cb77 alternator

[bikedoctor99]

My alternator recently stopped charging and left me stranded.
Does any one have a functioning spare to sell?
Currently running on total loss battery which is a pita!
Any help will be greatly appreciated.
Thanks,
Allan

[cadman]

Stator or rectifier?

[bikedoctor99]

Hello Cadman,
Thanks for your response!
Using a radio shack bridge rectifier for two yrs, installed a shorai in january.
All was good till labor day, died while riding.

Metered the wires at the rectifier- no out put and assumed that the stator was cooked.
Perhaps I should have checked the 4 wires from the alternator, but I'm at best an amatuer at electrics-----
Any simple diagnostic suggestions?
Thanks again,
Allan

[cadman]

There are 3 wires from the alternator on my CA77. 1 wire goes directly to the rectifier. The other two go through the ignition switch and on to the rectifier when the headlight is ON. (I assume yours is the same) So you normally get 1/3 output to the battery and the remaining 2/3 with the headlight ON.

All alternators basically work the same. They output AC voltage which goes to a rectifier and is converted to DC voltage. (In todays world there is a combo rectifier/regulator which also controls charging voltage to the battery). Most all alternators have 3 output wires. If you measure between any two of these wires you should see AC voltage. Measure between 1 and 2 then 2 and 3 then 1 and 3. You are looking for close to the same voltage for each set of wires.

How much voltage? When I check later bikes capable of 400-500 watts, the alternator output I can see is 50 to 70VAC. No one seems to know nor is the output of the early 305 motors published anywhere I can find. The best I have seen at fairly high RPM is about 35-40 VAC. I suspect the alternator is capable of about 150-180 watts of output hence the low AC voltage.

So all you really need to do to check is DISCONNECT all three wires from the rectifier and use a voltmeter to see what the output is. (The alternator must be disconnected for this test.) I might also recommend that you try a Kohler regulator/rectifier. Just bypass the headlight switch and connect directly to the Kohler unit. So far this seems to work fairly well and gives you maximum voltage to the battery without fear of overcharging.

[bikedoctor99]

Hello Cadman,
You are a wealth of knowledge! I knew all this but had no idea of how to check with out causing a major meltdown or combustion.
I will check tomorrow, had to leave the bike at work- battery didn't have enough power to crank.
Of course this test will tell me if the alternator is working----
Thank you so much, you guys are the best teachers i've met yet,
Allan

[bikedoctor99]

Hello Cadman,
I may have missed something in your description of metering the alternator for output.
In the last paragraph you instruct removing the wires to the rectifier and state that the alternator must be disconnected at this time.
If I unplug the three wires from the alternator will I get a reading at the rectifier?

[cadman]

No _ you are checking alternator output. Obviously no power to the rectifier means you are not checking rectifier at this point. If alternator has proper output then rectifier output can be tested.