(Archive) Which power supply for the CMB16D (DC) cards



Originally posted July 9, 2009

Hi all,
I'm going to get a few of these DC cards, just wondering what power supplies people have had success with.

There are a few on ebay, 24V, 30V etc.. just like to hear about other peoples experiences.



I bought some off ebay last year following a suggestion from Geoff (Brisbane). Epart138 was the seller. Had no issues, other than I used the wrong wiring to wire up the lights, power supply worked fantastic.



G'day Brad,

The characteristics of the power supply really depend on what your lights require, so every solution is going to be different. You need to know the required voltage as well as how much current your lights are going to draw.
In my case my current batch of LEDs operate on 24VDC and require approximately 30Amps (when all of the lights are on), so I chose to use 2 x 12V x 80Ampere Deep Cycle batteries in series to generate the 24V. I float charge the batteries with a 24V x 10A smart battery charger to keep the batteries topped up. In reality the battery charger float charges my batteries at approx 28V, but that seems to be within the tolerance of my LEDs.


Davidt, Ballarat


Hi Brad

As Dave indicated, what you need in a power supply (or supplies), depends on the requirements of your lights. I'm running a very mixed batch of LEDs from various sources. During testing, I found some worked directly on 24V DC, while others would not even light at this voltage, but needed around 30V DC. Consequently, last season, I standardised on 2 supply voltages 24V and 36V which were both available in the S-350 series switch mode power supplies. For Specs on these supplies, see the uploaded file "S-350-spec.pdf" (thanks Ben) below. For many of the light strings, I added resistors to achieve the required currents/brightness.

I bought several of the 350W supplies from the Eparts138 e-bay store at http://stores.shop.ebay.com.au/Eparts138-Store__W0QQ_sidZ290864554?_n... and these perforned flawlessly. Each supply will power about 4-7000 LEDs. Another member of our group recently found another supplier of this series of power supplies Asia Engineer - http://stores.shop.ebay.com.au/Asia-Engineer__W0QQ_sidZ149380788?_nkw... and their offerings included a 27V supply which may have been more suitable then the 36V units I purchased. I have had no purchase experience with this latter supplier, but their prices are slightly
better (free postage into AU).

Testing LED strings for voltage and currents has been previously discussed, but I still intend to post a discussion paper on my experiences and approach.

Regards Geoff-Brisbane


Re: (Archive) Which power supply for the CMB16D (DC) cards

I have just bought from ebay a 10A 36V supply like the ones below.

Got mine from:

The eBay store was "Stoneined2009". Free shipping to AUS etc. Took about 4-5 weeks to get here from Hong Kong. They do offer expidited shipping if you want to get it faster and want to pay for shipping.

The other ways I have gone is to get large 24V 50-60A switchmode rectifiers used in the telecoms industry. Occasionally they come up on ebay too.

Ultimately how you power DC gear depends on how you want to set up your controllers. In particular, DC power has some considerations if you want the controllers remotely mounted from the power supply (mine are 20m away).
If you are going to do that, you need heavy DC feed cables to ensure that you dont get excessive volt drop due to cable resistance, which if it is too much, will actually lead to one channel switching on and off causing a slight drop in intensity in all the others as the current changes on the feed cables. Do it with a high enough DC load per channel and it can become significant.

Grant VK5GR


Thanks all for the replies, I do prefer the idea of using power supplies rather then batteries inline.
Looking at ebay, I might just get 1 of these and see how some of my LED strings will operate.
24V DC 350w - S350 Series

Can anyone see any reason not to go with the power supply above?



Hi BassTeQ (sorry couldn’t find your name)
You will want to read Geoff in Brisbane's comments about power supplies and voltages which was posted on Friday 22nd of May,

My findings from experimenting is that most of the 24 Volt LED lights do not actually illuminate at a constant 24 Volts DC. (eg from either a battery of one of the Eparts Power Supplies)

This is because the power supplies that come with the lights give out 24 Volt AC, there is a simply full wave rectifier (4 Diodes) in the controller which then converts this AC to DC.

There is no voltage regulator in the LED controllers circuit so the output is not a clean DC supply but a bumpy DC supply (DC supply with lot of AC ripple on it)

In the case of the AC supply and the built in controller the LEDs actually fire ON at the peaks of this ripple.

If you were to supply a good constant 24 Volt DC supply to the LEDs they may NOT turn on at all.

As the previous thread identified, you should go for a higher voltage power supply (eg 30-36 Volt DC) and add a resistor into the circuit to limit the current and create some voltage drop to run the lights

The resistor value will need to be calculated to make the lights work correctly. (this value will be different for the different light strings that you have)

Remember also that the Eparts power supplies also come with a ±10% variable voltage control, which can assist.

In fact ....

If you were to measure the 24 Volt AC supply with a multimeter you would measure 24 Volts DC, this measurement is actually the RMS value of the sine wave. In fact the voltage is (1/√2) = 24 x 1.414 = 33.96 Volts AC Peak to Peak.

Insert a full wave rectifier and you lose 0.7 volts per diode (ie two diodes per cycle = 1.4 Volts dropped)

Actual DC output voltage = 33.96 - 1.4 = 32.56

So those little 24 Volt AC power supplies, and the controller, are actually putting out 32.56 Volts DC (with some AC ripple on the top)

Far more than the 24 Volt DC you are planning to supply to the string.

Remembering the LEDs turn on at the top of the rectified AC cycle, they may not turn on from a constant 24Volt DC supply at all.

Again you will need to read Geoff’s article about calculating the required voltage to drive the string by counting the LEDs in the sting and multiplying it by the volts required per LED (which changes depending upon their colours)

I determined that I actually need 30 Volts DC to drive mine, I will be purchasing the 36 Volt Supplies very soon and installing a resistor inline to create some voltage drop, also limiting the current and preventing any overcurrent. (you could also drop the supply voltage down a bit using the onboard ±10% variable voltage control to fine tune the result.

I have calculated that the 350 Watt supply would be a good size choice.

I hope this makes sense.

If anyone has any comments please do so.

Best Regards

Shane Chiddy

Camden NSW


I have just added a presentation to the "File" section that I did for our NZ "Lighters Workshop" held last month in Paeroa - of note for this thread is the second page of "What is a LED" and the graphs! You will note how adding a resistor smooths out the current vs voltage curve.



Re: (Archive) Which power supply for the CMB16D (DC) cards

Shane, thanks for this very informative reply, I'll go for the 36v power supply then!