6S vs 4S LiPo for FPV Drones: Which Battery Voltage is Higher for Effectivity and Efficiency

If you’re simply beginning out with 5-inch FPV drones, you would possibly discover it difficult to determine whether or not to make use of a 4S or 6S LiPo battery. On this submit, I’ll clarify the variations and assist you to make an knowledgeable resolution.

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Additional Studying: New to FPV drones? Check out our newbie’s information.

Professional Tip: Betaflight has launched a brand new function that enables powering a 4S quad with a 6S LiPo battery by lowering motor output.

Right here’s an inventory of my favorite 6S and 4S LiPo batteries.

Advantages of 6S Over 4S

A 6S LiPo battery has a 50% larger nominal voltage than a 4S because of two further cells. The utmost voltage of a 6S is as much as 25.2V, in comparison with 16.8V for a 4S.

The potential enhancements from utilizing a 6S over a 4S embody (a few of these factors is likely to be up for debate):

• LOWER amp draw
• LESS voltage sag
• LONGER flight time
• MORE responsive and agile efficiency

Decrease Amp Draw?

Some of the vital benefits of 6S over 4S is the decrease present required to provide the identical energy.

Energy is voltage multiplied by present: P = V x I

For instance, to provide 1000W, it takes practically 60A on 4S (at 16.8V) whereas it’s solely underneath 40A on 6S (at 25.2V).

Decrease amp draw leads to:

• Much less stress on the battery
• Decreased “voltage sag” all through the flight
• Much less vitality loss within the wires because of resistance, although that is usually negligible

Take a look at some DVR footage of a 6S quad:

Is 6S Higher for Your Battery?

The decrease amp draw means your batteries run cooler throughout flight, which is helpful for battery longevity. This additionally permits the usage of decrease C ranking packs for a similar energy, doubtlessly saving prices by deciding on inexpensive cells.

Nevertheless, to match the load of a 4S battery, we frequently select decrease capability batteries, which might restrict the most discharge present, since battery capability is a consider most discharge present. So, larger C ranking packs would possibly nonetheless be vital.

Max Discharge Present = C Score x Battery Capability

Responsiveness

Because of much less voltage sag underneath load, the motors keep constant acceleration, enabling them to alter RPM extra quickly and persistently. This leads to an total extra responsive and agile plane. The sooner RPM change fee considerably impacts the dealing with of your quad.

Larger Effectivity?

There’s a controversial idea {that a} 6S FPV drone provides longer flight instances than a 4S.

This isn’t essentially true, as we frequently choose 6S batteries of comparable weight or watt-hours (Wh) as 4S batteries. To realize related speeds on a 6S, the motors have to spin at comparable RPMs, requiring an analogous quantity of energy. Due to this fact, theoretically, flight instances must be corresponding to these of a 4S when flying on the similar velocity.

Longer flight instances with a 6S are doable by lowering motor energy (e.g., utilizing lighter props or adapt a much less aggressive flying model) or utilizing bigger battery packs with larger vitality capability. Nevertheless, both strategy will inevitably affect plane efficiency.

The profit in flight time is extra prone to be seen in AP (aerial images) platforms, the place motor velocity is extra constant, and speedy RPM adjustments like these in racing drones are much less frequent.

However why are there folks claiming they’re getting longer flight time on 6S than 4S? Perhaps it’s as a result of decrease present within the system, which results in much less overheat and total larger effectivity. Nevertheless this profit won’t be noticeable typically.

Is 6S Quicker?

A 6S quadcopter, with specifically chosen parts, definitely have some benefit over a 4S (as demonstrated by {most professional} racers have now switched from 4S over to 6S batteries). Nevertheless, in drone racing, race tracks usually function quite a few turns and gates, requiring as a lot pilot talent as uncooked velocity, if no more.

The decrease present draw and decrease voltage drop of 6S give racers extra room to experiment with motor and prop mixtures. This flexibility permits for extra strategic decisions find one of the best steadiness between effectivity and efficiency based mostly on the particular race monitor.

Selecting Motors for 6S

There are two sides to the argument when deciding on motors for a 6S FPV drone. Some advocate decrease KV motors to match the theoretical max RPM of 4S-equivalent motors, whereas others counsel utilizing related KV motors as on 4S to completely make the most of the additional energy from 6S batteries.

I’ll experiment with each concepts in my testing.

Decrease KV Motors

For a safer and extra environment friendly setup, select a low KV motor that gives a theoretical max RPM in the identical vary as an equal 4S setup utilizing a typical KV rated motor.

With extra volts within the system, you’ll be able to execute the KV extra successfully. Actually, you would possibly want even barely decrease KV than calculated to attain the identical RPM in flight. For instance, 1600KV on 6S would possibly equate to not 2400KV on 4S, however truly barely larger resembling 2500KV.

As KV will increase, the torque ranking is claimed to lower. Nevertheless, from my observations, voltage sag is a extra influential issue, stopping you from reaching the theoretical max RPM on 4S. That is likely to be why some folks declare 6S really feel “extra punchy”.

With a 6S setup, I additionally observed the flexibility to swing a heavier prop extra successfully (e.g., larger pitch props). If I have been utilizing a 4S LiPo, most excessive KV motors wouldn’t have the ability to swing a heavy prop at excessive RPMs like on the 6S setup.

Listed here are my motor suggestions.

Operating 6S LiPo on 4S Motors

I examined 4S motors (2350KV) on 6S batteries.

These motors are thought-about extremely excessive KV for 6S, they usually did present brutal straight-line velocity and spectacular cornering. Nevertheless, the downsides have been vital: extreme voltage sag and horrible inefficiency. The motors additionally turned extraordinarily scorching after a brief flight. Personally I’d keep away from utilizing 4S motors on 6S batteries, motors may simply get broken.

Nevertheless, Betaflight provides an answer to cut back motor output, which lets you energy 4S quad with 6S LiPo by setting motor output to 66%.

How About 5S?

Properly, the cell rely and voltage of 5S are in between these of 4S and 6S, so you’ll be able to count on its efficiency to even be intermediate. Nevertheless, 4S and 6S batteries are extra broadly out there, making 5S batteries comparatively uncommon.

Conclusion

Personally, I choose 6S principally for the lowered voltage sag. Aside from that, I don’t really feel it’s considerably completely different from 4S in different side. Oh, how many individuals nonetheless bear in mind the dialogue again in 2014/2015 once we have been deciding between 3S and 4S? It appears we’re nonetheless transferring up in voltage. Perhaps sooner or later, 8S and even 12S will turn into widespread – who is aware of? 🙂 Replace – Right here’s a brand new article discussing the potential of utilizing 8S Lipo in FPV drones in 2023: https://oscarliang.com/8s-fpv-drone-2023/

Edit Historical past

• Feb 2018 – article created
• Jan 2020 – added information about operating 6S on 4S motors
• Dec 2023 – up to date article