Unreliable switch on string of LED lights

Question

I have a string of LED lights (think Xmas tree lights) powered by a wall wart (3.2V 1A)

and turned on and off with a simple inline rocker switch

I had troubles with the lights flickering and randomly turning themselves off..I thought the switch was bad so I replaced it with a cheap switch from hardware store. However, this did not fix the issue..the lights sometimes flicker and dim, or altogether turn off (actually become very dim, but not completely off). I do believe the problem is with the switch as compressing the body of the switch (not even the rocker part) ameliorates the light, but that never lasts long. I've double checked a the connections, and the strain relief on the cables, and things look good.

I realized that the switch is rated 230V AC, so I'm thinking maybe the contacts are reliable only at this kind of mains voltage and we're not designed for low DC currents? Are there such in line switch specifically for DC circuits?

Answer 1

It sounds like the original system design is the problem.

If that wall wart is outputting a nominal 3.2v constant voltage into white LEDs, then it's asking for trouble.

LEDs should be current driven, they'll decide the terminal voltage for themselves, which will be in the 3.2v ballpark. However, the terminal voltage can vary up and down a little with temperature. Even without the switch, you might expect the LEDs to be very bright, or very dim, as conditions change slightly.

What the power supply ought to be doing is delivering a constant current, into a voltage that can vary significantly from 3.2v. A constant current output would make any small change in switch resistance completely irrelevant.

All switches exhibit some instability of contact resistance. However, you might expect a mains-rated switch to be worse than a specialist low voltage switch in that regard, as the contacts are designed to avoid damage when switching energetic circuits, rather than have a good stable low resistance.

It's quite possible that both switches are 'good' in the sense that they'd meet their specifications when used appropriately. This use between a constant voltage power supply and LEDs is completely inappropriate, the switch resistance has an inordinate influence over the current flowing.

Answer 2

Your problem is the wall-wart. Since the switch is between the wall-wart and the LEDs, it cannot be switching the 230 V. It is switching the 3.2 volts. Since the problem occurs with two different switches (although it is in principle possible that both switches are bad), this rules out the switch. The wall-wart is the next most likely candidate, followed by a faulty wire which has an intermittent break.