Reliability of LEDs: PF Members' Views and Experience

[sophiecentaur]

Yet again, I am getting furious about the reliability of domestic LEDs. I have been moved to ask for the current views and experience of PF about them. The top of my search list on PF has an old 2012 post of mine, moaning about the same thing. There are some interesting comments from PF on that thread.
All this time later, you would think that they would be more reliable but are they?
There is a particular location in my house where LEDs are particularly vulnerable but I have checked connections in the circuit and I can't put it down to 'fizzing'.
What could possibly be different about that location? Premature death has happened to three different models of LED. (I am miles away from any Radio transmitters.)
I am trying to be Green and I refuse to use yucky CFLs, which make everything(/ body ) look sick.
Any ideas about this? I have used cheap and expensive LEDs (Expensive real can be expensive, too, if you get no more than 6 months of life).

 

[Borek]

Side note, or clarification, or whatever: it is not LEDs (inside the LED lamp) that go belly up. I tried to cut the dead one open, what I found was that the LEDs were OK (I am using them now and then with another source of power), it was the switcher that has died.

 

[sophiecentaur]

Side note, or clarification, or whatever: it is not LEDs (inside the LED lamp) that go belly up. I tried to cut the dead one open, what I found was that the LEDs were OK (I am using them now and then with another source of power), it was the switcher that has died.

Was the lamp in question a budget version or an expensive one? I think it's iniquitous and that the companies are riding on the wave of the Green revolution. A switcher for a steady 10 or 15W load should work for EVER!

 

[Borek]

Bought in IKEA (relatively cheap place) for about €12 (rather expensive compared with other models). But then it is a Polish market, so it can be difficult to translate the price directly.

Actually the switcher was still working - once it started. That required switching the light on many times. Switcher was rated for tens of thousands of on/off cycles, it probably went through no more than 1k.

What I am doing now is I am writing with a permanent marker installation date on the white part below the bulb. So far no bulb ever worked as long as advertised.

 

[anorlunda]

So you say that it is not the LED, and not the switcher. What is the failure mode?

 

[Borek]

Perhaps my English failed me and I wasn't clear - it is the switcher that failed, but its failing mode is that it is still capable of supplying the current when it is in a working mode, it just can't get past the starting procedure.

 

[Svein]

Perhaps my English failed me and I wasn't clear - it is the switcher that failed, but its failing mode is that it is still capable of supplying the current when it is in a working mode, it just can't get past the starting procedure.

Possibly the startup resistor. Some voltage is needed for the switching circuit to start. It is usually supplied through a 100k resistor or thereabouts.

 

[anorlunda]

OK, you suspect some electronics that supplies start/run mode to the switcher.

You can't expect a company like IKEA to have the same kind of product engineering and testing as a company like Phillips. IKEA needs the flexibility to switch suppliers if necessary, and when switching they can't take a year or more to investigate and qualify a new supplier. They must depend on the statistics of customer complaints and returns to know when a product they sell is faulty.

LED bulbs at very low prices are sold in bulk on alibaba.com . I presume that they are bought by retailers who know next to nothing about the manufacturers.
Here's an example link to an alibaba ad for LED bulbs, €0,21 ($0.25) each in quantities of 60000 per day.. Use your own imagination to think of who buys them, and what names they stamp on them before sale.

By the way, the alibaba ad also says 2 year manufacturer's warranty. Your LEDs may be covered by the warranty. Lots of luck with that.

You should do your part by returning the failed units to IKEA and ask for a refund.

To avoid trouble in the future, you need to be a more vigilant consumer. Stick to Phillips/Seimens/ABB/Electrolux or other European brands that engineer/manufacture/and test their own products.

 

[CWatters]

I've had the LEDs themselves fail in some down lighters. Individual LEDs develop black spots or fail in "strings".

Heat is the main culprit. LEDs run cooler than halogen but are more sensitive to heat.

 

[Tom.G]

Here in Southern California, USA, the traffic signals were changed over to LEDs several years ago. For the first few years it was common to see them with several (6 or 8?) of the individual LEDs not lighting, presumably those in a series string. The Highway Departments seem to have found a reliable vendor and now that failure mode is rarely seen.

Good Luck. (and let us know if you find a reliable vendor!)

 

[Rive]

There is a particular location in my house where LEDs are particularly vulnerable ...

Could you please tell us more? Where is that location and how is the failure happening?

The most vulnerable point of the LED bulbs currently in use is the heat management. In theory, everything is designed according to the needs of the LEDs, but at the end the electronics just can't get rid of the waste heat on the available surface, so it heats up. Then it cools down as switched off.

The hot period eats up the capacitors, the cycling eats up the soldering.

 

[Baluncore]

I see two electrical problems.

1, The environmental temperature. This directly reduces LED light output. High temperatures age the LED, switching semiconductors and the electrolytic capacitors.

2, The starter resistor, as Svein pointed out. Manufacturers ignore the fact that 240VAC is widely used and seem to do their design and testing only for 110VAC. The startup resistor is always across the rectified AC, typically 155 to 350VDC. Resistors are now rarely rated for the high voltages. High voltage rated resistors are more expensive. It is a better investment to make a starter resistor chain from two or more resistors in series. That divides the voltage and heat between resistors.

Like Borek, I write the date of purchase, supplier and invoice number on all new techno-junk products. I have no problem taking things back for a refund or replacement with a different design.

 

[sophiecentaur]

I see two electrical problems.

1, The environmental temperature. This directly reduces LED light output. High temperatures age the LED, switching semiconductors and the electrolytic capacitors.

2, The starter resistor, as Svein pointed out. Manufacturers ignore the fact that 240VAC is widely used and seem to do their design and testing only for 110VAC. The startup resistor is always across the rectified AC, typically 155 to 350VDC. Resistors are now rarely rated for the high voltages. High voltage rated resistors are more expensive. It is a better investment to make a starter resistor chain from two or more resistors in series. That divides the voltage and heat between resistors.

Like Borek, I write the date of purchase, supplier and invoice number on all new techno-junk products. I have no problem taking things back for a refund or replacement with a different design.

That's all very well but I think you are being far too indulgent with the suppliers. They really should be getting a lot of stick about it and I sometimes feel I am the only person actually wingeing about it. At several pounds a throw, they should last as claimed. ~The aggro of returning a faulty one is a powerful reason to do nothing about it (mea culpa).
What you say about the 240V design is actually quite inexcusable when you think of the level of cleverness involved in the diodes themselves.
What do we want?
Reliability
When do we want it?
NOW!

 

[Guineafowl]

I can’t help but pull apart prematurely failed LED lights. Those facing downwards (ceiling lights) seem to fail quicker than those mounted facing up - I suspect convection has a role in this.

I tend to buy cheaper ones with capacitive dropper circuits, all with poor heat sinking - LEDs mounted on ally plate but with a plastic body and no heat sink compound. Every failure so far has been a single LED in the series string of 60 or so. These can be snipped out and bridged.

If you can get them apart, they are serviceable. Once you’ve found the bad one with the DMM diode test and bridged out, switch on and measure current through one LED by bridging with an ammeter. Most units are overdriven, ca. 30-40mA.

Aim for 20mA - so divide 20/(measured current in mA) and multiply the resulting factor by the dropper capacitor value. Swap for an appropriate capacitor, check new current and reassemble with a dab of heat sink compound.

This is time-consuming, but far more fun than buying a decent unit and having it boringly work for years.

 

[sophiecentaur]

This is time-consuming, but far more fun than buying a decent unit and having it boringly work for years.

Haha. You are incorrigible!
I have been trying to picture such an arrangement, strung from our living room ceiling in a decorative fitting.

 

[Guineafowl]

Haha. You are incorrigible!
I have been trying to picture such an arrangement, strung from our living room ceiling in a decorative fitting.

Are you in the UK? Poundland/world. Their £1 LED bulbs can be easily hacked to run at a cool 20mA, and will last (as far as current testing goes) 2 years or more. You’ll need a set of polyester caps 100-570 nF or so. Rated 400V.

The long winter evenings will just fly by.

 

[Baluncore]

It is hard to provide feedback directly to the design engineers since the manufacturer can be hard to identify from the customer end of an international supply chain. In Australia, the buck stops with the importer. If no one returned faulty products to the retail outlet, there would be no feedback and so no change in the available product or a careless importer.

~The aggro of returning a faulty one is a powerful reason to do nothing about it (mea culpa).

I have no problem returning faulty devices. There is no aggro because I know the consumer law here and I have the record to prove supply. I would find it very difficult to return faulty devices without that recorded information. Maybe you should record more data.

 

[Borek]

Most units are overdriven, ca. 30-40mA.

Aim for 20mA

We must be talking about different LEDs. LEDs in the lamp I took apart work at over 200 mA (I didn't test them at higher currents), which is not surprising at all. For my model lights I bought Cree SMD mounted diodes rated 350 mA (these ones).

 

[Guineafowl]

We must be talking about different LEDs. LEDs in the lamp I took apart work at over 200 mA (I didn't test them at higher currents), which is not surprising at all. For my model lights I bought Cree SMD mounted diodes rated 350 mA (these ones).

Mine use 60 or so LEDs in series, each with approx. 3V drop to give 180V across the lot. The balance of the 330V recified peak voltage is dropped across the series dropper capacitor.

60 of these running at 20 mA gives about 3.6 W. To get a higher rating, they just overdrive them by increasing the capacitance of the dropper.

 

[jim hardy]

Isn't it just Swiftian that these high tech monstrosities are mandated on us

when a plain 60 watt incandescent bulb reliably provides both light and heat , a boon to those of us not living in the Sun Belt ?

How did we let Lilliputians get the upper hand ?

 

[sophiecentaur]

Isn't it just Swiftian that these high tech monstrosities are mandated on us

That is a bit harsh, I think. LEDs are very expensive at the moment but the low amount of heat they produce is very relevant (it should be, at least) in avoiding overheating of enclosures and contacts. We have all suffered from the bad fish smell of a filament lamp socket in which the spring has become tired and lost its temper, producing an HR contact and damaging heat.
The cost of manufacturing and distributing strong glass envelopes for multiple filament bulbs will never go down but the cost of a single well designed LED for its 'proper' lifetime should mean that LEDs are actually better. The spectrum is amazingly good these days. CFLs on the other hand are the true monstrosities.
Candles have their own special charm . . . . . . .

 

[Guineafowl]

Isn't it just Swiftian that these high tech monstrosities are mandated on us

when a plain 60 watt incandescent bulb reliably provides both light and heat , a boon to those of us not living in the Sun Belt ?

How did we let Lilliputians get the upper hand ?

Filament bulbs - simple, cheap, reliable, dimmable, good power factor, good CRI. I think their efficiency should be calculated by factoring in the heat they provide - they’re only really inefficient in warm weather when the heating’s not on.

A case rather like fossil fuels for cars - a discovery that took us so far ahead that greener technology is struggling to be even NEARLY as good as what it replaces, in terms of performance rather than efficiency.

 

[CWatters]

I've been buying cheap GU10 LED lamps for perhaps 7 years and found reliability is very hit and miss. When you think you have found a reliable source they change their supplier so you can't buy any more from them without taking another risk. What's happened in my house is that gradually the unreliable ones have failed and been replaced, sometimes two or three times, but gradually I'm accumulating a set that seem to go on and on. The oldest are now at least 5 years old. A few in our bathroom are in totally sealed (IP67) fittings so far from ideal heat wise.

Initially I purchased cheap unbranded LEDs from china because branded bulbs were horribly expensive, however more recently the price has fallen so you can now get relatively cheap branded LED bulbs in DIY stores and I've generally found those reliable (but not always).

 

[thuyln2]

Good leds, but their accessories are very broken. I have used a bunch of LEDs at home, however unlike the commitment to longevity. Their drivers are very buggy.

 

[sophiecentaur]

Good leds, but their accessories are very broken. I have used a bunch of LEDs at home, however unlike the commitment to longevity. Their drivers are very buggy.

It's really shocking. They are all shamelessly riding on the Green Wave. It would cost only pence to sort out the peripheral problems.

 

[Paddy1337]

A bit off topic, but are there other alternatives (in the US) to LED and CFL? I hate them both for different reasons, and I truly believe the forceful switch away from incandescent bulbs has raised my blood pressure a measurable amount. I am of the crowd that does not care about efficiency, just performance.

LEDs seem unreliable, and in "bulb" form in a lamp they don't diffuse through the lamp shade, they simply send a Bat Signal straight up at the ceiling.

I've had better luck from CFLs, and I believe I had some that were dimmable, but I'd like to actually get light when I flip a switch and the CFLs barely illuminate until they brighten as they warm up. I'm not a big Green person, but the idea of mercury in my lightbulbs seems illogical if I was forced to stop using incandescent in part due to the environment.

Is it illegal to produce your own light bulbs? (kidding)

 

[anorlunda]

I truly believe the forceful switch away from incandescent bulbs has raised my blood pressure a measurable amount. I am of the crowd that does not care about efficiency, just performance.

Your neighbors, yard sales, and flea markets might be able to provide you with a lifetime supply of old incandescent bulbs. You could even place an ad on craigslist, "Wanted incandescent bulbs." As far as I know, it is not illegal to sell used bulbs.

You might also be able to buy Freon as well as old cars from the pre-seat belt and pre-emissions days. You can still buy buy leaded gasoline at the airport. It is called 100LL. Just kidding.

 

[Paddy1337]

You might also be able to buy Freon as well as old cars from the pre-seat belt and pre-emissions days. You can still buy buy leaded gasoline at the airport. It is called 100LL. Just kidding.

haha. I do work pretty close to BWI, but I'll probably keep getting the leaded gas for my race cars from VP. The exhaust smell from an un-catted engine on C16 is surprisingly nice ;)

 

[Rive]

LEDs seem unreliable, and in "bulb" form in a lamp they don't diffuse through the lamp shade, they simply send a Bat Signal straight up at the ceiling.

LED bulbs has a relative high price, so it is painful to lose one: also painful to cough up the price for a good one. No wonder many people tends underestimate them based on only a few cheap ones.
Just wait till' the price of the acceptable ones hits your mark. Won't be long. I did the same and yet I indeed have some crap LEDs somewhere around, most of the 'bulbs' in use at home are already LEDs.

BTW as far as I know incandescent bulbs are still available under the disguise of 'special use', so if you wanna' pay for a shock-hardened (sorry, I don't know the correct term used) one, for example...

 

[Windadct]

I'll also blame heat, that one location may have the worst ventilation - etc... Have you started writing the install date on them,,, that is about where I am at.

As for the evolution of the product, the main goal has been cost - and since there are electronics ( in addition to the LEDs themselves) - cost reduction is bad for reliability.

 

[CWatters]

Personally I'll never fit an incandescent or CFL again.

LEDs seem unreliable, and in "bulb" form in a lamp they don't diffuse through the lamp shade, they simply send a Bat Signal straight up at the ceiling.

I think you must have tried the wrong LEDs. I've had no issues with LEDs designed to replace incandescent bulbs in standard lamps, pendant light fittings or others with a shade.

Apart from a few early LEDs recessed down lights I've found them reliable. I currently have some unbranded LEDs in totally sealed fittings in the bathrooms. They have been in for several years now with no failures.

If you really must have an incandescent look at halogen... In the UK at least you can get a regular looking bulb that has a halogen bulb inside. Virtually identical performance to an old style incandescent but with the slightly improved efficiency of a halogen.

 

[sophiecentaur]

I've had better luck from CFLs, and I believe I had some that were dimmable, but I'd like to actually get light when I flip a switch and the CFLs barely illuminate until they brighten as they warm up.

They were a truly disgusting invention. In nearly every way, they are unsuitable. The illuminant colour is unbelievably bad the spectrum of any that I have seen has great gaps in it; no wonder they make people look ill. They are slow to warm up (even the later ones) and have short lifetimes. Also, they break easily.

If you really must have an incandescent look at halogen.

Still the nicest of all lights to have in the home - just expensive to run and not very long lasting. The point source of light is very attractive, too.
Once the LED quality settles down and customers get more discriminating, LEDS will be almost perfect. The almost continuous spectrum is very impressive.

 

[russ_watters]

I just had the first LED failure that I can remember, after several years running a couple dozen. I lost probably a dozen CFLs in the five years or so before that.

What I noticed that was frustrating about CFLs is they were all labeled "not for totally enclosed fixtures", which all of mine are. So I was basically required by law to use lamps that were incompatible with my fixtures. Annoying, but probably overall was worth it. LEDs have been better for me though.

 

[sophiecentaur]

I just had the first LED failure that I can remember, after several years running a couple dozen. I lost probably a dozen CFLs in the five years or so before that.

What I noticed that was frustrating about CFLs is they were all labeled "not for totally enclosed fixtures", which all of mine are. So I was basically required by law to use lamps that were incompatible with my fixtures. Annoying, but probably overall was worth it. LEDs have been better for me though.

I really would like to know what is going wrong in my houses (this one and the last one). They often die after a few days of flickering. If it truly is a thermal effect then there can be no excuse as the temperatures are not even hand-hot.
It could be due to mains voltage spikes then our mile-long overhead supply cable would be more susceptible than urban underground supplies - but the last house was well inside a town.
I like the pseudo-filament style bulbs (a-la carbon filament lamps of the 19th century) and they are all pretty expensive. I have had a couple of them fail after only a few months.
I guess I should find a way of logging mains volts and spikes, over a month or two. DIY or expensive off the shelf, I guess. Or I could just keep wingeing and wait for things to get better.

 

[arydberg]

We used to live near the beach. Many electrical appliances failed but the electrical company was no help. Finally a neighbor subscribed to a cable service. The serviceman refused to go up the pole until the wiring on the pole was corrected. Then the electrical company fixed the problem and all of our problems went away. in our case it was the salt air that corroded the wires.

 

[Baluncore]

I really would like to know what is going wrong in my houses (this one and the last one).

My filament lamps never failed in 10 years. They must have been very old lights because they were significantly red-shifted, well back towards the introduction of electricity. Then the power authority, as compensation for increasing demand in the valley, raised the voltage by moving up a few taps on the transformer that fed my road. Filament lamps could not handle the overly-increased voltage in expectation of more customers. I had no choice but to move, as my lease had expired.

My new location was purchased with a dedicated 11kV to 240V pole transformer. The voltage was OK, but in hot weather the lights would flicker and I had block periods of RF noise on the line. That noise was a real nuisance at antenna farm. The problem disappeared if I plugged in a load like a 2kW electric heater, so I fitted steep RF filters on my side of the power meters and put up with it. But the 11kV overhead lines still radiated phased spikes of RF all along the road, to the accompaniment of the wandering clicks of the district's electric stock fences, and the 19'th harmonic of the local LF air navigation beacon, very recently extinguished in favour of GPS.

Over a couple of months the line fuses to my transformer dropped several times, so the authority finally replaced the transformer. Turned out that, an internal nut on the 11 kV primary connection had not been tightened properly. That poor connection had arced and produced the voltage spikes that eventually took out the insulation. It was then RF quiet, and the newfangled CFL lights, (the early RF quieter ones, with the internal ballast transformer), did not flicker at all.

Power prices climbed, so cheap and noisy light-weight, (how much does light weigh?), switching CFL replaced all the older lamps. Then along came PV with grid tie inverters. Now the RF noise floor has grown like grass on the spectrum analysers, it is continuous in this world full of switching converters. During the same period, processor speeds have moved from 3MHz to 3GHz, and there are many more of them. There is now a certain and secure place for spread spectrum techniques and digital receiver technology.

At the moment, my PV keeps me slightly in credit, but the power authority plans to significantly drop the price they will pay for my excess PV energy next year. The network charge is greater than my power usage, so I guess the next change will be off-grid, to 12V DC LEDs, powered from PV and battery technology.

 

[NTL2009]

... It was then RF quiet, and the newfangled CFL lights, (the early RF quieter ones, with the internal ballast transformer), did not flicker at all. ...

I was reminded of those old not-so-compact-CFLs yesterday. I had to replace a couple of the last filament bulbs along my garage door and entrance - these lights are on a timer, ~ 6 hours a day average. I noticed that one of them was the old, original not-so-CFL. I'm sure I got two of them as a promotion from the utility, and I'm pretty sure it was back in the 1980's. It is still working (though it takes tens of seconds to come on, but no problem for these lights on a timer). I really can't say how many hours are on it, it may have sat in a closet for some years, and I don't recall when I put it in that fixture, but it could have been a few years ago to as much as 25 years ago. It;s mate died just a year or so ago.

They are big and heavy and poor light, and slow to come on - but they were built like tanks!

Oh, the reason I had some filament bulbs in was my old timer required a trickle current through the filaments to keep the clock alive (it worked in a 3-way switch set up, and they designed it so it would not need a neutral connection, in case one was not provided in the box) - so I needed at least one filament on the string to keep the clock active, the CFL or LED wouldn't do it. But I had to replace that 2 years ago, and the new one needed a neutral, which I was able to pull easily, so I'm good with all CFL/LED now (6 individual lamps). The new timer also adjusts to the seasons (enter your latitude zone) , so now I'm ON at dusk time, and OFF at midnight - nice.

edit - it looks like this one (I need to get on a ladder and unscrew 2 screws to get to it, so I'm going by memory - I'll take a picture when/if it burns out!)

 

[rootone]

Standard flourescent tubes have been around for a long time.
They just don't look very cool.
LEDs are now better than they used to be, and actually do last more than one year.

 

[anorlunda]

I think there should be a business opportunity for builders of new homes. They could include 12V or 24V DC for lighting only. It could be powered by a panel and and a battery, isolated from the grid, no rectifiers, wires run as twisted pairs, so that the DC would be extremely free from fluctuations. The light fixtures would be pleasant, versatile, low cost. very low energy consumption, and last nearly forever. They would stay lit during power blackouts. The homeowners would feel very green.

 

[jim hardy]

o I guess the next change will be off-grid, to 12V DC LEDs, powered from PV and battery technology.

That's where i'd go too. Propane for refrigeration heat and backup generator.

Right now I'm leaning toward 12V backup lights as anorlunda described for my guest house. A friend built his new home with such a 12V light and receptacle in every room . He could handle a months long power outage with just a lawnmower engine and automobile generator salvaged from discards.

 

[sophiecentaur]

I think there should be a business opportunity for builders of new homes. They could include 12V or 24V DC for lighting only. It could be powered by a panel and and a battery, isolated from the grid, no rectifiers, wires run as twisted pairs, so that the DC would be extremely free from fluctuations. The light fixtures would be pleasant, versatile, low cost. very low energy consumption, and last nearly forever. They would stay lit during power blackouts. The homeowners would feel very green.

The services are very reliable in the UK, compared with many other parts of the world and it would be hard to sell the idea to many people. The economics of PV are pretty marginal if you're not making use of the feed in tariff. I would think that you may just be able to sell a big UPS to UK consumers if it were only in lighting and central heating circuit (I mean the pump and controller) but that would only be for non-urban sites.
@anorlunda: your ideas about this may be coloured by your marine lifestyle - very attractive but not accessible for most of us.

 

[NTL2009]

I think there should be a business opportunity for builders of new homes. They could include 12V or 24V DC for lighting only. It could be powered by a panel and and a battery, isolated from the grid, no rectifiers, wires run as twisted pairs, so that the DC would be extremely free from fluctuations. The light fixtures would be pleasant, versatile, low cost. very low energy consumption, and last nearly forever. They would stay lit during power blackouts. The homeowners would feel very green.

Is there really much advantage? Doesn't an LED sourced with 12-24 VDC still need a switching circuit to convert that voltage to current? The switcher would be simpler with DC, since it would not need to store any energy between the AC cycles, and no flicker issues. But I'm not sure that would be worth the installation of a separate DC line. How much energy would be saved? Or do they just use a resistor to limit current (and waste energy)?

What I would like to see is, to have any new fixture or lamp fitted with the LED 'bulb' itself physically separate from the switcher/dimmer. That way, the heat of the LED would be kept away from the switcher, and as I understand it, heat is what kills the caps in the switcher and is a common failure mode. And providing caps rated for the higher temperature raises the cost of the unit. It would be nice to have standard components for this, maybe a third pin with a resistor that would tell the switcher the max current to apply, to support different wattage 'bulbs'?

 

[sophiecentaur]

Doesn't an LED sourced with 12-24 VDC still need a switching circuit to convert that voltage to current?

You refer to a transformer / voltage changer? That has to be done inside a mains voltage LED so having a low voltage distribution system would be virtually the same. Lengths of low voltage cable would (could) have 'significant' resistance and the bulbs could 'see each other' unless heavier wiring than strictly necessary were used. But a simple voltage regulator in each bulb could take care of that.
In fact, there is very little equipment in homes (outside of the kitchen / utilities areas) that actually use mains volts at all. There is good argument for changing the whole approach to electrical power in the home. The safety record of 'Wall Warts' (count how many there are in your living / media consuming /computing room) is not good and a proper central installation would be far safer.

 

[Baluncore]

LEDs can be connected in series to better utilise the available supply voltage. That often makes a linear current regulator a reasonable solution.

LEDs need a current regulator, not a voltage regulator. A switching current regulator is no more complex than a switching buck voltage regulator. There is no need for the on/off PWM brightness control that produces the strobe effect.

LED light output is temperature dependent, so it would be good to compensate the regulated LED current for temperature. It could also fold-back the current to protect the LEDs from high temperatures that reduce LED lifetime and reliability.

 

[anorlunda]

Doesn't an LED sourced with 12-24 VDC still need a switching circuit to convert that voltage to current?

No, that's not needed. There are at least 3 other ways.

1. There are DC-DC IC chips, all solid state.
2. There are also LEDs with built-in resistors for direct connection to 9V, 12V, 24V or more.
3. Put 4 LEDs in series to connect to 12V. I did that to convert light fixtures on my boat to LED, and they worked fine for 8 years.

You refer to a transformer / voltage changer? That has to be done inside a mains voltage LED so having a low voltage distribution system would be virtually the same.

No, you missed the point of my post, no AC-DC conversion necessary. I should have been clearer. I meant panel=solar panel.

t could be powered by a panel and and a battery, isolated from the grid, no rectifiers, wires run as twisted pairs, so that the DC would be extremely free from fluctuations.

 

[NTL2009]

No, that's not needed. There are at least 3 other ways.

1. There are DC-DC IC chips, all solid state.
2. There are also LEDs with built-in resistors for direct connection to 9V, 12V, 24V or more.
3. Put 4 LEDs in series to connect to 12V. I did that to convert light fixtures on my boat to LED, and they worked fine for 8 years.

No, you missed the point of my post, no AC-DC conversion necessary. I should have been clearer. I meant panel=solar panel.

A DC-DC IC is a switching converter, isn't it? At least for high efficiency, it is. As @Baluncore points out, if you use a series string of LEDS and get the Vf close to the supply voltage, there won't be much loss if you go with a linear regulator. But this moves in ~ 3.3 V steps, so for 12 V that's about 9.9V, and a 2.1V R drop, so a 17.5% added power lost in the series connection. Let's say 12 W of LEDs, so 1 amp, so 2.1 W loss in the R, for 14.1 W total. For a practical dimmer, you'd use a transistor/pot wired as a variable current source. The voltage would not change much, but the current would, so dissipation while dimming would be lower. Maybe that is an acceptable trade-off versus a switcher?

Connecting LEDS to a voltage source just isn't a good way to go, and not practical for large implementations. You cannot run them near maximum output,you will have batch-batch Vf variation, thermal variation, supply variation - if you run them to maximize light out, the voltage source will provide too much current when you hit the likely thermal runaway in some units.

You got away with it by using 4 LEDs in series rather than 3, so they are not running near their typical 3.3 V at their nominal current ratings. So you are running them at low current. So it works, but not really something that could be done commercially.

 

[anorlunda]

@NTL2009 , what about LED strips like in the picture below? I also used those on my boat.

I could cut them with scissors to have more or fewer LEDs in the strip. After cutting, I could still use both halves. I could feed the 12V from either end. The only thing on the circuit board besides the LEDs were the tiny chips about half the size of the LEDs with the number 212 on them. I assume they are linear current regulators, and they seem much too small to be switchers. Perhaps, the 212 are just resistors.

When making long-life KISS-principle lighting, I see no need to attempt to get maximum light out of each LED. It would be perfectly fine to get only 50% of max light and simply include twice as many LEDs.

Edit: Here is the https://www.ledwholesalers.com/v2/index.php?route=product/product&product_id=240&search=strip+12Vto those 12v strip lights. $2.50 for one strip, 20 LEDs per strip, only 3 watts for all 20 LEDs. I used 3 of them cut into 6 pieces in the cabin of my boat, providing me with plenty of light.

 

[NTL2009]

@anorlunda - The tiny chips are not active regulators, those are just resistors in those strip lights. 221 is 220 Ohms.

I have a similar strip, just 2x checked, and mine have a 150 Ohm R (marked 151) in series with three LEDS, and 300 LEDS per strip (100 groups of 3).

My 12V supply measured 11.76 when loaded down, 2.36V across the R, and 9.4 V across the 3 LEDS (3.16, 3.02 and 3.22), so about 20% power lost in the R. That may be an acceptable loss and trade-off for an R versus active circuitry. I've heard of people having problems trying to use these in a vehicle. The car battery will run ~ 14V when the alternator is kicking in, and that puts almost 2x the voltage across the R (the Vf on the LEDS won't change very much), so almost 4x the power dissipation on the R, and almost 2x the current for the LEDs.

My point was that in practice you can't reliably/practically run LEDs without some sort of current limit (even if it is just an R). You may be fine with running at low light and making it up with extra LEDS (we can get away with a lot on a one-off implementation), but a cost conscious producer, expecting to provide a consistent product, can't just throw 2x the LEDS at it.

The idea of running 12/24 VDC around the house is interesting. Most of our stuff that is plugged in the wall is low power. Looking around, the kitchen does use higher power stuff (toaster, counter-top u-Wave), and my wife uses a blow-dryer for her hair in the bathroom. Other than that, the vacuum cleaner ('Hoover' to some of you), but outlets in the hallways might be sufficient. Hmmm, then there is my "hi-fi" stereo - that's got a big-honkin' amp. SO I don't know, you still have to run power every where, and with the lower voltage, the wire size won't be that much smaller, then you still need some 120 V (North America) outlets - not sure it pans out in the end.

 

[jim hardy]

Looking around, the kitchen does use higher power stuff (toaster, counter-top u-Wave), and my wife uses a blow-dryer for her hair in the bathroom.

Indeed 10% of the 'things' consume 90% of the power. Some could be switched to gas , and the stereo could become a Class D amp .

Here's how son handles the toaster issue since moving to a boat -


a 1kw inverter would run the things you mention one at a time.

 

[NTL2009]

Hah-hah! I'll suggest that to my wife! I suppose that technique works to dry and style your hair too?

I was also thinking that for some of those things, a battery charged from the 12/24 V could drive a high power appliance for a short while. Still don't think it would catch on, but interesting to think about.

I've got a few smaller class-D switching audio amps. Really impressive what they can do in such a small package. I haven't looked into any hi-fi, high power beasts though, I think I'll look around.

Here's the two types I have - the smaller one to power some small bookshelf speakers for a small TV, and the larger one is hooked to some bigger stereo speakers on another TV, and to some small, but high quality speakers for a stereo in the bedroom.

https://www.amazon.com/dp/B0049P6OTI/?tag=pfamazon01-20

https://www.amazon.com/dp/B004JK8BDK/?tag=pfamazon01-20