Moving up in battery cell count has been an ongoing shift in the world of FPV drones. In 2015, 4S overtook 3S as the standard. By 2018, 6S was all the rage. Fast forward to 2023, the buzz now revolves around an even higher voltage – 8S. If you’ve wondered why, you’re not alone. In this article, I’ll delve into the reasons behind this trend, discussing the benefits and drawbacks of using 8S batteries, and help you determine if building an 8S drone in 2023 is a good ideal.
When discussing 8S, we’re referring to the number of cells in a LiPo battery, which determine the battery voltage. To learn more about the fundamentals, take a look at my LiPo battery tutorial.
Table of Contents
What Do You Need To Fly 8S?
Battery
Ready to take the leap to 8S? You can procure 8S LiPo batteries here: https://oscarliang.com/product-voun
Charger
Keep in mind, most Lipo chargers on the market only support up to 6S, so an 8S-supporting charger will be a necessary investment:
- GetFPV: https://oscarliang.com/product-8eq7
- AliExpress: https://s.click.aliexpress.com/e/_Dl7ba7L
Motors
In terms of motors, you’ll need those with an appropriate KV. Generally, a range of 1200KV to 1600KV fits well for 8S, comparable to 1600-2100KV on 6S. If you have 6S motors compatible with an 8S voltage, they can still be used by using a 75% output limit in Betaflight, similar to how people fly 6S on 4S motors.
RCINPower 2207 1600KV is one of the first motors designed specifically for 8S:
- AliExpress: https://s.click.aliexpress.com/e/_DeGIbiZ
FC and ESC
Additionally, an 8S-compatible FC/ESC stack is a necessity. As of now, the options are limited, the only option I’m aware of is the Foxeer stack:
- 8S compatible Flight Controller:
- AliExpress: https://s.click.aliexpress.com/e/_DBtazrx
- GetFPV: https://oscarliang.com/product-pxj7
- 8S compatible 4in1 ESC:
Advantages of Higher Voltages
Using higher voltage to power our FPV drones has many advantages, which explains why 6S is more popular than 4S nowadays for 5″ FPV drones. I’ve previously explained the benefits of transitioning from 4S to 6S in this article: https://oscarliang.com/6s-mini-quad-racing-drone/.
The main take away from the above article is that when delivering a certain amount of power, a higher voltage can achieve this at a lower current. This results in less heating everywhere – your battery, the XT60 connector, the wires, the ESC, and the motors. A reduced current also mitigates battery voltage sag, this in turn boosts throttle control and responsiveness and maintains consistent performance throughout the entire flight.
Switching from 6S to 8S carries many of these same advantages, such as less voltage sag, higher efficiency thanks to reduced system losses. However, as the voltage continues to increase, the returns begin to diminish. It’s crucial, therefore, to weigh these benefits against the potential drawbacks of higher voltage, as we’ll explore next.
The Issue with Higher Voltages
As explained in my motor buyer’s guide, Motor KV represents the motor’s speed measured in RPM per volt applied. In essence, to achieve the same RPM, you need lower KV motors when using higher cell count batteries.
To make a lower KV motor, we need more turns of the wire around the stator, which can potentially lead to worse cooling performance. When switching to 8S, the rise in motor stator windings might not pose a significant cooling issue compared to 6S, and most likely to be offset by lower current and efficiency gain. However, when considering even higher voltages such as 12S or 16S, cooling could become an issue, which requires further testing to verify.
At present, 8S batteries are quite rare, and if found, tend to be far pricier than 6S batteries. They also tend to be bulkier, adding weight to the drone and increasing the likelihood of battery ejection and damage during a crash.
Additionally, very few FPV drone components (such as FC and VTX) can handle the higher voltage of 8S. If incompatible, a voltage regulator would be needed to power your electronics. Most components are designed with 6S in mind and may not have undergone enough testing for 8S compatibility, potentially increasing the risk of failure.
When using 8S, it’s crucial to monitor voltage closely. Due to performance not degrading as significantly as with lower cell count batteries even at low voltage, it’s easy to overlook and overdischarge the battery, risking a sudden drone drop without substantial warning.
Conclusion
It’s tempting to build a 8S quad, but at this point in time, my personal advice would be to hold off for a bit.
Firstly, it’s likely to be a costly project. You will need to invest in new 8S batteries and compatible chargers. The options for motors and ESCs are limited. Even when available, durability can be a concern with 8S, given that most components are only tested for 6S, and comprehensive testing for 8S is yet to be conducted.
Secondly, the potential for damaging an 8S LiPo battery is higher, given the larger number of cells.
In a nutshell, 8S could potentially outshine 6S in terms of flight performance when paired with the right setup – on paper it should be more responsive and powerful. However, it does present significant challenges, such as higher costs and a lack of reliable hardware options. Also, it might not suit all flying styles. Over time, as more manufacturers delve into the development and testing of 8S-compatible components, it might become a more feasible choice. As always, your personal needs and flying style should be the guiding factors when deciding whether to switch.
Edit History
- Jul 2023 – article created
- Jan 2024 – updated product links
3 comments
i’m still on 4s, but using 6s motors
one of the benefits that were promised was that for the same power, a higher voltage needs less current. but judging from the fist picture, the 4s battery has the thinnest wires
kinda funny
Great stuff. Since I only recently build my first 5 inch quad I just immediately went for 8s. (I only flew 6s 3.5 inch for the past few years) I already have an older ISDT charger with parallel board which can do up to 8s.
Paired with the foxeer ESC + FC and a GNB battery, the price is not really more than 6s for me, since I would go for foxeer hardware anyway because of the reliability and quality compared to SpeedyBee. You can also pair 2x 4s if you worry about dead cells. The 5 pair batttery packs from gnb are like 146 euro for 8s, and 112 for 6s. That is the only thing I would save on.
I would go 8s if you don’t invested to much in 6s already. It is great to fly a 8s heavier frame and still be faster than 6s lighter frame :)
if flying long range, 4s is still usually better than 6s due to the same mah with less wight so a larger mah pack can be used for the same weight penalty, for freestyle i can see higher voltage make some difference as i do fly 6s most of the time but with higher voltage comes greater ability to short out components, arcs can happen easier the higher the voltage and sure the amperage drops but by how much, double voltage half amperage is how it goes but only going up 4.2 volts at full charge or 3.6 nominal makes me wonder how much lower the amperage really is vs the need to buy more bulky less mAh batteries at a higher cost and sure less voltage sag but wait, how so, the voltage will still sag and since the motors must be sized to match the initial voltage via kv rating, plus with 2 extra cells that is more sag is it not especially with more weight and slower spinning motors per voltage ie. 4s fully charged is 4.2 x 4 so 16.8 volts (excluding hv batteries obviously) now when drained or at the stated voltage of 3.6 per cell x 4 comes out to 14.4 right so nominal power only drops 2.4 volts while flying. now go to 6s and its 4.2 x 6 so 25.2 volts full and at nominal its 21.6 sp now flying causes a 3.6 volt drop off the top. I understand that flying by itself does not cause sag but by starting at less voltage it has to contribute to sag at times of high demand correct? now do 8 x 4.2 and its 33.6 so the actual drain is 4.8 off the top and while the drain voltage total is higher than even 6s charged it still has to go against the adjusted lower kv of the motor that can deal with that much voltage. idk add that to the extra weight and bulk and i cant see a great reason to go 8s now 12s i can see but then we are talking custom stuff or just much larger components but that justifies the voltage jump. as long as the voltage stays under 50ish volts it still makes sense for hobby stuff after that the risk of shock becomes something that starts to negate the rise in voltage just my thoughts and ramblings thanks for the info oscar