Monitor Battery Voltage & Decide When to Land

As a quadcopter pilot, it’s important to know when to land as flying too long can result in over-discharging your LiPo battery and even permanently damaging them.

There are many ways to determine the best time to land, in this article we will discuss the pros and cons of these methods and what you should use.

Make sure to check out this article to find out more about how to look after your LiPo batteries.

Checking your battery voltage

The most common way of finding out flight battery level, is battery voltage. There are many ways of measuring battery voltage in a quadcopter.

Land at 3.5V per cell!

  • 2S – 7V
  • 3S – 10.5V
  • 4S – 14V

Using Lipo Battery Voltage Alarm or Buzzer

The most popular choice is using a voltage alarm, which is connected to the balance plug of a LiPo battery. They are cheap, and widely available. The buzzer is triggered when any one cell drops below a set threshold, e.g. 3.5V per cell.

 

 

Built-in Voltage Sensor in flight controllers, FPV cameras and OSD

Many flight controller boards, OSD, and even flight controllers these days have built-in voltage sensors (a.k.a VBAT feature), and a low voltage alarm is triggered at a user defined value set in the software.

The biggest problem with voltage is that it goes up and down when the load changes. For example when you do a punch out on your quadcopter, the voltage drops badly, but when you lower your throttle the voltage will quickly recover.

Bad LiPo batteries tend to have worse voltage sag under heavy load, and false alarm might happen a lot with low voltage.

Checking your current

You can measure how much current is being drawn by the quadcopter in real time using a current sensor.

More importantly, you would be able to see how much battery capacity (mAh) has been consumed, and since you know the LiPo battery capacity, you would be able to work out how much capacity is left in the pack exactly.

“mAh consumed” is a much more accurate indicator than voltage to decide when you should land, because it doesn’t fluctuate and with throttle level like voltage.

The 90% rule… Must land when you hit 90% of the capacity! At this point the battery is probably at around 3.5V – 3.6V in theory.

However, you should not rely only on “mAh consumed”, because the data always resets to zero when power is disconnected, or when the FC restarts. This method also only works with fully charged batteries, as you won’t know what the exact initial capacity is on partly discharged batteries.

Therefore It’s best to have both the current sensor and VBAT (voltage sensor) on a quadcopter.

However current sensor might be inaccurate when you first get it, and need some calibration described in this guide.

If you don’t have a current sensor on your quadcopter, you can also set up a “virtual current sensor” as shown in this tutorial.

Timer

Using timer to determine when you should land is an extremely primitive method for quadcopter flying, as battery usage will always be different in each flight. The same battery pack might last longer or shorter, depending on how aggressive you are on the throttle stick in that flight.

Timing flights is probably the last resort for me to decide when to land if there is absolutely no other better options.

The Different “Low Voltage Alarms”

There are many different forms of low voltage alarms you can have on your quadcopter.

Buzzer/Beeper

If you have a buzzer connected to the flight controller, it will beep when voltage is low, or if you use one of those low voltage alarms that goes to the balance plug.

 

OSD

For pilots that fly longer range, one might get into situations where the quadcopter is too far away, and the buzzer on the quad cannot be heard. The best option in this case would be using an OSD to display the voltage on the live-streamed FPV video.

I personally prefer using OSD because I love seeing numbers! I can see what the voltage is and plan my flight better, rather than getting shout at by the buzzer only when voltage is nearly dead.

Telemetry

Similar reason to using the OSD, Telemetry is a great alternative to OSD (and it can also be a backup system that runs in parallel to OSD).

Many radio transmitters like the Frsky Taranis can display battery voltage on the screen. You can even set it up to speak to you what the values are in human voice!

 

 

Edit History

  • Dec 2014 – article created
  • Aug 2016 – Updated info about telemetry
  • Aug 2017 – Updated info about current sensor

5 thoughts on “Monitor Battery Voltage & Decide When to Land

  1. Szzz

    Hi Oscar,
    What do You think of this product?
    I’m from europe and shipping nearly double the price.
    I don’t like the talking Taranis telemetry and my simple osd is influencing my video quality.
    Wondering if the FLEA would also have a negative impact on the video or not.
    Great work you are doing here…

    ebay.com/itm/Meet-Flea-battery-telemetry-for-Fatshark-Dominator-maximize-flight-times-3s4s-/321826519999?hash=item4aee5afbbf:g:zEoAAOSwd0BVxPnp

    Reply
  2. Dustin Sallings

    Hi Oscar,

    I noticed there’s no mention of current here. I find a current sensor to be more valuable than voltage, as I can sag voltage pretty quickly while still having current remaining. Current gives me an idea of how much longer I can fly (even if I have to back down a little). Voltage can do similar, but is far more crude and depending on too many things.

    Reply
    1. Oscar Post author

      You mean battery capacity? yes it might work too, but capacity used/remaining is an estimation which depends on a lot of factors, so i won’t use it alone as a signal to land. I think voltage still a primary indicator.

      Reply
  3. Sam

    Thanks for this Oscar. I have a buzzer like the one shown in your picture, however my balance lead is already being used to power my FPV gear. Do you know of a way to split the balance lead so i can also attach a buzzer? Thanks again.

    Reply
    1. Oscar Post author

      sure, maybe some DIY an adapter for the balance plug or the XT60 plug to power your FPV gear? while available for voltage alarm?

      Reply

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