R:C Snubber network component values?

[G6Tanuki]

Are there any generally accepted design-formulae for R:C snubber networks (for use across switch-contacts)??

I have 12VDC motors (they take about 10A) controlled by centre-off DPCO rocker-switches, each wired to run their motor 'forward' when you press the rocker one way and 'reverse' when pressed the other way. The switches seem to last about a year - the contacts wearing because of arcing - and I'm fed up with the things packing up at a time of maximum-inconvenience and paying £50+labour having them replaced so a snubber seems the way to go.

The ones I'm familiar with for wiring across 240V relays/switches are usually something like a 220-Ohm resistor and 0.1uF of series-capacitance. My thought is that since the voltage in my application is 1/20 of this, I should reduce the series-resistor to 1/20 too, meaning something around 10-Ohms?

Or is there some other way to derive the 'right' resistance?

I would think that as the contact opens at the same speed for any voltage the capacitor will be in the order of 100nF, the resistor could be a bit smaller for lower voltages. I don't think it really matters though.

[G6Tanuki]

That's kinda my thinking too: 100nF and maybe something in the 10-30 ohm range. It'll need some waterproofing though, as it's to live inside a car door (the switches are for the window motors).

It'll need some waterproofing though

Or as it is only 12V put in a ventilated space, the odd drop of water won't matter. Sealing things in can also seal in any weeny leakage.

The switches on my motorcycle are not waterproof at all, they just have a path for the water to leak out.

[boxdoctor]

I fear that you are going to have difficulty in getting what is generally accepted as a good lifespan from these switches as they are switching D.C., and the problem is the age-old one of the D.C. arcing contact.
With A.C, due to the recurrent reduction to zero of the voltage across the contact, the contact arc is extinguished before it can get properly established, but D.C. will maintain a continuous arc (upon opening the contacts) until the gap is large enough to cause the arc to 'break'. Unfortunately a snubber will not prevent this.
Heavier switch contacts are the real remedy, as a snubber will, I beleive, have virtually no effect in this situation.
Fast-acting switch contacts are a partial solution. The real answer is meatier switches. Tony.

[Refugee]

If you really get fed up with those switches they could always be replaced with a MOSFET unit from a more modern car. They have "tact" switches and a block with 4 MOSFETS inside.

I fear that you are going to have difficulty in getting what is generally accepted as a good lifespan from these switches as they are switching D.C

I think not, look at the Kettering ignition system with the breaker points and coils and a capacitor as the snubber, lasted for may thousands of miles (goodness knows how many close/open cycles).

[G6Tanuki]

Time will tell if my homemade snubber [an old 0.1uF 500VW leaky-metal-canned Waxie and 22-Ohm 2.5W resistor] will make any difference.

I put them in a length of 20mm plastic electrical-conduit and filled it with Silicone-grease; it's now cable-tied inside the door a couple of inches from the motor.

It may fix the problem, it may not. It's unlikely to make it worse!