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Automatically balance Supercapacitor leakage in 12V systems

Robert Chao, president and founder of ALD Inc. just engineered and introduced a board that enables leakage current balancing for 12-volt systems used in automotive, gap power and remote monitoring applications.

The board is a six-channel supercapacitor automatic balancing (SAB) PCB. The SABMB6 balances any size of supercapacitor with zero added power dissipation. Each of these PCBs are able to balance up to six supercapacitors stacked in series, ranging in size from six to hundreds of supercapacitors with capacities from 0.1 to 3,000 Farads in voltages of 12 and higher. The design offers ultra-low power dissipation which enables energy-efficient supercapacitor balancing This is ideal for applications that require low-loss energy harvesting, long life, and battery backup or replacement.

The design does not focus on the DC voltage balancing; instead, the ALD method manages leakage current and is independent of the cell capacitance. Leakage current can be affected by many parameters in a supercapacitor, such as operating temperature, aging, initial leakage current input voltage, and the operating bias voltage.

12V battery applications are well suited for this kind of tool. Where six 2V-cells are increasingly used, developers are often required to stack supercapacitors in series or in parallel. This board allows up to six connected cells, reducing the risk of a short circuit and battery failure.

Each six-channel PCB is populated with three ALD9100XX SAB MOSFETs that automatically balance the leakage and voltage of each supercapacitor cell connected in series. Optional reverse-biased external clamping power diodes (Schottky rectifiers) can be installed when necessary across each SAB MOSFET to clamp surge current transients. ALD also has a blank SABMB6 PCB for customers to insert their own SAB MOSFETs.

ALD already has two- and four-channel SAB PCBs, the SABMB2 and SABMB16. The boards can be cascaded with mix-and-match configurability to balance multiple series stacks, i.e. combining ALD’s two-, four-, and six-channel PCBs as required.

This is a simple, out-of-the-box, plug-and-play PCB solution reducing time-to-market for existing and emerging applications. No electrical engineering expertise or board design is required; the user has only to mount the PCB and wire the appropriate connections from the SABMB6 board to the respective supercapacitor nodes.

The compact PCB is made from RoHS-compliant FR4 material, and measures 0.6 × 1.6 inch (15.24 × 40.64 mm). It is rated for operation at the industrial temperature range of -40 to +85o C. The product can be used for evaluation, prototyping, or production. Prices range from $12.20 to $38.97 each.

Visit the ALD website for more information.

4 comments on “Automatically balance Supercapacitor leakage in 12V systems

  1. DaveR1234
    February 27, 2019

    Unless the balancing FETs are big, it doesn't appear that they can maintain balance during charging and discharging.  In an automotive application, these currents can be in the tens or hundreds of amps.

  2. Hooey0
    February 27, 2019

    DaveR1234 – Your question comes up quite frequently. As you correctly noted, these FETs are neither capable of, nor intended to carrying either charging or discharging currents. They are only there to balance the l eakage currents . The leakage current in a particular supercapacitor, or any capacitor for that matter, can vary from capacitor to capacitor, and also with lot, time, temperature, phase of the moon, etc.

    It's no different than when you have a high voltage application and you only have lower voltage rated capacitors. When you stack the lower voltage rated capacitors in series, you need a properly sized and rated shunt resistor across each one in order to to balance the input high voltage across each. That way, none of the capacitors will have a voltage applied to them in excess of their rated value.

    If you check out the higher voltage supercapacitor modules, they will specify the “standby current”. This value will give you a clue as to whether the balancing is active, as in the FET configuration, or passive, as in the shunt resistor architecture. The shunt resistor architecture is typically more reliable, given proper resistor selection, but comes at a cost of a higher standby current.

  3. Michele Kinman
    February 27, 2019

    SABMB6 board only balances supercapacitor leakage current. It does balancing charging and discharging current. Additional technical data is available at http://www.aldinc.com 

     

  4. Steve Taranovich
    February 27, 2019

    @Michele Kinman—thanks for that clarification Michele!

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