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[Tony H]

Hi all I have set up some outdoor led lights, there are three sets which where originally all independant and where powered by small solar panels. I have since wired all three together in series and have converted them to run off mains supply via a transformer. Currently (please forgive the pun  ) running them at 3 volts as 1.5V was not available on the transformer. They work o.k. but I would like to see if I could get them to be a bit brighter would if be alright to up the voltage or would it fry the lot?

TIA for answers
Regards
Tony

[zirk]

Depends how the LEDs are wired as a each set, normally for High Voltage supply each LED is wired in series, for Low Voltage supply each one in parallel, what was the supply voltage originally and at what current, guessing if they worked of a Solar Panel then they would have been wired in parallel.

If youve wired all 3 sets up in series, cant help thinking you've actually connected each pair of wires from each together, so would actually be in parallel, but if in series then you have created a 0.7v drop across the addition 2 sets, so a 1.4v Drop in total, so in theory you can up the voltage by another 1.4v over what it should have been to compensate, if that makes sense.

[LC0112G]

Depends how the LEDs are wired as a each set, normally for High Voltage supply each LED is wired in series, for Low Voltage supply each one in parallel, what was the supply voltage originally and at what current, guessing if they worked of a Solar Panel then they would have been wired in parallel.

If youve wired all 3 sets up in series, cant help thinking you've actually connected each pair of wires from each together, so would actually be in parallel, but if in series then you have created a 0.7v drop across the addition 2 sets, so a 1.4v Drop in total, so in theory you can up the voltage by another 1.4v over what it should have been to compensate, if that makes sense.

LED's typically have a Vf of between 1.4V and 1.8V, unlike a normal silicon diode which is 0.6-0.7V. So 3 sets wired in series is going to need at least 4.5V to get them to light.

LED's usually have an If of between 5mA and 10mA per 'bulb' , but can be as high as 20mA. If you've wired the 3 sets in parallel, then you don't want more voltage, you want more current. Doubling the voltage will probably produce 4 times the current which may blow the LED's if you exceed their power dissipation capability.

How many bulbs are there in each set? If there are (say) 24 in a set, and you've wired 3 sets in parallel, then you need a supply capable of providing 1.5V @ (5mA * 24 * 3) = 360mA. So a 500mA supply should do it.

[Marks DTM Calib]

White LEDS usually have a V_f of 3.3V, as per all LEDS the key thing is constant current but that requires a current mirror circuit which is probably a bit to far for most.

Red, green etc LEDs have a V_f of circa 1.2V so we need to know what colour they are to determine max voltage.

If they are white then you could go up to 9V or green/red/orange 3.6V......but beware as most cheap mains adaptors are NOT regulated so err on the low side.