A project failure due to technical reasons - a supercapacitor problem

RE: A project failure due to technical reasons - a supercapacitor problem

kkazem — Mon, 17 Aug 2020 03:00:26 GMT

Sounds like the circuit needs a power mosfet to isolate the supercaps from the controller. WHen the controller goes to sleep, it can signal the mosfet to turn off, thus removing the supercap voltage from the controller and allowing the proper shutdown.

RE: A project failure due to technical reasons - a supercapacitor problem

Former Member — Tue, 14 Oct 2014 21:43:42 GMT

I am working on a similar project: A supercapacitor UPS for Raspberry Pi. The supercapacitors are also in parallel with the 5V power rail but can be (and also must be) isolated when charging or discharging. Here is a video showing how it works:

The supercapacitor UPS for Raspberry Pi - YouTube

You can find the project, the circuit diagram and the datasheet here:

www.juice4halt.com

RE: A project failure due to technical reasons - a supercapacitor problem

Former Member — Thu, 04 Sep 2014 13:39:32 GMT

The microcontroller on board needs about 60 seconds of power so that it could perform an orderly shutdown, store transactional data, etc.

That's quite a long time. Are you using a traditional file system for this? What is the RTOS involved? Reducing that time can mean reducing or eliminating the supercap.

--Thom

RE: A project failure due to technical reasons - a supercapacitor problem

mcb1 — Fri, 22 Aug 2014 22:59:20 GMT

Sounds like it needs something to isolate the supply (ie supercaps from the micro) so it can do the power down.

Mark

RE: A project failure due to technical reasons - a supercapacitor problem

johnbeetem — Fri, 22 Aug 2014 20:17:44 GMT

This is an excellent example of why a microcontroller needs a reset pin that actually resets the device. Hard reset. Same as power cycling.

Alas, reset is too often left as an afterthought or something for the summer intern to do.

RE: A project failure due to technical reasons - a supercapacitor problem

DAB — Fri, 22 Aug 2014 19:48:01 GMT

Looks like a good job for a watchdog timer and programmable dummy load circuit.

That or put a couple of pins out to let people test their voltage tolerance while it discharges through your fingers.

DAB