LED Failure? Partly solved but not quite!

Started by petercharlesfagg, July 03, 2015, 11:29:39 AM

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keithfre

Quote from: petercharlesfagg on July 06, 2015, 08:50:43 AM
(4) Reverse voltage I do not understand!  If I connect up the LED the wrong way it doesn't work, if it is the correct way around it does, job done!
If you connect the LED to an AC supply it will get forward voltage (which will cause it to light) for half the cycle and reverse voltage for the other half. (Think of the Alternating Current as switching between + and - the whole time.) If the reverse voltage is too high the LED will blow.

Steve.T

#46
Quote from: keithfre on July 06, 2015, 01:48:09 PM
If you connect the LED to an AC supply it will get forward voltage (which will cause it to light) for half the cycle and reverse voltage for the other half. (Think of the Alternating Current as switching between + and - the whole time.) If the reverse voltage is too high the LED will blow.

True.  :thumbsup:
Strictly speaking you should have another diode across the led in reverse to the led (cathode to anode or -ive to +ive) this can be a plain diode or another led, but it needs to use the same current limiting resistor. This protects the led from the reverse.
Typically the max reverse voltage is about 5V, and on 12V it can get higher than that in reverse (but briefly each cycle) as the limiting resistor does not act in the same way.
However, I have seen circuits for 9 and 12v ac with led & resistor without the added diode and I have had no failures.
Maybe because the reverse voltage is transient it works but strictly speaking it does need this diode you are right.
But I did not want to complicate things anymore than necessary.

I think we are all guilty of wanting to help Peter so much but as we all keep adding comments, like mine now  :-X, the threads get too long and maybe over complicate things for Peter.
I don't suffer from insanity. I enjoy every minute of it.

Steve

Newportnobby

Quote from: Bealman on July 04, 2015, 12:40:04 AM
[smg id=22373 type=preview align=center width=400]
You need one of these, Peter! One of the best bits of test gear I ever bought. It's especially useful if you have a bunch of clear leds and want to find out what colour they light up before you hard wire them into a circuit.

@Bealman
That looks a neat bit of kit, George, but the nearest I've seen is at Maplins for £9.99 and it looks positively 'clunky' compared to yours ::)
Did you source yours in Oz please?
(P.S. Surprised you haven't commented on Rohan Dennis's performance on the 1st day of the Tour de France!)

petercharlesfagg

Quote from: MalcolmAL on July 05, 2015, 11:21:20 PM
Quote from: Malc on July 05, 2015, 11:00:27 PM
At this stage, Peter hasn't connected anything to the PPI. He has just connected the common legs together and hot glued the LEDs into place. So we suspect the glueing has stuffed the LEDs. They just don't like getting warm.
I know I have been watching, you say "all the common legs", he is talking all the C1negs and C2pos, are you sure you(we) are talking the same language ? we need diagrams but he cant draw them :(

I just invited consideration of what Peter may have been on about in C1 negative and C2 positive you see. It dont connect with what I understood you woz on about. (in case the hot of his thingumy isnt as hot as yours ?! )

There are, all through these threads, a disconnect between what those 'in the know' mean by a phrase and what Peter understands the terms to mean , , u c ? (see the other "in-line" thread, oh forget that I already said it ! )

As I said, have we the stamina for,
obviously not,,
so I'll butt out again.
:(

Please accept my apologies I got the whole description wrong!

C1 and C2 are negative!

Please remember you are trying to help someone who has difficulty with being Positive about anything Negative!

Corrected, Peter.
Each can do but little, BUT if each did that little, ALL would be done!

Life is like a new sewer pipe, what you get out of it depends on what you put into it!

A day without laughter is a day wasted!

scotsoft

Quote from: newportnobby on July 06, 2015, 05:16:54 PM
That looks a neat bit of kit, George, but the nearest I've seen is at Maplins for £9.99 and it looks positively 'clunky' compared to yours ::)
Did you source yours in Oz please?
(P.S. Surprised you haven't commented on Rohan Dennis's performance on the 1st day of the Tour de France!)

Here you go Mick, if you are not in a rush for it you can get one from China for £1.51 which will take 3 - 4 weeks to get here:
http://www.ebay.co.uk/itm/Mini-LED-Tester-Box-Portable-Test-Light-emitting-Diode-Bulb-Lamp-9V-2-150mA-WE2U-/171749782393?pt=LH_DefaultDomain_3&hash=item27fd15b379

or

You can spend your money recklessly, pay £2.99 and get it from the UK:
http://www.ebay.co.uk/itm/Mini-2-150mA-LED-Bulb-Light-Lamp-Tester-Test-Checker-Box-Tool-With-9V-Battery-/371337947805?pt=LH_DefaultDomain_3&var=&hash=item5675776a9d

cheers John.

Newportnobby

Thanks John, but with Lawrence's help I reckon we've found the one George has, and it appears to have a better spread of power outputs so I'll be going for this one.............

http://www.jaycar.co.uk/productView.asp?ID=AA0274&w=led+tester&form=KEYWORD

Item AA0274

MalcolmInN

Quote from: scotsoft on July 06, 2015, 06:50:50 PM
or
You can spend your money recklessly,
Wot !
Point of order sir : members of this forum 'reckless', shirley not ?
or maybe there is an oxymoron lurking ? ;D :laugh3: :laugh: :bounce:

Bealman

#52
Quote from: newportnobby on July 06, 2015, 09:18:46 PM
Thanks John, but with Lawrence's help I reckon we've found the one George has, and it appears to have a better spread of power outputs so I'll be going for this one.............

http://www.jaycar.co.uk/productView.asp?ID=AA0274&w=led+tester&form=KEYWORD

Item AA0274
That's the one, Mick. I was getting back to you on that, but you've beaten me to it. Glad you found the site. Jaycar are a NSW-based company who have expanded dramatically since they started up. I'm lucky enough to have a local store where I live and can pop in and out whenever I want, and know the staff really well. It is truly an Alladin's cave full of all sorts of goodies (including helos and quadcopter drones, Scotsoft!), as well as electronic components of all kinds. You should have a look through their catalogue - it's very impressive. The British magazine "Everyday Electronics" publishes a lot of Australian designs and Jaycar advertise in it every month, so for all I know there may even be a branch or two over there in the UK.

Another neat thing about this LED tester is that it has two sets of 5 and 10mA outputs, which means you can compare the brightness of two LEDs on the same current. This means that you can match the brightness of two LEDs which may be side by side on a control panel, for instance, thus giving a professional appearance.

As for the Tour de France, Mick, I haven't seen it - Mrs Bealman (aka Anne) has had Wimbledon on.  :worried:
Vision over visibility. Bono, U2.

NinOz

Quote from: petercharlesfagg on July 06, 2015, 08:50:43 AM
I have ordered a a small tube of silicone sealant instead.
Well looks like my helpful comments weren't.  Apologies. 

Pity you are not within a 100km or so, could just nip over and sort it out.

The silicone rubber is a good solution.  I am not particularly fond of hot glue guns.  Mine tend to be like teething babies, dribble every where.

cfj
To be called pompous and arrogant - hell of a come down.
I tried so hard to be snobbish and haughty.

| Carpe Jugulum |

Webbo

Jaycar is indeed an Alladin's cave and like Bealman, I am also lucky to have one not too far away.

I seem to remember that Peter mentioned something about buying the LEDs in bezels and dispensing with all this hot glue cold glue carry-on. Jaycar carries a piece of kit called the Mini Chrome Bezel which come complete with either a red or green 3 mm LED complete with current limiting resistor suitable for 12 V. To install simply drill a 5 mm hole in your panel, push through, and fix with the supplied backing nut. Cost may be an issue as they are $4 a pop - but will save a lot of grief and look terrific. I use them on my panel. No doubt there is something like this in the UK or maybe even in China at a fraction of the cost.

Tennis - arrgh! Just seems to go on for ever and ever with same old players going round and round and gets in the way of other sports.

Webbo 

MikeDunn

Quote from: Webbo on July 07, 2015, 07:59:27 AM
Tennis - arrgh! Just seems to go on for ever and ever with same old players going round and round and gets in the way of other sports.
Oh, I dunno ... that Heather lassie gave the Williams woman a hellova run for her money - I'd put money on her pulling through next time !  Shame she just couldn't finish in the last few games  :-X

petercharlesfagg

Quote from: NinOz on July 07, 2015, 07:28:10 AM
Quote from: petercharlesfagg on July 06, 2015, 08:50:43 AM
I have ordered a a small tube of silicone sealant instead.
Well looks like my helpful comments weren't.  Apologies. 
cfj

It appears you are misreading my comments, OF COURSE your comments were helpful, if they had not been so I would not have bothered replying. (Like tennis!)

We have differing views that is all!

Warmest regards, Peter.
Each can do but little, BUT if each did that little, ALL would be done!

Life is like a new sewer pipe, what you get out of it depends on what you put into it!

A day without laughter is a day wasted!

Bealman

Quote from: MikeDunn on July 07, 2015, 08:56:54 AM
Quote from: Webbo on July 07, 2015, 07:59:27 AM
Tennis - arrgh! Just seems to go on for ever and ever with same old players going round and round and gets in the way of other sports.
Oh, I dunno ... that Heather lassie gave the Williams woman a hellova run for her money - I'd put money on her pulling through next time !  Shame she just couldn't finish in the last few games  :-X
I'm half to blame here, but let's get back on topic - LED failure!  :thumbsup:
Vision over visibility. Bono, U2.

petercharlesfagg

Thank you George.

.................................................................."..............................................................

FYI.

Our good friend, Malc has offered to visit my home and assist me with not only the LED issues but also with possibly helping me understand the basics with my Circuit tester!

I know from a previous visit by him that his knowledge will prove invaluable!

Regards, Peter

PS Watch this space!
Each can do but little, BUT if each did that little, ALL would be done!

Life is like a new sewer pipe, what you get out of it depends on what you put into it!

A day without laughter is a day wasted!

Bealman

That's great! Ex-NE guy as well.  :thumbsup: :beers:

George
Vision over visibility. Bono, U2.

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