Just curious for those of you who have tested the 2-battery setup, what the ambient temperature was vs. what you measured in the batteries. Basically what I am looking for is the total increase over ambient. Supposedly 50c is the damage threshold, and I will be routinely taking off where it’s 32 and higher these days.
Even in the winter 4 packs will get above 60c while 6 packs stay below 55c. I recommend 4 packs as the bare minimum. Specially if you are starting with them already hot.
Did you measure them in-flight or afterwards? And what did you use for the reading?
I used an infrared temp gun immediately after flight. That means they were even hotter during flight.
Huh. After a ten or twelve minute flight my four 6s packs are barley warm. Certainly not 60 degrees C. Even with ambient near 20, when I’m unstrapping them they’re only warm to the touch. If guess maybe 30-40.
4 packs after a 20 minute flight will be much warmer than after a 10 minute flight. I’d rather carry 6 packs and fly 25 or more minutes and not have to worry about heat than to have 4 batteries and only fly 10 minutes.
gotta get me a six pack…
Why the batteries are getting hot?
We have to look at the “true C rating” of the batteries…
One mayor factor is the internal Resistance of your battery cells and voltage drop. For example a 12S setup with 5000mAh packs and an iR of 2 leads to a total voltage drop of almost 3V when drawing the continuous current. The voltage drop of the whole pack/setup. This value is useful to predict the voltage drop during load in flight. So even with fully loaded packs (4.20V per cell) the ESC just gets 47.4V instead of the nominal voltage of 50.4V.
The iR of a battery changes depending on temperature, discharge rate and dynamic. I used 2 mOhm resistance per cell because this is what normally new packs will have. I do have packs which have just between 1.2 and 1.6 mOhm resistance. The problem is if your packs are well used it could be as high as 4-6 mOhm resistance and your usable Amp draw will drop significantly.
We have to differentiate as well between the X 4 with 180kv motors and 12S batteries and the X 4 with 150kv motors and 14S batteries or 12S batteries!
The x4 180kv uses at climbing 320 A with 12S batteries
The x4 150kv uses at climbing 250-260 A with 12S and 14S batteries
12S battery 22000mAh = usable max Amp draw 257 A
12S battery 44000mAh = usable max Amp draw 363 A
12S battery 66000mAh = usable max Amp draw 445 A
14S batteries will have the same usable Amp draw as the 12S - just the voltage drop will be different.
If you use 4 packs with the KV180 12S you will use at climbing 88% of your max Amp draw.
If you use 6 packs with the KV180 12S you will use at climbing 72% of your max Amp draw.
If you use 4 packs with the KV150 14S or 12S you will use around 71% of your max Amp draw.
If you split 4 packs with the KV150 12S for 2 motors/esc’s you will use 48% of your max Amp draw.
You will have cooler battery packs if you reduce the the Amp draw - that’s it.