PHOTOS: DAVE LOCKHART
A pair of Thunder Power G6 ProLite 25C 5S 5000 Li-Po battery packs (above left) will be used to power the Neu F3A-1 motor in Yuri. With a modest current rating (by today’s standard) of 25C, the text discusses why this Li-Po is preferred for Pattern applications. At the relatively modest average power output Yuriwill
not be the best pack for hotter setups (Neu F3A-1 or Plettenberg 30-10 Advance). Manufacturers provide specifications for dimensions (not critical with Pattern planes), weight, capacity, and discharge ratings (“C-ratings”) for both continuous and “burst” (generally accepted to be 5–10 seconds) operation. Quite honestly, it is very difficult to assess
likely battery performance based on manu- facturers’ specifications due to the variable methods used to determine ratings (even weight can be misleading depending on wiring length). I personally pay very little attention to manufacturers’ discharge rat- ings (“C-ratings”), especially the burst rat- ings, except when comparing packs from the same manufacturer. As an example, consider a 5S Li-Po pack
that weighs 600 grams. Manufacturer “A” uses testing methods that determine the pack is capable of 20C continuous discharge with a capacity of 4000 mAh, and therefore able to discharge 80 amps continuously (20 × 4000 mAh = 80 amps). Manufacturer “B” tests a similar 5S 600 gram Li-Po pack and determines the pack is capable of 16C con- tinuous discharge with a capacity of 5000 mAh, and therefore able to discharge 80 amps continuously (16 × 5000 mAh = 80 amps).
Seemingly, the pack from “A” has better
power density (more amps available for the weight) while the pack from “B” has better energy density (more capacity available for the weight). The best pack for Pattern is the one with the best combination of ener- gy and power density, and this is best eval- uated by the voltage of the pack under load in flight (at the beginning and end) and the temperature of the pack at the end of the flight (lower internal resistance packs are better as they will generate less heat for an equal amount of power delivered). My apologies to any of the engineering types objecting to my no doubt gross over simpli- fication of terminology. With a more specific look at the anticipat-
ed “feeding” requirements for Yuri, on an 80°F day, Yuri’s Neu F3A-1 will peak at about 90 amps (3400 watts) static and 82 amps (3100 watts) in the air at the begin- ning of a flight when fed by a healthy pack. An average FAI Preliminary (P13) sequence flown in moderate winds at an ambient tem- perature of 80°F will consume approximate- ly 3300 mAh at an average discharge of 33 amps. Flying style, airframe weight and
FLYING MODELS
operate at, the “sledgehammer” approach (above right) of high discharge rated (65C) Li-Po battery packs would minimally increase the power output but would increase life cycle longevity at the expense of added weight (approximately 5 ounces) versus more appropriate 25C packs.
drag, wind conditions, and ambient temper- ature (Li-Pos are more efficient at higher temperatures), can substantially increase/ decrease the amount of mAh used, but the given numbers will suit Yuri quite well. The “gold standard” for Pattern packs for
many years has been the Thunder Power ProLite series of Li-Pos. The current G6 (sixth generation) ProLites are rated at 25C continuous and 50C burst, which equates to 125 amps and 250 amps for 5000 mAh cells. This is clearly more discharge capacity than the 33-amp continuous (7C) and 82-amp burst (18C) power levels Yuri will operate at. In fact, those relatively modest power level requirements are met, on paper at least, by virtually all Li-Pos currently sold. The real reason the ProLite series are the
gold standard is because they have both good energy density and power density and maintain relatively high voltage under load in comparison to other packs of equal weight (1180 grams for the pair of ProLites). At this point, it should be no surprise that a pair of 5S 5000 Thunder Power ProLite G6 packs will be used for Yuri. In anticipation of Yuri seeing many
flights, it is worth noting that the expected number of flights from a Li-Po pack is pret- ty directly related to the discharge depth and increased heat that comes with it. Quite simply, for life cycle longevity, discharging 50% is better than 60%, which is better than 70%, etc. While the 5000 mAh capacity is more than sufficient for the average Pattern flight and substantial weight (approximate- ly 4 ounces) could be saved using ProLite 4400s, the 4400s would have substantially less cycle life (perhaps as much as 30% less), and would produce slightly less power (es- pecially at the end of a long flight). It is also worth noting that higher C rat-
ed packs (generally heavier) will generally have a greater life cycle when operated at the same power level since the average amp draw will be less (as the voltage under load is higher) and the amount of heat generated during discharge is less (higher C rated packs generally have lower internal resistance). The remaining task to complete the pow-
er system is literally connecting the parts. Connectors are sources of resistance and are potential failure points, so using the smallest number of high quality connectors is the goal. I prefer to directly solder the mo- tor and ESC wires together to save weight and eliminate these connectors. Should a
PHOTO: DAVE LOCKHART
High quality connectors are essential for efficiency and reliability. Poor quality, worn, or dirty connectors can add substantial resistance causing a loss in power and potentially high heat buildup leading to component failures and in extreme cases, fires.
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Schulze style ESC be used, or connectors be desired between the motor and ESC, high quality “bullet” style connectors of 3.5 mm size are available from Schulze, Castle, and Neu. For connection of the ESC to the motor pack(s), a number of options are available. Anderson Power Poles, bullet connectors (5, 5.5, or 6 mm sizes), Deans Ultra Plugs, and E-flite EC-5 style connectors are all high quality connectors that can be used between the ESC and motor pack(s). Each connector style has pros/cons. I prefer Deans Ultra as they are polarized and have large surface contact area and have proven to be very durable after many plug/unplug cycles. The downside to Ultra Deans is that they
are not the easiest to work with, especially with larger gauge wiring (10 AWG, bigger than will be used for Yuri). Anderson Power Poles require the use of a special crimping tool (a good option for those adverse to sol- dering). Bullet style connectors have the most contact area between the connectors and wires, but are not polarized making it possible to do some incidental “welding” if the correct plugs are not mated together. Various plastic housings can be added to eliminate this possibility, and this in essence is the EC style of connector.
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