SV-BAT-320 safety

[RockFLY]

I have a question about SV-BAT-320 battery packs please.

Considering a Li-ion battery fire is self-sustaining and can't be put out with a fire extinguisher, for in-flight safety I wish to know if every 18650 cell (x 6 I trust) in the SV-BAT-320 pack has its own internal protection circuit, or whether the pack as a whole is electronically protected by the SkyView system please?

The wires are also shorter than I would like for safe positioning of the battery packs.  I gather lengthening the wires (which the instructions say not to do) increases the resistance, so couldn't I user larger gauge wire to overcome that aspect? If not the reason, why can't the wires be lengthened please?

Kind regards, Stuart

 

[dynonsupport]

The battery itself has a single internal protection circuit which monitors each cell and disables the battery as a whole if needed. This is the standard way LiIon batteries are protected. I'm not aware of systems that protect with completely independent circuits per cell. The built in protection is for cell over and under voltage, as well as battery over current.

SkyView itself is also designed to be somewhat intrinsically safe. There are no voltages inside SkyView that can over-charge the battery. In fact, SkyView's battery is never fully charged (and cannot be) in order to maximize its shelf life an stability.

Dynon does not recommend extending the wires because of resistance losses, as well as possible electrical noise concerns. If you do choose to extend the wires, you need to make sure you keep the resistance of the wire below 0.05 ohms, and it will be up to you to deal with the possible noise created by the current transients on this wire when charging.

 

[RockFLY]

Thanks, but I'm confused.

How can it be possible that the "battery itself has a single internal protection circuit which monitors each cell and disables the battery as a whole if needed", but simultaneously, you are "not aware of systems that protect with completely independent circuits per cell"?

18650 cells are either protected (internal circuit board shrink-wrapped into the base of each cell) or not. If not, the entire pack requires a circuit for over/under-voltage protection etc, which is unlikely to be able to detect a 'rogue cell' within the pack itself ... unless there is a cell balancing circuit too (where any higher voltage cells are loaded to drain - balanced down - to match the lower voltage cell(s) to within a few millivolts).

I have a failed pack (>3 years, so not covered by warranty). With the cover off, it appears that the SV-BAT-320 pack is protected by a circuit board, but there aren't enough wires or space under the shrink-wrap for a battery balancer as well. The writing on the pack says 11.1V (three 3.7V pairs in series) and 4400mAh total capacity, so I guess it would be possible to use more expensive, high-quality 18650 cells (3400mAh Panasonic cells for example) to increase run time well over 60 minutes, probably more like 100 minutes, but the extra energy = extra burn time and/or ferocity in the event of a fire. That said, even a 2200mAh cell fire is ferocious and I would rather trust high quality Japanese 3400mAh cells than poor quality Chinese 2200mAh cells!

Thoughts?

 

[dynonsupport]

The confusion was that I interpreted your question as if each cell inside had it's own internal protection circuit built in (the ones with the internal circuit board). The cells are not these types.

The battery pack has a cell balancing and protection circuit. It monitors each cell voltage directly, and can shut off if any one cell is incorrect, but this is done by a single circuit, not individual ones per cell. I'm not sure what to say if you don't think there aren't enough wires. There are 4 connections to the pack which is all you need to verify and balance 3 cells.

The pack is a 2P3S pack. To the protection circuit, this looks like a 3 cell pack. The cells are welded in parallel at the factory and cannot have different voltages, so they don't need to be monitored as 6 cells, but rather as 3.

Dynon has sold over 10,000 batteries between the D10/D100 and SkyView series, and all have individual cell voltage checking, as well as pack current protection for discharge and charge.

 

[RockFLY]

Got it, now I understand and that makes perfect sense, thank you! I am far more comfortable knowing that the three cells (welded pairs) are balanced.