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Can this circuit be used as a dimmer for lamps

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DTaylor

New Member
Hi all,

I want to use a circuit to dim the lights in my lizard tanks to keep the temperature at a preset level.

Do you think the link below shows a circuit that could be used as a dimming thermostat upto 250W 240VAC? Also where would I connect the lamp.

Thanks guys.

https://www.redcircuits.com/Fan.GIF
 
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illconductor

New Member
holy smoke, pretty complicated circuit for a dimmer...
you know you can buy dimmers from the hardware

assuming u get an electrician to install it
 

Grossel

Well-Known Member
Do you think the link below shows a circuit that could be used as a dimming thermostat upto 250W 240VAC? Also where would I connect the lamp.

Assuming the circuit works, and you have chosen transistors that can withstand 240V * √2 = 340 Volts, then yoy'll connect you lamp in serie with the dimmer:
 

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Nigel Goodwin

Super Moderator
Most Helpful Member
Assuming the circuit works, and you have chosen transistors that can withstand 240V * √2 = 340 Volts, then yoy'll connect you lamp in serie with the dimmer:

I suggest you look at the circuit again - it only needs low voltage transistors.

As for the OP, this circuit IS a lamp dimmer, it's NOT a fan controller.
 

Grossel

Well-Known Member

DTaylor

New Member
Having assessed this circuit further the controls side is only a few volts. The Thyristor and rectifying part of the circuit is the only part carrying mains.

Nigel: I thought looking at it it was a lamp dimmer but the SCR in that circuit is a 5A unit. Even a 250W lamp is only roughly 1A.

I am building it regardless as it is temperature controlled and provides a dimming effect O/P. Accuracy on the control side of things may need some work.

Illconductor: I am a fully qualified electrician aswell as electronics engineer. A dimmer installation will be no problem.

Thanks for the replies lads.
 
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mneary

New Member
Nigel: I thought looking at it it was a lamp dimmer but the SCR in that circuit is a 5A unit.
Good that it has a "5A" SCR. According to ONsemi. It's 4A.. I would never use a 1A SCR for a 1A load; especially in a confined space such as a "dimmer".
Even a 250W lamp is only roughly 1A..
It becomes 1A after it heats up. When first turned on it's momentarily at least 10A. Hopefully not much more than that, since the non-repetitive surge rating of the C106 is only 20A.

Most dimmer circuits don't require a 4W resistor. The C106 SCR only needs 200µA to trigger! Putting a 2mA load on the gate makes little sense to me. Doubling the values of R3 thru R9 would cut the power consumption in half. C1 would be reduced to 4.7 nF.

R9 should be a special flameproof resistor since an "ordinary" resistor could be seriously hazardous.

As a fan controller, it was designed to increase fan power at higher temperatures. You would swap R1 and P1 to do the opposite for a heater.

I am a fully qualified electrician aswell as electronics engineer.
Also where would I connect the lamp.
Connect the lamp to SK1.
 
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