Led power supplies

[Justin Passing]

Again - sorry.
Point me to a Wiki,if there is one I haven't found.
Replacing GU5.3 12V halogens -
I need to supply separately,
:
1 x 6W
2 x 6W
5 x 6W

I see power supplies on ebay from 99p - I assume they blow up, catch fire etc, or are they "ok"?

What does 6x (1W) mean?
Is that 6 x 1 Watt leds in series??

thanks

 

[gblades]

6*1W would just mean there are 6 1W leds which may be in parallel or series or a combination of both.

A lot of the power supplies on ebay are pretty bad. They may be reliable but they often don't have the required mains separation to comply with UK safety regulations.

LED drivers are constant current so you do generally need one per LED cluster otherwise if it is driving some in parallel and one fails it will overdrive the others and cause them to start failing in quick succession.

 

[gblades]

What are you planning to fit?

 

[ericmark]

Most G5.3 lamps have built in drivers and need 12 volt AC. If that is the case then you need a real transformer wire wound not electronic. However the big problem with the extra low voltage lamps is there is a huge mixture of specials, you can get 10 ~ 36 volt DC, mainly for use in caravans and boats, you may be able to get LED,s without drivers built in where you do connect them in series using a proper driver, but I have not seen any.

You can get DC fixed voltage power supplies which also seem to be incorrectly called drivers, I am sure in most cases supplying a G5.3 MR16 lamp with DC is not a problem, but they are often marked 50/60 Hz which is clearly AC so you are taking a chance.

Also there are some switch mode power supplies called electronic transformers rated 0 - 105 VA so could work, those marked 35 - 105 VA will likely not work due to not drawing enough current, but the ones marked 0 - 105 VA as said likely will work, but are often marked in the kHz output and so have the output cable limited to around 2 meters and could with LED lamps transmit RF, and since bulbs marked 50/60 Hz in theory should not be used.

So although you may get away with DC or kHz 12 volt power supplies, your taking a chance, and the simple way is to use a toradol transformer and not take a chance.

 

[333rocky333]

You likely want Constant Voltage drivers available at screwfix etc, Constant Current drivers usually do larger lamps that contain 6 leds of 1watt each and are usually lamps wired in permanent to a fitting
If your also dimming then it gets more involved.

 

[333rocky333]

When they speak of 6 x 1w leds there usually lamps like this, this example is likely 9 x 1w

Im quessing what you have are 6w lamps something like these

These will likely do up to 2 of your 6w lamps, and being screwfix you have some comeback if they dont.

http://www.screwfix.com/p/halolite-...l+Content&utm_content=TextLink&utm_term=58258

 

[Justin Passing]

...

 

[Justin Passing]

There is some confusion....

I'm replacing 12V halogens with LEDs.
Just Using the same bulb shape so it fits.
GU5.3 - parallel pins. The leds I have are from Ledhut, look like single COB arrays.

I know I probably can't simply use the old power supplies.
( though one LED on the same psu as some halogens seems to be OK, a single 6W LED on its own 50W filament bulb supply flickered and failed in an hour or so.)

Sounds like the common-on-ebay transformer/power supplies marked with things like 6x(1W) are not what I want. I have a single, a pair and 5 in a row.

It's not worth paying much for a LED power supply to replace one 50W lamp which only costs 1p an hour or so to run! I could try these: http://www.ebay.co.uk/itm/LED-Drive...rmer-240V-DC-12V-12V-LED-Driver-/290883688146
12W £3.39

Thanks

 

[ericmark]

This type of transformer does not care if one lamp or 10 lamps, it does not matter if the extra low voltage cables are 2 meters long or 20 meters long, you can replace the quartz for LED without changing anything else,

the bulb show is clearly marked 12 volt 50 Hz and will work with the transformer shown without a problem.

There are other combinations that will work, it is simply a case of reading what is marked on them. However this is the advert for the bulb shown and the point is reading the advert no where does it say AC or 50 Hz only looking at the picture can you see it is clearly marked 50 Hz. This is the problem with G5.3 MR16 bulbs it does not say in the advert AC.

It is the same with power supplies often you have to find and down load the spec sheet before you find 2 meter limit on extra low voltage cable length and 43 kHz output frequency.

The power supply linked to clearly states DC so you also need a bulb designed for DC to work with it, not one marked 50 Hz.

 

[333rocky333]

Was it not established that they have a rectifier built in, similar to a GU10 type hence they are not polarised and will work with Dc + or - any way round as well as AC

 

[JohnW2]

Was it not established that they have a rectifier built in, similar to a GU10 type hence they are not polarised and will work with Dc + or - any way round as well as AC

I would imagine that's correct (although the circuit you show, with the 1MΩ/220nF on the input, would obviously only work with mains voltage input). However, in the case of a 12V lamp, I would imagine that the LEDs would be a fair bit less bright with 12V DC (either polarity!) than with 12V (RMS) AC - since, with a reasonable size reservoir capacitor after the bridge rectifier, the 'DC' voltage feeding the LEDs (through the current-limiting resistor) would be something approaching the peak voltage of the AC (~17V).

Kind Regards, John

 

[Justin Passing]

For 0.5A load current and a couple of volts ripple you'd need about a 2000µF electrolytic at 100Hz, which is one reason why SMPS are used. I won't be faffing about with discrete components .

 

[JohnW2]

For 0.5A load current and a couple of volts ripple you'd need about a 2000µF electrolytic at 100Hz ...

Indeed, but the load (at 230V) will usually be an awful lot less than 0.5A when driving LED elements in a single LED lamp, so that a smaller reservoir capacitor would be needed for any given amount of ripple.

... which is one reason why SMPS are used.

Again, indeed yes, for standalone '12V' LED power supplies and 'drivers'. However, my understanding was that Rocky was talking what is inside a '!2V' LED lamp - and I think that will commonly be little more than a bridge rectifier and a current-limiting resistor. Particularly in the cheaper ones, they may well be no reservoir capacitor at all, but, even then, the peak voltage fed to the LED (which seems to be an important determinant of perceived brightness) will be higher when the unit is fed with 12V RMS AC than when fed with 12V DC (of either polarity).

That's how I see it, anyway - as always, I might be wrong! I don't have any 12V LED lamps (don't use the things!), so I cannot 'do the experiment' unless I buy one!

Kind Regards, John

 

[Justin Passing]

Justin Passing said: ↑

For 0.5A load current and a couple of volts ripple you'd need about a 2000µF electrolytic at 100Hz .

Indeed, but the load (at 230V) will usually be an awful lot less than 0.5A when driving LED elements in a single LED lamp, so that a smaller reservoir capacitor would be needed for any given amount of ripple.

But you just wrote
"with a reasonable size reservoir capacitor after the bridge rectifier, the 'DC' voltage feeding the LEDs (through the current-limiting resistor) would be something approaching the peak voltage of the AC (~17V)."

Now you're saying it's not necessary. Make ee mind up!

4.7µF is a waste of time.
Caps on the HT side don't affect it, & of course it's not 0.5 A.

Yes the cheapies have a simple bridge rec, whereas dimmables have a high frequence cct. My leds are £2, so plain.
I need to cut the failed one open, but only out of curiosity...

 

[ericmark]

My problem with 12 volt MR16 lamps is we are only guessing about what is inside the lamp. This advert for a 3 watt lamp states:-

• MR16 (GU5.3) Halogen replacement LED bulb
• 3 x 1W High Brightness LEDs
• Lumens: 160L (Warm White) or 180L (Cool White)
• Colour Temperature: 3000K WW or 6000K CW
• Wattage: 3W
• Voltage: 10v – 30v DC
• Current draw (at 12.7v): 250ma (0.25A)
• Approximate Equivalent to 25W Halogen bulb

It says without any problem it is DC and the voltage 10 - 30 so very likely a pulse width modulated unit built in to drive the LEDs, however this is unusual most seem to have a very vague description with 50 Hz printed on the side clearly are AC but we as the user have no idea if that marking is so we will not use it on 47 kHz supplies because it may cause interference, is it so we will not use it on supplies with a minimum output, or is it because it uses a capacitor as a current limiting device and will only work correctly with 50 Hz?

So we have four possible power supplies for a 12 volt MR16 bulb.
1) Battery charged by a unit so giving smooth DC output ranging between 11 and 15 volt according to state of battery.
2) A transformer giving an RMS output of 12 volt at 50 Hz.
3) An electronic transformer marked 0 - whatever, which may have a 47 kHz output but will work with LED's.
4) A DC power supply at 12 volt which may use a pulse width modulated circuit so may have spikes in the supply.

There to me is the problem, there is no one GU5.3 MR16 lamp or power supply. They need to match each other and all we can really do is read the spec, the whole idea of dismantling a lamp to see how it's made I see as flawed, if it says 50 Hz we need to give it 50 Hz we can't assume it will also work with DC or 47 kHz.