0
\$\begingroup\$

I'm trying to create a portable raspberry pi with an lcd screen.

My lcd screen requires 12v and 4A to work properly and i already tried to follow guides like the following: http://www.makeuseof.com/tag/pi-go-x-ways-powering-raspberry-pi-portable-projects/ (the battery pack diy solution)

I'm thinking about using a battery pack of 6 AA (12V)

From what I understand so far, i need to wire the battery to a regulator like this sparkfun.com/products/107 to force 5v on output to the pi board to make it work. Then again from the battery to the lcd controller. Am I missing something?

I would like to make it portable, but not to change batteries every single time. Using the rechargeable ones, is it possibile to charge them? (with a usb, micro usb charger for ex.). Do I need a particular adapter?

Edit:

Thanks for the answers, i will try the several solutions you proposed. As you asked this is the model of my lcd screen: LQ121S1LH03 As i get it from a really old laptop i bought online a controller for that specific lcd, and on the requirements page was clearly written 12V and 4A. I tried to power it up with a charger i had at home (the charger is 12V and 1.2A) and i got a white screen as result. After googling i discovered it was a lack of current, that's why i thought about 4V.

The controller i used is the following one: http://www.ebay.it/itm/M-NT68676-2A-HDMI-DVI-VGA-Audio-LCD-Controller-Board-DIY-Kit-Power-Adapter-/121059321784?hash=item1c2fb2a7b8:g:4AUAAOxyjNlRym3z (the power adapter was not included)

\$\endgroup\$
  • 1
    \$\begingroup\$ You cannot drain an AA battery at 4A. Not for very long. Also, 6 AA batteries is typically referred to as 9V. You would want 8 batteries for a nominal "12V" system. This would provide over 12V initially, dropping down to around 8V when batteries are dead. However, your LCD probably does not really need 4A. \$\endgroup\$ – mkeith Jul 29 '16 at 15:46
  • 1
    \$\begingroup\$ Please post a link to your LCD screen documentation. \$\endgroup\$ – mkeith Jul 29 '16 at 15:47
  • \$\begingroup\$ I'd go with 4S (14.8V ~ 16.8V) RC batteries and 2 buck converters, one for the LCD and other for the RPi.. \$\endgroup\$ – Wesley Lee Jul 29 '16 at 15:49
  • 1
    \$\begingroup\$ 4A for an LCD sounds too high. Are you sure about this requirement? \$\endgroup\$ – user41391 Jul 29 '16 at 19:17
  • \$\begingroup\$ @mkeith 4A drain for a typical rechargeable AA is not even 2C, many of their characteristic uses have substantially higher drain rates. \$\endgroup\$ – Chris Stratton Jul 30 '16 at 4:19
0
\$\begingroup\$

I'm thinking about using a battery pack of 6 AA (12V)

An AA-battery is usually 1.5V, so 6 AA-batteries connected in serial would be 9V and not 12V. Furthermore, depending on the specific AA-batteries, they might not be able to deliver the 4A that your screen requires and the current that the rest of your system requires.

My lcd screen requires 12v and 4A

Just make sure that the LCD display really requires 4A. It seems unlikely to require so much current. Consider using an LCD which requires less current if it is the case.

I would suggest using a Lithium Ion (LiPo) battery. They are commonly available at hobby shops and on-line. Usually, they can output high amounts of current. Be sure to design some protection into your circuit against over-voltage, over-current, accidental short circuits, polarity protection etc.

is it possible to charge them

LiPo battery chargers are commonly available.

From what I understand so far, i need to wire the battery to a regulator

You are correct that you can use a voltage regulator to step down the 12V voltage to 5V for your Raspberry Pi. However, a linear voltage regulator like the one you suggest in your question dissipates power and will become hot over an extended period of time. The difference between the 12V and the 5V output voltage for the voltage regulator is also a relatively large voltage drop which will cause the heat generated by the voltage regulator to increase. Consider putting a heat sink on your voltage regulator.

A better option would be to use a buck converter for the Rpi, or even better get a battery with a higher voltage (14.8V, 4S LiPo Battery) and use two buck converters - one for the Rpi and one for the LCD. A buck converter is more efficient than a linear voltage regulator.

Edit:

As someone in the comments mentioned, rather find an off-the-shelf solution in terms of protections circuitry. There can be a fire hazard with LiPo batteries if you don't know what you're doing.

\$\endgroup\$
  • \$\begingroup\$ Thanks for your answer, seems to be exactly what I was looking for. I edited my question to add details about the lcd monitor and the controller I use for it... Maybe it doesn't require really 4A to work correctly, but I have actually no clues to prove that the controller seller is wrong about the current required. \$\endgroup\$ – Lykos94 Jul 29 '16 at 23:06
  • \$\begingroup\$ I'd warn somebody at the skill level of the op to avoid building protection circuits for LiPos, and to instead find some commercial off the shelf full system \$\endgroup\$ – Scott Seidman Jul 29 '16 at 23:21
  • \$\begingroup\$ @Lykos94 It is true what Scott Seidman says. Take note. Some LiPo batteries come with protection circuits built in. There can be a fire hazard if you make mistakes with the LiPo battery. \$\endgroup\$ – user41391 Jul 29 '16 at 23:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.