Originally Posted by billdelong
The difference in efficiency is not linear, you will get longer than 33% more run time on 3S of the same capacity compared to 2S, given that you re-gear the 3S appropriately such that both setups run comparable motor temps for respective FDR... both will have similar top speed, but 3S will offer faster acceleration. By far the biggest advantage is that the 3S pack won't be worked nearly as hard and will be less likely to swell and age considerably longer... expect most 2S packs to need replacement around 6 months to a year and 3S packs may last 2+ years before they start to lose noticeable capacitance.
I agree that there will be less current draw, which translates to less voltage drop during hard acceleration, so it will take longer for LVC to kick in.
The point about load on batteries being reduced is true. But it isn't true that *all* batteries will only last 6 months. I have 3 2S Gens Ace that are 3 years old (used to run 4wd SCT) and still have the same IR as a brand new "Zippy" battery with the same capacity and "C" rating.
But I cringe a little when I hear people say that higher voltage is more "efficient".
Efficiency of a motor varies dramatically based on load, and increasing voltage does not change efficiency! If higher voltage was more efficient, the world would be running on 99.9% efficient motors that run on 1 million volts!
The reason why a higher voltage motor runs cooler (but still warm) in an RC car is because it's max output is higher, meaning that it will be maxed out less. If it mostly stays below 85% load, it will not over-heat. This 85% load is where the motor is most efficient, but above 85% and the motor becomes increasingly less efficient, which results in producing a lot more heat. I fact, above 85% load, the majority of additional energy is turned directly into heat, with little increase in output power. (But total heat generated is roughly constant below 85% load...)
Occasionally going above 85% is still okay...but it becomes dangerous when over-loading adds heat faster than the heat can dissipate...like filling up a funnel faster than the liquid can flow out the bottom.
The higher voltage system is like a funnel with a bigger hole...sort of...
The efficiency of a motor is very poor at low loads, and gradually increases as load is increased up to ~85%. Above 85%, and efficiency falls off dramatically.
So the motor that is most efficient is the one that runs closest to 85% max load.
