• Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
    Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.

12v wiring question

B

Brev

n00b
Joined
Aug 21, 2021
Messages
4
G'Day all, while not directly PC related, i was hoping someone can help...

I was wondering if it were possible for a 12v, 2.5amp power supply I purchased will be good (powerful?) enough to power a bunch (about 50) of LEDs that I have, and also could it power a couple of USB charger sockets at the same time.
I'm building a table and incorporating all of this into it.

These are the Power supply and LEDs I have...
Power Supply
https://www.jaycar.com.au/12v-dc-2-5a-power-supply-7dc-plugs/p/MP3490
LEDs
https://www.ebay.com.au/itm/382536135649?var=652390173618

and this is the USB chargers I'm looking at
https://www.amazon.com.au/WYMECT-Ch...rds=usb+charger+socket&qid=1629560170&sr=8-68

Can all of this be wired up in serial from the one power supply?
Also any advice on how to wire it up would be great!
Thanks in advance :)
 
Those LEDs have a series resistor to set the current, but the listing doesn't say what the current is set to. If we assume that the resistor is a sensisble size so that the current is 20mA when the supply voltage is 12V, then 50 of them in parallel will draw 1A.

The listing for the USB charger doesn't say what its maximum input current is. Generously assuming it's 100% efficient, the input current would be (5V * 4.2A) / 12V = 1.75A at full load.

The maximum total current for USB charger + LEDs would then be 2.75A, which is too much for that PSU.

Even if it was less than 2.5A total, I wouldn't recommend running that sort of PSU close to its maximum current for any length of time. If I was doing this, I would be looking for a PSU around 5A.

I would also consider a 12V LED strip instead of individual LEDs. They are easier to wire up, and more efficient (they generally group the LEDs 3 in series, so less power is lost in the current-setting resistors).
 
Need more power. Each charging socket will want 2+amps, unless we are going back to 500ma charging(please, no). 50 LEDs likely use very little power, but it depends how they are wired. In series, almost nothing. In parallel, 3ma x 50 = 1.5 amps. AC/DC converters are not cheap.

Should add that in series they would likely need 120v to run not 12v, so they are almost certainly in parallel.
 
Ahh yea sorry, I meant to say in parallel.
Looks like I'm gonna need either a bigger Amp power supply or just to run the USBs on a separate system.
If I was to run all the LEDs, and 4 of those USB chargers, what Amp power supply would you recommend?

Oh, also the LEDs are 12V 20mA (or so I believe)

Thanks guys :)
 
This is more of a design question than a wiring question.
You've chosen 12v as your supply voltage. This might be best, but you should investigate +5v as that is usb charging voltage and your charging modules might be cheaper.

Assuming we move forward with 12v there are many questions,
I only briefly looked at your LEDs but they don't appear to have current limiting resistors already, so you'll have to add those. You will need to determine the current you want to provide, they are rated to 20ma, but that is max and will likely be obnoxiously bright. Most LEDs are best run between 2 and 5 ma.

Mr Evil broke it down pretty well above, I didn't see an efficiency rating on the chargers, they have step down converters inside them. 2 amps at 12v would be a reasonable guess, per charger.
My quick math above was way off on the LEDs, but you will need somewhere between .5 and 1A for the LEDs.
4 chargers@2A + 1 is 7A,
Divide that by 0.75 to give your power supply some headroom for component degradation, 9.3A.
I wouldn't use anything less than 10A.

Or trim some charging modules.

10A is nothing to scoff at either, use quality connectors and adequate wires, it will not hesitate to burn your house down. 12v may be safe to touch, but overload a component at that current and you will get a fire.
 
Last edited:
  • Like
Reactions: Brev
like this
Brev said:
...Oh, also the LEDs are 12V 20mA (or so I believe)...
Click to expand...
If you're going by the 20mA mentioned in the listing - that data appears to be taken directly from the datasheet for the bare LEDs rather than the complete assembly of LED + resistor. The actual current will depend on what value of resistor they chose.

travm said:
...I only briefly looked at your LEDs but they don't appear to have current limiting resistors already..
Click to expand...
Look closely at the second photo and you can see resistor-shaped lumps under the heatshrink. Resistors are also implied by the "9-12V" description.
 
  • Like
Reactions: Brev
like this
Mr Evil said:
Look closely at the second photo and you can see resistor-shaped lumps under the heatshrink. Resistors are also implied by the "9-12V" description.
Click to expand...
I did only take a cursory look, and straight for the datasheets, no attention paid to photos, if that's the case I would say not ideal choice, strip lights are more likely to meet the requirements. The voltage could be tweaked with a single power resistor of an appropriate rating to adjust the brightness, or even a trimpot.
 
You must log in or register to reply here.
Back
Top