Cessna 400 Series Voltage Regulator Upgrade Kit

[CRDedrickson]

I came across this post and it might be related to an issue I have with low voltage when at idle. I have accepted that at low RPM (~1000) there may be insufficient voltage to charge the battery, but this always resolves at higher taxiing RPM and certainly always in flight.

My understanding is that the voltage regulators adjust the alternator field current to maintain the set voltage. Should I be able to achieve rated charging voltage at idle, nominally 1000 RPM? I don't think this should adversely affect the scenarios, but I'll mention that the alternators were upgraded to 60 amp units by a prior owner. I am seeking to understand if this low voltage at low RPM is a design limitation, or if there is a remedy (voltage regulator adjustment or model change)?

My most recent interest in this voltage is because I've added an electric air conditioning system that requires a voltage in the 24 +/- area to prevent an unplanned battery drain. So, at idle and while taxiing, the AC system may shut down. The system is Peter Schiff Aero's SOFIE system. It provides up to 18,000 BTU and rejects heat to the outside by liquid antifreeze piped to the condenser located in the rear engine compartment. The cycle is a freon system with electric compressor for the evaporator in the cabin.

Russ Dedrickson
N8CV 1973 T337G Pressurized Super Skymaster, standard TSIO-360 Continentals

[mshac]

Directly from the POH:

"The ALT NOT CHARGING lights will normally stay out during idling and taxi operations. Occasionally a light may come on when electrical loads are at a minimum and one engine is operating at a much lower RPM than the other. If one light constantly comes on during idle or taxi with equal engine RPM, or during cruise, the voltage differential between the voltage regulators is too great and the regulators should be adjusted."

One of the last steps in my 400-Series voltage regulator upgrade installation is to adjust the new regulators to the same voltage output at 1600 rpm with a load on the electrical system. This, along with the new paralleling circuit, prevents the lights from coming on at any time unless there is truly a fault in the system.

Also, the trigger voltages for the high output and low output warning lights are fully adjustable. If all you have is the OEM amp gauge, get a cigar lighter digital voltage gauge so you can watch the actual voltage in real time. Here's one at Amazon that displays up to 30 volts and provides two USB power outlets: https://smile.amazon.com/dp/B01N00I4...XBN6VJS7V3F5P1 If you don't like that one, there are many other styles available.