ESC Still foggy.. Motor , esc, batter ....etc..

jtropesjr

New Member
OK, So for response to this vid which is why im here. best vid on this subject yet.... Matching Motor, ESC, & Battery - YouTube

I have a 420 watt 1000kv brushless motor. i want to run a 3s battery. So... 420/11.1=46.6...? Thats a huge esc for a small motor.. right? But, If i want to run it on a 4 cell then its.... 420/14.8=28.3.. ? Hmm. Am i thinking about this backwards? The motor requires more amps from a 3s battery then a 4s therefor requiring a smaller esc for a bigger battery? Doesnt the 4s batter spin the motor faster?

your help is much appreciated... I am just starting to understand the electrics now.

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By the way, I asked this question in some random place a few minute ago. sorry, im new. haha
 

Tony

Staff member
Actually 420/11.1=37.84, so a 40a ESC will be fine. Your equation for the 4s is correct.

To figure out your KV, or the RPM Per Volt, you would mutiply the KV by the voltage. But remember, a full 3s battery will be 12.6, 11.1 is the middle pretty much on the battery.

So 1000*12.6=12,600
1000*16.8=16,800

The higher the voltage, the faster the motor will spin. But, you must make sure your motor can handle that high of voltage. A lot of the smaller motors can only handle up to a 3s.

Hope this helps.
 

jtropesjr

New Member
ok. true!! sorry for the mis-calculatioin. how did i mess that up.haha so why do i need a bigger esc for a 3s then a 4s? i think im still stuck on the ole saying ..."bigger battery, faster motor,," .. is the esc amp per cell?

example.. 420watt motor running 3s 2200 30c battery requires 38amp esc(roughly) and, 420 watt(same Said Motor) running a 4s 2200 30c battery requires 28amp esc?

I was running 420watt motor, 30amp esc and 2200 30c battery... it was pulsing most of the time. so.. more battery to push the motor that askes for more ampres from the esc. I think i was thinking this whole thing backwards.
 

Tony

Staff member
Yeah, the setup you had was taxing the ESC beyond it's limits. As for the amps, that is just how it works, with the watts being the same, as you add voltage, your amps will go down. It's like a teeder todder. More volts = Less amps | Less volts = More amps. That motor definitely needs a 40a esc on it, and a battery that can handle at least 50a draw contentious.
 

jtropesjr

New Member
Hey Tony, I hate to beat a dead horse, but ... since i talked to you last(long time ago), ive been pretty good with matching batteries, esc and motors... until now...! haha.. OK. i have a Precision Aerobatics Extra 260 that is really nicely built and pretty light. My power system is as follows.. i have an e-flight Power 15 950kv motor(575 watts), a 45 amp esc and a Blue Lipo 4s 2200mah 30c pack... By your account, the pack is capable of 66amps, and the motor asks for 44 amps and we should be all good..... She flys good, nothing to crazy, I'm a very easy flyer, i like to do a couple of passes around, maybe a few small maneuvers then make a few passes at landing befor i actually land. ... Heres where im puzzled.. when i take the battery out, its SUPER hot.. and PUFFY.. now im scared to charge it again... this happened with 2 seperate batteries(both the same make/model) ... i ve had batteries come out of planes that are warm, but never HOT!! Whats my problem... RC problems only please.. haha.. Thanks in advance my friend....
 

Tony

Staff member
Sounds like the resistance of the cells has went up and it's causing more heat to generate in the pack. How old are these batteries?

You may need to put a watt meter on this plane and see just how many amps you are really pulling from that battery. That is what I would do anyway. I think you can get pretty good watt meters for about $15 from china, and they are decently accurate.
 

jtropesjr

New Member
Sounds like the resistance of the cells has went up and it's causing more heat to generate in the pack. How old are these batteries?

You may need to put a watt meter on this plane and see just how many amps you are really pulling from that battery. That is what I would do anyway. I think you can get pretty good watt meters for about $15 from china, and they are decently accurate.



The batts are a little older.. yes... maybe 3 years total with about 10-15 flights on each... still yes, they are older.. im going to go out with 2 brand new batts taro. they are 50c 4s 2650.. hoping nothing gives me an issue.

By the way, motor calls for a 8x8-13x6 prop.. i was using an 11x7 when having the heat issue, and now actually went with a 10x10.. i'll see how it is with new bats and prop size.

thanks again for your 2 cents.. its always nice to have your opinion on these issues. i'll let you know if i run into anything this time around..

jt
 

Tony

Staff member
that 10x10 is going to pull more power with the larger pitch. I would go with a 10x6 myself and test that. But that 11x7 is a pretty good prop. I would not run the 10x10 if you think you will still have heat issues.

As an example of pulling too much power, I purchased a motor that stated 500w. When I did a static test on it, I was able to pull 640w out of it at 62 amps with teh power drop. That is way above what they said it would pull. Thankfully, my batteries can handle it, for the time being anyway lmao.
 

jtropesjr

New Member
that 10x10 is going to pull more power with the larger pitch. I would go with a 10x6 myself and test that. But that 11x7 is a pretty good prop. I would not run the 10x10 if you think you will still have heat issues.

As an example of pulling too much power, I purchased a motor that stated 500w. When I did a static test on it, I was able to pull 640w out of it at 62 amps with teh power drop. That is way above what they said it would pull. Thankfully, my batteries can handle it, for the time being anyway lmao.


you are right.. i'll leave the 11 x 7 on there for now just for the heat issue.. XROAR! its a nice balanced prop too... thanks... i'll let you know sometime tmro afternoon how everything works out.

Thanks for the input, i sure do need it.

jt
 

jtropesjr

New Member
Flew again today.. same issue. HOT batteries. Im thinking that the motor is actually pulling a lot more then its rated for. I also put a smaller prop on and even that one got the battery hot. I ordered a watt meter.. i guess we'll see. Thanks again. I'll repost results when i get the meter.
 
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