LED stabilised power supply

Rigger Mortice said:
Nigel,

I know it's probably difficult to put a figure on it, but how much difference (if any) was there in light output between 35mA and 20mA?
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Certainly not 150% at 30mA over 20mA. At around 15mA I started to see a significant loss, so went back to 20mA.

I've built a matrix of LEDs on my control panel to monitor alternator regulator errors, shore power chargers and water, see attached. I had to add external resistors because at 10mA they were too bright!
 
Rigger Mortice said:
Nigel,

I know it's probably difficult to put a figure on it, but how much difference (if any) was there in light output between 35mA and 20mA?
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LEDs are very current dependant.
If you take a nominal 20ma led and drive it at 35ma my guess is that its brightness will be about 3x normal, but its life will be reduced from 30,000 hours down to an hour or less.
 
nigelmercier said:
Absolutely right. I bought 100 30mA LEDs on eBay, and ran a few of them at 30mA, they lasted about 20 hours. Replaced the the LEDs and dropped current to 25mA, this time they lasted about a week. Currently installed in light fitting running at 20mA, and all OK so far.
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LEDs have a lifetime of ten of thousands or even hundreds of thousands of hours. I've never seen an LED fail except by intent or freak accident. Did you destroy them on purpose?
 
nigelmercier said:
No, I ran them at their maximum current, as quoted by the eBay seller. As I had about 50 to install, I wanted to test them beforehand.

Note that this was long before all those nice SMD LED lights started to appear.
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Hard to imagine why they only lasted a week, drawing a current of 25mA, if IF was specified as 30mA.
 
nigelmercier said:
The seller probably lied!
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I'd suspect they're manufacturers rejects. They dispose of vast quantities of out-of-spec rejects, and many end up in the grey market.

Sir Clive Sinclair manufactured his first successful product, an audio amplifier, using transistors bought as rejects, and re-tested by himself.
 
Hoolie said:
Yes, current, of course. But the el cheapos I have, do have components mounted on the back similar to the ones shown here. Resistors I suppose - one for 3 leds - plus another 4-lead component, a stabiliser of some sort?
The brightness doesn't seem to vary much with voltage.
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To avoid confusion the LED lamp is resistor controlled and I suspect designed for use in motor vehicle interiors, where light quality is not particularly important. The small components are actually SMD resistors connected in series to drop the voltage applied to the LEDs strings. The larger component is a 4 diode bridge rectifier installed enable the lamp to be connected without polarity being an issue. This lamp is not in fact regulated, it is designed for a specific voltage. If it has resistors designed for vehicle charging voltages of around 13.8 volts, the light output at 12V would be very much sub optimal.

I will post a photograph of the rear of a resistor controlled 6 SMD lamp next to a 6 SMD constant-current controlled lamp. The latter will give exactly the same light output at 8 Volts as it will at 30 Volts. Supply voltage fluctuation does not have any detrimental affect on light output or service life.

Regards
 
I have some of those resistor controlled LED lamps.
Some of them are used in my lock up garage where I have no mains.
They do the job very well and are very cost effective.
For this sort of use, you can simply mount them in a bit of choc block, and screw the chock bloc to a joist.
Although the brightness varies with voltage level, it is not as noticeable as you might expect, as the light remains white, unlike a normal bulb. Our perception of brightness is also logarithmic, so a small percentage increase on top of an adequate light level is of little benefit. Twice the light is only one f-stop in photography! It's more important to get the light in the right place.
I might get some of the ones with bridge rectifiers in, I have several reading lamps at home, the last lot of halogen bulbs don't seem to be lasting too well!
At those prices, you can afford to experiment.
 
elton said:
I'd suspect they're manufacturers rejects. They dispose of vast quantities of out-of-spec rejects, and many end up in the grey market.

Sir Clive Sinclair manufactured his first successful product, an audio amplifier, using transistors bought as rejects, and re-tested by himself.
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The Chinese factories buy electronic components by the container load. Stuff I've had made out there, the prices for branded good quality components are ridiculously low, but only if you want a TFE worth of them.
As a result there is a complicated market where factories have a few tens of thousands of something left over from a production run, already paid for. Some of these are sold very cheaply to the factories lower down the food chain, who make some perfectly OK product, but maybe the components are not quite so traceable.
A lot of 'rejected' electronic components are also perfectly reliable. They just might have the odd parameter slightly off spec. For instance transistors can fail for having too much gain, which might be a very bad thing in the standard circuit, but ideal if you tweak the circuit around it.
I've had to buy grey market parts from brokers to go in very expensive UK-made equipment, because the manufacturers are simply not going to fire up a production line to make a couple of hundred parts. Never had any excessive unreliability problems, most bits that fail are due to bad design or operator abuse.
 
Resistor controlled LEDS are indeed second best, but they're cheap as chips.

My original post was to discuss the merits of using a single regulator from the CB for ALL the LED lights rather than having each assembly with its own individual regulator. Set to optimum voltage and surge resistant.
 
Hoolie said:
Resistor controlled LEDS are indeed second best, but they're cheap as chips.

My original post was to discuss the merits of using a single regulator from the CB for ALL the LED lights rather than having each assembly with its own individual regulator. Set to optimum voltage and surge resistant.
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Could work well.
Resistor controlled LEDs also don't generate interference to upset your GPS, Navtex, VHF etc.
I would look at low dropout regulators to take the 12.5 (?) to 14V battery voltage down to 11.8 or so as a first thought.
A lot of domestic 12V from LED supplies is pretty close to 12V, if the few I've measured are typical. Unlike vehicle 12V which is always more, so lamps intended for domestic use are probably going to be close to nominal current on 11.8 or so volts. Whereas a vehicle part intended for 13.5V may not.
 
Just to add my two penny worth. I converted all the internal lamps bar one-14- on our boat to cheapo EBAY led's four years ago. We use the boat a lot. When the engine is charging a lowish battery bank the voltage reaches 14.6v and when hooked up to shorepower the charger reaches 13.6. So far no failures, but I changed 3 for a better reading light in stategic locations. My cheapo led's are MR16 type, not meant for automotive applications where voltage goes up and down. The first one I bought was £18.00, a proper marine one. I multiplied that by 13 and said not bloody likely. The rest were 30 quid for the lot and are still going strong. You pays yer money and yer makes yer choice-I've made mine......................
 
My conclusions from the earlier part of the thread are that I'll use eBay cheapos, with some spares, and see how they go. I've already installed some and they have worked without problem.

Interestingly, there's not much info on comparison with fluorescent, but I've found my recent purchase LEDs are noticeably brighter and use about half the current.
 
Hoolie said:
My conclusions from the earlier part of the thread are that I'll use eBay cheapos, with some spares, and see how they go. I've already installed some and they have worked without problem.

Interestingly, there's not much info on comparison with fluorescent, but I've found my recent purchase LEDs are noticeably brighter and use about half the current.
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If you're going that route, I got one of these after think it was riggerM recommended on another thread. http://www.ebay.co.uk/itm/320894112976?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Seems fine, stable,, you could power a whole lighting circuit and have 12v bang on no matter how high or low the batts are.
 
I have something similar but much more rugged (and expensive). Hence my original post. But I'm minded to keep it for something else - like my Asus EeeBox micro PC, rather than waste it on LEDs.
 
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