Ok, I'll ask  what is the benefit from having an external regulator
    as opposed to an
    internal?  T.W.



The issue is not so much that external is better than internal, but
rather what failure modes are there & how can they be addressed.  By and
large, internally regulated alternators do not provide external access
to the alternator field current.  The SL alternator which comes stock
for the RX-7 falls into this category.  The reason you might care about
this is in the event of a regulator failure.  Should the regulator fail,
uncontrolled voltage will flow to the aircraft.  In the case of the
RX-7's SL alternator there is no way -- by design -- to shut the
alternator down without stopping all engine rotation.  The alternator is
designed to use +12V on the "S" line to initiate the field current, but
once established, removing the +12V will not shut the alternator down --
only stopping the engine will reset the alternator to "off".

So - in this case there is a compelling reason to "fix" the design, and
using an external regulator is the only way.

Mark Supinski


Mark sent a 4.7 meg pdf but I converted it to 9 jpgs which are smaller overall.
Here are the first five. I suggest you print them and take them to the shop.

-- 
Paul Lamar ...No rotor no motor.

Nice article!

Isn't another alternative to use a battery contactor which allows you
to take the alternator completely out of the loop in the event of an
overvoltage?  This would require recognizing the overvoltage and
manually killing the "Alt" switch, however.

Scott Gettings

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