embarassingly simple dimmer question

[earckens]

I have a standing lampshade (living room lamp) which came with a dimmer included. This dimmer has always been flickering at most of its dimming settings until I go fed up and dismantled the sucker.
Now I cannot figure out what could be wrong on this circuit, I compared it with a dimmer I had self-fabricated which gives no flicker at all: the only difference is an extra 0.2uF capacitor between supply and the regulating pot (see attachment, cap with question mark).
What causes the flicker in this dimmer circuit (the capacitor with question mark is not present).

 

[alec_t]

Did you mean to post a schematic?

 

[earckens]

Did you mean to post a schematic?

indeed, funny it did not upload (or I forgot ). Here it comes..

 

[alec_t]

Try adding the 0.2uF cap (of appropriate rating).
If the X2 cap were to break down intermittently it might explain the flickering.

 

[earckens]

Thanks alec_t, I will do, and replace the X2 cap afterwards if needed; I will let you know.

 

[dr pepper]

Not enough load might be causing it, try some other bulbs.

 

[throbscottle]

May be a bad joint. Try re-working the whole thing.

 

[earckens]

Not enough load might be causing it, try some other bulbs.

Well, I did try the extra capacitor but that only caused the dimmer to be 0V out until 3/4 of the pot travel, and then go to only half brightness when it should be full brightness. But no flicker.
Dr pepper's remark above I thought sceptical about but it did make me try the same load as was in the lampshade originally (a 220V halogen quartz bulb) and the flicker was back.
Not so with a classical tungsten-wire lamp. So indeed, the load does cause the problem in this case.

But why would a standard 230V 53W halogen E60 bulb cause trouble?

 

[ci139]

just a thought - years ago there was some promotion price portable multi tool - it took ages to charge and you could then work about 10min or even less - when i opened it up it had a powerful 9 or 12 V dc motor installed but the battery pack was 6 or 7.2 V one . . . another one was the automotive boost cables that were at local tool-store cheaper and with higher rating than the quality ones we had in our whole sale storage the copper inside was about the 3x thinner (at least it got decent clamps about worth the investment) . . .

there are bullsh¡t on a market you never know it's that until it's obvious

 

[dr pepper]

Sorry earckens I didnt mean to be sceptical.
But it looks like you gathered some evidence.
I'm sure I've had something similar a while back, something to do with resistance changing with brightness.

 

[ci139]

a dimmer I had self-fabricated

if you have made one of these you must know that the regulator is (depending on design) in more critical operating range at the dimmest settings

0V out until 3/4 of the pot travel

as said (depending on design) while filament is dim the voltage drop at regulator/dimmer is high ??? the flicker might be some sort of automatic protection /!\ it also might be an out of range or bad/failed component

while ago i made a thyristor experiment with a std. circuit that allowed dimming from etremely faint glow to near max -- i also made an experimental design hi-voltage transistor circuit that started to overheat at below 40% of visual output luminosity -- the most possible reason -- existing(/present) but too slow closing time (NOT at zero crossing // a way much longer than in corresponding spice simulation) -- in such condition the auto thermal (disconnect) would cause the circuit to strobe /output to flicker , again (depending on design)

anything near-above RMS 5W dissipating would have potential to heat the circuit fast e.g. a 20mA leakage . . . or such as a SUM of "turn on"-s or "turn off"-s at not too good picked phase