Switch doesnt work properly.

Hello,

I have just ordered 100 of the following switch: Part number = SDC-1-014

Switch (SDC-1-014)
https://uk.farnell.com/erg-components/sdc-1-014/switch-dil-dt-1way/dp/422680?ref=lookahead


...I am using this to switch 10mA in a 24V circuit. The switchs basically don't work..none of them. When one moves the slider strongly along...then the switch is in a kind of half connected state, and I can hear the relay coil that's being switched clicking away as it repeatedly switches....there is a series led, and I can see that flickering as the contact is not made properly.......after switching it, then in order to get a good contact, one has to 'tinker' with the slider until the contact becomes permanent....fiddling with it, gently nudging it until a good, continuous contact occurs

How could I have known that these switches were going to be like this (i.e. 'rubbish'?)

I wish to order a different switch to replace it. -one that works

How can I tell if the following switch is going to work or not?....
https://uk.farnell.com/jsp/search/productdetail.jsp?sku=1201430

Do you use the switch for a 24V relay coil?

The switch original purchase is a Single Pole Double Throw (SPDT), is this the required configuration?

Can you post a schematic of the circuit design?


BigDog

its a 12V relay which is driven ultimately from 24V, so theres a 750R resistor and a led in series with the relay coil and switch..the coil resistance is 1200R

Was the problem immediate, when switch was first installed, or did it increase in severity with use?

You maybe experience contact arcing if driving the relay directly with the switch.

You might need to implement some arc suppression across the relay coil.

BigDog

the relay coil has 1200R resiatance.....thers no arcing, and the switches, before they were soldered in to the circuit, it was obvious they were dodgy like this.....you would switch them and then the ohmmeter was giving an intermittent reading ..............these switches are just useless....but how could I have known this...?...and how can you avoid it in future?
There is a diode across the relay coil as expected.

I don't think one can predict something is deffectice when it looks fine from the outside... till he tests it
Once, I bought a lot (200 pcs) of MCUs that looked great, to find out later that about 50% of them were defective. Though the retailer accepted to refund me their cost, but it was a loss of time with the doubt that the remaining ones are runing properly but marginally.

It can be said there is often truth in the old adage, "You get what you pay for," although at £1.62 a piece for quantities of 50+ I would not consider these switches excessively cheap.

You might consider implementing a quasi-hybrid relay, across between a solid and mechanical, with the mechanical relays you currently have in stock.

The technique could certainly diminish switch bounce and any possible switch contact arcing.

You may also want to consider using a rocker style switch which minimizes both dead time and contact bounce.

Does the relay feel warm or hot using the current configuration?

BigDog

Could the switches have become contaminated by some soldering or washing process? Maybe they got wet in shipping?

That type of switch isn't really intended for DC power switching and you may note that there is no DC operational characteristic in the data sheet. Having a resistor in series with the relay does nothing to protect the switch from the back EMF as it opens, you still need a diode across the relay to protect it. Nevertheless, I would have expectd it to work better than you describe, have the PCBs been cleaned with water or any chemical solvent after soldering? There is a special version of the switch for use where such contamination of the contacts could occur.

It could just be a bad batch of course but I must have used hundreds of thousands of similar switches and I don't recall ever seeing a failure.

Brian.

the pcb's haven't been cleaned, but anyway, this is seen before the switch is soldered in. As I say, we have to "tiddle" and "fidget" about with the slider before we can get a decent contact....and then heaven forbid if someone nudges the pcb, then it looses contact again.

why put a LED in series with a relay - even given the resistor?

have you tried using the switch with 12V [NOT 24V, w/o the resistor and LED]?

- - - Updated - - -

betwixt said:

..............does nothing to protect the switch from the back EMF as it opens, you still need a diode across the relay to protect it

Click to expand...

i never heard of a switch needing protection against back EMF..............can you quote a recognized authority?

A switch in series with any significant inductor, such as a relay coil, is going to arc when it opens if there is no EMF snubber. It sounds like the switch contacts are burned from arcing.

My authority is E=LdI/dt. Calculate the coil voltage vs. time as the switch opens....;-)