PWM SSR 230v possible?

[toolate]

Hi

I'm making an incubator for my sister,  and being an incubator it must be held within 1 degree of 38degrees less the better. the idea for the circuit will slowly adjust the duty cycle of the PWM to keep a constant temperature. and I have some questions about different ways of going about it.

Firstly here are some details:

PICAXE 18x for the main brain which has 1 PWM output at a minimum of 4kHz
2 x 60W 230v light bulbs as the heat source

First try I opened a mains light dimmer and replaced the dimming pot with an LDR which had an led coupled to it and taped up, and yes it did work, but it was anything but predictable, like it might be 80% and an our later at 10%.

Second try I didn't think it through properly and tried using a zero crossing SSR with a max switching speed of 50Hz and at 4kHz well you can guess!

I have no idea if this has any merit or is even possible, but to rectify 230ac to get about 330Vdc then connect the lamps in series and switching it with a mosfet??? would I be able to just use a rectifier or would I have to smooth it somewhat for the mosfet?

and another thought which I haven't really thought much about yet is to use a /100 on the output PWM to make it 40Hz, but that would stuff everything up wouldn't it? or would it?

any help for pointing me it the right direction would be very appreciated!
Thanks 

[justDIY]

maybe look for a mains incandescent dimmer that accepts either a PWM or 0-10v control signal... they're usually sold for commercial lighting setups, where you have a big room of lights controlled with a touch pad.

or dig a little deeper into the dimmer you were modifying ... if it's using a POT to control the dim, most likely it's reading some sort of DC control voltage, which you could replicate with your PIC (PWM into a RC network to convert digital to analog)

[toolate]

I would rather not spend any more money on a pwm dimmer if possible.

put my meter across the pot and it read from 0-200vac across the range.  think I might have to stay with the LED/LDR

when I pwm the led over the 0 -100% range, I can only get about a 60% range on the LDR, by changing the resistor on the led it changes the range from 0-60 through to 40-100% can you think of a way to over come this?  Thanks heaps

BTW the incubator is for chicken eggs if any one was wondering.

[cadstarsucks]

I would rather not spend any more money on a pwm dimmer if possible.

put my meter across the pot and it read from 0-200vac across the range.  think I might have to stay with the LED/LDR

when I pwm the led over the 0 -100% range, I can only get about a 60% range on the LDR, by changing the resistor on the led it changes the range from 0-60 through to 40-100% can you think of a way to over come this?  Thanks heaps

BTW the incubator is for chicken eggs if any one was wondering.

standard triac dimmer for a  heating element...they do not, however, work properly with light loads (like leds, since it drops below the triac holding current)

Dan

[toolate]

thanks for the replies guys, what I've done is set the range from 0-60% with the dimmer, and set up another light to turn one when the temp still needs a boost.