Powering Raspberry Pi 2 and TFT screen at once via battery?

[Exceen]

Hello everyone,
I'm currently trying to build my very own Gameboy, based on a RPi like most of you here I guess. The parts I use there are a Raspberry Pi 2, one of these Car Rearview TFT displays (3.5") and this battery: http://www.ebay.at/itm/BAK-3-7V-2650mAh ... 0940947029 (3,7V 2650mAh 9,80Wh 804172P Lithium Polymer LIPO).

The problem is that I'm not able to power both, the RPi and screen, at the same time just via the battery. It's possible to power just one and in that case everything works fine, but as soon as I want to power both just via the battery, the screen isn't working properly (it's flickering). And the RPi crashes every few seconds and then restarts.

I tried to solder both directly to the battery and I tried to solder only the battery and the Raspberry Pi together and use the GPIO pins for the screen. Both options result in the behaviour I just described.

So I'd say that the battery doesn't output enough current (?) at once. One solution would be to get a second battery, but that would be really complicated to implement and I don't really have enough place for that in my case.

Here's a video in case that's of any use: https://dl.dropboxusercontent.com/u/341 ... .10.31.mov

Oh and btw, I own a a Rasbperry Pi (1) as well and tried everything I described above with it as well. Same result.

So can anyone help me with that please?

[wermy]

Hello everyone,
I'm currently trying to build my very own Gameboy, based on a RPi like most of you here I guess. The parts I use there are a Raspberry Pi 2, one of these Car Rearview TFT displays (3.5") and this battery: http://www.ebay.at/itm/BAK-3-7V-2650mAh ... 0940947029 (3,7V 2650mAh 9,80Wh 804172P Lithium Polymer LIPO).

The problem is that I'm not able to power both, the RPi and screen, at the same time just via the battery. It's possible to power just one and in that case everything works fine, but as soon as I want to power both just via the battery, the screen isn't working properly (it's flickering). And the RPi crashes every few seconds and then restarts.

I tried to solder both directly to the battery and I tried to solder only the battery and the Raspberry Pi together and use the GPIO pins for the screen. Both options result in the behaviour I just described.

So I'd say that the battery doesn't output enough current (?) at once. One solution would be to get a second battery, but that would be really complicated to implement and I don't really have enough place for that in my case.

Here's a video in case that's of any use: https://dl.dropboxusercontent.com/u/341 ... .10.31.mov

Oh and btw, I own a a Rasbperry Pi (1) as well and tried everything I described above with it as well. Same result.

So can anyone help me with that please?

I think the most important factor here will be what charging/boost board you are using. Can you post a link to that?

[Exceen]

I think the most important factor here will be what charging/boost board you are using. Can you post a link to that?

http://www.ebay.com/itm/130725341903

It's possible that I did something wrong there, I'm still not quite sure how it works. I attached a charger board (http://www.ebay.com/itm/Adafruit-Micro- ... 1820103982) to the "charge" side, in the middle (bat) there's the battery connected and the output is a simple USB-cable right now which is plugged into the RPi.

http://dev.exceen.at/gameboypi/entries/ ... .48.33.jpg

[wermy]

I think the most important factor here will be what charging/boost board you are using. Can you post a link to that?

http://www.ebay.com/itm/130725341903

It's possible that I did something wrong there, I'm still not quite sure how it works. I attached a charger board (http://www.ebay.com/itm/Adafruit-Micro- ... 1820103982) to the "charge" side, in the middle (bat) there's the battery connected and the output is a simple USB-cable right now which is plugged into the RPi.

http://dev.exceen.at/gameboypi/entries/ ... .48.33.jpg

It's hard to tell, especially with how rough their english is, but it looks like you may not need the Adafruit board. They mention over/undercharge protection several times in their listing, maybe indicating that this is both a charging board and a boost all in one.

[wermy]

@Exceen
This guy talks about that same board you have in his video: https://www.youtube.com/watch?v=9eOg5CIRD2M
It sure sounds like that's an all-in-one board. Can't say for sure but that is what it sounds like.

Edit: Well, someone in this thread mentions that you would need a charging board in combination with it (like you have): https://www.reddit.com/r/raspberry_pi/c ... pberry_pi/

So I don't know what to think. :\

[Exceen]

It's hard to tell, especially with how rough their english is, but it looks like you may not need the Adafruit board. They mention over/undercharge protection several times in their listing, maybe indicating that this is both a charging board and a boost all in one.

But does it even matter in this case if I use this Adafruit or not? The power from the battery goes throught this step-up board thingy and then into the Raspberry Pi (which powers the screen via the GPIO pins then).
Even if I cut that Adafruit off I would still need a way to charge the battery via USB.

... or did you mix up the Adafruit board with the power up board? Because there's something with 5V on the Adafruit board.

[wermy]

It's hard to tell, especially with how rough their english is, but it looks like you may not need the Adafruit board. They mention over/undercharge protection several times in their listing, maybe indicating that this is both a charging board and a boost all in one.

But does it even matter in this case if I use this Adafruit or not? The power from the battery goes throught this step-up board thingy and then into the Raspberry Pi (which powers the screen via the GPIO pins then).
Even if I cut that Adafruit off I would still need a way to charge the battery via USB.

... or did you mix up the Adafruit board with the power up board? Because there's something with 5V on the Adafruit board.

Right I was saying the board you have looked like it might be an all in one, like the Adafruit Powerboost boards (so charging + the 3.7v -> 5v boost). After digging some more though I'm not so sure.

[Exceen]

Right I was saying the board you have looked like it might be an all in one, like the Adafruit Powerboost boards (so charging + the 3.7v -> 5v boost). After digging some more though I'm not so sure.

But what could I do to make it work? You said it's possible that the problem is caused by the board, but isn't it possible that the problem is caused by the battery as well?

I just don't know a lot about power curcuits and that kind but I have no problem to get another battery just to try things out with it.

[wermy]

Right I was saying the board you have looked like it might be an all in one, like the Adafruit Powerboost boards (so charging + the 3.7v -> 5v boost). After digging some more though I'm not so sure.

But what could I do to make it work? You said it's possible that the problem is caused by the board, but isn't it possible that the problem is caused by the battery as well?

I just don't know a lot about power curcuits and that kind but I have no problem to get another battery just to try things out with it.

This page lists a bunch of specs for what looks to be the board you have:
https://translate.google.com/translate? ... rev=search

It mentions the max output current as being 500mA. So that looks to be your issue right there: 500mA just isn't enough to drive both the Pi 2 and a screen, from what I've seen. I think you'll need a different board.

[Exceen]

This page lists a bunch of specs for what looks to be the board you have:
https://translate.google.com/translate? ... rev=search

It mentions the max output current as being 500mA. So that looks to be your issue right there: 500mA just isn't enough to drive both the Pi 2 and a screen, from what I've seen. I think you'll need a different board.

Alright, thank you!

So it shouldn't be the battery in any case? How many mA do you think do these two devices need? Is there a simple way to find it out?