Creating a battery circuit to power a screen and media box

[evfan42]

I have a project that is on a time restraint hopefully somebody and shed some light for me. I understand that the circuit is going to be pretty simple.

Here goes,

So basically I want to power both a screen and a media box with a rechargeable battery and need to build the circuit to do so

The screen:
usb powered at 5v, 2.0A

The box:
Wall powered at 5v, 200mA

I was thinking I could use a hobby r/c car battery and create a circuit to step down the battery voltage to power both the screen and box. Basically I am wondering if somebody would be kind enough to point me in the right directions to what parts to use, some of the math to pay attention to, and what to look out for.

 

[evfan42]

So for some of my own research I have found this so far

http://www.batteryspace.com/nimhbatterypack12v3800mah5x2x43abattery.aspx

for the battery, probably overkill but the setup needs to last for a while on one charge

http://www.linear.com/product/LT123A

for part of voltage step down circuit.

the regulator is only rated for 3 amps, but with the screen and the box it will be pushing about 2.4 ish amps. Will this regulator be able to handle the battery, or will it not matter cause the screen/box wont be pulling over three amps?

 

[davenn]

hi there

since you are going to be running off a battery, I suggest you look at a DC-DC buck converter
they are substantially more economic than a linear regulator .... ie. waste much less power and all low the battery to last longer

here is an example .....
http://www.ebay.com.au/itm/like/271...2&ops=true&viphx=1&hlpht=true&lpid=107&chn=ps

cheers
Dave

 

[evfan42]

oh nice! I should've just looked for something like that. I would be able to just run both the screen and the box with that connected to the same battery, right?

 

[FvnnyL3tt3r1ng]

Buy it from a reputable dealer. I bought two recently and both were broken. Best I could get was a partial refund after the month long wait.

 

[davenn]

oh nice! I should've just looked for something like that. I would be able to just run both the screen and the box with that connected to the same battery, right?

yup

These things are so cheap buy several of them to cover you for future projects

 

[Kenneth Tan]

I've build dozens of lipo psu's from reclaimed laptop batteries.
There are some good and cheap charging pcb's with undervoltage and current protection build in.
Then using a boost converter you could get a nice 5V power supply.
Here's an example with 4x 18650 all parallel but in pairs of two. Each pair has a charge board that charges each Lipo @500mA (charge board max =1A)
So depending on the capacity od the 18650 you could calculate the time it takes for a full charge)
The outputs of the charge board are tied together and fed to a boost converter. You need to pick the right one that supports your output current.

With the 18650's free of cost this project can be build under €5.
And with the charge protector boards safety is ok within it's limits.

 

[Kenneth Tan]

And here is my favorite battery psu.
It uses two buck-boost converters.
The top one is a digital one and can be programmed to specific voltage and max current. Also it shows capacity used and power consumption.
The lower one sits beneath the 7 segment display and outputs a fixed 3.3, 5v and 12v output.
The 7 segment display is for monitoring the battery voltage (4× 18650 in series)
This psu has no charge boards. The batteries are in a holder so they can be charged in a seperate charger.