raven_squire wrote:I am using the raspberry pi3 on an Atrix lapdock and want to use a capacitor to make sure the pie will stay powered up when power is removed for 3 seconds (accidental lid close).
I assume it will go in the range of 5F or more. Im powering a Rpi-zero during shutdown for a three or five seconds during shutdown from 2F and the voltage drops during that from 5,2V to 4,6V. The current of this setup is only about 200-300mA. A RPi3 (and more additionally components) will pull much more of course ...
raven_squire wrote:A 1000uf capacitor was needed to boot without the lightning bolt coming up on the screen. This tells me that there is not quite enough power being supplied by the lapdock.
Could I use something like a bunch of 4700uf capacitor? At what point would too many capacitors become a problem?
Remember that a very big bunch of capacitors will draw a high amount of current in the power-on-moment. Or if you can not deliver this current, it would take a longer time. Remember also, that it will take a very long period to, after "switching off" before these capacitors are discharged enough, to leave all your components in a defined state.
raven_squire wrote:I am also thinking about some getting micro usb break out cables so that I can measure the resistance from my home made power cable just in case that is causing power problems. What resistance value would be troublesome?
If you can measure it under "normal home conditions" it will be probably to high! 0,05 ohms in plus and 0,05 ohms in minus give at 2A a drop of 0,2V. And it is not easy to measure 0,05 ohms with a normal multimeter ... There exists milliohm-meters for such. (See also four-lines-method.)
A step-up will also not help very much in this case ... if capacitor discharges, voltage goes lower ... to keep output of step-up constant it will draw higher current (Because you can not make power from nothing!) ... higher current means faster discharging again ...