Good advice, Joe. For now, I'm inclined to isolate circuit ground from
chassis ground on the secondary side of the controller's power transformer.
Of course, there's no guarantee during a strike event that a ground path won’t
be created that would undermine this isolation.
Paul, W9AC
-----Original Message-----
From: Joe Subich, W4TV
Sent: Friday, May 15, 2015 12:17 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rotator Lightning Protection
I'd be most tempted to install contactors in both "rotate"
leads that were only closed when turning the antenna. Consider
making your "common" disconnect a three pole device.
73,
... Joe, W4TV
On 2015-05-15 11:15 AM, Paul Christensen wrote:
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
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