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LED's flickering

Does what it says on the tin
csearle
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Re: LED's flickering

#130831

Postby csearle » April 8th, 2018, 10:50 pm

ten0rman wrote:I have had the situation where a CFC, in the same fitting would you believe, used to glow faintly when it was supposed to be off.
This can happen if the switch is switching the neutral rather than the line. C.

ten0rman
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Re: LED's flickering

#153831

Postby ten0rman » July 20th, 2018, 9:06 pm

An update.

Two of the original three LED's now replaced under warranty. All now seems ok. More or less convinced that it was a bad batch although the shop says not.

ten0rman wrote:
I have had the situation where a CFC, in the same fitting would you believe, used to glow faintly when it was supposed to be off.

This can happen if the switch is switching the neutral rather than the line. C.


Not checked this. Doesn't happen with LED lamps. Other than changing the switches (by me) and adding an earth to the (metal) light fitting (also by me) I believe all wiring is as originally installed, probably to 15th Issue regs.

As an aside, and nothing to do with the original report, we bought a new, as in brand new caravan. Complete with electronic this, that and the other, including LED lamps some of which are dimmable. Guess what, we discovered that when we turned off the water from the sink, hence stopping the electric pump, the dimmable LED's flashed on & off. Spoke to the caravan manufacturer, and "Oh yes, there's a suppression kit for that problem!". Well if they know about it, then why don't they install it from the start!

ten0rman

csearle
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Re: LED's flickering

#153842

Postby csearle » July 20th, 2018, 11:15 pm

ten0rman wrote:Guess what, we discovered that when we turned off the water from the sink, hence stopping the electric pump, the dimmable LED's flashed on & off.
Might be wrong but I think this is because the LED lighting (when off) has a very high resistance, which is then prone to voltages being induced onto it from electric fields in the vicinity. The LED lamp's electronics effectively integrates this until there is enough energy stored to light the LED up. Only as there is nothing behind it it results in a flash and then the cycle repeats. If the field is transient then it may only result in a single flash.

Cheers,
Chris

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Re: LED's flickering

#153851

Postby jfgw » July 21st, 2018, 12:05 am

ten0rman wrote:...Eventually we changed to CFC's...
ten0rman


Did the CFCs produce a very cool white? :lol:

(I assume you mean CFL: Compact Fluorescent Lamp.)

Julian F. G. W.

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Re: LED's flickering

#153852

Postby jfgw » July 21st, 2018, 12:40 am

tjh290633 wrote:I have a lamp which is a 3-bulb chandelier on our landing. I changed to LEDs and find that there is only one setting of the 2-way switches which works. On the other it flashes. I haven't investigated, but assume that one of the paths has a problem. I might get my friendly local electrician to look at it.

TJH


If the two-way switching worked before, logic would say that it should still work.

Are the lamps 12V? So-called electronic transformers have a minimum power as well as a maximum power. If, for example, the luminaire was designed to take three 30W halogen lamps, it may have a transformer rated for, say, 35 to 105W. If you replace the halogen lamps with 3W LEDs, the transformer may not work correctly.

csearle wrote:It is conceivable that there might be a difference in behavior between the two 2-way combinations because of the proximity of the "strappers" (as they are called) within the three core cable.


Especially as one of these (the grey or blue one) is partly shielded by the earth. I am not sure how this is likely to affect the "on" positions, though.

Julian F. G. W.

ten0rman
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Re: LED's flickering

#153926

Postby ten0rman » July 21st, 2018, 11:39 am

ten0rman wrote:
Guess what, we discovered that when we turned off the water from the sink, hence stopping the electric pump, the dimmable LED's flashed on & off.

Might be wrong but I think this is because the LED lighting (when off) has a very high resistance, which is then prone to voltages being induced onto it from electric fields in the vicinity. The LED lamp's electronics effectively integrates this until there is enough energy stored to light the LED up. Only as there is nothing behind it it results in a flash and then the cycle repeats. If the field is transient then it may only result in a single flash.


From my days as a Strowger technician, I well know that "large" (define "large") inductors can create huge back emf spikes when disconnected unless steps were taken to suppress the spike. Although I can't prove it, I was at one time involved with producing a circuit to detect if the suppression device had gone faulty. During my testing I regularly saw spikes of many 100's of volts on an oscilloscope from which it follows that if the caravan water pump, which is nothing more than an electric motor driving a pump and controlled by a pressure switch, was not suppressed, then when the tap was closed, and thus the pressure switch opened, then the conditions for a large spike are immediately generated. It only needs said spike to be induced into the LED dimmer controlling electronics for the flash to occur.

jfgw,

Yes I did mean Compact Fluorescent Lamp. A slip of the finger, or more probably, of the mind. Sorry about that.

-----------------------------------------------------------------------------------------------------------------------------------

FWIW, and for interest. When I was doing the above testing, this was on magnet coils of either 50 ohms resistance or 75 ohms resistance - can't remember which. The coil had a "smartie" connected directly across its terminals. Can't remember what the "smartie" was - this was in the early 1970's after all - but it was red and about the size of a genuine smartie, hence the nickname. For testing, I was using a Solartron CD1400 oscilloscope with a divide by 10 probe and the input setting of 50V per/cm, thus giving 400v for a full screen deflection. For fun one day, I connected two divide by 10 probes in series, and still managed to see a very high, theoretically about 900V pulse. Of course, I don't know how the calibration would be affected using two probes like this.

By heck, that were a long time ago - getting on for half a century!

Regards,

ten0rman

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Re: LED's flickering

#153939

Postby AleisterCrowley » July 21st, 2018, 12:49 pm

It's normal practice to put a reverse biased diode across relay coils to suppress the 'back EMF' generated when the coil is disconnected and the magnetic field collapses.
Sometimes a metal oxide varistor is used, which is what your smartie probably was

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Re: LED's flickering

#154021

Postby ten0rman » July 21st, 2018, 6:28 pm

Aleister,

Yes, it probably was a varistor - at least I do recognise the name. But, in typical GPO style, it was probably called something like Resistor, Non-Linear, 250V (or was it 650V?). I seem to recall there was a brown version as well. Probably for different voltages.

Yes, I've used plenty of diodes for that purpose, CV8805's in the main, although depending on what it was suppressing, I used to use the CV7875 which was physically smaller. (CV8805 = BYX26-150, CV7875 = OA202). A useful feature of shunting a relay coil thus was that it slowed the release which could sometimes be a decided advantage in preventing a race condition.

It's interesting that the older Strowger circuit designs used to have a 200 ohms resistor in series with a 2 microfarad capacitor connected across the selector magnets, and this practice continued right up to the end of Strowger. However, later designed circuits eg those using the miniature uniselectors used "smarties". I've a feeling that diodes across coils was an innovation possible with the TXE2 type reed relay exchanges, certainly I've no recollection of using them in general on Strowger. Having said that, I was involved in a project which used some rebuilt & rewired Strowger selectors so the standard Strowger kit of resistor/capacitor was used - that was until I ran out of space, so I replaced the resistor/capacitor combination with a 1500V 1.5Kv Silicon Avalanche diode just to gain a bit of space. It worked extremely well.

On the caravan, had it been up to me, i would have used a diode, possibly of the 1N400x series. Or maybe the larger version 1N580x, however, I understand that the supplied suppression kit may include a ferrite ring. I shall have to wait and see, because apparently the caravan manufacturer is rather tardy in supplying spares - 30 days or more being quite common I believe. When all said and done, it is under warranty so I really shouldn't be mucking about with it.

Regards,

ten0rman

p.s. I've just been reading the Wikipedia entry on varistors. I could have done with that all those years ago as it explains some of what I encountered - the variability of the devices which thus made failure detecting somewhat difficult. Interesting.

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Re: LED's flickering

#154028

Postby AleisterCrowley » July 21st, 2018, 7:40 pm

I've always used a 1N4001 , probably not optimum but life's too short!
Belt and braces seems to be two diodes - one to +VE and one to 0V- from junction of switching element/relay coil
From memory the CV series are military part numbers (Common Valve, oddly)

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Re: LED's flickering

#197646

Postby ten0rman » January 30th, 2019, 4:38 pm

Well now, a final, final update.

Absolutely no problems since the last change back in July last year. Oodles of lovely light making the previously used incandescents & cfl's look like miniature candles. All in all then, I had two duff lamps out of three. Which doesn't say much for the manufacturer.

Cheers and thanks for all the original thoughts.

tene0rman


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