I have a POE splitter capable of delivering a maximum of 1A at 12V. This device is intended to power a Raspberry PI 3B+ and a 3.5 inch hard drive. The Pi gets the 5V from a DC to DC step down converter, and the hard drive utilizes the 12V to drive the motor, and it is connected to the Pi via a USB to SATA adapter. This arrangement consumes on average 10W at full load, so I have 2W "to spare".
As expected when the hard drive spins up the platters, the instantaneous power consumption of the entire arrangement spikes to about 20W for around 2 seconds and it stabilizes at 5s, if connected to the splitter, the device cuts off power as soon as it detects the excess power draw. When the splitter restes and the power returns, the arrangement attempts to start up again and the cycle repeats. So I need to devise something to handle this peak load, and if possible have enough energy to allow the Pi to do a soft power off when the power goes out.
The peak handler would need to limit the power consumption to 12W, deliver power to the Pi and the Hard Drive while routing the rest to an energy storage device. If the power required by the arrangement exceeds the 12W the POE splitter can deliver, it should source energy from the storage. Optionally, the device could be configured to not deliver energy to the Pi until a minimum amount of energy is stored, if super caps are used I'm guessing a simple comparator and a voltage divider could be used given that the energy is a function of the voltage on the caps. Ideally I would want to use supercaps, as I think it will make the circuit much simpler, without the extra complexity using batteries implies.
How can I implement such a device? How should the circuit diagram look like? Related to this I could only find this question (Low power device with high current peak), and I'm not very well versed in "practical" electronics, building circuits and such, so I'd very much appreciate any guidance.
I found the article Supercapacitor Charger with Adjustable Output Voltage and Adjustable Charging Current Limit by LT that describes the use of a LT3663 IC to charge the supercaps at a constant current and output at a constant voltage, this seems to be exactly what I need. I'll evaluate this option and post an update if I get something out of it.