Triac and Reed Switch AC Load Switch

[Knife]

Hi All

I want to make and switch to control light in cabinet. I need to switch 220 VAC with triac and reed switch. I will place a magnet to door and I will place main box across magnet. The maximum lenght is 15 cm between door and main box.

You know reed switchs are normally open and when magnet is getting closer, reed switch will close. I couldn't realize this system on schematic. Could you help me for this issue ?

 

[red_alert]

http://www.talkingelectronics.com/projects/DataBook1/DataBook1-22-41.html (look for the page 38 - Triac switch)

 

[Knife]

Thank you for your answer but the question is reed switch is normally open. The reed switch is open when the door is open and it is close when the door is close. This circuit works when the door closed. I want to make it reverse but I couldn't realize that yet. The light will work when the reed switch is open, it means when the door is open.

 

[kam1787]

I am fairly sure you can buy SPST reed switches that are NC [they are just hard to find]
else
buy a SPDT reed switch

 

[red_alert]

You could use a triac driver (MOC series) like in the diagram bellow:



but you need a low voltage supply (or mains derived one).

The better solution is still a SPST/SPDT reed switch.

There is a mechanical solution, too. When the cabinet door closes, it pushes away the magnet from the reed switch. The magnet should be mounted on an elastic piece of steel/plastic, near the reed switch (not on the door).

 

[Knife]

I am fairly sure you can buy SPST reed switches that are NC [they are just hard to find]
else
buy a SPDT reed switch

Yes, you are right but this products are special and really expensive.

You could use a triac driver (MOC series) like in the diagram bellow:

View attachment 113705

but you need a low voltage supply (or mains derived one).

The better solution is still a SPST/SPDT reed switch.

There is a mechanical solution, too. When the cabinet door closes, it pushes away the magnet from the reed switch. The magnet should be mounted on an elastic piece of steel/plastic, near the reed switch (not on the door).

The mechanical solutions didn't accept from customer. MOC series solutions are expensive too. I'm trying to make simple and cheap circuit like this but I didn't make it yet. I'm looking for alternative views or suggestions.

- - - Updated - - -

Also we can use 2 magnet to reverse NO reed switch to NC but it is hard to arrange magnet's power and distances.

**broken link removed**

 

[red_alert]

What about this? It should work OK in both I and III quadrants.



The reed switch (sorry for the wrong symbol) is normally connected.

 

[red_alert]

Just in case you (or anyone else) want to try it, I updated the diagram (to avoid collector-base conduction):

 

[Knife]

red_alert , thank you for your suggestion. I will try this schematic and inform you about this issue. This is your idea or did you find on internet ?

 

[red_alert]

I struggled to draw the schematic using the poor software I have on my laptop - so yes, it was my idea! (I even made some mistakes in the first circuit; it was more like a concept).

I don't see any bugs for now. Good luck with your tests!

 

[Knife]

I tried this circuit like this. It didn't work. When reed contact is open, the circuit is working. When reed contact is close, the circuit is flashing. Triac didn't close all cycle of AC. Could you offer anything to close triac all cycle of AC voltage.

 

[kam1787]

.......buy a SPDT reed switch

SPDT reed switches are about 1 USD. You are spending almost as much [or even more] on the extra electronics to use a SPST reed switch and making it larger and more complicated.

 

[Knife]

I checked SPDT reed switches prices before and see it is special design, hard to find 220VAC model, high cost (5 times expensive than normal switches). I'm checking new suppliers prices again. If you have any suggestion, please suggest one.

Is there anyone to suggest any solution for my problem ?

 

[kam1787]

Use a capacitor to drop the voltage https://www.ehow.com/how_7917023_use-capacitors-lower-input-voltage.html

 

[FvM]

I tried this circuit like this. It didn't work.

An obvious requirement of this circuit hasn't been explicitely stated, the PNP and NPN transistor must be high voltage types with > 300V Vce0. If the triac is too sensitive for the leakage currents, a gate-A1 parallel resistor may be considered.

 

[Knife]

I listed part number of components. Could you suggest anything ?

PNP STR2550
NPN STR1550
Triac ACT108W-600E

 

[FvM]

The transistors are well suited, the triac is specified with "Exclusive negative gate triggering" and can't work. A standard 3 or 4 quadrant triac should be fine.

 

[Knife]

I tried Z0107MN triac, it can trigger all quadrant and I have same problem. Could you suggest a part number for triac ?

 

[red_alert]

Try with larger values for R1 and R2 (220k.. 470k) because your triac is very sensitive and R2 alone (when the reed switch is closed) could supply enough current to trigger it (parasitic operation mode).

 

[Knife]

I also tried this but it didn't solve my problem. I tried 100k to 330k different values. But I will try again tomorrow.