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Using higher cell LiPos
#1
Many of us start flying FPV on a 3S battery (12.6v fully charged) and quickly move to 4S (16.8v) which is often enough, providing plenty of power for even the fastest pilots. From time to time we see videos or posts about 5S (21v) and 6S (25.2v) and curiosity creeps in Smile

I recently tried 5S, the experience was both scary and exhilarating. I wanted to share the steps I took to prepare my quad for the higher voltage. (These same basic steps apply for moving from 3S to 4S as well, however many of the components generally support 4S directly.)

1. ESCs
Check the label or pull the specs. Most ESCs can handle 4S, tho not all (DYS-XM10A). Many of the modern 30A ESCs can handle up to 6S (DYS XM30A), some cannot (UBAD30A) - always check the specs.

2. Motors
I found this trickier,  manufacturers do not often publish this info. Motors should not have problems with high voltage, unless there are issues with the coils, the enamel, heating etc. Best is to research if your motors have ever been tried on the higher voltage. In the end, like most things in this hobby, proceed at your own risk.

3. Flight Controller
If you are powering the flight controller directly from the LiPo (KISS, Dodo) make sure it can handle the higher voltage. KISS can handle up to 6S directly. Otherwise, use a 5v step-down voltage regulator.

4. VTX + Camera
Most VTX work fine on 4S, many claim they can handle 5S. However with aggressive ESCs spiking the voltage, it is a good idea not to push it. Best practice is to wire the VTX after a 12v step-down, even on 4S. Ensure the step-down can provide enough current for both the VTX and the camera. Powering the camera directly from the battery is rarely a good idea. Most VTX have 5v step-downs that are filtered and well suited for powering a camera. 

5. Step-down voltage regulators
Make sure they are rated with input voltage at, or higher than the target LiPo. I've found my trusted 600ma polulus do a poor job on 5S, overheating after some time and fluctuating the output. The Matek Micro BEC 5V/12V-ADJ seems to hold pretty good for both 5 and 12 volt options.

6. Any other electronics
Generally make sure they are behind the step-down, if not specifically rated for the higher voltage. This includes LEDs, servos, OSD, etc.

When all is checked and upgraded as needed:
  • Remove propellers
  • Carefully connect the battery, preferably with a current limiter (smoke-stopper) of some sort
  • The ESCs and FC should boot normally
  • Inspect the craft for a few seconds, for smoke, smell or overheating
  • Check that you still have video in your goggles and that the radio still works, including failsafe
  • Arm the motors (without propellers) for a few seconds, check temperature - they should not be hotter than before
If all looks good, put some propellers and try flying it. Do not push it at first, anticipate the extra power, early throttle response and that your PID tune might be out of whack.

Last step is to retune your PIDs. If you expect to switch between cell counts, creating a pid/rate profile for each might be a good idea.

Here is my first flight on 5S with DYS30A (flashed with Multishot), EMAX 2205 2600KV, Betaflight 3.0
The next build will be perfect! | Fleet and build info | YouTube Channel |
[-] The following 6 users Like Jordan Marinov's post:
  • KonradS, Oscar, tozes, sloscotty, BigglesFPV, sirdude
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#2
I still need to move to 4 cell from my 3 cells. But I'm too broke from buying everything to afford 4 cells XD
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#3
(12-Sep-2016, 10:14 AM)Red Sun Wrote: This is a bold attempt, after read your post, I want to move a 5 cell lipo battery replace my 3 cell lipo battery . I think it must very funny.

Bold indeed. Keep in mind, the craft will feel very different and your tune might be considerably out of whack. I would recommend trying 4S first, even for just a few flights. What is the rest of your setup?
The next build will be perfect! | Fleet and build info | YouTube Channel |
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