Nelectra is crowdfunding a supercapacitor based micro-UPS for Raspberry models B and B+, enabling brownout protection and “last gasp” shutdown sequences.
Bratislava, Slovakia based Nelectra’s first product was a generic “Juice4Halt” supercapacitor based micro-UPS (uninterrupted power supply) module aimed at single board computers used in industrial and embedded applications. The adapters protect the SBC’s operation from power brownouts and failures, and support so-called “last gasp” applications in which the SBC performs a fairly lengthy shutdown procedure. Today, the company launched an Indiegogo campaign to raise funds for manufacturing of a pair of Juice4Halt models that stack directly onto the 2×13-pin GPIO headers of Raspberry Pi SBC models B and B+.
How it works
The two Raspberry Pi Juice4Halt models share a common design, shown in the figure below, but differ in where the supercapacitors are installed. A 26-pin GPIO header connects to the Raspberry Pi, and the supercapacitors are contacted via holes on the PCB. You can purchase this version with several types of supercapacitors.
The Juice4Halt board integrates an Atmel ATmega328P microcontroller running open source Arduino code. A bidirectional step-up/step-down converter mediates between the stable 5C supply rail and the supercapacitors. During charging, the step-down mode transports power from the external supply to the supercapacitor. In case of power failure, the Raspberry Pi SBC is powered by the converter working in step-up mode. The second, front-end step-down converter converts input voltage down to 5.1V for the 5VC rail.
Thanks in large part to the use of supercapacitors instead of batteries, the Juice4Halt module is claimed to offer the following features and benefits:
- 1 minute backup time for a safe shutdown
- 12 second protection against short-term power failure or brown-out
- High reliability of operation with peripheral devices attached to the 5V supply output (no risk of tearing down the power, e.g. at hard drive spin up)
- No battery maintenance
- No battery holder, no mechanical contacts
- Shock and vibration proof
- PCB to PCB mounting using edge-plated contacts
- No hazardous materials for disposal — non-toxic materials
- Wide operating range (-40 to 85°C )
The supercapacitors used by the Juice4Halt UPS fall somewhere between standard capacitors and batteries. They offer more energy density than other capacitors, storing more energy per unit volume or mass, but have less than half the power density (energy per unit time). Compared to batteries, supercapacitors have only about 10 percent of the energy density, but have 10 to 100 times more power density. They’re often used in vehicle power systems, such as recovering energy from braking, storing energy short-term, and providing burst-mode power delivery.
According to Nelectra founder Pavol Sedlacek, the Juice4Halt module offers the following basic modes:
- Charge — When charging the supercapacitor using the step-down converter and external power supply, the SBC stays disconnected from 5V power rail until charging is complete.
- Normal — When the SBC is powered externally, the supercapacitor is directly connected to the 5V output to ensure reliable operation without short-term power failures or brown-outs.
- Brownout — When voltage falls below 4.9V, the external supply is disconnected, and the SBC is powered from supercapacitor. When voltage falls below 4.75V, the external voltage is checked, and when external supply voltage is present, it reconnects to power supply and charges the supercapacitor. Otherwise, it enters shutdown mode.
- Shutdown — When external power is still not present after brownout, the SBC is powered from the supercapacitor via the step-up converter. After finishing shutdown procedure or when the voltage at the supercapacitor falls below 1V, the SBC is disconnected from 5V supply rail. Charging resumes once external supply voltage returns.
For more detail: Raspberry Pi supercapacitor micro-UPS seeks funding