mark.bitterlich(at)navy.m
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 Posted: Thu Jul 27, 2017 7:55 am Post subject: [Non-DoD Source] B&C Alternator Conversion and Russian Hori |
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The B&C SK-35 can easily handle the Motor/Generator or Inverter Power Supply (whatever name you choose to call it) used for the both of the AI's in the 52. With one warning. You must have your batteries in good condition. The SK-35 is rated at, amazingly enough, 35 amps. That said, I would not recommend pulling 35 amps out of it continuously. Personally on my installs, I have recommended a 30 amp circuit breaker versus 35, which still leaves you with over 800 watts of power. What I have learned is that the SK-35 is not tolerant of instantaneous current draws that exceed 35 amps directly to the alternator. This kind of situation would normally never happen UNLESS you have bad batteries (assuming two 12 volt batteries in series). Since we do not use batteries for starting, it is easy to miss the fact that the batteries are getting weak. Good enough to open an air valve and power shower of sparks to start the engine maybe... but then with the engine at idle, the batteries trying to charge, Inverters powered up, along with everything else, then yes... it is possible to take out the alternator under those conditions. This happened to a B&C equipped CJ at an airshow one year when a spectator happened to flip on the Master, it went unnoticed, and the batteries went dead. The owner jump started the airplane, so far so good. When the jumper cables were removed, the SK-35 had to assume all the load and all at once. POOF. $700+ alternator now inoperative. Another fact worth repeating once every few years or so is the fact that regardless of what charging system you are using, the AGM, or Gel Cell batteries typically used have a maximum charging voltage *AND* current. Both can easily be exceeded in our day to day operation, causing the battery to vent, lowering the capacity and leading to an eventual demise. If you run your batteries until they actually fail, again this is asking for bad things to happen. So once in a while, before starting the engine, turn on the master, look at your ba!
ttery vo
ltage, and then turn on a big load, like Pitot Heat for example. If the battery voltage drops down below 20 volts or so, it's time to replace the batteries.
Yes, the short answer was simply that the SK-35 will be fine, as long as you have good batteries, but I repeat the long version every so often as I see folks installing TINY batteries to save weight, or whatever other reason, and then never realize there is another side to that coin. I.E. The smaller the batteries, the lower the maximum charging current, thus the above becomes more likely to happen.
Mark
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