Alternator - Internal -v- External Regulator

Alternator Failure - Updating wiring

Our Balmar 100Amp Alternator failed on July 4th. After leaving the dock, the Tach showed Zero RPM and the Analog Voltage Meter read 12.4v (ish). 

Upon arrival at the Bahia Mar, we did some fault finding, suspecting that the Field wire to the Alternator had failed, but the wiring and connectors were ok.

I removed the Alternator and took it to Fort Lauderdale Battery & Alternators on 3rd Ave just off of State Road 84 in Fort Lauderdale ( Map link here).

They put the Alternator on their test bench and confirmed that there was no output. Despite the Alternator being setup for an external regulator, there appeared to be a short between the Field Terminal bolt on the back of the alt, and the surface of the regulator. They confirmed that the Regulator was fried.

So I left the Alternator with Greg to fix and it should be ready in a few days, it was - they have never failed me to live up to their word. With repaired Alternator in hand, I headed back to the boat. Thinking about it, I have a really nice Alternator with an Internal single stage smart regulator that is not used and an expensive external smart regulator that is used. But what if the external regulator failed? What would it take to switch over to using the Internal Regulator.  Time for some research.

The good news is that there's a great diagram on the Balmar website that shows how to wire the Alternator to use either the Internal Regulator or an External regulator.

At home, I complete my research and draw the wiring diagram in Open Office

The SPDT (Single Pole - Double Throw) switch is used to select either the Alternator's Internal Regulator or the External Regulator

I purchased the switch (a pack of 3) from Amazon. It's an On - On switch, so it cannot be in the Off Position which would cause both Regulators to be Off line!

With the Switch in the Internal Regulator position

• The 12v from the Ignition Switch is connected to the Excite connection on the internal regulator. This powers up the Internal Regulator
• The internal regulator senses the voltage on the +ve Output Terminal and adjusts the output of the Alternator as required.
• With the Switch in the External Regulator position

• The 12v from the Ignition Switch is connected to the Reg On connection of the External Regulator. This powers up the External Regulator and Powers down the Internal Regulator
• The External Regulator Field connection to the Alternator now adjusts the output of the Alternator as required.
• The External Regulator Sensor connects to the +ve of the Battery (actually to a shunt close to the Battery) and senses the Battery Voltage, rather than the Alternator Voltage which can be a volt or more different from the Battery Terminal voltage due to losses in the wires from the Alternator to the Battery. So the External Regulator adjusts the Alternator output more accurately. 

The Alternator's Stator or Tach connection is connected to the Tachometer which uses the signal to display the RPM of the Engine.

If the External Regulator ever fails, we simply shut off the engine, flip the switch to the Internal Regulator position and restart the Engine. Now Alternator output will be managed by it's Internal Regulator.

Life is good.