In a previous Tech Tip, I discussed how to buy a battery for your CH250 and how to test it’s condition. Here’s a few pointers on how to check your scoot’s charging system. All you need is a cheap multimeter or voltmeter or ammeter (fused digital multimeter preferred) and the Honda service manual.

Start by recharging the battery. Then attach the voltmeter, to read DC voltage, to the scoot’s battery with the ignition switch off.  The voltage should read above 12 volts. Specifically, a fully charged battery will read 13.0 to 13.2 volts. An undercharged battery will read about 12.3 volts.

Now fire off the engine and let the idle stabilize. Bring the revs up to 2200 rpm and read the voltmeter. If the charging system is working correctly, the voltmeter will indicate about 14.0 to 15.0 volts. If, however, there is a problem, the voltmeter will read about 12 volts or less.

If your reading is low, the next step is to see if the culprit is the alternator or the regulator (sometimes it’s both).  Pull the regulator plug from the engine case. To check the battery through the regulator, connect the voltmeter to the black and green terminals on the regulator coupler terminals with the ignition switch on. The correct battery voltage should appear.  Also, check that the correct battery voltage appears when the voltmeter is attached to the black and green wires of the coupler terminals. If either does not, check the wiring harness for  an open circuit. Replace the regulator and retest.

To check the alternator output, remove the fuse holder cover near the battery. Disconnect the red wire lead from the fuse holder terminal and connect it to your ammeter. Connect the other end of your ammeter to the fuse holder terminal where the red wire was. Remove the black wire from the regulator coupler and reconnect the coupler. Start the engine and read the amps. The unregulated alternator amperage should be between 14.5 amps @ 5000 rpm and 18.0 amps @ 10,000 rpm. If the alternator is putting out the desired amperage, then the regulator is the problem. If, however, the alternator is putting out less than acceptable amps, the alternator would have to have be pulled, checked, and the stator or pulse generator (or both) replaced.

To check the pulse generator, disconnect the coupler and measure the resistance between the green/white and blue/yellow terminals. The resistance should be 50-180 ohms. If not, replace pulse generator. 

Also, the resistance of the stator should be checked that continuity exists. If none, a short or broken winding may exist. Also, where the wire harness enters the case is where a certain amount of fatigue occurs and eventually a break tends to happen.  It is a spot where oily grime builds up degrading the mesh weave fabric of the outer wrap on the wire. Check there for problems.

Once the regulator is in place, run the test again to make sure the proper voltage is being sent to the battery. If you had to change something on the alternator, retest the system to see that the regulator is working properly.  A bad regulator may have burned out the alternator by pulling too much power from it, which would be indicated by a very high voltage reading at the battery when the engine is running.  A regulator that’s bad this 
way will also kill a battery.

Randy Pozzi   (Rev. 04/2006)