Deke wrote:

http://intermatic.com/Default.asp?ac...d=58&sid=1 07

Does this have any desirable hysteresis? Their K4123C control cycles 1200
watts of HIDs with a 2-minute period with about 6 footcandles of daylight,
esp if some of the light controlled reflects back into the sensor. I'm
thinking of adding a 1K resistor in series with the white wire and 39K
from there to the red wire to stop the cycling, which wears out the HIDs.

I've had sensor nite lites and know there are periods of the morning
and evening that confuse the sensor. So while in there, add a 20
minute timer and you will eliminate all the triggers but the first one.

Making a minimum 20-minute on-time seems to require more stuff.

I'd like to try 2 resistors first, like this, viewed in a fixed font:

normally-closed thermal relay
-------------------
| / relay o
| / heater |
|---www--- |
| Rd | | Intermatic K4123C
| | |
| | |
| photo --- | The photoconductor has a high dark
| cond. | ~ | | resistance, about 4K ohms at 6 FC.
| --- |
. . . .|. . . . .|. . . . |. . . . .
V Blk | | |Wht |Red
--------- Io| | |
Ic| | |
v | Rf | -----
|---www-------| HID |---
Vs| ----- |
| new |
| resistors |
| w |
Is| w Rs |
| w |
v | |
| |
neutral | |
-------------------------------------------

20 RD=42000!'daylight threshold resistance (ohms)
30 RS=3300'series resistance (ohms)
40 RF=330000!'feedback resistance (ohms)
50 V=277'voltage (volts)
60 IO=V/(RD+RF*RS/(RF+RS))'open-relay current (A)
70 ICS=V/(RS+RF*RD/(RF+RD))'closed-relay series current (A)
80 VCS=ICS*RS'closed-relay series voltage (V)
90 IC=(V-VCS)/RD'closed-relay current (A)
100 HYST=100*(1-(IC/IO)^2)'hysteresis (%)
120 SPOWER=ICS^2*RS'closed-relay series resistor power (W)
130 IRF=(V-VCS)/RF'closed-relay feedback resistor current (A)
140 FPOWER=IRF^2*RF'closed-relay feedback resistor power (W)
150 PRINT RS,RF,HYST,SPOWER,FPOWER

Rs ohms Rf ohms Hyst % Rs watts Rf watts

3300 330000 1.970381 .1539285 .1962148

Nick