1-phase motion detector, how does it work? - Page 1
Forum section: electronics / beginners

author: somlioy
author_rank: Regular Contributor
timestamp: March 06, 2012, 06:15:25 pm
content: HiMe and some of my colleagues had a discussion about how 1-phase motion detectors work. They're used for controlling lights etc. Connected like this:How do they power the electronics inside the detector?Normally we would use two phase in and get both out to the lights.Talking about 230v 50hz mains for the records.

author: IanB
author_rank: Super Contributor
timestamp: March 06, 2012, 06:24:48 pm
content: Could just be a mercury switch?

author: somlioy
author_rank: Regular Contributor
timestamp: March 06, 2012, 06:52:58 pm
content: Theres definitively electronics inside. Including a coil, triac, some caps etc. You have the option to choose on-time, lux sensitivity and movement sensitivity with some onboard pots or something.It's this detector:http://translate.google.com/translate?sl=no&tl=en&js=n&prev=_t&hl=no&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Felko.no%2Fwsp%2Felko2_nor%2Ffrontend.cgi%3Ffunc%3Dcatalog.show%26table%3DPRODUCT%26prod_id%3D12321%26func_id%3D1001%26l3exp%3D1848%26l2exp%3D%26l1exp%3D1845%26template%3DproductDatasheet (page 2 for english):http://elko.no/elko2_nor/frontend/mediabank/17942/Bruksanv4860.pdf

author: cybergibbons
author_rank: Frequent Contributor
timestamp: March 06, 2012, 07:11:43 pm
content: It will either charge a battery or supercap when the lights are on, or pass a very small current through the lamps (not enough to light them) and use this.

author: somlioy
author_rank: Regular Contributor
timestamp: March 06, 2012, 07:14:13 pm
content: Quote from: cybergibbons on March 06, 2012, 07:11:43 pmHow does that work considering its the same mains potential at the both side of the detector when the switch is closed.Quote from: cybergibbons on March 06, 2012, 07:11:43 pmWhat about the first power up? And you only have one potential.

author: aluck
author_rank: Regular Contributor
timestamp: March 06, 2012, 08:48:42 pm
content: Quote from: cybergibbons on March 06, 2012, 07:11:43 pmthat's exactly how they work, and for that exact reason they are not suitable for driving energy-saving bulbs

author: T4P
author_rank: Super Contributor
timestamp: March 07, 2012, 11:05:44 am
content: Well , a phototransistor .Then the relay on the live line .

author: somlioy
author_rank: Regular Contributor
timestamp: March 07, 2012, 06:38:59 pm
content: Quote from: aluck on March 06, 2012, 08:48:42 pmOk, so how does that work in practice?

author: cybergibbons
author_rank: Frequent Contributor
timestamp: March 07, 2012, 07:12:46 pm
content: Quote from: somlioy on March 06, 2012, 07:14:13 pmAre you stating that there is the same mains potential at each side of the device because you have measured it? Or because you are viewing it as a simple switch, and have assumed that is the case?

author: aluck
author_rank: Regular Contributor
timestamp: March 07, 2012, 07:20:31 pm
content: Quote from: somlioy on March 07, 2012, 06:38:59 pmWhy don't you just disassemble one?

author: somlioy
author_rank: Regular Contributor
timestamp: March 07, 2012, 07:28:11 pm
content: Quote from: cybergibbons on March 07, 2012, 07:12:46 pmThe latter.Quote from: aluck on March 07, 2012, 07:20:31 pmYeah, I will. But since I'm an electrician tracing pcb routes arent my stronges side.

author: sacherjj
author_rank: Frequent Contributor
timestamp: March 07, 2012, 07:37:25 pm
content: These are just a PIR sensor:http://en.wikipedia.org/wiki/Passive_infrared_sensorThe information from that controls a power switching circuit, either solid state or relay.

author: SeanB
author_rank: Super Contributor
timestamp: March 07, 2012, 08:21:28 pm
content: Generally they have a capacitor power supply, with a triac providing the drive. They get power when on by only switching the triac on after the instantaneous voltage is over around 20V, so they can have an internal regulated rail.The problem with them and energy saving lamps is the low power draw when off is often enough to charge up the internal capacitors in the lamps, and this causes the lamp to flash every few seconds ( a single short dim flash normally) as the internal lamp circuit starts up and discharges the capacitor. This kills the CFL unit quite fast from the repeated failed starts.

author: T4P
author_rank: Super Contributor
timestamp: March 07, 2012, 09:28:07 pm
content: Quote from: SeanB on March 07, 2012, 08:21:28 pmBeyond normal operation ( like if they are pulsed , as you might have seen with capacitive dividers ) they get pure DC and what does that do ! Well , THE CAPS ARE KILLED !If you pulse a capacitive divider they are gonna blow up !CFL's die from repeated starts yes , but the capacitor blows up first .

author: qno
author_rank: Frequent Contributor
timestamp: March 10, 2012, 08:47:14 pm
content: I think these devices use a thyristor.They work the same way as a dimmer.Only the potmeter has been replaced wit a LDR.If you look to the voltage over these devices with a isolated scope or a scope with a differential input (do not use a standard scope) you can see that the first 5 or 10 volts of the mains sinus is used to trigger the the thyristor.