I'm Stuck on this thermostat.. Please help.

Luke,

My apologies for the delay ! It appears that the circuit is triggered 'ON'
ALL the time.

1. Is the Light(LOAD) is OFF when you disconnect pin 6 to the gate of the triac ?

Let's insure that pin 4 and pin are connected somewhere, And NOT left floating.

2. Tie pin 2 to Vcc with a 100K resistor for R3.

3. Tie pin 4 to Vcc with a 47K resistor(R1).

With these values the circuit should trigger at ~ -2.9V or >.

Try again ! Please attach the present form of the circuit with ALL part values.

Fred

SUCCESS!!!! (least I think so)

Hi Fred

Sorry for the late reply.

Well I think we have broken the back of this problem. When I reversed the ac wires earlier(as you advised) I did not change the wires for the triac. With this setup the light stayed on all the time.

I changed the wires to the triac and now it appears to work. The lamp flickers
when the sense voltage is around -2.75volts and it goes off at around -3.00volts and when it is really low eg: -1.0volt it is on constantly(just the occasional flicker).

I believe that I now just need to play around with the resistor values in the divider and It will be working.

I would like to add a fuse to this circuit( for safety), where should this be added?

THANK YOU FOR ALL YOUR HELP!!!!!

You have been so helpful.

I hope I am not jumping the gun with this circuit, I dont think I am.

Cheers

Luke

Luke,

Great call on observing to reverse the leads on the triac. (sorry that I missed that one) !

Now you know alot more about electronics. ( NTC thermisters, capacitors,
triacs, Leds, and breadboarding prototypes)

This is quite an accomplishment AND for a good cause...Python Eggs !

What made you think to change the triac leads ?

I would place the fuse (3AT @220VAC), in series with the 'HOT' lead that feeds the common connection Cathode of the 1N4004 and 300W bulb.

Are you O.K. with calculating the voltage divider 100K(NTC) and Rdef ?

The NTC @ x degrees C = x K ohm( say 100K @ 25C), Then
Rdef(4.7K)/ R ntc + 4.7K ~ 2.75V....the set point.

Take care of those Python eggs !

Cheers,

Fred

Hi Fred

Thanks for the compliments.

To be honest it was a bit of a guess. I just thought it had too be something with the triac. Everything else seemed ok. And with changing the supply wires I thought I might need to change where the gate fed from.

I should be ok with the calculations.

Thank you again for all your help and support. My pythons will benefit from your help.

Honestly I think forums such as this and the people on them such as yourself are what makes the internet so great.

I definately feel motivated to learn more about electronics now.

Thanks again

Luke

Luke,

I am glad to hear that you are motivated with electronics !

Yes, I agree about this forum. I learned something too !

Take care,

Fred