For a 12 VDC incandescent lamp total load of about 4.8A at steady state, there's an initial cold filament turn-on inrush current draw of maybe 50A until the filaments heat. Lasting for maybe 40ms, with a sharp decay..
This is being switched with a relay on the high side of the lamp (or array of lamps wired in parallel). Inrush is hard on relay contacts. I'd like to keep the relay small and spec'd lower than one with contacts rated 50A.
I know I could limit inrush putting a series resistor in line with the bulb. But then I need to get the resistor out of the line or I'll just be heating that up, and robbing power to the light, and probably need a hefty power resistor to prevent it going up in smoke. Space is a premium.
Was wondering if using a series inductor with the lamp load instead of a resistor would be better? Of the three basic elements RCL I have a good grip on R and C and my maths and theory of L are less developed, shall we say.
The relay switching frequency is 0Hz (constant on) up to 3Hz (flashing), square duty cycle.
My thinking is putting an inductor on the supply side to the relay NO contact, relay wiper to lamp load. I'd put a flyback diode over the inductor so when relay opens the inductor dumps back to +12V supply... to prevent arcing over the relay contacts.
Would any kind of inductor work? What value would it have to be to limit inrush current to something less than 20A.. and the dimensions of such a beast?
Or is this scheme folly? Inductor would interfere with incandescence and lamp lighting, or not be able to meet the 3Hz frequency, or not be able to limit current in a meaningful way to get inrush down to a level that makes the relay contacts happier? ...