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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10620
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a Mercury 20 HP - 4 stroke engine bought in 2013. A

Customer Question

I have a Mercury 20 HP - 4 stroke engine bought in 2013. A year ago, the cable from the battery was cut by the prop.
We installed a new cable, but the motor wouldn't charge the battery. I replace the rectifier on the motor, but the motor still won't charge the battery.
any ideas?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. My name is Tan. Then the only other thing it can be is the stator. You have 3 components in the charging system. The stator which produces the AC voltage then the rectifier which changes the AC voltage to DC voltage intern charging the battery. We know the rectifier is good it is new and the battery isn't an issue as it will start the engine leaving only one component stator. Does this make sense?
Customer: replied 1 year ago.
What is the testing procedure to verify if the stator or rectifier is bad? How do I replace the stator? Do you have a parts diagram?
Expert:  Tan replied 1 year ago.
The rectifier is new we don't need to test it unless you connected it incorrectly. The stator is tested with an ohm meter. Test between the 2 leads coming from the stator. I will need the engine serial number for the parts. To replace the stator you must remove the flywheel then stator. Install new stator and flywheel.
Expert:  Tan replied 1 year ago.
Do you haver a red wire coming from the rectifier connecting to the same location as the battery cable connection?
Customer: replied 1 year ago.
I will have to check on the red wire the next time I'm on the boat. What ohm reading should it read between the two wires from the stator?
Expert:  Tan replied 1 year ago.
I don't have that spec till I get the engine serial number. I can tell you it will be 1 ohm or less. Test between the 2 wires and test for shorts ground. This is done by testing from each wire to ground. Connect red meter lead to one of the stator wires then the other test lead to engine ground. You should have no reading do this test on both wires.

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