On 20/02/2014 23:09, wrote:
On Wednesday, February 19, 2014 5:27:03 PM UTC, Adrian Brentnall wrote:

Hi Folks
Still working on that DIY glass kiln -
done all the nasty itchy stuff (it's lined with ceramic fibre -
think fibreglass roof insulation & then some!)
So the kiln controller is powered by AC, from a 12 - 0 - 12 v
centre-tapped transformer - which is half-wave rectified on-board the
module to
give +12v.

12v transformer hw rectified would give 12x1.414 -0.6v = 16.4v on full load.
No load would be plus transformer regulation of anything from 5% - 33%.

Yup. The module specifies 12vAC - so we'll hope that it's OK.
I might check it against the other (commercial) kiln - which uses the
same module - see what AC input that transformer gives.


My other bits of circuitry (the thermcouple conditioner and the famous
latching relay / logic module) wants 12v dc, plus a stabilised reference
voltage in the region of 10v. Will add suitable c's to take any relay
switching spikes off the 'instrumentation' dc line.
Both modules share the same 0v line.
Can anybody see any snags in running all the electrics from the same
centre-tapped mains transformer (it's got sufficient current available)
- simply by adding another half-wave (2 diodes) circuit, smoothing cap &
so on...
- see diagram here http://www.ambquality.co.uk/power-supply.html
I had bought two c/t transformers, but if I can get away with just one
then that frees up some space in the enclosure.
Thanks
Adrian

Should be ok, but if you're feeding anything sensitive I'd use a voltage regulator.

Yes - the AD594 doesn't seem to mind too much - but there's a need for a
reference voltage of about 8.5 - 9v for the 'over-temperature' facility
- so I might just regulate the whole lot, apart from the relay power.


PS whats shown there is full wave rectification

You're right.... I was thinking 'half a diode bridge' and making that
mistake....

Thanks
Adrian