LEDs … The Good, The Bad, and The Ugly

[HowiParticipant @howi]

There seems to be a lot of scaremongering regarding LED bulbs, buy from a reputable source in the UK and you will not have any problems. Buy this sort of thing from China at your peril, why you would want to, I don't know. Have a look at CPC prices on LED bulbs, they do a vast selection.

One thing you will notice is that LED bulbs come in all shapes and sizes, mains voltage, mains voltage dimmable, 12v DC, 12v ac/DC.

I have used compact fluorescent bulbs in my small workshop as I had plenty in my lamp collection, I have recently bought a clip on led light for the mill and lathe which gets light where I want it without burning myself on a similar sized halogen bulb type lamp. I have also just installed a 10 watt LED flood lamp (mains powered) directly above the lathe which gives me a superb spread of light. The compact flourescents will be replaced in due course with LED bulbs as will all the bulbs in my house.

Just remember, like most things in this world, you ( usually!) Get what you pay for, cut corners/cost at your own peril. LED bulbs being no exception, just use common sense.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Winwood on 29/09/2014 09:00:46:

There seems to be a lot of scaremongering regarding LED bulbs

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I see no scaremongering on this thread, Howard

I see a small group of people with enquiring minds; sharing what they have learned, for the common good.

MichaelG.

[WALLACEParticipant @wallace]

Hi Les.

Presumably, they’re designed to be able to run on ac not just because the sockets aren’t polarised but because some fittings just rely on a ‘old fashioned’ transformer to get the 12v from the mains. I imagine the 12v from an ‘electronic’ transformer is a bit rough – it would be interesting to hang a ‘scope across one.

I’m probably going to try an led bulb in the lovo light I have on the lathe – as when I replaced the stainless storage tin I was using as a shade with something a bit more in keeping, the halogen MR16 bulb I had fitted came out with only one pin intact !

I’ll measure the lovo light voltage out of curiosity but I’ll probably suck it and see and not bother regulating it – it will be interesting to see how long it lasts. But I may miss warming up my hands on the shade on cold winter evenings in the garage with the cooler running led bulb fitted !

The other point possibly of interest with led bulbs is the viewing angle – I’m going to fit two on the front of the bike, a 61 led wide beam of around 140 degrees and a brighter switchable more concentrated one of around 30 degrees – this only has 3 leds which actually use the aluminium ‘reflector’as a heat sink – something new to me on an led !

W.

[Rod AshtonParticipant @rodashton53132]

Happy now with general lighting as will go with standard domestic bulb sockets and fit LED bulbs.

Still a bit confused with the 12 volt setup. Could I get some guidance as to a safe transformer and what bulbs and bulb holders to employ locally on the machines please.

[Michael GilliganParticipant @michaelgilligan61133]

Rod,

My personal preference is tending towards the G4 based lamps… these are very versatile, and there is an enormous range available … many of them can be plugged-in either way round, and will also run on AC [if you must] … all this convenience is provided by the simple expedient of including a bridge rectifier within the package.

No, I don't like 50Hz AC as a supply for LEDs … full-wave rectified, this will produce flicker at 100hz.

MichaelG.

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Edit:  Useful G4 sockets are available here, if you want to DIY

Edited By Michael Gilligan on 29/09/2014 12:33:46

[WALLACEParticipant @wallace]

Hi Michael.

I wouldn’t imagine they’d flicker as the internal capacitor must smooth the ripple.

I will put a scope etc across them but not until the weekend – I’m in London, lathe etc is at Dads house !

I would personally go for a basic 12 volt transformer for workshop lighting – I don’t altogether trust the ‘electronic’ ones as they don’t provide isolation from the mains. I also think rectification etc wouldn’t be necessary – raw 12v ac would be fine.

W.

[Michael GilliganParticipant @michaelgilligan61133]

Sorry Wallace, you have me confused … What internal capacitor ?

Looking back a your earlier post, I see that you have found some MR16 lamps with extra circuitry [beyond the bridge rectifier and resistor] … I would greatly appreciate details of the components used.

Thanks

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Another recommendation … [too late to edit into my reply to Rod]

These little 2W units have integral heatsinks and seem to work very nicely.

MichaelG.

[WALLACEParticipant @wallace]

Hi Michael.

I will do a picture at the weekend – from memory, 4 diodes ( bridge rectifier ), 8 leg chip, a couple of resistors, small inductor and an electrolytic capacitor. …47uf or thereabouts rings a bell. And in that order from the input to output connections.

The circuit board for the higher power 3 led one had a couple more components but still had the diodes, chip, inductor and capacitor so both are presumably some kind of high frequency chopper regulator.

That’s why I’m assuming they won’t be over fussy on input voltage – obviously within reason !

But I have only run them on dc so far.

The red led lights merely had a single package rectifier and one large resistor – nothing fancy at all.

W.

[Les Jones 1Participant @lesjones1]

Some further comments.
Both the GU10s (240 V) and the MR16s (12 V) have smoothing capacitors but they are too small in value to prevent all of the 100 HZ flicker. The ones I have seen have 2.2uf in the 240 v units and 100 uF 16V capacitors in the 12 V ones. (16 volt rating is cutting it fine 12 x root 2 = 16.97 It would actually be about 1.2 volts less due to the drop in the bridge rectifier.)

Wallace, The electronic transformers DO provide isolation. There output is a 12 V peak to peak square wave at several tens of KHZ In the workshop they would have the advantage that the smoothing in an MR16 lamp would be enough to stop flicker at the several tens of KHZ frequency.

Les.

[WALLACEParticipant @wallace]

Hi Les.

I personally prefer to have a magnetic field between my fingers and the mains !

W.

[Michael GilliganParticipant @michaelgilligan61133]

On the subject of "Isolating Transformers" …

I managed to buy a couple of new [ex-display] unused Crabtree Shaver Sockets, for £2 each.

These have a good quality 20VA Isolating Transformer and alternative outlets for 110V and 240V shavers.

…. Ideal for powering unknown Mains LED drivers !!

MichaelG.

[Les Jones 1Participant @lesjones1]

Hi Wallace,
You still have the power coupled via a magnetic field in an electronic transformer. As the transformer works at a much higher frequency it can be much smaller for the same power rating. I WAS WRONG ABOUT THEM NOT PRODUCING FLICKER AT 100 HZ. The mains is first rectified and fed to a high frequency inverter. The high frequency from the inverter is then stepped down to 12 volts by a transformer. I had assumed that there was a smoothing capacitor after the bridge rectifier but there is not. The result is the high frequency square wave is modulated in amplitude at 100 HZ I found this circuit on the web by Googling "electronic lighting transformer schematic" I have verified the output waveform wit an electronic transformer I had in my junk box.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 29/09/2014 14:49:25:

… the high frequency square wave is modulated in amplitude at 100 HZ …

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Les and Wallace

This is one of the reasons why I have settled upon using a Sealed Lead Acid Battery as my power source for Microscopy. 100hz flicker may not be particularly troublesome visually, but it causes interference banding on some cameras.

MichaelG.

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P.S. [Wallace] Thinking about the chip inside your MR16 lamp … I suspect it's probably a Constant Current Driver [which would be particularly useful in that situation; where the LED lamp is intended as a drop-in replacement for Tungsten-Halogen] … I look forward to your disclosure of the details.

[WALLACEParticipant @wallace]

Hi Les.

I know the type you mean – they use a ferrite core in the transformer – the ones I’m wary of are the ‘choppers’ which I don’t think are electrically isolated from the mains. The choke or inductor on the output is purely for smoothing.

Is there a different name for them ?–I always assumed they were also ‘split mode’ but could well be ignorance on my part !In fact, I don’t actually know why they are called ‘split mode’ – can anyone enlighten me ?

Michael – I’ll put a scope across them and post the results at the weekend – should be easy to do as I extended the original wiring so will be dead easy to hang a probe across. I’ll try and do ac as well as dc.

W.

[john swift 1Participant @johnswift1]

a youtube link to National Semiconductor / Texas Instruments :-

**LINK**

high power LED driver video could give you some ideas

John

[Michael GilliganParticipant @michaelgilligan61133]

Posted by WALLACE on 29/09/2014 18:11:33:

Michael – I'll put a scope across them and post the results at the weekend – should be easy to do as I extended the original wiring so will be dead easy to hang a probe across. I'll try and do ac as well as dc.

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Thanks Wallace … Device ID Numbers too, if you would be so kind.

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by john swift 1 on 29/09/2014 18:18:28:

a youtube link …

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Thanks, John

… I will watch that one tonight.

MichaelG.

[john swift 1Participant @johnswift1]

Hi Michael

a date sheet to add to the Bob Pease video :- **LINK**

see page 15 for 12V MR16 lamp

John

[Les Jones 1Participant @lesjones1]

This is the schematic of the driver used in the 12 volt version of 10W floodlights.

I have some drivers for 3 watt lamps (3 x 1 watt in series) bought on Ebay. The circuit is the same but with changes in the component values.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by john swift 1 on 29/09/2014 19:14:21:

… to add to the Bob Pease video :- **LINK**

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Thanks again, John

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 29/09/2014 20:01:44:

This is the schematic of the driver used in the 12 volt version of 10W floodlights.

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Thanks for the schematic, Les

Is this the type of 12V 10W floodlight that you are describing ?

MichaelG.

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Note: despite the pictures on the listing, I presume it does not have a 3-core "Mains" flex attached! Edit: Just realised … it has a Mains PSU with it … I need Coffee!

Edit:  Refreshed with Caffeine … I still find that ebay listing very confusing.

Edited By Michael Gilligan on 30/09/2014 09:06:24

Edited By Michael Gilligan on 30/09/2014 09:21:24

[Les Jones 1Participant @lesjones1]

Hi Michael,
It looks similar to the one in your link. In my photos folder "LED lighting" there is a picture of the actual fitting. I bought it in March 2013 but have not been able to identify the seller. I think it was from one of the Chinese sellers that ship from the UK.

Les.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Les Jones 1 on 30/09/2014 09:29:09:

It looks similar to the one in your link. In my photos folder "LED lighting" there is a picture of the actual fitting.

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Thanks, Les

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 29/09/2014 17:28:23:

P.S. [Wallace] Thinking about the chip inside your MR16 lamp … I suspect it's probably a Constant Current Driver [which would be particularly useful in that situation; where the LED lamp is intended as a drop-in replacement for Tungsten-Halogen] … I look forward to your disclosure of the details.

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Wallace; for info …

I suspect that this [or something similar] is the additional circuitry in your MR16.

If so, then I agree that the lamp should work OK on an unregulated supply; because the Constant Current Driver will overcome the Voltage fluctuations.

MichaelG.

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