Super capacitor balancing boards

I am building a small super capacitor module consisting of 10 or 12 cells of Maxwells 360F 2.7V. Do I need to to add anything else to the SABMB910027 auto balancing board to protect my supercaps?
It looks like I can connect 4 caps for each board?
I am open for other recommendations and I am also considering just passive balancing with a resistor.

The cells are to be connected in series!

Hi Marius, welcome to the Tech Forum.

The best method of balancing depends on your application and what is most important to you. Passive balancing with resistors is the simplest and least expensive, but will mean significantly more current draw than active balancing schemes and there is a trade-off between balancing current and balancing capability. The higher your balancing current, the more effective the balancing. You typically need to choose resistors which will allow a balancing current of at least 10 times the capacitor leakage current for reasonable balancing, and it may need to be 100 times for some applications. If this is not a problem in your system, then this is a simple and effective way to go.

If you can’t afford that kind of continuous current draw, then active balancing is the way to go. The Advanced Linear Devices (ALD) cell balancing IC’s are very nice for cell balancing, but you must look at how they are defined to figure out which version is most appropriate. For instance, the SABMB910027 uses the ALD910027, which has a “threshold voltage” of 2.7V. They define “threshold voltage” as the voltage which, when applied between the gate and source, will cause a source-drain current of 1uA. At 2.8V, it will pass 10uA. At 2.94V, it passes 100uA.

The Maxwell BCAP0360 P270 S18 has a maximum voltage of 2.7V and maximum leakage current of 750uA. Based on this, the SABMB910027 would not bypass nearly enough current to overcome the leakage current to prevent overvoltage. Looking at other options, the 2.2V devices will pass 1mA at 2.72V and 3mA at 3.02V. Assuming that the typical leakage current of the BCAP0360 P270 S18 is somewhat less than 750uA, then the SABMB222, which uses the ALD910022SALI might be a better choice.

What you are saying makes a lot of sense. What is the “recommended” highest current these balancing boards can bypass for a longer period of time?

I guess the tables for the ALD 81/9100XX stops at 10mA so it might not be a good idea to have the threshold be as low as 1.7V for the ALD910017. I dont think the continuous leakage current through a resistor will be a problem for my application but I will have to look further into it.

Hi Marius,

The absolute max current for the ALD balancing FETs is 80mA. I wouldn’t want to run this rate continuously, but it shouldn’t need to go anywhere near this level continuously. If you are in this realm, then you may as well go with resistors.

If you want better clamping characteristics using the ALD products, you can parallel them to increase the clamping capability. Additionally, they make another board which uses separate P-channel MOSFETs to amplify this clamping effect significantly – the SABMBOVP series boards. Unfortunately, we do not stock every version, but we do stock the SABMBOVP223, which has very low bypass current below 2.3V and very rapidly increases above 2.3V. Here’s the datasheet for these parts. For your application, the 2.5V would probably be the best choice, but we do not stock that one. However, you could use the information in the datasheet to make your own board using the 2.5V version.