[TowerTalk] Rotator Lightning Protection

[Paul Christensen]

Jim,

> "what about mechanical limit switches on the rotator motor?"

A possibility but that's probably best done when these units are back on the 
ground for service.  That shouldn’t be for quite a long time.

> "Since it's a DC motor, you put a diode in series with each of the two
switches, which are then paralleled."

Maybe I'm just being dense this morning, but I don’t see how a 
series/parallel diode combination helps in this case.  I just drew-out the 
electrical diagram but don't see how the diode would limit current during an 
MOV fault while still allowing rotator current during a normal turning 
operation.

A bit more info:  The prop pitch uses two windings: one for CW and the other 
for CCW.  A common lead connects to the ends of each and ultimately, this 
common lead routes to the controller's MOSFET.  The M2 controller uses a P&B 
frame relay that directs +48V to either the CW or CCW winding, depending on 
the called direction.  The relay's NC contacts are on one or the other 
windings.  I forgot which.  But the MOV failure would result in current in 
this NC winding since its connected to +48V via the NC relay contact.

Paul, W9AC