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Do they have a glass on the front? If not those are potentially pretty dangerous. Cheap ones often only have the power circuitry on one leg, so those solder terminals on the face have potential to be at mains voltage (boom boom!)Quote:
Originally Posted by Phage
LEDs themselves don't run at 12V, depending on the LED configuration the voltage can be stepped down or even up. I've not done detailed tear downs, but I've always noticed inductors and various ICs in both the GU10 and MR16 LED bulbs I've trialled and taken apart suggesting some form of switching conversion.Quote:
Originally Posted by wasabi
Any failed GU10 I've taken apart lights right up at normal brightness when you hook up the simplest last leg of the circuit (cathode and anode) to a 12v battery. Suspect many of them have some kind of polarity checker given the simple 2 pin thing going on in both GU10s and MR16s. And maybe a capacitor to smooth the delivery and a heatsink/fan on the higher wattage units. Or flashy dimmers / colour changers. None of it needed really though in simplest form.Quote:
Originally Posted by DDY
Never had an MR16 fail, only had 3 GU10s out of dozens last for multiple years (cheapy Lidl ones strangely, suspect due to low 1.8 wattage, and intermittent usage in porch).
Never personally encountered consumer LED lights that don't natively want to run at 12v. I've dabbled with LEDs in the home / aquarium / electric bike / shed and car for years now.
Rob.
In hope my electrical work is OK. ;)
Led hut is great for lamps. In use them all in my house.
I use these GU10s - http://www.ledhut.co.uk/spot-lights/...eam-angle.html
The all come with a 5 year warrenty. If the fail, the company will replace.
I reckon the workmanship is up to scratch Chris ;)
Amazon reviews for the bulbs I have suggest they do go easily, I've seen those ones on Amazon Chris, wasn't sure if the beam would be too focused, guess I didn't read the description! (30% off LEDHUT at the moment too :))
Ended up with 5 of these for £27.12
http://www.ledhut.co.uk/spot-lights/...50-lumens.html
That's with 30% off + there is 20% quidco (about a fiver) to come :)
Fingers crossed these ones last!
I have 18 lamps in the kitchen (it is an odd L shape) and frankly really didn't want to re-wire a single bulb.Quote:
Originally Posted by wasabi
These seem to work fine with the old constant voltage transformers.
Will be a while before I find out if the 15 year lifespan is reduced.
It's not uncommon for lower wattage LED systems to use resistors for current limiting and can be on die as mentioned by PeterB. Hence, you can stick a good few volts at without worrying about the current across these LEDs.Quote:
Originally Posted by wasabi
However, high power and high efficiency LED systems are unlikely to use resistors for current limiting because they ruin efficiency and dump heat where you don't want it. For these, sticking 12V or any other voltage that's not constant current can be a bad idea.
Now that I've mentioned high power LEDs, now's a good time for a gratuitous show-off of my current project, a portable 100W lipo powered LED torch. I'll be testing it outdoors soon, will post pics when I do.
Quoted 7500lm of light with a tested battery life of around 70 minutes. Body crudely designed and 3D printed by myself, any resemblance to an 80s sci-fi prop is coincidental.
http://img.photobucket.com/albums/v6...h__DSC3241.jpg http://img.photobucket.com/albums/v6...h__DSC3242.jpg http://img.photobucket.com/albums/v6...h__DSC3243.jpg http://img.photobucket.com/albums/v6...h__DSC3248.jpg http://img.photobucket.com/albums/v6...h__DSC3245.jpg
More info once I get the outdoor tests done.
I'm fairly clued up about LED lights these days so want to dispel a few points:
All commercially available LED's that I've seen either run at 12V or 24V
You cannot run LED's off mains (230/240V) without some form of transformer stepping down the voltage to the required level. Typically 12V.
The step down in voltage is often within the housing of the GU10 bulbs you get so they can be directly fitted into existing systems
GU10 and GU5.3 (or MR16 as people are referring to them here) refers to the pin connection type on the back, MR16 is the reflector (housing) size...see here: http://en.wikipedia.org/wiki/Multifaceted_reflector
LEDHut are a good internet supplier, but you can also try V-TAC (london based importer). If you're doing a full re-wiring setup you can see if Sunpower UK (Reading based) will supply you with the Transformers (LED transformer specialists).
From what I've seen Philips would be the brand to go with for high end.
Just some notes regarding LED:
LED are very voltage sensitive. If the wiring in your house isn't providing a highly stable voltage this could be the cause of them burning out. I'd recommend reading these 2 articles if you want to know more:
http://www.digikey.com/en/articles/t...t-power-supply
http://www.amperor.com/products/led/...ed_driver.html
To try and simplify the explanations in the below links LED have an activation voltage (they aren't linear like traditional bulbs where doubling the voltage would double the power and therefore ~ 2x the brightness). What this means is upto 11.9V lets say, you will see no effect at all, then at a certain voltage you will see the LED activate, apply more voltage and it will get brighter, but this will reduce the life expectancy (thus they have an optimal voltage they should be run at).
As the LED heats up it actually requires LESS voltage to push the same current through the circuit, unfortunately it also becomes less efficient at producing light as it warms up. The second point has a greater overall bearing on performance when both factors are taken into consideration, so LEDs run more efficiently (less power needed) when cool, hence high powered LED have metal heat sinks to dissipate the heat build up.
The voltage they operate at is VERY sensitive. For example if we look at these two graphs:
http://www.digikey.com/en/articles/t..._How_Fig_2.jpg http://www.digikey.com/en/articles/t..._How_Fig_3.jpg
3V produces 1 amp = 400 lumen approx.
3.2V produces 1.8 amp = 700 lumen approx.
...a 0.2V increase nearly doubles the light output! Hence a voltage stable system is required to stop early bulb failure.
This sensitivity to voltage is also the reason you can only put so many in series before the ones on the fair end of the setup simply stop lighting. This is due to V drop over the length of the circuit. If you imagine you have a 12V circuit. You'd expect 12V LED bulbs to work on it (and they will, but only upto a limited number). If you think of it this way, every light in the circuit reduces the voltage for the next light in the series. So the first bulb receives the full 12V, the second maybe 11.95V, the third 11.9V and so on. This is known as V drop and happens as resistance (LED bulbs in this case) build up. I've already explained that LED are highly voltage dependent, so eventually you reach a situation where the V drop is too great and the voltage the circuit is supplying to the end bulbs doesn't reach the actiation voltage required.
My final point would be with regards to the transformers. You can get CC (constant current) or CV (constant voltage). The articles above explain the difference. But in a nutshell CV are "dumb" transformers stepping down the mains voltage to the voltage they're designed to do...typically 12V or 24V. They also have a maximum rated wattage (like PC power supplies, no difference there). In fact PC power supplies can be used for 12V LED systems, as they provide 12V outputs :)
CC have feedback systems which vary the voltage to maintain a constant current. Now I know we talk about LED in terms of voltage, but technically this is wrong, they should be rated at an optimal current. It's just that voltage is a term people are more familiar with so manufactures use that, confusingly. If we accept LED's should run at a rated current, you can now see why a constant current transformer would be a good thing! CC transformers will vary the voltage to ensure constant current at different operating temperatures, maximising the life span of the LED bulbs and ensuring they are not over powered and "burnt out".
Having said this, most setups use constant voltage systems as it's "good enough" and cheaper to buy.
Good choice.Quote:
Originally Posted by Rob_B
If they fail within the warranty period, the will be replaced gratis.
The ones I linked to in previous post are these one I have and look like this in my kitchen. Very bright
https://www.dropbox.com/s/4dt9et211j...24148.jpg?dl=0
Looks good, I went for the 120 degree ones, as you've seen our bathroom is tiny so not sure why I did that but oh well it's done now!
Can't get away with cool whites in the kitchen, looks far too bright, maybe when I get around to changing the counter top it might look better but for now I'll stick with the cheapy 'warm' SMDs I've got.
The 120 deg are the ones i have and they are very good. Nice spread of light.
Merry Christmas to everyone by the way.
Yes of course they doQuote:
Originally Posted by herulach
While I wouldn't disagree in principle with that, an LED operating voltage is 2.4 volts (as the graphs show) not 12 volts, and so any LED lamp that runs off any voltage above that voltage needs some form of regulation.Quote:
Originally Posted by cptwhite_uk
But it is slightly more complicated than that. An LED is no different electrically from any other diode. It has a maximum reverse breakdown voltage, a maximum reverse current, a forward voltage drop and a maximum forward current. An LED forward voltage drop is, as stated, 2.4 volts, and when that is reached, the forward resistance is very low, and so the current has to be limited by other means, hence a constant currant source.
You can run an LED cut at any voltage above 2.4 volts by running it in series with a resistor, which is what you do for an LED indicator or panel light. The resistor, combined with a steady DC voltage forms the constant current source. If the LED is shorted out, the current drawn through the resistor will not change.
Most LED lamps for general purpose illumination consist of arrays of LED elements, each one has to be fed with a constant current. The challenges depend on the source supply for the array, 12 or 230, AC or DC, and providing that supply as efficiently as possible.
That's not quite how diode voltage drop works. If you put a load of diodes in series, each diode will need a potential equal to or greater than its Vf in order to pass current and light. If you put a multimeter in volt mode across an LED, you'll measure the voltage drop across it, which provided it's lit will be around its Vf i.e. something like 3.2V. Add up the voltage across each diode and you end up with the supply voltage, minus any resistive drop in the cables, drop resistors, etc. This is why for '12v' chains, you'll generally have three LEDs in series along with a resistor which is chosen based on desired current, any more than that and you'll find there are simply more chains of three added in parallel. If you try adding more diodes so the combined forward voltage is greater than the supply voltage, you'll reach a point where they'll just stop conducting and the whole chain will not light.Quote:
Originally Posted by cptwhite_uk
If you start adding larger numbers of diodes to each chain, you can run into problems with the variability of Vdrop resulting in significantly uneven power to the LEDs, which in turn will shorten lifespan.
This is more of an immediate problem when trying to run LEDs directly in parallel however - unless you select them with closely matched Vf, they can be a nightmare to control. E.g. in order to power one with a higher Vf efficiently, you might be over-driving the other and vice-versa. So you end up with different current, and therefore power, flowing to each LED.
Voltage then isn't just a throwaway term when it comes to LEDs at all, it's quite an important metric when e.g. designing driver circuits, matching them to run in circuit, etc, just like it's important for any diode. Current and voltage aren't interchangeable so you need to know both when designing drivers. E.g. it's no good designing a CC driver for a chain if its output voltage is lower than the combined Vf of the diodes.
For powering a single LED/series chain, a CV/CC supply would be ideal as it would both limit no-load voltage and prevent thermal runaway killing diodes. However, CC isn't without its problems - speaking in terms of a lighting transformer supplying multiple spotlights for instance, it would be near useless unless you had one for every lamp, and even then you'd be very limited to what lamps would be compatible.Quote:
Originally Posted by cptwhite_uk
E.g. imagine your bathroom has an LED CC supply for say 3 spots, supplying say 1.5A if each lamp wants 500mA. What happens when a lamp fails or is removed? The other two share that 1.5A between them, 750mA each, and probably go pop, or if its supply voltage is close to the ideal voltage anyway, you essentially just end up back with with a CV supply. You're also pretty much wasting your time using a CC supply for >1 series chain anyway because of the variability mentioned earlier; you can potentially still end up with one chain hitting thermal runaway without the CC regulator reacting.
Just received and fitted them, wow they're bright, I know my previous ones were 4W and these are 4.5 but the difference is unreal!