Small Engines (Lawn Mowers, etc.): B&S wont charge, zener diode, bridge rectifier

Question
Hi,

I have changed the alternator and the regulator on my 16HP B&S tractor mower engine but still it won't charge the battery. The battery is fine.

I get 14 volts AC from the alternator, at slow speed and 27 volts at full throttle. But I get no voltage from the regulator. Also, if the battery lead is disconnected with the engine running, it stalls. What could to be the problem with this?

Answer
Are you checking for DC voltage?  The stator produces AC and the rectifier changes it to DC to charge the battery and run the accessories.  

The easiest and fastest way to tell if and how much charging current is getting to the battery is to install an ammeter in series so that the current moves through the meter to the positive battery terminal.
You should have 10 - 12 amps.

Check the connection between the stator and the reg/rectifier.  If it is dirty the battery will have a poor charge rate.  

Be sure to check the grounds on the entire tractor and do not forget the head light ground if running dim.  

All said and done I think I would go back to the regulator rectifier.  It is a series of diodes including a zener diode.  A zener diode is a powered diode.  Current only flows one way till a pre determined voltage is reached from the output of the alternator.stator. It then changes and blocks the current or lets it flow both ways.  If all is good the zener is bad.  Replace the bridge rectifier.

Two wires coming off the stator or out from it one charges the battery and the other runs lights. Lights should be dim at low rpm and bright at high. The engine dieting when the + battery cable is disconnected is normal. It is called battery ignition. Remember AC will not charge a battery or run most of your accessories if any.