Why are some ESC's only rated to 3s or 4s Lipos ?

Here is a bench test I have done to find out if a 2s to 4s Afro ESC's can run on 6s.

ESC’s  and Label Specs

Afro Slim ESC 20amp 2- 4s battery afro_nfet.hex firmware

Afro Bec ESC 30amp 2- 4s battery afro_nfet.hex firmware

Afro HV ESC 20amp 2- 8s battery afro_nfet.hex firmware (control)

ESC component specs taken from the manufactures data sheets.

Afro Slim 20amp 2-4s:

5v MCU supply regulator LM78L05 Max input 30v Max load 100ma

NFets FDMS8018 Max Voltage 30v, Continuous Drain @ Ta=25°C = 30amps

BC817-40W 6CW max Voltage 45v 500ma

All components are rated up to 150°C

Afro bec 30amp 2-4s:

5v MCU supply regulator LM78L05 Max input 30v Max load 100ma

NFets FDMS8018 Max Voltage 30v, Continuous Drain @ Ta=25°C = 30amps

BC817-40W 6CW max Voltage 45v 500ma

All components are rated up to 150°C

Afro HV 20amp 2-8s:

5v MCU supply regulator LM78L05 Max input 30v Max load 100ma

(But this LM78L05 is fed from two DAR transistors that take the HV voltage and step it down to 12v, their Max voltage is 40v) this is why I think the Afro HV was de-rated from 12s to 8s.

NFets FDMS86540 Max Voltage 60v, Continuous Drain @ Ta=25°C = 20amps

 (If the 5v MCU supply was by-passed and you fed the MCU with 5v from another source the Nfets are rated at 60v) So I would assume the ESC will run at 12s with a new 5v supply for the MCU.

All components are rated up to 150°C 

Test equipment:

Power supply 60amp 24v power station

Amp and Watt meter Turnigy 130A

Tarot 4114 motor with 15 x 5.5 prop fitted

Test meter with temperature probe

Motor stand with weight scale attached for thrust readings

Servo tester for PMW control 



Apply a constant 24v supply to a power meter then to an ESC to measure amps drawn with the esc connected to a standard motor and propeller running at 50 % PWM throttle controlled by a servo tester and run for 10mins whist monitoring temperature, amps, watts and thrust.   


ESC                                                         Amps Draw                         Watts                    Temp                   Thrust 

1st Afro slim 20A                                5.65                                        133                         47.1C                     1114g

2nd Afro BEC 30A                              5.68                                        134                         53.8C                     1160g

3rd Afro HV 20A                                 5.3                                          125                         46.0C                     1111g


It Appears as if the Afro Slim 20amp and the Afro Bec 30amp ESC’s are capable of handling the use of a 6s battery as a power source, according the specs of the components provided by the chip manufacturer,  the temperature of the components was very similar and the amps drawn the same. So if you wanted to hide the ESC’s in the arms of the Multi-rotor (provided cooling holes for air was allowed for) then this will be fine and they will run on 6s power.



Slim ESC wiring was upgraded to suit a higher amp draw and the use of 6s batteries, (although the original wiring fitting is 20amp rated so should be fine for most Multi-rotors) the other component’s on the boards were not investigated, so no information on them is known.

Use this info at your own risk.

Video https://youtu.be/91rc37c5YBQ





Views: 5487

Comment by JB on January 30, 2016 at 9:36pm


Have you tested them to full throttle as well?

Comment by James masterman on January 31, 2016 at 2:13am
Have you had much experience with these?

I've had one 30A afro catch fire while on the ground (running off a 3s, throttle in neutral) and two others produce stuttering at high throttle settings. The stuttering turned out to be due to poor solder joints on the power lines, but it hasn't given me much confidence in them. I know others like them, though, so I'm keen to hear your thoughts.
Comment by JB on January 31, 2016 at 3:07am

Um do you mean me James?

I have the afros on two quads and haven't had any issues so far. I have however gone over to the DYS Esc's now from BoltRC (Hobbyking sells them too, but Bolt is faster) and have had no issues with them either, but they are much smaller and lighter than the afros and seem to have better QC. They also have higher manufacture cell ratings. 

Comment by James masterman on January 31, 2016 at 3:14am
I meant Reuben, but good to hear your experiences, too :-).

I'll have to give the DYS models a go. QC is terrible on most ESCs so it's something I deliberately look for now. Try pulling the heatshrink off the bullet connectors on a random ESC. In many cases the soldering is very poor.
Comment by Peter Seddon on January 31, 2016 at 8:39am

You have interpreted the component capability based upon their maximum values. For instance, a 78l05 on 24v input will not be able to carry a current of 0.1A as it will have to dissipate about 1.9W. You need to calculate the junction temperature based on the heatsink capability to see if it remains within spec. I would suggest it will cook itself to death!

You have also not considered the practical aspects of the FET's working in a switching environment with inductance and capacitance that can result in voltage spikes above the supply voltage. It is not unusual to allow for a 2 to 1 margin when using a power component. I would suggest 6S which is 25v gives no margin on a 30v rated FET. 

I would not recommend running the Afros at anything greater than their rated values. I would also not recommend putting ESC's in tubes as they are designed to have cooling air passing over them to limit the junction temperature rise.

regards Peter  


Comment by David Kraus on January 31, 2016 at 9:04am

I agree with Peter, you have to had quite big safety margin to make sure you never exceed maximum voltage rating on FET. This voltage consist of battery voltage and induced voltage on motor wiring during transitions of speed(braking). Here is application brochure from infeon for MOS-FET in baterry aplication, and for 24V at battery is 60V MOS-FET voltage recommended. If you will use 4S ESC on 6S battery, ESC probably burn out sooner or later.

Comment by Quadrocopter on January 31, 2016 at 1:12pm

You can run those HV's at 12S  :-)

Afro's are bulletproof, have quite a few machines running them, those slims are my personal favourite...

#timecoprules ;-)

Comment by Reuben on January 31, 2016 at 1:48pm

Hi Guys 

I welcome any and all comments as I am not purporting to be a professional electronics engineer.  I did run these ESC's at full throttle too .. in fact they ran better and the motor ran quite hot, (it is a well know fact that ESC's run better at over 75% throttle, at 50% they are working the hardest). I was careful though not to exceed the amp ratings for motor and ESC .. I would also like to point out that you will notice the fet temp on the Afro Bec 30amp was the highest ..I put this down to, it was the only one to still have its heat shrink on.. also Peter talks about the temp of the 5v regulator as it has to dissipate 1.9w , I did notice the temps of the LM78L05 was barely warm.. I did have my fingers sandwiching the boards on some of the runs to feel for any component that took a rise in temp. I also note that on most bigger Multi rotors you hardly pull much more that between 4amp and 10amp per motor when flying. on one of my machines carrying a payload of 7kgs, I get up to only about 65amps total. 

Comment by Reuben on January 31, 2016 at 2:02pm

Due to the fact that these ESC's are labeled 2-4s and they would have been used on a professional machine that our governing body (CAA) have registered on their books (we are 102 Certified by CAA), we will only use ESC's that are labeled to the correct battery and setup we are using, just in case there is an accident and an investigation followed. We would not want to be found using underrated components in an aircraft that is approved by CAA. My test was to prove to myself that you can use a higher cell count, as in the past have used higher voltage without any investigation into ESC components in airplanes that i fly, this was quite a few years ago and I never had an ESC burn out on me. So for our professional machine I have ordered some "ZTW 30amp small" ESC's to test and fit, I will be stripping these down to investigate what components they are using :) 

Comment by Reuben on January 31, 2016 at 2:06pm

For James 

I never use the bullet connectors, on all the machines I build, all wires are soldered direct, the less connections I have the better. Yes I have come across poorly soldered connections before and these will bring down a craft .. never trust what someone else has done. 


You need to be a member of DIY Drones to add comments!

Join DIY Drones


Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2020   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service