Westerbeke 90A FOUR — Testing the Alternator
Testing & diagnosis · DC Alternator / Charging Circuit
For the Westerbeke 90A FOUR, from the Westerbeke operator's manual.
Before you start
- Do not use a high voltage tester (i.e. a megger) when performing tests on the alternator charging circuit.
- Never shut off the engine battery switch while the engine is running.
Procedure
- Start the engine.
- After a few minutes, measure the starting battery voltage at the battery terminals with a multimeter set on DC volts.
- If voltage is increasing toward 14 volts, the alternator is working; go to checking the service battery.
- If voltage remains around 12 volts, a problem exists; continue with the remaining steps.
- Turn off the engine and inspect all wiring and connections.
- Check the battery voltage with the engine off; a good battery should read 12 to 13 volts.
- Check the voltage between the alternator output terminal (B+) and ground.
- Start the engine and check the voltage between the alternator output and ground; should be 13.5 to 14.5 volts.
- If over- or under-charging, have the alternator repaired at a reliable service facility.
Tools required
- Multimeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Properly operating alternator voltage: 13.5 and 14.5 volts
- Service battery: 13 and 14 volts when the engine is running
- Ensure 12 volts DC excitation is present at the EXC terminal
Source: Westerbeke operator's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.