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Standby alternator checks; what's normal?

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Hi All, 

I had not been routinely checking my standby alternator. As it is part of the IFR pre-flight, esp. in FIKI planes, I started doing it recently. 

My question is: what do you normally see in the part of the procedure where you have the Stdby field ON, Main alt field OFF, and pull the 70A BAT breaker? It says the warning light should extinguish (I also look for positive charge). The manual warns that this doesn't occur below 2000, but I am seeing it happen a bit higher. Maybe because I drained my battery pre-start, but who knows...

Figured I'd ask the hive mind. 

Thank you, 




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  • 5 weeks later...

Pulling the BATT CB just reduces the load so you can get a positive charge indication at a lower RPM than 2000. If you are getting a positive charge with the STBY Alt on there is no need to pull the BATT CB. I do my engine run up at 1700 then increase to 2000 and check the Standby. If I’m showing a positive charge at 2000 I don’t load shed the BATT bus; No need to. You’re just checking that the Standby Alternator works.

Sent from my iPhone using Tapatalk

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  • 2 weeks later...

It might be a good idea to let it run on the standby for a few minutes.

On my 252, with the avionics upgrade, when testing, they found that the #2 was over volting to the point of the regulator shutting it down.  But it was slow ramp up to 32 volts.

They traced the wires and found the sense wire for the #2 alternator was not connected and was capped off.  But it was not a mistake on their part as the cap was not a type they used or even had in shop.

I had been doing the quick check that the standby picked up the load, but only was on it for a few seconds.

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