Switch spark on turn on

[laejf]

How do I avoid sparking in my cheap slide-switch when I turn on the circuit? Is it a sign of too large capacitance? It does not spark when turned off.

[bob91343]

The problem is that C1 draws a lot of current when you connect power to it.  You can add an inductor in series with the switch but then you may have sparks when you switch it off.  Add a resistor if you can afford the voltage drop.

[laejf]

Perhaps a charge resistor for the cap with a parallel discharge diode? Never seen that being used really so perhaps there are more elegant solutions. Thanks

[bob91343]

That won't work.  The capacitor needs to charge and discharge frequently so a diode will not allow that.  A series resistor will destroy the capacitor's function; it needs to be low impedance.

[jaycee]

Do exactly what you would do to spark suppress a relay. Put an R-C snubber across the switch terminals.

[S. Petrukhin]

Do exactly what you would do to spark suppress a relay. Put an R-C snubber across the switch terminals.

The damper does not save from the charging current of the capacitor.

[jananetha]

Finally what is the best method to suppress the sparks

[Zero999]

How do I avoid sparking in my cheap slide-switch when I turn on the circuit? Is it a sign of too large capacitance? It does not spark when turned off.

(Attachment Link)

As you've said, it's a sign of too larger capacitance. The data sheet for the LM1117 shows a 10µF, on the input, and you are using 470µF.
https://www.ti.com/lit/ds/symlink/lm1117.pdf

Why are you using 470µF, rather than 10µF? If it's powered from a power supply, with a lot of ripple, such as rectified mains frequency AC, then put the switch between C1 and your circuit and use another, lower value capacitor, right next to U5 and U6. If the wires to the switch are short, you can use an even smaller capacitor than 10µF.

[laejf]

I thought that it couldn't hurt having a large tank-capacitance, especially for the DC-motor/pump. The power supply has a bit of ripple, but I could try a smaller capacitor. Thanks!

[laejf]

I replaced the 470u cap with a 10u and now there is no sparking!

Thank you for the help!