Originally Posted by dharban
I have been testing various combinations of ThunderPower 65C packs (850 and 1300, 3S and 4S packs) under carefully controlled conditions on the bench. (These tests were primarily to test various motor/propeller combinations, but I gathered battery data while I was doing this.)
The takeaway from these tests is my recommendation that these cells be used at LESS than 50C rates for 30 second ALES motor runs. Under these conditions, a battery starting at 80 degrees and operated in an unventilated glider nose will have about a 40 to 45 degree temperature rise with max temp being realized about a minute after the end of the motor run. While 125 degrees sounds pretty warm, it is not as hot to the touch as you might think. And manufacturers generally recommend that operating temperatures not exceed 140 degrees. Factor in a 95 degree day, and you are getting pretty close to the manufacturer limit.
Practically, this means that you can operate the 850's at about 42 amps (400 or so watts for the 3S, 500 or so watts for the 4S). [In actual operation at these rates, the output voltage will be somewhat lower than the nominal voltages]. The 1300's are good for about 65 amps (650-700 watts for 3S, around 900 watts for 4S).
I have had good results with the Thunderpowers operating them at 50C or below with no failures of any packs since they were introduced (a far and a half ago?).
I am just setting up for some in-plane tests using my Eagletree V4 and I will update when I get those finished. I intend to try a little ventilation on the fuses to see if there is any difference -- I do not suspect that it will make much difference since the temperature buildup occurs over a short period.
I operate these packs at the high rates cited because I am trying to balance planes which have very narrow fuselages with long noses which stick the motors out pretty far. For the less finicky, keeping these 65C packs down in the 35C to 40C range will give you more launches and, as Marc suggests, lower operating temps.
BTW: I have attached graphs from one set of tests on an 850 4S pack which shows about 600 watts of output on a 30 second motor run and a 45 degree temperature rise from 85 degrees. This is pretty typical of my other results. An 850 3S pack should easily put out 450 watts without overheating.
Great Info Don...right in line with what I need to know with my Supra-E I'm working with just now...I have a Neu 1506-5200-2d-6.7 which is rated at 12 Volts running on a TP 65C 3s 1300. I originally went with a 16x10 with the result of the ESC cutting off after 10 seconds or so when the battery voltage drops below 9 volts (tried two batteries). Runs pretty well on a 2S 65C 1300 with a 17X10 but I need more thrust than this. I am stuck for the time being with the relativly low voltage 1506 so I intend to go with a 15x8 prop to bring down the current and prevent the low voltage cutoff.
I'l love to get in the future an 1107 like what you use which woul be 2.3 oz lighter and allow a larger prop with lower current.. anyway I really appreciate the work you are doing.