Re: 1982 Honda CB 650 -- Electrical / Charging problems (as usual)


ben@xxxxxxxxxx wrote:
Also, I just found out my battery is garbage, I had it on the charger
for the night, and then took it to my friend's house, we put it up on
his bike, it started the first time, and voltage output was like
14volts or whatever so I knew it was charging, we shut it off after a
few minutes and tried it again, the battery cranked a bit but not
enough to start the bike. tried to start a third time and it barely
cranked.

Well, the rotor has a very low resistance of about 0.5 ohms and I
suppose the wiring in the circuit might have another 1.0 ohm and maybe
the brush contact is another 0.5 ohms, for a total of 2.0 ohms.

The current that would flow through the rotor the moment you turned the
ignition key on might be equal to the battery voltage divided by the
total resistance I mentioned above. I don't know what the resistance
through the transistor is, so I'll just have to stick with 2.0 ohms
through the rotor and its associated wiring.

So, 12 volts divided by 2.0 = 6.0 amps. That's quite a bit of current
for a mostly dead battery to put out, and, if you have the headlight
and tail light on too, that's another 4 or 5 amps of current draw.

So the combined load would be 10 or 11 amps and it's going to flatten
the battery quickly.

But even though the battery is dead, it should still ouput at least
13volts when the bike is running, and revving past a 3-4K RPMs... so
that shouldnt be the issue... right?

It sounds like your rotor is OK if you can get the voltage to rise
above battery voltage when you rev up the engine.

You need to run the charging voltage test with a fully charged battery
in good condition. I would expect to see 14.5 to 15.0 voltage with the
high beam ON as the engine reached 5000 RPM.

Then I would expect to see the voltage drop sharply back to 12.5 or
13.0 volts. When the throttle is rolled OFF and then ON again, the
voltage should keep rising to the same peak and dropping off every time
you roll the throttle on and off.

That tells you that the votlage regulating function is working
correctly.

.

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