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# 3 Volt LED's in Series on a 12V supply, how many watts.

#### Lightingplan

##### Newbie
Hello all and thank you in advance for this probably dumb question. If I have four 3 volt 1 watt LED's in series on a 12 volt supply is the wattage 4 watts at 12 volts? Ergo I could have twelve of these four chip assemblies on a 60w 12v PSU? Best WIshes, Mike

Power calculation is correct, it's however no good idea to drive LED lamps by constant voltage, actual forward voltage is temperature dependant and undergoes type variations. Dedicated LED supplies are using constant current.

Many thanks, it is going through a dedicated DMX LED controller with a 12v 60w PSU. I'm grateful to know 4w at 3 volts is also 4w at 12 volts.

Power calculation is correct, it's however no good idea to drive LED lamps by constant voltage, actual forward voltage is temperature dependant and undergoes type variations. Dedicated LED supplies are using constant current.
Some led strips are constant voltage like 12v or 24v and these repairs constant voltage power supply

Yes,4x3V=12V @ 1/3A =4W *12 = 48W then /60W =%80 of maxtemp = 100 'C rise?

But details depends on VI curve of LEDs and cooling design.

Hi,

Some led strips are constant voltage like 12v or 24v and these repairs constant voltage power supply

But only because they have built in current limiting resistors. (so These resistors dissipate extra power.
Unnecessary waste of power, just drive them with constant current.

I mean the LED companies try to develop high efficiency LEDs .. but then you add resisitors to destroy all their effort.

Klaus

Thanks Klaus, I did a mock up yesterday and they drove well for all 24 hours of the test.

But only because they have built in current limiting resistors. (so These resistors dissipate extra power.
Unnecessary waste of power, just drive them with constant current.
Yes have resistors

Thank you again. Sadly no data sheets are they were just a generic amazon product - https://www.amazon.co.uk/dp/B07C97WKHD?psc=1&ref=ppx_yo2ov_dt_b_product_details

I just really wanted to know a 60w TX would cover 4 or 6 of these four way 3 volt series clusters.
Sadly these are cheap LEDs with wide tolerances. i.e. not 3V ... this may be safer for you to limit the current but they may not be from all the same batch.
Generally you need 1 to 2 sq'" of Cu heatsink per Watt.

Were they hot to touch?

• Power: 1W
• Voltage: 3.0~3.6V