How to get a light buld to light momentarily.

March 13, 2005 8:39 PM

I want to turn on a 60 watt light bulb when I press down on a switch. I bought a RadioShack Momentary Pushbutton Switch. Can I splice a an extension cord, and use this switch? It is rated at 3A at 125VAC, 1.5A at 250VAC. Dangerous? Wrong switch?

The goal is to have control of a light with a momentary switch. Thanks!

posted by mildred-pitt to Technology (5 answers total)

The operating current of a 60W bulb is, of course, about .5A. The inrush current, which is the current when you first turn the bulb on and the filament is still cold, is likely to be much higher. So my guess is that the switches rating of 3A is marginal, it might be good enough, but it might fail. The failure would most likely be carbonizing of the contacts I guess, if it happens at all.

Weather it is safe or not has as much to do with your construction as it does with the switch. If you mount the switch in a grounded metal box with strain relief on the line cords coming in and going out it is likely to be pretty safe.

You could also look for safety agency marks on the switch, which would indicate that it is approved for use switching AC...

I will look for examples...
posted by Chuckles at 8:53 PM on March 13, 2005

b1tr0t has the right idea.

small mini-contactor should do the job. control it with 12V dc.
posted by Frasermoo at 7:01 AM on March 14, 2005

I think the real benefit of the relay is de-bounce. Bounce occurs in the period of transition between on and off (or vice versa), the switch contact can make and break several times before stabilizing in the new state.

With a lamp load that could be a reliability problem because the filament will heat up more slowly, and the current will be higher longer.
posted by Chuckles at 9:02 AM on March 14, 2005

Response by poster: Is it easy to wire in a relay? Does the power just wire into the relay - then the swich from the relay too? If you haven't noticed - I'm pretty new at this....
posted by mildred-pitt at 10:27 AM on March 14, 2005

You'd splice the relay's switch terminals into the mains cable, and then wire the relay's coil in a simple circuit with the push button and a 9V battery or a DC power supply. When you push the button, the relay's coil activates, moving the switch inside it and switching on the lamp. You don't need any extra components or fancy wiring.

The two circuits are kept separate or there's not much point.
posted by cillit bang at 11:02 AM on March 14, 2005