# Need help with powering a project

#### Ollie C

Joined Mar 6, 2015
5
Hi,
I'm new to this forum but I hope you guys can help me out. I'm working on a project for my school DT lessons and I need some help with the electronics. I am making a bedside device that has Bluetooth speakers, RGB LED lights and a charging hub. I would like to power all three with one 12v DC power supply (they all run on 12v apart from speakers which I can use a transformer to power it with 5v). I originally thought to run the three by splitting the PSU into three in parallel to maintain the voltage but then I realised the problem with amps. The LEDs need 2A the speaker needs 1A and I'm not sure what the car charger needs but it runs from a cigarette socket in a car and the output is 7.8A (not sure if this has some kind of built in amplifier or not). So this is where I need help how shall I do this. I am in the UK if that makes a difference for PSUs.
Any help appreciated,
Ollie

ps: here are the parts i was thinking of using
http://www.amazon.co.uk/ORICO-Universal-Charger-USB-powered-Devices/dp/B00LVX17AW
http://www.ebay.co.uk/itm/Marmitek-...-Speaker-/231464760086?_trksid=p2054897.l4275
http://www.amazon.co.uk/Tingkam-Cha...F8&qid=1425676777&sr=8-1&keywords=5050+led+1m

#### mcgyvr

Joined Oct 15, 2009
5,394
You just need a single 12V supply capable of more current than all 3 will require.. Typically 125% or more (and "or more" being highly recommended)..

#### Ollie C

Joined Mar 6, 2015
5
Thanks for the quick reply! Oh ok so if I calculate the the amps divided be three (because i'm running them in parallel) then it should be fine. How much amps do you think the usb charger will need? So if I give something to many amps it doesn't matter.

#### GopherT

Joined Nov 23, 2012
8,012
Thanks for the quick reply! Oh ok so if I calculate the the amps divided be three (because i'm running them in parallel) then it should be fine. How much amps do you think the usb charger will need? So if I give something to many amps it doesn't matter.
no, no, no.
The LEDs need 2A the speaker needs 1A and I'm not sure what the car charger needs but it runs from a cigarette socket in a car and the output is 7.8A
2 A + 1A + 7.8A = 10.8A

mcgyvr recommended 125% of that number, so

10.8A x 1.25 = 13.5A

Now, you could tell the user that the car charger is meant for smaller loads (e.g. 1 amp) and then you could get buy with much less. 7.8 A is the MAXIMUM for that car adapter (Charger). Most phone chargers run at 0.5 amp (traditional phones), recent smart phones are using 1 amp and more (newer chargers are often rated at 2 amps). Definitely not 7.8 though.

Cheers,

#### Ollie C

Joined Mar 6, 2015
5
So if I just split the dc jacks in parallel and supply enough current (13.5A) then will the devices draw the current they need

#### GopherT

Joined Nov 23, 2012
8,012
So if I just split the dc jacks in parallel and supply enough current (13.5A) then will the devices draw the current they need
yes. The current flow is a result, a result of what ever voltage you supply (12) and the resistance of the load(s) you attach. Ohm's law is wonderful.

Power supplies are designed for maximum loads as well (not to exceed 10 amps, for example). Exceeding a power supply's current rating usually means that the designed voltage cannot be maintained (it drops to 11, 10, etc. as the load is exceeded). Often there will be a fuse or current limiting circuitry to prevent a fire or damage to the power supply.

#### Ollie C

Joined Mar 6, 2015
5
Will this still work if i use a 12v to 5v transformer for the speaker.
Power supplies are designed for maximum loads as well
So if i had a power supply with 14A is that ok or do I have to stick as closely to the 13.5 as possible

Thanks so much for your help btw

#### Ollie C

Joined Mar 6, 2015
5
Oh also do I need to worry about watts

#### mcgyvr

Joined Oct 15, 2009
5,394
14A is fine... 25A is fine... 1000A is fine..
You can always have more..
As stated above the loads (led/charger,etc...) pull only what they need from the power supply.. It doesn't "force" current into them.

watts is just another side of the whole deal..
Watts = volts x amps
So say you find a 12V @ 10A power supply.. Its capable of supplying 10 Amps or another way of saying that is that its capable of supplying 120 watts (12x10=120)