Re: Europa-List: OV protection

[Nigel Charles <nigelcharles@tiscali.co.uk>]

I have been following the discussion on the OV protection aspects and would
like to include my thoughts:

1. I can endorse that Rotax require the capacitor to be connected directly
to the regulator output. As they know the internal circuitry and we don't I
think it is wise to follow their guidance.
2. We have had one event so far (to my knowledge) where the OV crowbar unit
has operated as intended. The subsequent voltage runaway did destroy the
capacitor but that is a relatively cheap item to replace.
3. Bob Nuckolls indicates that overvoltage is a problem to batteries and can
cause them to fail in a short time. I would imagine that this problem is
just as relevant (if not more so) with the newer RG batteries. I have been
also told that most modern avionics include OV protection. This is cheap to
do and improves the reliability of the unit which reflects well on the
manufacturer. On that basis the concern would be for the battery not the
avionics. In any event if you look after one you look after the other.
4. Bob Nuckolls also advocates using a CB and not a fuse with the OV unit.
5. Any aircraft with an all electric fuel pump system should have some means
of OV protection. The most likely reason for total electrics failure is a
regulator runaway. Splitting the sources of power for these pumps helps. One
on a normal busbar and one directly connected to the regulator output helps
to ensure redundancy as well as providing a constant load for the regulator
should the alternator become isolated.
6. The intentional shorting of the CB to ground is part of the Nuckolls
crowbar unit design. It ensures that the output is isolated quickly. Any
concern about this design philosophy should be taken up with him.


Regards

Nigel Charles