Featured Articles
Announcing Pi
Technical Specifications
Raspberry Pi FAQs
Win a Pi
Raspberry Pi Wishlist
Actions
Forum Thread Details
  • Replies 23 replies
  • Subscribers 670 subscribers
  • Views 3867 views
  • Users 0 members are here
Related

Battery-powered Pi?

mgt6910

I would like to use my Pi on a robotic platform, for which an onboard power supply will be

necessary. I  have a rechargeable 6-volt battery. How can I regulate this down to 5V ?

  • in reply to rew

    Roger, I wasn't intending to suggest switching from serial to parallel I was suggesting switching from batteries in series to charged batteries being isolated from the 'string' via the switching mechanism. So battery_bank_initial =  b1 --- b2 --- b3        one of those 3 batteries becomes charged the others not so - battery_bank_part_charged = bX --- bX --- (bZ)(isolated battery bZ). .

  • in reply to bodgy

    That suggestion is almost as complex as switching from parallel to series.

     

    It does solve the "large currents because you connect non-equal-batteries" problem.

     

    Hmmm.... Interesting indeed. For each cell, the "incoming" connection is the "bottom of the next-higher" cell. That needs to be connected either to the TOP or the BOTTOM of the current cell. You can use logic level N-FET for the connection to the bottom of the current cell. You have 4.2V available for when this is neccessary. You can use a P-FET for the connection to the top of the current cell. You have (at least) -3.0V available for that when this is neccesary. If you use a weak pulldown on this, you might be able to recover from "drained-too-far" cells.

     

    You could use an attiny45 to control each individual cell. Each attiny measures its internal 1.1V reference voltage with respect to its own VCC (the cell voltage). If that drops below 268 (out of 1023, the full range of the ADC), the cell voltage is at 4.2V. Very interesting project. :-)

    (A dual optocoupler, or maybe some capacitors can provide level shifting communications channels with the "main" processor).

     

    Hmm. Attiny processors (like the '44 and '45) have increased in price 25% over the last two months. Weird!

  • in reply to rew

    For a high efficiency small boost convertor you could consider the TI63020 (Farnell 1815784) - synchronous so no series diode, very fast so tiny inductor. Downside is that it's in a package that some will find difficult to prototype and it is not very cheap.

     

    Michael Kellett