Nigel Charles wrote:
> There is no guarantee that a small aircraft battery (13 -
> 17Ahr) will be able to hold the battery voltage down to
> acceptable levels.
There can be, but dependent upon the load on the bus. If you have 10A
of normal stuff on the bus, and the reg fails wide open at cruise RPM,
there's less than 6A extra for the battery if voltage across it rose to
16V. That's barely enough (Nuckolls allows for up to 18V) to trip the
OVM in the first place! It's about a "C/3" charge rate which will have
little short-term effect on the battery, and initially shouldn't cause
the batt rise to even 16V anyway. Switch on the lights, and overvoltage
disappears.
That's why my setup (dual alt/battery, which makes this all moot) relies
on aural/visual warning at a lowly 15.0V, meaning an OV module will do
little good. It certainly can pop on the ground before stuff is
switched on. Is that when it happened in the example you cited?
>>It's easy to add a circuit to prevent excess volts to the pump while
>> keeping it safely running off a runaway regulator, <
> This means more complication. One voltage control circuit for the
> pump and an OV unit for the avionics.
You snipped my next sentence which said that such would be dumb!
Actually 3 add-on systems. A possibly worthless OVM, a circuit to
prevent it from blowing up the electrolytic cap and fuel pump, but a big
honkin' Zener on the avionics bus is not a complication.
Regards,
Fred F.
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