• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

ESC Voltage

d8veh

Well-known member
#1
I'm just finishing off my FT3D, when I encountered a slight problem. I was going to use a GT2215/09 m0tor from one of my C-packs with one of those yellow no name ESCs that you can buy for about $3. It worked fine with a 3S battery, but with a 4S one, it kept losing sync at full throttle. I then tried a Surpass C2814 -910kv motor with the same ESC, which seems to work perfectly with a 4S battery and the same propeller.

A little digging around shows that many of the cheaper ESCs are only rated for 2S-3S. can anybody tell me why that is? Given that my motor now seems to work OK with that ESC, are there any impending disasters waiting to get me?

Another thing that I noticed with ESCs is that the more cells you use in the battery, the lower their rating is regarding the number of servos recommended. I've seen one that went something like 2S - 4 servos, 3S - 3 servos, 4S - 2 servos. Can anybody explain why? It sounds counter intuitive to me.

Am I going to have to spend $15 on a decent ESC or are there any better options for 4S and 30 amps?
 

Hai-Lee

Old and Bold RC PILOT
#2
I'm just finishing off my FT3D, when I encountered a slight problem. I was going to use a GT2215/09 m0tor from one of my C-packs with one of those yellow no name ESCs that you can buy for about $3. It worked fine with a 3S battery, but with a 4S one, it kept losing sync at full throttle. I then tried a Surpass C2814 -910kv motor with the same ESC, which seems to work perfectly with a 4S battery and the same propeller.

A little digging around shows that many of the cheaper ESCs are only rated for 2S-3S. can anybody tell me why that is? Given that my motor now seems to work OK with that ESC, are there any impending disasters waiting to get me?

Another thing that I noticed with ESCs is that the more cells you use in the battery, the lower their rating is regarding the number of servos recommended. I've seen one that went something like 2S - 4 servos, 3S - 3 servos, 4S - 2 servos. Can anybody explain why? It sounds counter intuitive to me.

Am I going to have to spend $15 on a decent ESC or are there any better options for 4S and 30 amps?
As for the ESC voltage ratings just remember higher voltage semiconductors normally cost more! Therefore it stands to reason that something that is built as cheap as possible is definitely going to be meant for lower voltage operation.

As for the decrease in servo handling it is quite simple. Most onboard BECs have a temperature fold function as part of their over temperature protection. Being a Series regulator the heat generated climbs quite rapidly as the input voltage is increased. For a 2S BEC the voltage drop would be 2.4 volts and if drawing 1 Amp then the BEC would need to dissipate 2.4 watts. Now if the input was 3S then the voltage drop would be 6.1 Volts and so the power to dissipate would be 6.1 watts. Finally if the input was 4S then the voltage drop would be 9.8 Volts and the dissipation would rise to 9.8 watts! As you can see this dissipation is done as heat and so the temperature at higher voltages will be much higher. Higher heat means a shutdown of the BEC and a loss or Rx voltage and control.

When looking for a high voltage ESC ALWAYS look for a switchmode BEC normally labelled as a UBEC. A UBEC has extremely low heat issues and can handle a greater load for less heating.

To overcome the issue you could spec a separate UBEC and use QUAD ESCs , (No BEC onboard and possibly even cheaper).

have fun!
 

Merv

Well-known member
#3
cheaper ESCs are only rated for 2S-3S. can anybody tell me why that is?
I agree with @Hai-Lee, it cheaper to make them that way. 3S is just cheaper, cheaper ESC, cheaper battery.

I’ve got an FT-3D, that I run on 3S, I’ve got a 3730 1000kv motor turning a 12x3.8 slow fly prop. It has unlimited vertical, will hover on 60% throttle. I run a 2200 3S battery & 50 amp ESC. It works great.
 

d8veh

Well-known member
#5
I agree with @Hai-Lee, it cheaper to make them that way. 3S is just cheaper, cheaper ESC, cheaper battery.

I’ve got an FT-3D, that I run on 3S, I’ve got a 3730 1000kv motor turning a 12x3.8 slow fly prop. It has unlimited vertical, will hover on 60% throttle. I run a 2200 3S battery & 50 amp ESC. It works great.
Do you know know how many amps you're using? With a bendy 9x4.7 and the C2814 with 3S. I scored 13.5" on my thrust gauge with only 18 amps. That thrust is insane - something like double the weight of the plane. With a 3S and 10x4.7, I only scored 10" and 21 amps, so 75% of the thrust and 17% less efficiency. I think a big prop, like a 12x3.8 is going to draw massive current, so I'd need a new ESC.
 

Merv

Well-known member
#6
Do you know know how many amps you're using? With a bendy 9x4.7 and the C2814 with 3S. I scored 13.5" on my thrust gauge with only 18 amps. That thrust is insane - something like double the weight of the plane. With a 3S and 10x4.7, I only scored 10" and 21 amps, so 75% of the thrust and 17% less efficiency. I think a big prop, like a 12x3.8 is going to draw massive current, so I'd need a new ESC.
I just put a watt meter on it, I'm pulling 42-43 amps at full throttle. I seldom run it at full power, just no need to. In the summer I get about 10 min flights, 7 min in winter, on a 2200 3S battery. Sorry to say I don't have a thrust stand.
 

DamoRC

Well-known member
Mentor
#8
I scored 13.5" on my thrust gauge with only 18 amps. That thrust is insane - something like double the weight of the plane. With a 3S and 10x4.7, I only scored 10" and 21 amps, so 75% of the thrust and 17% less efficiency.
Isn't the FT3D about 1 lb without battery?

The 10" prop results are a little weird. I wonder is your battery struggling a little with the higher load?

DamoRC
 

Merv

Well-known member
#9
What prop are you running that seems awfully high on the amp side for that size motor.
I'm running a 12x3.8 slow fly, it produces a lot of thrust. I just bought some heaver 11 inch props, have not tried them yet. My slow fly's were cheap, but I'm sure they are flexing.