LED panels (on 12Vdc – step up)
Recently a very nice LED-panel on Ebay caught my eye, it looked something like this:
Now these LED panels are available in a large varieties, both circular, square or rectangle, starting at 3 Watts up to 30 Watts or even higher. Most of these panels are from China and are pretty cheap. A driver is included that work on AC from 100 to 240 Volts, so it works worldwide.
Very nice panels but if they could be converted to work on 12 Volts, they would be much easier to use in solar installations or even in RV or Marine applications.
To test I used an average 15W panel (8″ round) and I am wondering if it’s possible to convert LED panels to 12 Volt instead of regular AC-grid.
On the driver it reads: Output 48-58Vdc at 300mA, so that gives about the 15 Watts.
The measured output (with the panel attached) of the driver was 48Vdc indeed but the current was a bit less, about 260mA.
Part 1 handles about stepping down in voltage, for smaller panels than 6 Watts or maybe if you use 24Vdc it might be nice to read that part first. Read it here.
Step-up to a higher voltage
To optain 48V (in this case) from a 12V source is relatively easy with the right DC-DC converter, a step-up converter, since we need to higher with the output voltage.
One of my favorite shops on Ebay chivazhu sells these (under $10) and much more electronics.
This inverter can convert from input-range 10-32V to and output-range of 35-60V. This all with a maximum power of 120Watts, it’s recommended to add cooling when exceeding 80W, but since we need only 15W, it should not really be a problem.
Start to disconnect
The driver can be openend with a screw-driver, it’s simply clicked together with the small PCB in the middle.
The wires can be removed from the board with a soldering-iron. It should be unnecessary to say to leave the driver disconnected of the mains. But if your driver won’t open easily or you want to get the panel disconnected real quick, just use a wire-cutter of pliers and cut the wire.
I disconnected the wires with the soldering iron, and that leaves a nice, clean driver behind.
That also keeps the wires at maximum length, but still seem a bit short, so I extend them just a little bit with some cable, but that is not really relevant for the project.
Get the DC-DC converter and connect it to you 12 Volt lines on the input-side, watch the polarity. Without connecting the LED panel measure the output. The factory-default maybe lower or higher than the desired 48Vdc for our panel. Adjust the ouput of the inverter if needed to approx. 48 Volts. Then disconnect the 12V Volt input and connect the panel.
Put the 12 Volts back on and enjoy your 15W LED panel.
With the new connection made to the panel, it’s good to measure things in the end process:
- Output voltage: 48V (as set on the DC-DC converter)
- Output current: 250mA (as it was before with the driver)
- Input voltage: 12V (bit higher since it’s a battery but the output remains stable)
- Input current: 1.2A ( as expected)
The input current is a lot higher than the output current to the LED Panel.
Ohm’s law defines: Voltage x Current = Power, so 48V x 0.26A = 12.48W (just a bit lower than the promised 15W). That same power must goes in, so 12.8V (actual battery output) x 1.2A = 15.36W. The fact that the input power is higher than the output power has to do with the efficiency of the DC-DC converter, which is now calculated as nearly 82%, not bad.
The output voltage of different driver varies on output power, these drivers are usually constant-current outputs, that means the generate a maximum amount of current for the LED-panel, very different from the output of the DC-DC inverter, that could handle 5A or more. This can easily damage your LED’s in the panel or worse. Measure the output voltage with the panel connected is the best way to go.
A driver of a 12W panel shows 25-42Volt/300mA, so always measure the output voltage first (with the panel attached) before you connect a fixed voltage.
Some more work
- Put the DC-DC inverter in an enclosure !
- Use fuses, never connect directly to the battery.