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Discussion Starter #1
hi i have a 1980 Honda cm400t with around 21500 miles the bike was running great up until recently. lost the key so i put a switch on for the lights and power over a year ago. it runs around 10.5 volts when the lights are on but when the power switch is off it runs at 13 volts with the battery connected and when i disconnect the battery and turn off the power it will run around 20 volts at idle and 40 if i throttle up.
i have checked the stator, took it off and cleaned it. wasnt burnt. didnt see any bad connections and resealed the copper wires.
i check and replaced the fuses and connections.
replaced the battery.
is there anyway to test the regulator/rectifier?
any ideas what my problem could be?
 

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Sounds to me that the regulator/rectifier is not working properly. Is the battery getting extremely hot after you ride for a while? The voltage at your hot and ground terminals at the battery should not exceed 15 volts.
 

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Please clarify: is the engine running for all these measurements? How does the engine run if the power switch is off? Your wiring must be really odd; normally, the power switch disconnects the coils from the battery and R/R when off, so I don't know how this is possible.

The regulator/rectifier requires a battery be present to control the voltage, so disconnecting the battery will cause the voltage to rise, just because there is no load to soak up the power. If the battery voltage drops to 10.5V under load, it probably has a bad cell; have it tested. The regulator may not be able to keep up with the load at idle if the battery is bad, so may not be bad. It works by shorting out the alternator stator when the battery voltage rises above the set point (around 14V, but it varies).
 

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Discussion Starter #4
hey

the motorcycle is running for all the testing. it runs even with the toggle switch off and that is the only time it will charge the battery good. i get around 20-25 volts ac from the 3 yellow stator wires when the bike is running and the battery doesn't get hot but i have replaced it with a new battery because i thought that was the problem but it made no difference.
 

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OK, so the switch just turns the lights off; is there another switch to turn the ignition off?

With the engine running, battery connected, the battery voltage of about 13V is normal; if you rev the engine, it should rise some. The engine, alone, draws about 2-3 Amps, on average, operating just the coils, assuming you have 5 Ohm coils.

When you switch the lights on, and the voltage drops to 10.5V, I'm guessing it is at idle. If you increase the rpm, does the voltage rise with the lights on? With the lights on, you are adding a much bigger load, and the voltage drops, indicating the battery can't support the load, and the charging system, alone, can't either. The charging system of that vintage a bike may let the battery drain at idle, and not begin charging until about 1500 to 2000 rpm; it cannot overcome a weak battery. A voltage of 10.5V indicates 5 of the 6 cells in the battery are working, and one is not, or the battery is really drained. Again, have the battery tested, or replaced, as the measuresd values indicate it is weak. Even with the switch on and the engine not running, the voltage should be above 11.5V with a good, fully charged battery. Once you have a known good battery, try again; if the voltage drops below 12.5V still, the charging system is the reason the battery you have is weak. Check the connections between the stator and the rectifier/regulator, as these often overheat and stop conducting enough current.
 

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Wintrsol covered most of it, but...

A fully charged battery shows 12.6 volts or above.
A battery 50% discharged is at 12.3 volts

With a WORKING voltage regulator, well above idle, you should see 13.8 volts or so.

Running ANY alternator/generator without the battery connected, or disconnecting the battery while running is a recipe to destroy the whole thing.

Loose connections, at the battery, ground, wherever can easily make the voltage regulator "see" less voltage than is actually being produced. The result could be it putting out 15V or more while attempting to charge.

Trying to fix auto or motorcycle charging systems without a reasonable background is....a great way to spend more money than it would cost you to hire a MC mechanic to fix it for you.

So if you want to learn, proceed, if you want to ride, get a pro to fix it for you.
 
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