12v verses 24v LED lights and drivers
- Thread starter ey143
- Start date
Sponsored Links
- Joined
- 27 Jan 2008
- Messages
- 23,668
- Reaction score
- 2,666
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
Very little, in the main 12 volt used as with bathrooms 12 volt is the regulation limit in some areas, so if going extra low voltage may as well go to a voltage which can be used anywhere.
An LED is current dependent not voltage, there may be around 3 volt across a white LED, but it is the current that matters, so we use a driver, which will supply a set current DC to the LED, the simply driver may be no more than a resistor, so 3 white LED's and a resistor in series placed on a 12 volt supply. But clearly the resistor produces no light, just heat, so although the LED may produce 100 lumen or more per watt, as a package with the resistor it may drop to 75 lumen per watt.
So if we use a pulse width modulated driver, we lift the lumen per watt back to 100, so bulbs designed for caravans and boats often have a voltage range of 10 - 30 volt because inside the bulb is a PWM driver, which also means more light per watt.
It does however seem a little daft to have power supply feeding a power supply, if the LED is rated 340 mA then having a 340 mA driver seems the way to go, not a 24 volt power supply feeding a 340 mA driver. So you get a 15W 340mA Constant Current LED Driver, 10-44Vdc which is designed to run the LED direct. As we use different colours of LED so the volts change, so red LED around 1.2 volt.
So I bought some Lidi LED strip, it has an output of between 2 and 22 watt, and it has tricolour plus two white LED's one warm the other with high colour temperature, and the controller does not permitted you to use them all at max output, seem to remember a 6 wire control, and the controller is matched to the LED strip. I use it both under counter lights and display cabinet lights, with latter set to minimum of 2 watt. I would not dream of trying to change the power supply or zigbee controller, I have bought it as a package, and fact than strip will unplug is really only to make it easier to install.
An LED is current dependent not voltage, there may be around 3 volt across a white LED, but it is the current that matters, so we use a driver, which will supply a set current DC to the LED, the simply driver may be no more than a resistor, so 3 white LED's and a resistor in series placed on a 12 volt supply. But clearly the resistor produces no light, just heat, so although the LED may produce 100 lumen or more per watt, as a package with the resistor it may drop to 75 lumen per watt.
So if we use a pulse width modulated driver, we lift the lumen per watt back to 100, so bulbs designed for caravans and boats often have a voltage range of 10 - 30 volt because inside the bulb is a PWM driver, which also means more light per watt.
It does however seem a little daft to have power supply feeding a power supply, if the LED is rated 340 mA then having a 340 mA driver seems the way to go, not a 24 volt power supply feeding a 340 mA driver. So you get a 15W 340mA Constant Current LED Driver, 10-44Vdc which is designed to run the LED direct. As we use different colours of LED so the volts change, so red LED around 1.2 volt.
So I bought some Lidi LED strip, it has an output of between 2 and 22 watt, and it has tricolour plus two white LED's one warm the other with high colour temperature, and the controller does not permitted you to use them all at max output, seem to remember a 6 wire control, and the controller is matched to the LED strip. I use it both under counter lights and display cabinet lights, with latter set to minimum of 2 watt. I would not dream of trying to change the power supply or zigbee controller, I have bought it as a package, and fact than strip will unplug is really only to make it easier to install.
Some evaluation I did recently, Sheath on the strip removed to access resistor's solder pads.
Calibrated meter used to verify 12 volts to strip
Current is 19.92 mA
Power dissipated in resistor ( in mW ) = V x I = 3.51 x 19.92 = 69.91 mW
Voltage across the three diodes = 12 - 3.51 = 8.49 v
Power dissipated in the ( in mW ) = V x I = 8.49 x 19.92 = 169.12 mW
Check on measurements and calculations
Total Measured power 69.91 mW + 169.12 mW = 239.03 mW
Total Supplied power from power supply = 12 Volt x 19.92 mA = 239.04 mW
Calibrated meter used to verify 12 volts to strip
Current is 19.92 mA
Power dissipated in resistor ( in mW ) = V x I = 3.51 x 19.92 = 69.91 mW
Voltage across the three diodes = 12 - 3.51 = 8.49 v
Power dissipated in the ( in mW ) = V x I = 8.49 x 19.92 = 169.12 mW
Check on measurements and calculations
Total Measured power 69.91 mW + 169.12 mW = 239.03 mW
Total Supplied power from power supply = 12 Volt x 19.92 mA = 239.04 mW
- Joined
- 27 Jan 2008
- Messages
- 23,668
- Reaction score
- 2,666
- Location
- Llanfair Caereinion, Nr Welshpool
- Country
I remember in university doing tests on red LED's to try and make them brighter, the idea was to over drive them, but have a mark/space ratio so would not burn out.
However there was a problem, they looked to human eye brighter, but it did not fox the lux meter, so although they looked brighter we could not measure how much brighter.
We also tested over driving to destruction, and once over driven the light output was reduced even when back to rated mA.
So there is a problem if the lamp is every over driven, so there is a problem if for example a 3 LED and resistor array is used on a battery supply which could be 14.8 volt when on charge.
So a 2.6 watt MR16 (G5.3) 10 - 30 volt DC bulb cool white is 349 lumen.but this 4 watt again DC is just 300 lumen and the voltage is simply shown as 12 volt. It is however half the price.
But the big question is do we care? I have just bought some 5 watt GU10 smart bulbs from Lidi, 350 lumen, which is not really that good, but I really don't care, it does what I want.
But a LED is not 24 volt or 12 volt, it is the LED package which is 12 or 24 volt, as an LED is current dependent not voltage and are between 1.2 and 3 volt depending on colour.
However there was a problem, they looked to human eye brighter, but it did not fox the lux meter, so although they looked brighter we could not measure how much brighter.
We also tested over driving to destruction, and once over driven the light output was reduced even when back to rated mA.
So there is a problem if the lamp is every over driven, so there is a problem if for example a 3 LED and resistor array is used on a battery supply which could be 14.8 volt when on charge.
So a 2.6 watt MR16 (G5.3) 10 - 30 volt DC bulb cool white is 349 lumen.but this 4 watt again DC is just 300 lumen and the voltage is simply shown as 12 volt. It is however half the price.
But the big question is do we care? I have just bought some 5 watt GU10 smart bulbs from Lidi, 350 lumen, which is not really that good, but I really don't care, it does what I want.
But a LED is not 24 volt or 12 volt, it is the LED package which is 12 or 24 volt, as an LED is current dependent not voltage and are between 1.2 and 3 volt depending on colour.
Sponsored Links
Lower voltage drop for the 24V version, which is of use when using particularly long or high powered strips.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
