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Ultracapacitor Charge Balancing

Balancer
Balancer

I have finally  got round to designing the balancing circuitry for my ultracapacitor banks, which have a total voltage of 15v when fully charged. The 2600F capacitors have a max working voltage of 2.5v each, so to ensure reliable operation, balancing is required to make sure that each capacitor is charged fully.

The circuit above is a simple shunt regulator, which uses a 2.2v zener diode to regulate the voltage across the capacitor.

A 10W 1Ω resistor is connected to the BALLAST header, while the capacitor is connected across the INPUT. Once the voltage on the capacitor reaches 2.6v, the MOSFET begins to conduct, the 1Ω resistor limiting current to ~2.6A.

Each capacitor in the series string requires one of these connected across it.

PCB
PCB

Below is a link to the Eagle project archive for this. Includes schematic, board & gerber files.

[download id=”5555″]

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SEPIC Regulator Test Rig

Regulator Hookup
Regulator Hookup

Here’s the regulator hooked up with test clips, on the right is the supply from the ultracapacitor bank, while on the left is the output, feeding a 2.3A brushless fan as a test load.

These regulators do get warm, even with no load, with a 2.3A load on the output, the temperature stays warm to the touch.

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Ultracapacitor Voltage Regulation

MuRata Switching Regulator
MuRata Switching Regulator

As an ultracapacitor has a pretty linear discharge curve, some electronics are required to make them behave more like batteries, such as as SEPIC converter.
On the right is a MuRata Power Solutions UQQ-12/8-Q12P-C switching regulator, which will accept a 9-36v input source & output a constant 12v at 8A (96W).