Is 20 C enough?

[Paul Taylor]

How much C rating do we need when looking at batteries for a SV 11 size plane?

Seems like the more C’s the more G’s. G’s being grams. 🤣

[Ken Culbertson]

I would be cautious.  Most everybody I fly with uses 25c batteries.  They might work but you might have an issue with boost with an active timer.  I had two 4s 10c 2200 Lipo batteries I got a "great" deal (2 for $25) on the internet.  Both started swelling at around 30 flights on a 45oz plane powered by a Cobra 2820/12 with a fixed rpm timer. Still not a bad deal.  $.46 a flight.

Ken

[Bill Schluckbier]

Lower C rating batteries tend to be lighter so they can save you some weight but you need to be careful.  If you discharge your battery at 10C in principle you would get 6 minutes of run time (60/10) and the battery would be completely depleted. If you do this, the battery will not last very long.  This should be true in principle regardless of the C rating.  When trying to figure out the capacity you need I assume a discharge rate of about 8C; after 5 1/2 minute flight you will have a little more than 20% left in the battery.  You also want to have some excess battery capacity (i.e. mah) because as the battery ages it will not be able the hold the voltage under load as well as it did when new.  As a result, to make the same power, the ESC will pull a slightly higher current. During a normal flight, as the battery drains the ESC will demand higher current levels towards the end of the flight (to produce the same power).

In my experience, most companies inflate the C rating of the products they sell and it is possible that the 20C pack you are looking at is closer to being a 15C pack.  The same applies to the 25C, 30C, 35C, etc. packs.  As Ken suggested, the norm is to use packs with a 25C rating and this probably represents what the community has learned over time.  If you really want to try out the 20C packs I would suggest adding about 10-20% to the capacity you think you need to be on the safe side. Another option would be simply to buy a single pack; try it out and if it works then commit to purchasing more.

I also happen to fly R/C pattern (not well, AMA advanced and learning Masters) and for a long time I used 20C packs of 4400 mah capacity (5S x 2).  When that brand became unavailable I switched to a different brand which offered 30C packs, in this case of 4000 mah.  Both packs flew the model just fine, but the 4000 mah batteries were slightly lighter so performance improved slightly as well.  In both instances the mah consumption per flight was very similar and I was only using about 60% of what the 4000 mah pack offered.  I could probably get away with less capacity but the packs generally last about 3 seasons; not sure that the smaller packs would last as long.

Good luck

[Paul Taylor]

Thanks guys.
Going for more G’s 🤣

[Fred Underwood]

The C rating is the discharge rate, not capacity.  The Capacity the mah that the battery holds.  A 20 C battery will discharge at 20 x Capacity so a 20C battery with a capacity of say 2500 mah will discharge at up to 50 amp/h rate.  If you fly for 5 min and 20 seconds and use 1800 mah on recharge, then your average discharge rate is about 20 amp/hr.  Well below the 50 amp rating.  25C is a commonly used C rating because it works for out output needs and is relatively light and inexpensive.  Also made by many manufacturers.  I hope that I understand and that is helpful.