Raspberry Pi, portable power supply


9 posts
by ksieluk » Sat Nov 03, 2012 11:35 pm
Hi guys,

Project that I am currently working on, determines useage of portable power supply for my Raspberry Pi. As I read, RPi works on 5V, where current is ~500mA. Additionaly, I need to mention that there is going to be wireless USB WiFi card plugged into USB slot and maybe camera. That will be additional +300/400mA.

My solution is to use 9V rechargable battery and to stabilize that tension with LF50CV. In datasheet there is information that output current limit for that device is 1A.

Shall I pay attention to some other parameters of LF50CV? Here is the link to datasheet: http://www.datasheetcatalog.com/datasheets_pdf/L/F/5/0/LF50CV.shtml

Or maybe someone of You used other solution of portable power supply for RPi and can share with me his idea?

Thank You in advance for answers.
And I do apologize for all language mistakes I made;)

Greetings,
ksieluk
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by redhawk » Sat Nov 03, 2012 11:55 pm
"My solution is to use 9V rechargable battery" - bad idea the capacity of a 9v Ni-MH battery is typically around 200mAh it will not power your PI for very long.
A better solution would be to use a 6xAA multi-block pack to make 9v and since one Ni-MH AA is approximately 3000mAh you have a total of 18000mAh to play with. :)

Richard S.
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by ksieluk » Sun Nov 04, 2012 11:02 am
Thanks for fast reply.

I had that aspect in my mind. I am going to buy something like that:
http://www.ebay.com/itm/4-X-AA-3800mAh-NI-MH-Rechargeable-Battery-Green-1-2V-/170912500669?pt=US_Rechargeable_Batteries&hash=item27cb2dcbbd

I had one more question about LF50CV.
How do you think: is it going to be neccesary to use some radiator?

Greetings,
ksieluk
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by exartemarte » Sun Nov 04, 2012 11:28 am
redhawk wrote:A better solution would be to use a 6xAA multi-block pack to make 9v and since one Ni-MH AA is approximately 3000mAh you have a total of 18000mAh to play with. :)

I don't think you do. If one cell gives you 3000mAh at 1.2v then six of them in series will give you 3000mAh at 7.2v, not 18000mAh. You would get 18000mAh if the cells were in parallel, but at 1.2v.
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by drgeoff » Sun Nov 04, 2012 12:16 pm
exartemarte wrote:
redhawk wrote:A better solution would be to use a 6xAA multi-block pack to make 9v and since one Ni-MH AA is approximately 3000mAh you have a total of 18000mAh to play with. :)

I don't think you do. If one cell gives you 3000mAh at 1.2v then six of them in series will give you 3000mAh at 7.2v, not 18000mAh. You would get 18000mAh if the cells were in parallel, but at 1.2v.

Correct. Multiple cells in series do not increase the mAh.
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by ksieluk » Sun Nov 04, 2012 1:21 pm
However, as redhawk mentioned, it is still better solution than 9V NiMh 250mAh.
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by pygmy_giant » Sun Nov 04, 2012 1:31 pm
Ive found lipos work very well but you've got to be careful and use matched chargers, over/under charge protectors and never connect more than one together unless they are both identical and hold the same ammount of charge.

or they can combust - apparently
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by exartemarte » Sun Nov 04, 2012 1:45 pm
pygmy_giant wrote:Ive found lipos work very well but you've got to be careful and use matched chargers, over/under charge protectors and never connect more than one together unless they are both identical and hold the same ammount of charge.

or they can combust - apparently

I have little experience of Li-Po's, but I'm using them in a current project and I have been reading up.

I don't think they are dangerous when used in series, although letting the charge get out of balance can result in damage to a battery. If unbalanced cells are connected in parallel, however, high currents can flow resulting in overheating and possible conflagration - which is also true of NiCds or NiMHs, although I understand Li-Po's do it more spectacularly.
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by ciudadverde » Sun Nov 04, 2012 5:42 pm
ksieluk wrote:Hi guys,

Project that I am currently working on, determines useage of portable power supply for my Raspberry Pi. As I read, RPi works on 5V, where current is ~500mA. Additionaly, I need to mention that there is going to be wireless USB WiFi card plugged into USB slot and maybe camera. That will be additional +300/400mA.

My solution is to use 9V rechargable battery and to stabilize that tension with LF50CV. In datasheet there is information that output current limit for that device is 1A.
This device waste the energy , is linear. In ebay you can buy step-up regulators swicthed from one lion cell 3.7->5v these only waste 10% of energy.
Shall I pay attention to some other parameters of LF50CV? Here is the link to datasheet: http://www.datasheetcatalog.com/datasheets_pdf/L/F/5/0/LF50CV.shtml

Or maybe someone of You used other solution of portable power supply for RPi and can share with me his idea?

Thank You in advance for answers.
And I do apologize for all language mistakes I made;)

Greetings,
ksieluk
Posts: 20
Joined: Mon Sep 03, 2012 11:46 am