Alternator Replacement

Well that was easy! This is probably one of the easiest jobs I’ve done on the boat. Just a quick test to find the fault, 2 easily loosened bolts, and slide on a new alternator belt. Done!

One day while motoring on a calm day, I noticed my battery monitor wasn’t displaying any charging amperage. Here are the steps I took to troubleshoot and replace the alternator.

1. Testing
   1. I first brought the rpms up to max cruise and double checked the Voltage and Amperage on my Link 2000 Battery Monitor. Nope, no change.
   2. Volts should be above 13.0V and positive amps should be flowing into the batteries. I still showed 12.8V and -0.5 amps, normal battery voltage and normal discharging. Not charging as it should be.
   3. Back at the dock, I followed the troubleshooting section in my Balmar Alternator Regulator Manual.
      1. Check battery health, terminals for corrosion or any other easily recognized suspicious issues.
      2. With the ignition OFF, place the head of a steel screwdriver near the nut on the pulley shaft. There should be no magnetic pull on the screwdriver.
      3. Turn the ignition on, wait for any regulator start up delay (mine is 45 seconds), and you should now feel a magnetic pull on the screwdriver.
      4. I felt a very small magnetic pull (almost like it was my imagination pulling the screwdriver) which shows the voltage regulator, alternator brushes and rotor are working properly. So my issue must lie with the alternator itself.
      5. If no pull is felt, the alternator regulator is suspect. Follow your regulator’s manual for further troubleshooting.
2. Remove the old alternator
   1. Take a photo of the back of the alternator so you remember where all the wires connect.
   2. Beware of live wires! With a multi-meter, ensure no voltage is present on the alternator terminals. Even with all batteries off and disconnected from shore power, the positive wire going into the alternator still had 12.8V. Tape the end and ensure it doesn’t ground out on any metal!
   3. Remove all wires from the back of the alternator.
   4. Remove the two bolts holding the alternator onto the engine.
   5. Remove the alternator.
3. Install the new alternator
   1. Replace the old belt with a new one since we’re here anyway.
      1. My old belt: Goodyear 17501
      2. My new belt: Goodyear 15391
      3. Recommended from Perkins: Perkins 4-108 Gates 1/2″ Extra Long Life V-Belt
   2. Install the alternator with the two mounting bolts. Leave them a little loose so you can set the belt tightness.
   3. Use a long screwdriver or pry bar to hold the alternator up so that it tightens the drive belt. Tighten the bolts most of the way and feel the slack in the belt.
   4. The drive belt must not be too tight or too loose. Too tight and it can damage the crankshaft of the engine.
   5. The belt must have about 1″ of play when tightening the alternator bolts. (See the video.)
   7. Once the slack is good, tighten the mounting bolts the rest of the way.
4. Test the new alternator
   1. I ran my fridge for two days bringing the new batteries down to 60%. Then started up the engine and watched the battery monitor.
      1. The Balmar Regulator waited 45 seconds, then clicked into Bulk Charge mode (2 LED lights)
      2. 14.1V and 35A. Yesss! It’s charging!
      3. I didn’t test further, but it would be nice to know someday if the Bulk Charge successfully moves to Accept Charge and to Float Charge.