12volts into 4.5 volt leds?

Hi, i have a string of battery LEDs and id like to connect them to the mains. I have a 12v LED driver. The lights powered by the battery arent very bright so i wondered what would happen if i connected them to 12v?
You might ask, why dont i get mains powered ones to begin with but they all have this stupid combination flashing settings so they are all useless to me.

Oh, im not an electrician as you can tell so please dont suggest just put a resistor in somewhere as i dont have a hope in hell of doing this.
Cheers
Tom

Tomdas said:

Hi, i have a string of battery LEDs and id like to connect them to the mains. I have a 12v LED driver. The lights powered by the battery arent very bright so i wondered what would happen if i connected them to 12v?
You might ask, why dont i get mains powered ones to begin with but they all have this stupid combination flashing settings so they are all useless to me.

Oh, im not an electrician as you can tell so please dont suggest just put a resistor in somewhere as i dont have a hope in hell of doing this.
Cheers
Tom

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I wouldn't connect them to 12 volts. 5 volt power supplies are very common these days for phones, tablets etc usually with USB connector outlets. I would try one of these.

Thats why i deleted my post.

I dont think its a power supply he wants
I beleive he wants them to be BRIGHTER by connecting a higher voltage

LED's are current not voltage dependent. There is a Zener or Avalanche voltage which will mean there is a set voltage for every diode but it is no good trying to adjust voltage you have to adjust current. But knowing the likely voltage required can help.

So with a 340 mA diode white you expect the critical voltage to be around the 3 volt mark (Red 1.2 volt) so with a 12 volt power supply and three diodes using ohms law and assuming 9 volt across the diodes so 3 volt at 340 mA means likely a 9 ohm resistor will cause the correct current to flow. Simple ohms law.

A LED driver with have a maximum voltage which will show how many diodes can be in series and a set current which clearly should match the LED.

LED's are often sold as a package with some current or voltage limiting built in and so buying a 12 volt 3 watt GU10 LED the unit already has the control components built in.

One of the major problems is we don't know what has been built in. Using a switch mode regulations a 12 volt device could run 10 ~ 20 volts AC or DC but with a simple resistor is may required a smooth DC supply at exactly 12 volt.

LED's also produce heat and heat sinks are required. Clearly with a 3 mA red LED really no problem but with a 340 mA white LED it will require a good heat sink.

Now in university I was given a project to try and squeeze a bit more light out of an LED. The idea was to feed it with pulses of a much higher current then they were designed to use giving a brighter LED without burning it out.

However theory and practice were very different. Using a Lux meter we were not able to get more light without damaging the LED. However we felt with the eye they seemed brighter. We concluded the LUX meter did not really mimic the human eye. In theory it should but in practice it does not. This is a major problem we are given lumen output which should match human eye but they got it wrong.

Latter I swapped 10 x 8W CFL for 10 x 3W LED this in theroy means 3500 lumen is reduced to 2500 lumen so should look dimmer. However the LED's look much brighter. I am not the only one to have noticed lumen does not do as it says on the can. And some have required it is measured after the light has been running for one hour. This has made it even worse as you have now at least three standards for the lumen.

Oh what a tangled web. So to answer your question it should not make any difference battery powered or mains powered but in real terms we really have no idea.

Eric, you may as well have have posted that in Greek - it would have made as much sense to him.

Tomdas. Its like this.
Suppose that you have a room lit by a single 40watt light bulb, but the bulb is not bright enough.

What would you do? Increase the voltage?
No! You would go down to Tesco and buy a different light bulb, maybe a 60watt one.

That is the simple solution to your query. You need to buy some brighter LED lamps.

Cheers for all the advise guys, It does make sense.
I guess my question was how much you could push LEDS without them failing too much,
For example, if i was to put a 6volt LED driver on these would the extra 1.5 volts mean they only last a week and burn up or something?
I apologise for my lack of LED understanding.

Ideally id like to find 100 LEDS in a string that ran from a 12v LED driver but they either seem to be aorund 4.5 v if they are battery powered or 30v of from the mains

Cheers again

Tom

Tomdas said:

For example, if i was to put a 6volt LED driver on these would the extra 1.5 volts mean they only last a week and burn up or something?

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It might mean that. They might 'blow up' immediately. They might work fine (and brighter), without problems, for ages. Without having a detailed understanding of what goes on within your string of LEDs, we couldn't say.

Kind Regards, John

Tomdas said:

Cheers for all the advise guys, It does make sense.


Ideally id like to find 100 LEDS in a string that ran from a 12v LED driver but they either seem to be aorund 4.5 v if they are battery powered or 30v of from the mains

Cheers again

Tom

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Here you are:

http://www.ebay.co.uk/itm/5M-300-LE...t=LH_DefaultDomain_3&var=&hash=item2349e50d75

winston1 said:

http://www.ebay.co.uk/itm/5M-300-LED-Strip-Light-3528-5050-5630-SMD-12V-LED-Flexible-Light-Waterproof-/151563603317?pt=LH_DefaultDomain_3&var=&hash=item2349e50d75

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I get the impression that the OP is probably looking for 'Christmas tree'-type strings of LEDs, rather than LED lighting strips.

Kind Regards, John

Thanks guys, yes sorry for not being clearer, i did mean christmas type lights.
When you say that they might blow up or they might be fine depending on the lights, can you tell me how to test this?
I do have a pocket meter and if you can tell me what to do i can try to work this out?

Thanks again
Tom

Tomdas said:

When you say that they might blow up or they might be fine depending on the lights, can you tell me how to test this?

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That's the problem - you can't really test. If you want to, you just have to try and see if they blow up! There is a theoretical possibility that they could 'burst into flames', but that's fairly unlikely - more likely, some (or all) of the LEDs would just 'die'.

If the lights are designed for 4.5V, you might 'get away' with 6V, but 12V would probably be pushing your luck in a fairly big way.

Kind Regards, John

There is only one way to know for sure if a higher voltage would increase the brightness without shortening the life of the LED elements.

That is to know exactly how the current through the LEDs is controlled.

To find the answer would require opening up the unit and reverse engineering the circuitry to get the circuit diagram.

bernardgreen said:

There is only one way to know for sure if a higher voltage would increase the brightness without shortening the life of the LED elements. ... That is to know exactly how the current through the LEDs is controlled. ... To find the answer would require opening up the unit and reverse engineering the circuitry to get the circuit diagram.

Click to expand...

Indeed so ... as I wrote:

Tomdas said:

...Without having a detailed understanding of what goes on within your string of LEDs, we couldn't say.

Click to expand...

As I've just written, the only alternative would be to 'suck it and see', and probably learn the answer the hard way!

On the assumption that the current control is crude (probably just a resistor for every 1-3 LEDs), increasing the supply voltage from 4.5V to 12V would probably increase the current through the LEDs 'many-fold', I imagine probably killing the LEDs. Even going from 4.5V to 6V could easily double or treble (or more) the current, again quite possibly killing the LEDs - fairly quickly, if not immediately. I am therefore pretty pessimistic in my view of what the OP is hoping/wanting to achieve.

I really think the OP should continue his search for LEDs which are bright enough for him when supplied with the intended voltage!

Kind Regards, John

Ok, i think its best to source a string of leds without flashing options and then match the LED driver exactly.
Cheers for the advise, i didn't think this would be quite as complicated as it is.
you live and learn

Thanks
Tom