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Wrong AC adaptor = Fried DMD?

Posted: Fri Dec 27, 2013 2:07 pm
by SrBatracio
Hello all again,

I have tried to add an external power supply to the DMD by using a AC adaptor with a 5V, 300mA output.
At first, it looked fine, but after some seconds It started to smell weird and I unplugged the wires. Now it's not working with the Arduino board, however, if I plug the AC adaptor and I touch the bus conector, some leds are lightning.

For the next time, wich adaptor should I use?

Ignacio

Re: Wrong AC adaptor = Fried DMD?

Posted: Fri Dec 27, 2013 2:26 pm
by stryker
Hi Ignacio

So long as it's a regulated 5V DC adapter what you describe you've done shouldn't have harmed it at all. When you state it's an AC adapter you do mean the output is DC, right?

Geoff

Re: Wrong AC adaptor = Fried DMD?

Posted: Fri Dec 27, 2013 2:30 pm
by SrBatracio
Yes, the output is DC... Maybe 300mA is to much?

Re: Wrong AC adaptor = Fried DMD?

Posted: Fri Dec 27, 2013 2:38 pm
by stryker
Hi

300mA could actually be too little, though in this case that's not so important. The voltage rating and DC matters; the amperage only states the maximum current it can provide. A device will only draw as much power as it needs so 5V at any really big crazy number of Amps output will be just as effective as 5V 1A if the device powered needs less than that.

In this case 300mA would restrict the DMD when it needed more, so it would probably just run dimmer than it could. But it's also more than the Arduino will output, so it should have been fine for a single DMD panel.

Is it a regulated supply? Non-regulated supplies will output a higher voltage if the load is low, though if it's an old phone adapter or similar these are usually regulated to a constant 5V.

Are any of the ICs on the back of the DMD visibly damaged? I have one here that we hooked up with 12V (reverse polarity, to make matters worse) and it has visible melted parts on several of the ICs.

Geoff

Re: Wrong AC adaptor = Fried DMD?

Posted: Fri Dec 27, 2013 3:00 pm
by SrBatracio
Mmm I've just checked what you said...

The adapter is a phone charger, and supplies 5V constantly. I have also look for some melted or fried connections but at a first glance, all looks fine :(
Who knows, unless there is still something to try or test I will check if the product has warranty or something.

Ignacio

Re: Wrong AC adaptor = Fried DMD?

Posted: Sat Dec 28, 2013 12:14 am
by andrew
Hello

You need a regulated 5V supply that can deliver at least 3A of current per DMD. An ATX power supply for desktop computers is a cheap option.

Re: Wrong AC adaptor = Fried DMD?

Posted: Mon Dec 30, 2013 5:32 am
by Brissieboy
SrBatracio,

Most small AC adaptors have a thermal sensor included within the windings which go open circuit when they reach their designed temperature. This is most likely what has happened to your unit as it would have been well overloaded trying to drive more than a handful of LEDs. The DMD should be OK.
The DMDs contain 512 LEDs, each of which draws around 30 milliAmps or more, but only a quarter of the LEDs can be on at any one time because of the way the DMD operates. Hence a power supply capable of AT LEAST 4 Amps at 5 Volts is required for a single DMD. As suggested by stryker above, a regulated 5 Volt (but 4 Amps) supply would be best unless you are careful not to light too many LEDs.

The DMDs are fairly tolerant of their applied voltage and can operate from around 2.0V to 5.5V, but a regulated 5V supply is strongly recommended. THE ARDUINO IS NOWHERE NEAR AS FORGIVING!!

Re: Wrong AC adaptor = Fried DMD?

Posted: Mon Dec 30, 2013 11:36 pm
by Brissieboy
OOPS!!

I made a silly mistake in the above post!!

There are actually 512 LEDs per DMD - not 256!!

You will need a power supply capable of delivering 4 Amps for a single DMD.

Sorry for the misleading information.