Is anything wrong with my voltage regulator circuit? - Raspberry Pi Forums

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my end goal power raspberry pi roomba (and plug roomba's serial interface). built basic voltage regulator circuit on breadboard shown here:

image

circuit works great standard batteries. tried 9v battery , 8 aa's (12v), , raspberry pi booted , stayed powered on no problems (no peripherals other hdmi monitor). when plug directly roomba battery, pi begins boot, , gets way desktop, screen begins flicker on , off, , pi crashes (black screen).

took multimeter readings, , here observations.

using 8 aa batteries:
  • with rpi turned off, voltage measured @ battery 10.78v (some batteries presumably weak or dead). on regulated side of circuit, measured consistent 4.97v.
  • with rpi turned on, voltage measured @ battery fell 9.5v. on regulated side, voltage steady 4.94v.
using roomba battery:
  • with rpi turned off, voltage measured @ battery 15.50v. on regulated side of circuit, voltage consistent 4.97v.
  • with rpi turned on, voltage on battery side didn't drop much, 15.35 -- fluctuated quite bit +/- 0.05v. on regulated side of circuit, voltage dropped 4.80v, apparently point @ rpi says "not enough juice" , starts go haywire.
different roomba battery cause more drastic voltage drop? capacitors not enough μf, or much? 7805 task of regulating voltage roomba battery?

the 7805 linear regulator. drops voltage converting excess power heat. roomba battery needs dispose of 10 volts @ more 0.5 amps. 5 watts. unless have heatsink 7805 hot thermal protection comes play.

better use switching regulator this. generate less heat , run time 3 times long.


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