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DC to DC Converter

Former Member

I want to run my RPi from DC sources.  (1) 12 volt sealed cell battery.  (2) 2 to 4 cell lithium packs, and (3) perhaps even a set of AA batteries.  As we know, the RPi gets glitchy if not running right around 5v, with a load applied.  Therefore I am looking for a converter (or converters, if one is needed for each situation) that will work with the above sources.  With the 12v and lithium batteries I'll need to set a cut-off voltage, so I don't kill the battery.  If the output voltage can't be maintained at 5v when under load then I'll need a method of tweaking the output for a given load situation.  Obviously, since this is for an RPi project, I don't want a converter that is the size of a PC power supply; the smaller the better.

 

Are there such off-the-shelf converters that I could use and if so then can someone point me to them?

 

Thank you in advance,

Andrew

Parents

  • Andrew and Morgaine,

     

    It is kind of easy, but it all depends on how much electronics you're into. The trickiest part is if you want to be able to charge the batteries while using the R-Pi.

     

    So, let's drill into it! Powering the R-Pi:

     

    (1) 12 volt sealed cell battery.

     

    This is the most easy one: a linear regulator (LM7805) with a heat dissipator and 2 bypass capacitors should do the trick.

     

    (2) 2 to 4 cell lithium packs

     

    It depends... with the packs in series  (2S or 2P2S) you have between 5.6V and 7.3V. In that case, the voltage is too low for a 7805.

    The circuit is almost the same, but using a LP2954-5V or a LM2940CT-5.0, the last one being more common. A 2S2P pack would drain in around 1-2 hours.

     

    (3) perhaps even a set of AA batteries.

     

    I would go for 4 AA batteries and a LM2940CT-5.0. The problem is that they will discharge very quickly and the system will shutdown.

    The most beautiful solution I can think of is a 2AA pack running thru a LT1302 boost converter (see the Minty Boost http://www.adafruit.com/products/14). The main problem is that they would drain in around 1 hour...

  • in reply to Former Member

    Rafael, although I know that sealed lead-acid batteries recombine their H and O  so that outgassing through the pressure release valve should occur only rarely or never, I remember an issue I encountered while researching uninterruptible power supplies.  They're pretty universally spec'd to require ventilation, despite using these "sealed" batteries.  This makes me anxious.

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  • in reply to Former Member

    Rafael, although I know that sealed lead-acid batteries recombine their H and O  so that outgassing through the pressure release valve should occur only rarely or never, I remember an issue I encountered while researching uninterruptible power supplies.  They're pretty universally spec'd to require ventilation, despite using these "sealed" batteries.  This makes me anxious.

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