High Cell Count Packs

Sonny P. Writes:

What is the proper way to charge a 14 cell A123 battery?

Sonny,
I take from your question that your concerned about the large cell count and not the rules of charging this particular chemistry of pack.

Since you need to balance it from time to time, it should be charged as multiple lower cell count packs from time to time. All rules must be observed regardless of cell count or type of lithium chemistry. So, were I building a 14 cell aircraft pack for myself, I’d build it probably as two 5 cell and one 4 cell packs. In this way I could hook up to my balance charger and balance it. If you have a charger capable of balancing 8 cells, you could do two sevens. I am un-aware of any chargers capable of balancing more than 8 cells even though there probably are chargers that could manage a non-balance charge of 14 cells. Even if you owned one, you’d still want to be able to break the pack down (electronically) and charge it in shorter segments from time to time to maintain balance.

In the case of two 5 cell and one 4 cell packs for example, The pack could be literally 3 packs that are put in series in the model. You might use Anderson Power poles to do this to minimize the number of connectors needed. Each pack would of course have it’s own balance harness for plugging into the node port (balance port) of you charger.

It would also be possible to build the pack as one 14 cell block with one set of output wires for the ESC. However, you could put tap wires in that are heavy enough for charging at the union between the 5th/6th cells and 10th/11th cells. You would build in balance harness respecting this same cell spacing. So that “electronically” (if not physically) you have 3 battery packs, two 5’s and one 4. NOTE! This type of pack bould, the central tap wires would be positive or negative depending on which segment you were charging.

With a 14 cell charger you might be charging through the main output leads while your at the flying field. Yet, when your prepping the model for a trip to the field, you would be able to charge the pack in 3 steps (one step for each pack division 5 cell, 5 cell, 4 cell) with balance harnesses connected to your charger. In this way you’d be getting regular balance charges to keep all cells equalized.

Happy Flying!
Dave

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