Upgrading to a solid-state voltage regulator

My 1967 Mooney M20F had the original style voltage regulator with vibrating points that opened and closed the field circuit in order to provide a relatively constant generator output voltage. This 50+ year old technology leaves a bit to be desired when it comes to performing the job of voltage regulation. Not only was the regulation poor, but the set-point seamed like it constantly needed adjustment.

There’s really 2 solutions to this problem: 1) remove the generator system completely and install an alternator. Or 2) replace the regulator with a solid-state unit.

Since the first option requires different mounting brackets, engine baffle modifications, re-wiring, new circuit breakers, FAA approvals, yadda yadda … it’s never been a modification that I’ve been highly motivated to take on. After all, there’s really nothing inherently wrong with a generator — it does a fine job of translating kinetic energy into electric potential when controlled appropriately.
So, I ordered up a Zeftronics G1500N Generator Controller Unit (50 Amp GCU). It is a PMA replacement part for most airplanes from the generator era, and as such only requires a log book entry to install (i.e. no FAA 337 Field Approval required). Installation is nothing more than remove the old one and bolt the new one in place — as a direct replacement part, it’s the same form-factor right down to the bolt pattern and wire locations. After some simple checks, it was time to fire it up and see how it performed.

I was quite surprised what an improvement it made in regulation stability. Even at relatively low RPM, the voltage is held at a constant 14.1 volts. At normal engine RPM’s, turning on full electrical load only causes a 0.1 to 0.2 V drop while the old regulator would easily allow 0.5 V or more drop. I’m quite pleased.

Cost: $140 and ~1 hour install time.
Installed 9/10/2006 @ 5071 hours. At the same time, the generator was also replaced.

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