Delay On Switch SCR for Relay

Thread Starter

DC_Kid

Joined Feb 25, 2008
1,072
anyone see any pitfalls?

i am replacing a mechancial switch on an old drill press with something like this. a green NO and a red NC button, hold NO for ~5sec and SCR clamps on, press NC and SCR dies. the led is actually a led in a opto relay (ssr).

the delay is to prevent accident on by a switch bump, etc. does the gate need a small R (~100ohm) between it and cap?

 

AlbertHall

Joined Jun 4, 2014
12,345
It could do with a resistor between the NO switch and the CW end of the pot. As it is turning the pot fully clockwise and pressing NO will kill D1 as there is nothing to limit the current from the battery.
 

Thread Starter

DC_Kid

Joined Feb 25, 2008
1,072
i was figuring it would never get there because i will need a delay, and once found the whole thing gets potted. but point well taken.

maybe the pot is ~1meg and the wiper hangs on the CCW side, near 900k between CW and wiper, etc.

but look at the cap, once it hits trigger voltage it can dump into the gate, so was figuring maybe a 100R on the gate. batt voltage will be ~5v, etc.
 
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