Circuit to soft-start 300 watts of lighting? - Electronic Circuits Projects Diagrams Free

NewUser · 1st October 2007, 02:34 AM

Something to bring them from off to full brightness in around a second would be spiffy.

I already have a 500 watt dimmer - is there such a beast as an automatic and time-adjustable "electronic pot" that I could build and just substitute for this dimmer's pot?

Sceadwian · 1st October 2007, 06:01 AM

How does the 500 watt dimmer work? If it runs off of a signal from a POT then you could replace the POT with a large capacitor and a resistor tuned to go from 0 volts to full voltage over a short period of time.

NewUser · 1st October 2007, 09:19 AM

Quote:

Originally Posted by Sceadwian

How does the 500 watt dimmer work? If it runs off of a signal from a POT then you could replace the POT with a large capacitor and a resistor tuned to go from 0 volts to full voltage over a short period of time.

http://www.geocities.com/tomzi.geo/dimmer/dimmer.gif

Assuming this circuit is similar to what I have, would it be as simple as
replacing the 470k pot with a series-connected capacitor and resistor?

ericgibbs · 1st October 2007, 09:28 AM

Quote:

Originally Posted by NewUser

http://www.geocities.com/tomzi.geo/dimmer/dimmer.gif

Assuming this circuit is similar to what I have, would it be as simple as
replacing the 470k pot with a series-connected capacitor and resistor?

hi,
The dimmer posted works by the pot/cap changing the firing angle of the triac.

Changing as you stated wouldnt help.

NewUser · 4th October 2007, 10:54 AM

Would a FET work in the above 230V circuit as a substitute for the pot?

eblc1388 · 4th October 2007, 12:20 PM

You still have to control the FET even if you can find one that works high voltage.

I would suggest a simple and effective solution using optical feedback. It involves using an additional small wattage(1~3W) 230V filament lamp and a LDR(light dependent resistor). Mount the LDR close to the lamp so that the lamp shines onto the LDR, but the setup should be light tight.

Set your dimmer POT so that the small filament lamp just start emitting light. Due to feedback action, the lamp(and the 300W external lights) will eventually goes full brightness.

ericgibbs · 4th October 2007, 01:22 PM

Quote:

Originally Posted by NewUser

Would a FET work in the above 230V circuit as a substitute for the pot?

hi,
No.
Have a look at this circuit I have added a NTC thermistor and a 'heating' resistor, this would give an initial slow start.

NewUser · 5th October 2007, 08:18 AM

OK thanks guys, will give those ideas a shot.

mneary · 5th October 2007, 06:35 PM

Digikey sells "inrush current limiters", basically very low resistance NTC thermistors. For 300W 230V you might get KC013L-ND which starts out cold at 50 ohms and then heats up to about 0.75 ohms. $2 or less.

There's a similar device in most PC SMPSes that I've taken apart.

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1st October 2007, 02:34 AM	(permalink)
NewUser	Circuit to soft-start 300 watts of lighting? Something to bring them from off to full brightness in around a second would be spiffy. I already have a 500 watt dimmer - is there such a beast as an automatic and time-adjustable "electronic pot" that I could build and just substitute for this dimmer's pot?

1st October 2007, 06:01 AM	(permalink)
Sceadwian	How does the 500 watt dimmer work? If it runs off of a signal from a POT then you could replace the POT with a large capacitor and a resistor tuned to go from 0 volts to full voltage over a short period of time. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

4th October 2007, 10:54 AM	(permalink)
NewUser	Would a FET work in the above 230V circuit as a substitute for the pot?

5th October 2007, 08:18 AM	(permalink)
NewUser	OK thanks guys, will give those ideas a shot.

5th October 2007, 06:35 PM	(permalink)
mneary	Digikey sells "inrush current limiters", basically very low resistance NTC thermistors. For 300W 230V you might get KC013L-ND which starts out cold at 50 ohms and then heats up to about 0.75 ohms. $2 or less. There's a similar device in most PC SMPSes that I've taken apart.