Doorbell button spark

perfectly normal for a battery doorbell its caused by back EMF

When asking questions like this it is best if you give make/model and/or operating principle (or the sound it makes).

Here's my guess. If the doorbell is battery powered and uses a solenoid to strike one metal gong or bar when the button is pressed and then retracts under spring tension to strike another metal gong or bar on releasing the press button (produces the ding - dong sound), then the sparking at the button is most likely due to back emf from the solenoid. Nothing to worry about....

I'm sorry my info was a bit scant.

It's a Byron wired doorbell of the 'ding dong' chime bar variety. It's battery operated. Does that still sound normal?

Thanks,

Daz

yes

Perfectly normal with DC. That's why an AC switch has a lower rating current wise on DC.

The effect is rather like how a basic car ignition works. Build up a flux in an inductor, which a doorbell is to a certain extent, and then switch off the current. The flux collapsing produces a high voltage. In an ignition system you use a transformer (coil) to get an even higher voltage.

Yes - the solenoid is almost a pure inductor.

"Kroma" schreef in bericht news:4333cee0$0$22097$ snipped-for-privacy@news.zen.co.uk...

Every time you interrupt a current flowing with a mechanical switch you will have sparks. Even when you switch on you can have sparks due to the contactbounce. During daylight you will not see them but you can often hear them through an AM radioreceiver. Your lightswitches in the house will also spark although you may not see them. They can can for instance ignite gasexplosions (if there is gas in the room of course.) Doorbellswitches will spark even more because of doorbells contain coils and the back EMF will give a high voltage pulse when you switch off. You can try to reduce the sparking by placing a capacitor over the switch. But there's no reason to worry. Millions of doorbellswitches are sparking every day and you only realize it because you saw it in the dark. BTW. Did you ever put off a shirt or a pully (wool or synthetic, cotten hardly sparks) and hear the crackling of *that* sparks? You can even see them when its dark enough.

petrus bitbyter

Thank you for your in-depth replies everybody! I have now stopped panicking and will leave the doorbell as-is!

Thanks again,

Daz

To add to Dave's excellent analogy of the car ignition system ( or at least the old Kettering ignition that used to be fitted, rather than the new fangled electronic variety that they now have ), you can suppress the contact arc by fitting a capacitor of somewhere between 0.1 and 1.0uF and rated 200 to 400v, across the bell-push contacts. The sparking that occurs is the exact reason why such a capacitor ( also known in the motor trade as " The Condenser, mate " ) is fitted across the points in the distributor head. There is a school of thought, however, that with intermittently used, unplated contact sets, such as are to be found in bell pushes, it's a good idea to let them spark, as this keeps the oxide layer, which inevitably builds up on the contact faces, ' punched thru ' to clean contact metal.

Arfa

Still the same principle of cutting off the current flowing in an inductor, though, - it's just that the mechanical switch in the form of points has been replaced by a more sophisticated electronic one.

IIRC, it also formed a tuned circuit to improve efficiency.

And the coil has been replaced by a quad unit that doesn't require a distributor ...

;-)

Very probably. Years ago, I built many electronic ignition units for friends, based on a circuit published in Practically Witless magazine. That had a CTV 0.47uF 1000v boost resevoir capacitor in the output, effectively placed in series with the coil. It was charged to a high voltage, then dumped into the coil by a thyristor, controlled by the points. This caused the coil to ring as an LC tuned circuit with the cap. This resulted in a ' long ' spark, which was basically AC, thus having the effect of making the plug electrodes last much longer, as no metal migration took place. The plug gap was increased to around 50 thou as I recall, to take advantage of this massive long AC spark. I also seem to recall that this circuit still pushed a comparitively significant current through the points, via a resistor, to overcome the oxidation insulation problem that I mentioned. It was essential that a new set of points was fitted at the same time as the ignition unit, otherwise, the engine would soon come to a stop due to the quick oxidation of the ( already ) burnt points surface.

These ignition units were so good ( remember the commercially available " Sparkrite " models - three of them as I recall ) that when I took one off of a car that I was about to sell, the engine, which had been running perfectly, turned out to be so far out of tune, that it wouldn't even start.

I guess all modern cars now have something along these lines, which accounts for why, in conjunction with the automatic self tuning engine management sytem, modern engines can go 20,000 miles between services, and start first flick of the key, under all weather conditions.

Arfa

But still coils. So the same principle. ;-)

Capacitive discharge.

It got round one problem but caused others? At least you could switch it back to points if the electronics failed. As they often did.

Yes - dwell angle is important with points to give the coil enough time to build up the correct flux. Not so with CD.

Well, many modern cars will do 100,000 miles without the ignition system being touched in any way - long life plugs. If it doesn't break first, of course. Servicing consists more of just changing some fluids and filters.

"Kroma" bravely wrote to "All" (23 Sep 05 10:45:42) --- on the heady topic of "Doorbell button spark"

Kr> From: "Kroma" Kr> Xref: core-easynews sci.electronics.repair:342888

Kr> Hello,

Kr> I recently installed a wired doorbell and it works very well indeed.

Kr> However... I was leaving the house in the dark (and it was VERY dark) Kr> this evening and pushed the bell push in order to hear how loud the Kr> doorbell would be to callers. I was shocked to see that the bell push Kr> briefly lit up as I released the button. As it is not an illuminated Kr> bell push (I have the unit installed with batteries) and owing to the Kr> fact that the light had a blue tint, I am assuming that the light I Kr> saw was in fact a spark within the bellpush. There was no spark as I Kr> pressed the button - only on release. In fact the spark isn't visible Kr> in daylight - it has to be VERY dark!

Kr> In all other respects the unit appears to be working perfectly well Kr> and the spark isn't apparent during daylight but can anybody tell me Kr> what could be causing the spark or is this normal? I had checked the Kr> bell push very carefully before securing everything in place and the Kr> connections appeared to be good.

Kr> Thanks in advance,

Kr> Daz

When the button is closed some energy is stored outside the wire just like an electromagnet. When the button is released that collapsing magnetic energy induces charges in the wire. However the switch contact is open leaving only air which has a very high resistance. The induced charges generate a high voltage which ionizes the air path and allows a current to flow. The longer the wire the greater the voltage. The resulting spark is like a mini thunderstorm.

A small network called a snubber, which consists of a resistor and capacitor in series, can be placed across the arcing contacts to safely dissipate the stray inductive energy and eliminate sparking.

A*s*i*m*o*v

... Chico of Borg: "Resistance? Atsa no good!"