Plz help ! Reed switch fails within a few operations

[j37prakash]

I need to design a circuit to switch on a warning lamp or sound a hooter when a door is opened and the reed switch is activated by the magnet. I have herewith attached the circuit diagram of the test setup. My problem is that the reed switch fails within a few (3 or 4) operations though the current measured is in very small units.
Kindly advise me how to go about it to solve the problem.

 

[cobra1]

is the reed fusing itself closed?

 

[Reloadron]

Can you provide a data sheet for the reed switch? Also, I don't understand what you are doing? You have DC coming in and the switch is switching the DC into a full wave bridge rectifier? Is the switch N/O or N/C?

Ron

 

[alec_t]

I assume 110VAC input was intended?
How small a current is 'very small'? The inrush current to charge the cap across the SMPS (wrong polarity shown on SMPS, btw) and the reservoir cap within it may well be enough to weld the contacts of the reed switch. What are the AC and DC current ratings of the switch contacts?

 

[4pyros]

How is the reed switch failing?

 

[Boncuk]

I guess it doesn't make a big difference if the switch fails open or closed.

Anyway a reed switch is designed to switch signals (no consumers).

0.5A might seem low current but it's about 50 times a reed switch can stand without damage.

Boncuk

 

[j37prakash]

is the reed fusing itself closed?

Yes Cobra1, the switch keeps failing by fusing itself closed (welded)

 

[j37prakash]

I assume 110VAC input was intended?
How small a current is 'very small'? The inrush current to charge the cap across the SMPS (wrong polarity shown on SMPS, btw) and the reservoir cap within it may well be enough to weld the contacts of the reed switch. What are the AC and DC current ratings of the switch contacts?

Yes alec it was intended to be 110VAC. Normally is it wrong to wire a reed switch in series with a an SMPS ? Can I alternatively put the reed switch on the`secovdary side ?

 

[KeepItSimpleStupid]

Here is a set of specs from a manufacturer. https://www.actsensors.com/reed_switch.htm Note that they are all over the map. The SMPS can probably be considered an inductive load and therefore surge suppression is mandatory such as a ZNR across the contacts. Specs of the switch would be useful.

The secondary side is also permissable if the ratings aren't exceeded.

 

[Boncuk]

Yes alec it was intended to be 110VAC. Normally is it wrong to wire a reed switch in series with a an SMPS ? Can I alternatively put the reed switch on the`secovdary side ?

No! You can put a reed switch into a signal circuit - not into a load circuit, may it be on the "primary" or on the "secondary" side!

Look at the switch (encapsuled in a glass body!) It can stand a current of a few mA while you are trying to "chase" 50 times more over it.

You will fry more and more of the reed switches if you don't decide to use an equivalent power transistor to switch your load!

Boncuk