On Sunday, April 28, 2019 at 9:17:57 AM UTC-4, wrote:
On Sun, 28 Apr 2019 06:18:34 -0400, John H.
wrote:

On Sun, 28 Apr 2019 01:19:50 -0400, wrote:

On Sat, 27 Apr 2019 21:43:45 -0700 (PDT), Its Me
wrote:

On Sunday, April 28, 2019 at 12:31:07 AM UTC-4, Bill wrote:


Why were the MOV to ground, instead of across the lines? Or a bigger value
Varistor to ground?

Because of the twisted pair, the danger isn't usually voltage spike across the pair, but rather the spike potential from the pair to ground. That's what we were trying to protect from. And what protection components on 66 punch blocks from back in the day did as well.

As far as the value, it's a bit of a tightrope. Too low of a value, and it's always firing and causing issues like we experienced. Too big of a value, and you may as well not have any protection on there at all. Even a transformer doesn't protect you, as it has an arc-over value. We thought the 180v parts would be OK, but we didn't realize that the lines would be as dirty as they were.


===

I'm wondering if you couldn't use an isolated op amp with differential
inputs to extract the signal. It would have to be totally isolated
from any ground reference to protect from the high voltage common mode
spikes. It would need a floating power supply of course, with the
output through an opto isolator or some such.

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I'm wondering if we could talk about artillery and tanks for a while, with maybe a bit of C-4
discussion thrown in! :)

===

Sounds good, and I'm sure we'd all get a bang out of it. Is C4 what
they use in the combat simulation exercise during basic? I was right
next to a ring of sand bags when one of those charges went off. It
certainly gets your attention.

A cousin of mine gave my dad two artillery simulators years ago. I remember them being a plastic bottle almost the size of a drink can with a tube down the side that had a string you pulled. Then you had so many seconds until it went bang. Wow.