Originally Posted by
Bengo
IIRC from Mk2 days, you have to have 24v on the third pin of the DC external power connector in order to get the socket to accept external power. It works the other way round too, so where you could run a drum fuel pump just by plugging it into a Wx, because the external pins are always live, you needed a battery to energise the third pin to get the SK to provide the power.
N
Unfortunately the problem was more complex than that, our red box was producing 26.1V but a diode or relay in the aircraft circuit was not seeing that and allowing the power through - we have had problems diagnosing why the EXT PWR caption on the CWP stays on even after the plug is out and some of the rectification work seems to have caused this new issue. Anyone have any ideas?
The only way was to disconnect the aircraft battery and hot wire the aircraft connecter to a separate battery to get the engine turning over fast enough - it worked but I don't think it's in the Topic 5 anywhere.