Why bother with resistor when balancing?

[Roswell Bob]

I am familiar with circuits that switch resistors in and out to balance cells. I am curious to know of any balancers exist where a mosfet is used in the active region. A mosfet can dissipate as much power as a similar size resistor and the power can be varied as necessary to balance the pack. A simple op-amp can be used to control the gate voltage so as to control drain current. A grade A battery would probably not benefit from such a device, but some of the lesser valued cells could be coaxed to work where otherwise they may best be scrapped.

So any active balancers being used?

 

[FilterGuy]

So any active balancers being used?

The term 'active' balancer normally refers to a system that pumps energy from a high voltage cell into a capacitor and then dumps that energy into a low voltage cell. There are a lot of stand-alone active balancers and the JK line of bms's use an active balancer circuit.

 

[Roswell Bob]

The term 'active' balancer normally refers to a system that pumps energy from a high voltage cell into a capacitor and then dumps that energy into a low voltage cell. There are a lot of stand-alone active balancers and the JK line of bms's use an active balancer circuit.

Yes, thanks, I mis-spoke when calling it active. I am a little bit familiar with the capacitor method in principal, although I wonder about it's efficiency. When moving charge from one cap to another a good portion of the energy is lost, although it should be better than straight out bleeding charge off whether resistor or transistor junction. I have seen 8S systems with a charger on each cell. These are used on commercial jets. They seem to work well. The real solution i suppose is to use quality cells that need little coaxing to balance. Thanks.

 

[Capt Bill]

A grade A battery would probably not benefit from such a device, but some of the lesser valued cells could be coaxed to work where otherwise they may best be scrapped.

Exploring this thread topic because I have some lesser value 280Ah EVE cells I'd like to add to my 24v x2 battery banks running on Chargery BMS8T w 300 Amp Shunts. I have a third set of 280Ah (below par cells I rotated out after some below 2.5v mistakes) with some cells that peak high above the good cells (above the 3.65v) at top charge cycles (unless I drop bulk charge down to float charge value?) PLUS others that show big drops in voltage at < 3.0 cell volts (showing reduced Ah). ... Researching JK BMS with Active Balancers now, and stand alone active balancer options. ... What I like about my Chargery BMS8Ts are: The LCD with 5 pages of battery info. / plus 2 pages of parameter adjustments, plus two channels of relay release triggers (one for Charge side triggered relay releases/ and the other for Dis-charge side triggered relay releases). ... See some folks trying out JK's with Active Balancer, wondering if those have the two channel triggers or not? ... what total amp options they have; and what the LCD, BT, and/ or PC options are for adjustment and views of info. ... I will be watching this thread for more info., plus seeking more info. via DIYSolar's amazing Search engine :+) Wondering what my best option might be for putting my below par cells online with two good 24v 280Ah battery banks / to then have 3 battery banks on three separate BMSs. ... I'd like the idea of active balancing. and would prefer a BMS that has separate triggered / charge side and discharge side release if possible (but that might get canned/ for a smart BMS w active balancer. LOOKING at my next learning curve of options :+)

 

[RCinFLA]

Chargery 16T BMS uses MOSFET's to provide 1.2 amps of balance current dump.

 

[Capt Bill]

Chargery BMS uses MOSFET's to provide 1.2 amps of balance current dump.

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Would love a web Link to sales page for the price, specific model, & data specs page?

 

[Substrate]

Use of mosfets also depend on the quality of the manufacturer and design paramaters around it.

That is, if a mosfet blows, does it fail open or shorted? Those that fail shorted obviously kill a cell. Those that fail open no longer do their job.

The hope is that the manufacturer has a quality designed product, and maintains that quality - albeit it is tempting to build up a name for itself, and then later cut corners with cheap mosfets or poor design in later models.

Ah, such is life I suppose.