Make the following modification at your own risk!
The purpose of this modification is to obtain an inexpensive motion detector. Although its intended use is for outdoors (which is how I plan to use it), it could also be used indoors. I do not recommend using it for security applications. It is better suited for occupancy sensing. It detects motion through a 110 degree arc. It does not have a configurable pulse count.
This modification will take the motion detector from a 110 vac dual floodlight outdoor security light and convert it to work on 24 vdc and provide a contact closure when motion is detected. This mod does not require the addition of any parts, only the removal of 2 components and 4 wires.
The bottom of the motion detector has a sensitivity adjustment and a switch for setting test mode and the on-time for the lights. There is also an internal photocell that prevents the relay from energizing in daylight. However, the test mode overrides the photocell and allows motion to be detected no matter what the lighting is. Test mode gives about an 8 second contact closure each time motion is detected. Since I want to detect motion outside at all hours, I am going to use test mode.
First, what motion detector security light should you start with? This mod applies to the Intelectron model BC8008KW. The catch is that there are 2 different versions of this beast, both with the exact same model number on the box.
The box you do NOT want - Navy blue and gray box labeled 'Motion Detector Security Light'. The text on this box is all in English. The circuit board is enclosed in a metal cover, which appears to act as a heatsink for the triac that is used to switch the floodlights on and off. I suppose this version could be modified, but it would be harder since it uses a triac, not a relay. I did not look into modifying this version any further.
The box you DO want - Blue and black box labeled 'Motion Detector Twin Flood Security Light' with a picture of the floodlight on a wood grain background. The text on this box is in both English and Spanish. The circuit board is enclosed in plastic only (no metal). A relay is used to switch the floodlights on and off.
I found this floodlight at The Andersons and at Sears. It was $10 or less at each of these stores.
Refer to the drawing of the circuit board below.
I should probably add that if you want a cleaner looking connection for the 24 volt wires, you could remove D1 and Z1 and use the holes left behind to insert the 24 volt supply wires into. I have tried both ways and they both work.
The unit requires about a 1 minute warm up period after an initial power up.
For those of you that think it will work on 12 vdc, think again. The relay coil is rated at 24vdc. I tried lower voltages and here is what I found:
12 volts - didn't work at all
15 volts - worked one day, but then not the next
19 volts - worked every time