Mini Quad: 3S, 4S Setups Comparison and Migration
In this post we will have a look at the differences of mini quads running 3S and 4S lipo batteries. Many who are building their first mini quad might struggle in deciding which setup is best for them, I hope this post can answer some of those questions. I will also talk about how to move from a 3S mini-quad setup to a 4S setup, as I have been asked by FPV’ers who are looking for more power and speed.
* 3S and 4S refer to the number of cells in series in a LiPo battery. Learn more about the basics of LiPo batteries in this guide.
I am just beginning, should I start from 3S? Or go straight to 4S?
4S has now become the standard voltage level for 4″, 5″ and 6″ mini quads to use, so you should really just start with 4S. There is just too much extra investment, both time and money goes to waste when migrating from 3S to 4S later on.
If you think a 4S mini quad is just too powerful and hard to control, you can always adjust your throttle output range to 75% or even 50% to tame it down. This effectively reduce the power of your quad to a more manageable level. You can crank it back up as you gain confidence. You can do this in the Mixer page in Taranis TX, reduce weight to 75 or 50, and adjust the Offset so the range starts at -100.
Difference between a 3S and 4S mini quad setup
Obviously, the biggest difference is the voltage delivered to the motors. A 3S Lipo has a nominal voltage of 11.1V or 12.6V when fully charged, while a 4S Lipo has a nominal voltage of 14.8V and 16.8V at full charge.
Motors can spin faster when the applied voltage is higher. The RPM (rotation per minute) of the motor under no load is determined by the KV value of the motor – RPM = voltage x KV. (Read this post for more motor basics)
Let’s say we have a 2300KV motor, when powered with a fully charged 3S lipo (12.6V), RPM would be 2300 x 12.6 = 28900 in theory. That means the motor spins approximately 28,900 times a minute without any propellers. When you power the same motor with a 4S lipo (16.8V), the RPM is 2300 x 16.8 = 38640, and as you can see that’s a significant increase in RPM.
This increase in RPM means the motor can generate higher thrust, more power, faster flight speed and agility. But the throttle stick also becomes more sensitive and harder to control.
Note that 4S setups are usually a little heavier than 3S’s due to the additional weight of the voltage regulator, heavier batteries etc.
Upgrading from 3S to 4S
In case you have already built a 3S mini quad, and you are ready for a faster and more responsive setup, here is how you can upgrade it to 4S. If you can afford it, you might also consider building new quad purely designed for 4S power. It’s not a bad idea to have two quads when one is down for maintenance.
Motors and ESC’s
First question to ask: can your motors and ESC’s handle 4S for the increased voltage and current?
Most modern 2204, 2205 and 2206 motors are compatible with both 3S and 4S. Some 1806 motors might be only rated for 2S-3S, so it would be ideal to upgrade your motors to 22xx class which are rated for 4S.
Be aware of the current draw increase too, with the same setup, higher voltage would actually increase the current draw because of the higher RPM. When current gets higher than the safe limit, the motors will get hot as the winding starts to gather heat. If you keep pushing it, the enamel on the motor winding will burn off, causing electrical shorts inside the motor between poles. Eventually it will lead to fatal power loss, and the motor will fail while your quad is travelling at high speed. And BANG! Your quad crashes into pieces.
As for ESC’s, most ESC’s these days supports 4S some even up to 6S, but it’s always worth checking first. Make sure the current draw of your motor and propeller would not exceed the current rating on your ESC. In some cases it’s necessary to upgrade your ESCs from 12A-18A to 25A-30A or higher.
Other Electronics – VTX, FPV camera, OSD etc
Depends on what input voltage your electronics support in your quad, voltage regulators might be required to convert 16V at 4S to something lower such as 5V or 12V. Fortunately there are many options these days, some FPV cameras and VTX support wide voltage range up to 6S, while there are PDB that provides 5V and 12V outputs.
To sum things up, 3S has moved to the back seat as the hobby has started to standardize things around 4S builds. Similar to an F1 flight controller, they work and fly well but F3/F4’s have become the norm, with F7’s probably to follow. Some pilots are now even using 5S and 6S LiPos in their mini-quads!
- 2015 April – Article created
- 2017 June – Article revised
Review: FrSky XSR-M Radio Receiver RX
Forum Highlights #5 – Betaflight filter adjustment, why ESC signal ground, how to keep old cleanflight GUI, why test new components and more
Leave a Comment Cancel Reply
This was the best
I think your equations with higher voltage => higher current are wrong.
You need to compare the power of the quad with 3S vs 4S lipo voltage and from there get the current:
Let U to be voltage of 1S lipo, and I3 is current related to S3 battery and I4 is for S4 battery.
S3: P = 3*U*I3
S4: P = 4*U*I4
3*U*I3 = 4*U*I4
I4 = 3*I3/4
Thus with S4 you will need only 3/4 of the current to get the same power as with S3.
Of course this is the simplification but to get the same power you definitely need less current with S4 than with S3.
“When voltage increases, current draw will also go up.” How is it possible? sudden change in laws of physics?
Voltage increases RPM, and that leads to motor drawing more current. Just check thrust data and you will understand
The real technical explanation (still somewhat simplified, but good enough) for the increased current draw is this: let’s say the resistance of motor windings is 2 ohms. If we applied 12V to the windings, the current would be 12/2=6A. Now let’s take the 16V from 4S and apply that to the same motor with 2 ohms winding. The current would be higher, 16/2=8A. Really simple, Modzel, you just have to understand the formulas 🙂
Rpm increases with throttle, going to a higher voltage does not increase current draw, that’s inaccurate.
A higher 4s voltage will draw less current for the same amount of thrust as 3s does.
While you have more throttle to play with and the potential to draw a higher current, using more throttle power is a human choice and not an unavoidable effect of using a higher voltage.
If you produce say 2kg of thrust on 4s it will draw LESS current than it would producing the same 2kg of thrust on 3s.
Your post on current draw is inaccurate and misleading and should be revised.
If you want to keep the power of the motor at a constant, than what you say is correct, BUT it’s different on mini quads…
one of the reasons we use 4S over 3S is because of the higher RPM we can get out of our motors.
When the motors are spinning faster, it uses more power, and so is the current. Don’t forget RPM and current is not a linear relationship, it’s exponential. So the current draw situation gets worse the higher the RPM goes.
change? try the formula yourself and you will understand 🙂
PROOF: If V=I*R, theN 2V=(I*R)/2
when you go on the website of DYS, dys.hk/ProductShow.asp?ID=91, you can read that a 1806 2300kv, can run a 5045 without any problem and they never use 5030. Why?
they have changed the spec since. When they came out they were only supposed to run on 3S although some use it on 4S as well.
How do You get OSD alarm work with both of battery types? Generaly You have to choose that you use 3S or 4S.
I have a question about the eachine 250 racer drone, i would like to upgrade the esc’s to 20a ones but the stock esc only has 6 conection points ( that must be including the servo wires )
How to solder a new esc with more poles to it ?
my suggestion is… leave the 250 racer as it is, and build a new one with a better frame 🙂
I have t motors mn2204 2300kv and kiss 12a , Im thinking to give 4s a try , what do you think can i go with 4s ??
definitely as long as your other gear can support it and you stay within a 5040 propeller. It will give you a lot more power.
Thank you for taking the time to make all of this information available. I enjoy reading it and I feel like I’m beginning to learn.
I’m building my first quad – I’m not in any rush to get into the air. I’d really like to make sure I have a firm understanding of as much as I possibly can to begin with, and make sure I create a build with the greatest chance of success.
I’ve begun purchasing the parts – I might have made some bad decisions. I hope you can find the time to give me your opinion.
I’m building on the HobbyKing FPV250 Ghost Edition frame (with the cool looking LED lights). I’ve purchased the following setup:
Cobra 2204 2300kv Motors
Turnigy 18A ESCs
Multiple sets of multiple propeller sizes for testing (all Gemfans, three sizes: 5030, 5045, and 6045)
Turnigy 4S 20C 4000maH battery (this is now a source of concern at this point – worried it might be too big and heavy)
I’m concerned that running that heavy of a setup (with that battery) might burn out the Cobras, especially if I try running the 6045s.
For starters I will not be placing any FPV equipment on it, so the only other things will be a CC3D FC, the PDB that came with the frame, whatever wiring/velcro/sticky pads I will be using, my low battery warning beeper, and the receiver from my Turnigy 9X transmitter.
The overall weight (even with the huge battery) will be coming in at around 800 and 900 grams, depending on solder/double-sided pads, velcro, etc.. (current weigh-in is 824 grams, but some wires will be trimmed down from ESCs and motors, and then the solder/velcro/etc… will be added).
I’m considering purchasing a 3S 2200maH battery out of concern for burning out those Cobras. Any thoughts?
Motors and ESCs all look fine.
As for props, 2300KV motors mostly runs 4 or 5 inch props, 5030 on 4S is good enough, with 5045, the thing is going to fly like a rocket! 6045 is probably too much i don’t recommend it.
Yes the lipo is too big!, 1300mah-1800mah is a good range of capacity, while the weight isn’t too much.
you should defintely check out this parts list
and this cobra motor thrust tests
Thank you for the reply! I’m going to purchase a Turnigy Nano-Tech 4S 1800maH battery (hopefully they will be back in stock in the coming months) for this build.
I am confused about one thing – I’m hoping you can answer this question for me:
Every article I’ve read has suggested that the thrust power needs of a quadcopter is at least 2:1 in grams – some even suggest multiplying your quads weight by 2.2 and making sure you have a max thrust power at least equal to that (so if your quad weighs 1000 grams – multiply by 2.2 and you need a setup with a max thrust of at least 2200 grams, or 550 grams of thrust per motor). Easy enough to understand.
My question is this: if my current build weight is at max 900 grams even with that huge 4S 4000maH battery, and the Cobra 2204 2300kv motors with 5045 props on a 4S battery produce 710 grams of thrust per motor (by your own measurements) – then I would be at 2840 grams of thrust versus 900 grams total weight, with a thrust-to-weight ratio of over 3:1 – much greater than the suggested minimum of 2.2 times the total weight.
Going only by that calculation, it seems like my quad should have more than enough power to be able to fly with that battery.
However, virtually everything I’ve read says that it’s way too big (yourself included) – and everybody with similar builds to this is using much smaller batteries (like what you suggested 1100-1800 maH size) – what am I missing here?
Please understand that I’m not doubting you, and like I said above I am ordering the smaller battery. I would just like to know what it is I’m not grasping about this – obviously I am missing something!
Thanks again for your reply (and for providing a great web-site), I hope you are able to answer this as well.
For mini quad, people generally use it for racing and fly really fast, so we want to achieve the greatest thrust:weight ratio possible.
It’s not uncommon to find someone building a quad with thrust:weight ratio of 7:1 .
the 2:1 or 2.2:1 is the bare minimum you should have on a multicopter, it flies… but it won’t go fast…
Update from last fall: I completed the 250 mini-quad (ended up going with a QAV-250 type frame, but everything else the same)… Amazingly, even with that 4000mah 4S battery, this thing is still crazy-fast. “eCalc” claims that the top speed with that battery and 5030 props is around 60mph, 85mph with 5045 (all GemFan), and a flight time of about 15 mins (AUW is around 815g).
I can confirm the flight time, I flew for about 13 mins and my low-voltage buzzer had not gone off yet. I looked at the cell voltage when it landed, and it was still at about 3.72v per cell, then after rest it came back up to about 3.83v/cell, so pretty near storage. I have my buzzer set for 3.5. I can’t confirm the mph as I don’t have a radar – but I can say:
You were right: this thing is FAST! (even with the massive battery)
I was actually getting kind of stressed out flying it because it felt like it just wanted to run away from me. I had a lot of trouble just getting it to hover and stay in one spot – and the slightest pitch in any direction sent it flying off much faster than I was expecting. I did one punch-out for about 3 seconds and had to stop because I couldn’t believe how high it got, and how quickly it climbed! I’m going to try to correct the drifting with PID settings (I’ve read that the “I” setting might be able to help with that) – it’s a CC3D in “attitude” mode.
I’m going to change to a 3S 2200mah battery. That will drop its weight down to the 560g range, and lower max speed down into the 40mph range on 5030’s (again – according to “eCalc”). I think that would probably be best for me right now, until I get a better handle on controlling this thing. It is NOTHING like my toy quad that I’ve been flying (a “UDI 818A”) – that’s like comparing a Ford Mustang to a go-cart. I can’t even imagine what it would be like to fly one of those professional racer quads (or a “WarpQuad”), topping 100mph. Just crazy! Honestly, at this point: I wouldn’t be able to handle it, since right now I can barely handle this, and I didn’t even push it that hard.
At least I didn’t crash, lol… the worst thing that happened was I nicked up the props a little bit in a brief brush with the side of my house (bricks).
Thank you again for all of your time and energy in making this blog available. It has been very helpful and educational to me as I was putting this thing together.