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battery, alternator, landing light, or normal?

After doing a night landing currency flight, I got a low voltage note from the JPI for 12.0 volts. I did some troubleshooting the next day and everything looks normal after start. Showing 14 volts on the bus and battery charging normal after start. I put on all the external lighting and as soon as I put on the big landing light I could watch the system voltage dropping about .1 volt every few seconds and the battery shows a slight discharge. I have a Hartzell 70 amp alternator, and the landing light is an older GE (halogen?). Data on line shows this could be up to a 250 watt light = over 20 amp draw.

I'll be doing a little more data gathering the next flight, also will tweak up the voltage on the Plane Power regulator.

Does any of this sound familiar, or is there a significant issue in there somewhere?

Attaching the JPI plot for volts showing exactly where the landing lights come on and off.

smallvolt.jpg - 38.4 KB

Model: Bonanza S35
Aircraft Serial Number: 7338
Posted 11/16/2023 - 3 months ago
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Voltage should be set at 14.2 with a digital voltmeter attached to the main buss bar. DO NOT use onboard instruments to set the voltage.
An LED landing light will greatly reduce the load and also allow you to use it in the pattern for better aircraft visibility.

Bob Ripley
ABS Technical Advisor

Posted 11/16/2023 - 3 months ago
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What RPM were you running during the test of turning on the landing light? Yes, if it is an original incandescent lamp, those things are amperage hogs and require more than idle RPM to keep the voltage up. Would highly recomment changing the landing and taxi lights out for LED's. You will see much improved electrical performance. While you're at it, if you have not already, changing the Nav lights for LED's will also help a lot.

Posted 11/16/2023 - 3 months ago
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S35
If the alternator-charged system has a healthy battery and resistance-free connections, the voltage regulator senses the aircraft electrical system voltage and varies the excitement current flow to maintain a charging-system voltage between 13.8 and 14.2 volts in a 12-volt system. If yours is indicating 12.0v while charging, you might want to “up” the regulator to the 14.2v with a digital gauge as Bob mentions above. However, these older landing lights do have a large draw. The newer Whelen type LED bulbs max current according to the data is ~6.0 AMPS @ 14v. Available from Aero Mach Wilco at https://www.wilcoaircraftparts.com or Toll Free: (800) 767-7593 or (316) 943-9379.

Jim
ABS Technical Advisor
BPPP Instructor & Ambassador
CFII/MEI, A&P/I-A

Posted 11/16/2023 - 3 months ago
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Thanks for the guidance all. The reason the volts went all the way down to 12, was the unusual amount of ground time with all the taxi backs for 3 night landings, and generally low power settings after level off. Will definitely upgrade the lights soon.

Posted 11/16/2023 - 3 months ago
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RPM is critical. I have several AFMs where the procedures for a LOW VOLTS indication begin with "If the engine RPM is less than 1,000 RPM. . . " increase power and see if the indication goes away. That's with alternators. Vintage generators don't produce power until much higher RPMs.

Often in the electronic display systems, aka G1000, we inhibit Voltage / Amperage related messages and indication if the RPM is low to prevent nuisance messages of what are essentially normal conditions.

Posted 11/16/2023 - 3 months ago
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Voltage should be set at 14.24 +/- .25 using a digital multimeter attached to main buss. Do not rely on onboard instruments. Make sure electrical system is operating for several minutes so all the components are up to temperature.

Bob Ripley
ABS Technical Advisor

Posted 11/16/2023 - 3 months ago
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battery, alternator, landing light, or normal?