Low voltage protection

J

jockelager

Member
I don't fully understand how low voltage protection works on my s800. It flies well for about 15 min with 2 6s 5000Mh. Now comes the tricky part:
Green flashing kicks in (some say it's yellow…) and shortly after is goes over to red and the S800 goes down for landing. I must be real quick to make a gentle landing.
The assistant software shows 20.4 V.
First level protection is set to 19.8 -> Loss 0 -> 19.8 Led warning
Second level protection is set to 18.6 -> Loss 0 -> 18.6

I thought there would be more time between first and second level.

Jocke
 

Z

zeng

Member
Their battery monitoring seems to be screwed up in V5.06. I had to switch it off. Hope they fix it in the next update.
 

N

nisouck

Member
For a 6S battery a fully charged Lipo voltage should be about 25.2 V.
If your charged battery show 20.4 V that may be the problem and you should make or a full charge or a Calibration.
 


N

nisouck

Member
Yes I undestand but if your voltage is 20.4, when on charge, voltage drop below 18.6 so, you land .....

What is the voltage before to start a flight?
 

KopterX

KopterX

Member
Hello Jokerlager

1. A fully charged Lipo Battery is a 4.2V/cell, that is 25.2V for a 6S Lipo.

2. I suggest about 3.6V/cell per cell for first level protection, this is 21.6V for 6S .

3. For second level i suggest to not go lower than 3.3V per cell because you might damage the Lipo pack, for a 6S this is 19.8. Your current setting at 18.6 means 3.1 per cell, with this setting you may damage the Lipos sooner or later.

4. Put around 0.6V Line Loss (0.1Vper cell for new batteries), and try again. After you land, measure again, if the voltage is still higher than you wanted, increment with more 0.1V until you find the correct line loss and get the end voltage you want. But if the Lipo is in good condition, your line loss must be around 0.6V for a 6S pack. Usually this is about 0.1 volt per cell with a new Lipo and it will increase in time when the battery will be older. You shoul check this again after 20-30 cycles.

5. If the time between first voltage protection and second is to short increase the value at first level protection until you get about 25-30 seconds time.

6. This voltage protection on DJI is a solution only if you dont have voltage and current telemetry. So i suggest you buy some telemetry and don't use the DJI voltage protection anymore since is not very accurate because of LIPOs discharge dynamics. I won't go deeper with this because is a big topic.

Line loss is the difference between voltage of your LIPO when you fly and the Lipo is LOADED (meaning there is a current load on the battery) and the voltage measured when the Lipo is disconnected from your copter, and there is NO LOAD on the LIPO pack.

There is an alternative way. You can measure the LOADED voltage by strapping the copter to your table and measure the voltage while motors running and stick is at 50%. Be very carefully if you do it this way, propellers can easy cut your fingers off!
 
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Z

zeng

Member
I believe Jokerlager's problem is similar to mine - DJI WKM just doesn't monitor the voltage correctly. I fly 4S batteries. Fully charged and calibrated in the monitor is 16.8V. Voltage protection first level set at 3.5V per cell, (14V) second level at 3.3V (13.2V) per cell. However, after the first level kicks in and I land, I measure 15.2V.
 


Z

zooks

Member
KopterX said:
Hello Jokerlager

1. A fully charged Lipo Battery is a 4.2V/cell, that is 25.2V for a 6S Lipo.

2. I suggest about 3.6V/cell per cell for first level protection, this is 21.6V for 6S .

3. For second level i suggest to not go lower than 3.3V per cell because you might damage the Lipo pack, for a 6S this is 19.8. Your current setting at 18.6 means 3.1 per cell, with this setting you may damage the Lipos sooner or later.
Click to expand...

If you set the second level at 3.3V per cell without line loss, it means that with line loss 0.1V it will be 3.2V flying...
So it is not bad for the lipo to go lower than 3.3V under load?
 

KopterX

KopterX

Member
zooks said:
If you set the second level at 3.3V per cell without line loss, it means that with line loss 0.1V it will be 3.2V flying...
So it is not bad for the lipo to go lower than 3.3V under load?
Click to expand...

No. It's normal for LIPOs to go under 3.3V under load. That's actually why DJI introduced the line loss in the equation, to compensate between ON LOAD and NO LOAD voltage readings. It could be bad to go with LIPOs under 3.3V when you measure this value after flight when is no load on the LIPO.

There is a 80% rule of the LIPOs, you may find a lot of chats subject searching google: "LIPO 80% rule". However, this rule is about a 10 year old technology. With new generation LIPOs i found that is ok to go even close to 100%.

I go usually go down to 3.0V per cell and about 100% of battery capacity. I may lose some cycles, but this is a compromise i make for longer flights. But i would not recommend this if you does not use telemetry for Voltage, Current, Capacity and battery temperature and you fly aggressively.

My conclusion, and please take it as personal opinion, is that you can go to 95% of battery capacity without loosing cycles.

Anyway battery are not so expensive anymore. So, if normally a LIPO goes easy up to 300-400 cycles using the 80% rule, and goes only 250 Cycles at 95% rule, why not chose to "abuse it" using the 95% rule? You will have longer flights but you will buy new batteries more often. It's more joy, and you deserve it. After all is a just comfort/price choice.
 
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F

fritz99

Member
Hello !

I had to disable the feature because the kopter came down much to fast.
I did not see any parameter were I can change the speed of comming down.

Fritz
 




V

vislaw

Member
A very interesting post, KopterX. I have wondered about how ironclad the 80% rule is. Not all that long ago it was considered a given that you shouldn't charge Lipos at a rate above 1X and that's changed with newer batteries supporting faster charge rates.

Thanks for your info and your advice. I think you raise a very worthwhile point in suggesting that people weigh the importance of flight time vs extending battery life. It's a personal decision based on a number of individual factors. I would emphasize that the closer you get to emptying the tank, the closer you are to dropping like a rock. The dropoff from flyable voltage to becoming a boat anchor is surprisingly abrupt!

KopterX said:
No. It's normal for LIPOs to go under 3.3V under load. That's actually why DJI introduced the line loss in the equation, to compensate between ON LOAD and NO LOAD voltage readings. It could be bad to go with LIPOs under 3.3V when you measure this value after flight when is no load on the LIPO.

There is a 80% rule of the LIPOs, you may find a lot of chats subject searching google: "LIPO 80% rule". However, this rule is about a 10 year old technology. With new generation LIPOs i found that is ok to go even close to 100%.

I go usually go down to 3.0V per cell and about 100% of battery capacity. I may lose some cycles, but this is a compromise i make for longer flights. But i would not recommend this if you does not use telemetry for Voltage, Current, Capacity and battery temperature and you fly aggressively.

My conclusion, and please take it as personal opinion, is that you can go to 95% of battery capacity without loosing cycles.

Anyway battery are not so expensive anymore. So, if normally a LIPO goes easy up to 300-400 cycles using the 80% rule, and goes only 250 Cycles at 95% rule, why not chose to "abuse it" using the 95% rule? You will have longer flights but you will buy new batteries more often. It's more joy, and you deserve it. After all is a just comfort/price choice.
Click to expand...
 

T

toptweaks

Member
i am using 3s lipo 5000mah at the moment, planning to have paralel conection into my f550 hexa running with dji naza... can some one please check if the value used is correct in below picture.

if not correct please suggestion for me as per explain by KopterX
as below:

first level protection

4.2v / cell x 3s = 12.6v

3.6v / cell x 3s = 10.8v

second level protection

3.3v / cell x 3s = 9.9v


View attachment 4670
 

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T

toptweaks

Member
i upload the pics big but it turn out small well load it from another page..

voltprotect.png


what is the best value to put it ... let says if the batt is all new ....
 

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