Airline Pilot Central Forums - High/Low voltage

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High/Low voltage

Hi,

On some cessnas, especially the older 152 and 172, I see Low voltage warning light and some I see High Voltage warning light. Can you help me understand why some planes have Low and some High? I just don't understand why they are not all Low or all high.

thanks!

depends. What are you doing when you notice Low Voltage and High Voltage? It's not uncommon to get a low voltage light at low idle.

If you're noticing either high or low voltage during normal flight ops, it could possibly be a problem with the voltage regulator or the alternator.

Most GA planes (except very old ones) have a high-voltage shutoff in the voltage regulator...if it gets too high, it turns the alternator off.

You will then get a low voltage light of course, and can reset the alternator as usual.

Good to keep in mind that a low voltage light may have actually been caused by a high-voltage (or over-current) condition.

On older airplanes, it's common for the VR to trip off occasionally...just reset it per the AFM. On airplanes less than ten years old, the VR is pretty reliable...if it trips off, you most likely have a real problem.