse that keeps popping-trace the wires and probably you will find a broken wire somewhere.Something is causing it to heat up and pop.Good luck.

[mro]

99.9 percent of the time rectifiers when going south either get an internal short and no longer cut the wave in half, or burn out and have an open.

Have seen a couple that would run for a while then just quite. Cool off and work agin and others that caused sever arcing between commutator and brushes but still run.

Had one that tried to act like a switch, turn on power then would act normal for a few seconds to minuets, then nothing like it had an open. Turn power on off a few times and it would do it agin.

DC (standard bridge rectifier) rectified motors I've worked on draw close to the max amps for a 110/1120V AC circuit which is normally run here in the US on a 20 amp breaker.
_______
When first read your post thought maybe a wire might be getting short/grounded when coming to a stop but would think it would happen also during regular riding during accell./decelerating. If all wiring good, leaves a few electrical components with but two variables, length of time system running and voltage (voltage drop with lower RPM and amp draw with brake lights). Still kinda strange as same conditions should occur when riding.


mro

[randy]

Current draw is directly related to voltage available. So, let's say, if a lighting circuit requires 10 watts, that's 12 volts at .83 amps. If you only feed it 10 volts, the current draw jumps to 1 amp, get it?

So it is possible that when idling, your voltage is low enough to spike a current draw that blows the fuse when you hit the brake lights. Check voltage at various RPM's and let us know what you find

[skids]

Randy, I don't follow that.

Power is varied by the amount of current, and current is increased when the resistance is reduced or when the voltage is increased.

When my battery is low, my headlights are dim and not brighter, even though the lights are rated at 50 watts. Perhaps you are speaking more about the way the volt regulator works?

[Mathh]

Battery has been switched with a one when the problem started. the old one was four years old and as good as dead. I will check voltage at different rpm anyway.. thanks for thinking with me.