Battery Volt Reading Drops 1V when motors start

Hello ,

i have a 6s battery and a smartAP PDB. My voltage reading is correct but when the copter is on the air (using motors) my voltage reading drops almost exactly 1 volt , when i land goes up again (by 1V).

  • Is this a normal behaviour ?

  • can i fix this to always have “correct” value?

  • I have my BATT_LOW_VOLT at 21.6V should i put it to 20.6V to compensate ?

Thank you for your time,

Are we really at this level?

Am sorry , i should have known this ?

Knowing that battery voltage drops when under load? Should you know it? I don’t know what you think?

Hi @Corrado_Steri,

If i knew it i wouldn’t be here :D.

Now that we have established the lack of knowledge i have, can you tell me if the BATT_LOW_VOL should be set with the Volt drop on load or not ?

at 21.6 when on load (22.6V not on load) when i charge my battery (22000mah) i charge 11000mah (50% of full batt) which is way less than the 80%.

  • is it safe to set BATT_LOW_VOL to 20.6V so its actually 21.6 V ?

best wishes!

Drone type, weight, motors, props, log file ecc ecc…

It is not the lack of knoledge that irritates me, it is the lack of search trough forums for an answer that has been given dozens of times and can be even spotted on any log file posted by other users. Just get a log file, open it look at battery voltage on take off and you have your answer, but i guess it is easier to ask useless questions here.

Hello ,

Its not very polite what you said , ive searched the forums and read the docs . i still cant find the answer am looking for.

All i want to know is what my failsafe voltage should be? Should i take into account the voltage drop or not?

If there is some doc page i missed or some threat could you please point that to me ?


What you don’t understand in:

“Just get a log file, open it look at battery voltage on take off and you have your answer”

Am sorry ,

so i open a log see the voltage at take off and that my failsafe ?

so my bat is 25.2~V before take off , at take off its 24.2~ V so my failsafe is 24.2 V? am sorry i dont get it ?

Ok no prob, have a nice day.

So you want Failsafe action (RTL, land, etc) immediately after take-off? Think about that. You need to read the Wiki. Start here: Battery FS
And then read about Lipo batteries in general, there are countless guides. Google “Lip0o Battery Guide”.

Hello @dkemxr,

What i wrote there is following @Corrado_Steri instructions “Just get a log file, open it look at battery voltage on take off and you have your answer” . (Which btw he has edit his posts from before)

All i want to know is what i should use for a battery failsafe value, the value that i read on load which is -1 volt or the value that i get when drone is not flying.

Eg. If i have the failsafe at 21.6v when the drone is on the air my curV is 21.6 but actually is at 22.6V, should i change my failsafe ro 20.6 so it uses this sag volt values ?

Thank you for the links (ive been there before)


21.6 for a 6S battery is fine. But you need to make many flights and determine what work best for you. Look at the consumed mah also. I try to plan on landing between 80-85% of pack capacity, I actually don’t pay close attention to battery voltage. You also have the option of setting the FS based on Sag voltage with BATT_FS_VOLTSRC.

Hi @dkemxr,

Am afraid to use BATT_FS_VOLTSRC but as you suggested i was checking how much mAh i was charging back the battery and usually is around 11000~mAh which is half of its the capacity.

I’ll do what you suggested and start checking capacity instead of voltage .

Thank you ,

You can also set a FS on mah consumed. Just be sure the battery monitor is configured properly and calibrated.

I would say it’s a pretty normal drop 1 volt at say 20 amp comes to 50 milliohms of resistance in wiring, even less with higher current. Good old ohm’s law.

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Yep thats what i meant to use the BATT_LOW_MAH and yes ill fine tune the current readings