Re: programmable circuit breaker

On Wed, 5 Mar 2025 18:05:55 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:

Liz Tuddenham <liz@poppyrecords.invalid.invalid> wrote:

john larkin <jl@650pot.com> wrote:
 
[...]

Maybe I shouldn't diode clamp the relay coils. I'll have to test the
dropout time.

 
Put a resistor in series with the clamp diode, the value can be chosen
to keep the inductive spike just below the maximum allowable voltage and
that will give the fastest turn-off.  By using higher voltage switching
transistors you can have a higher voltage spike and a faster turn-off -
but there is the risk that the spike might be capacitively coupled to
somewhere vulnerable to damage.
 
 

>
Or even just a resistor and no diode! The extra few percent current
consumption is often not a problem and a resistor is very reliable, more
durable than a diode.

I tried a BSS123 logic-level mosfet driving my 12-volt 33 mA relay
coil. It avalanches at about 120 volts and runs cool at 20 Hz.

I'l let it run for a zillion cycles, but it's noisy.

https://www.dropbox.com/scl/fo/i9xxdnw7bveuegm373sky/ALKsKJsIlT1fWhCehkHaa8w?rlkey=5ttkfyzl52prxvyd7xztguzh4&dl=0