Plane loses power mid flight

[Boiii]

Hi, yesterday i was flyimg my DIY trainer. After 7 minutes of flying I suddenly had to use full throtle to stay in the air. I had low voltage buzzer which was set to 3,6v and my ESC had low voltage cut off set lower than that. When I landed it I checked the buzzer readings and cells were about 3,9v or something like that.
What could possibly cause this?

 

[Ketchup]

First, you should probably set your alarm a bit higher, maybe 3.7 or 3.8 volts as that would give you some good headroom just in case your flight goes a bit long. Also, your problem could be voltage sag. I'm not sure why or how it happens as I'm no battery expert, but I know that if you draw a lot of current from a lipo the voltage tends to temporarily drop, but it can recover soon once you lower the throttle. My guess is that after 7 minutes of flying the power decreased, so you increased throttle and that just made things worse as the voltage sagged. Then when you landed the battery recovered and by the time you were able to check it, you had 3.9 volts again.
Also what plane/power system is this and what battery is this? If the C rating of your lipo is too low that could contribute.

 

[Boiii]

First, you should probably set your alarm a bit higher, maybe 3.7 or 3.8 volts as that would give you some good headroom just in case your flight goes a bit long. Also, your problem could be voltage sag. I'm not sure why or how it happens as I'm no battery expert, but I know that if you draw a lot of current from a lipo the voltage tends to temporarily drop, but it can recover soon once you lower the throttle. My guess is that after 7 minutes of flying the power decreased, so you increased throttle and that just made things worse as the voltage sagged. Then when you landed the battery recovered and by the time you were able to check it, you had 3.9 volts again.
Also what plane/power system is this and what battery is this? If the C rating of your lipo is too low that could contribute.

I have 40Amp ESC with 3a linear BEC. And I use 2200mah 3s lipo. I think that it has 30 or 40C rating. So as I understood Could I continue to fly till the buzzer turns on.?

 

[Matthewdupreez]

I have 40Amp ESC with 3a linear BEC. And I use 2200mah 3s lipo. I think that it has 30 or 40C rating. So as I understood Could I continue to fly till the buzzer turns on.?

As long as your battery has a C rating higher than 20C you should be fine...
What prop are you running on your motor?
Another thought... What charger are you using to charge your battery??

 

[Boiii]

As long as your battery has a C rating higher than 20C you should be fine...
What prop are you running on your motor?
Another thought... What charger are you using to charge your battery??

I am using 10×6 prop qnd i have imax B6AC v2 charger(original)

 

[Matthewdupreez]

I am using 10×6 prop qnd i have imax B6AC v2 charger(original)

What motor??

 

[Boiii]

What motor??

Emax mt 3506-650kv. But i think that it is ot original because it did not come with x mount. I got that mltor for free

 

[Matthewdupreez]

Emax mt 3506-650kv. But i think that it is ot original because it did not come with x mount. I got that mltor for free

All in all I can't think why your setup isn't working.... Only solution would be the battery is a bad battery... You do get them occasionally... Or your battery is overheating....
How much airflow does your battery get??

 

[Boiii]

All in all I can't think why your setup isn't working.... Only solution would be the battery is a bad battery... You do get them occasionally... Or your battery is overheating....
How much airflow does your battery get??

It was 1st successful flight for my plane. I am gonna post picture qith my plane

 

[Boiii]

.

 

[Boiii]

I use packing tape to secure lipo inside

 

[Matthewdupreez]

.

Try cutting some holes so air can travel around the lipo

 

[quorneng]

Boili
An Emax mt 3506-650kv should not be taking even 10A at full power with a 10x6 prop on a 2200 mAh 3s LiPo so at full power it is only taking 5c from the battery. If it is properly fully charged you should manage 12 minutes. Longer if you fly at reduced throttle.

What does you B6 AC show as the final voltage cell voltages when the charger stops saying 'full'? In case you don't know, press the "Inc." button to display the cell voltages. They should all be the same at 4.20 V.
It sounds to me like you battery was not fully charged at the start of the flight and after 7 minutes the ESC simply cut out at its Low Voltage setting. The voltage once the battery is switched off does not tell you what it was during the flight.

Be aware that flying until the ESC cuts out the power (if that is what happened) does not do a LiPo any good at all. It will degraded the battery every time it happens.

It pays to ensure a LiPo is fully charged, preferably using the 'balance charge' option and ideally take notice of what the cell voltages were at the start of the charge and how long it took to reach full charge at a 1c charge rate, which would be 2.2 A for your 2200mAh battery. If it takes longer than 1 hour for the charger to stop then then the battery is likely weak and will no longer deliver its full capacity.

 

[Boiii]

Boili
An Emax mt 3506-650kv should not be taking even 10A at full power with a 10x6 prop on a 2200 mAh 3s LiPo so at full power it is only taking 5c from the battery. If it is properly fully charged you should manage 12 minutes. Longer if you fly at reduced throttle.

What does you B6 AC show as the final voltage cell voltages when the charger stops saying 'full'? In case you don't know, press the "Inc." button to display the cell voltages. They should all be the same at 4.20 V.
It sounds to me like you battery was not fully charged at the start of the flight and after 7 minutes the ESC simply cut out at its Low Voltage setting. The voltage once the battery is switched off does not tell you what it was during the flight.

Be aware that flying until the ESC cuts out the power (if that is what happened) does not do a LiPo any good at all. It will degraded the battery every time it happens.

It pays to ensure a LiPo is fully charged, preferably using the 'balance charge' option and ideally take notice of what the cell voltages were at the start of the charge and how long it took to reach full charge at a 1c charge rate, which would be 2.2 A for your 2200mAh battery. If it takes longer than 1 hour for the charger to stop then then the battery is likely weak and will no longer deliver its full capacity.

Just charged it. All cells are at 4.20 v. In that flight the buzzer did not start to beep and ESC low voltage cut off is 3.2v

 

[Matthewdupreez]

Just charged it. All cells are at 4.20 v. In that flight the buzzer did not start to beep and ESC low voltage cut off is 3.2v

it seriously does not make sense......
try fly it again...

 

[Merv]

....What could possibly cause this?

A bad cell. When you land, check the voltage of each cell. One of them could be significantly lower than the rest. That is, two cells at 3.7 & one at 2.7 or lower.

An old battery pack. All packs, as they age, lose the capacity to supply the amps. The pack is still useful in a low amp draw situation. Use it to power your FPV or some other project.

Something is overheating. When you land, it is good practice to check the temperature of everything by touching them, the motor, ESC & battery. Warm is OK, but if you can't comfortably hold it, that's too hot.

 

[CappyAmeric]

There is a reason why many off the shelf transmitters default to 5 minutes for the flight timer. If you start having to use full power, it is time to land no matter how long it has been. Also, I never fly below 3.5 volts per cell - not the average of cells - and usually try to land with 3.7 volts per cell.

BTW, most LIPOs will have their voltage bounce back up after landing when you have been drawing them under stress.

 

[quorneng]

All cells are at 4.20 v

And so they should be at full charge. What were the cell voltages at the start of the charge? Were they all pretty close like within 0.02 V of each other?
If you really "had to apply full power to stay in the air" it can only be either a weak battery or the ESC over heated. Note some ESCs first reduce power at a low voltage and only cut it completely at a lower setting. ESCs can do the same when they over heat. However at 10A with a 30A ESC over heating is rather unlikely so it looks like a battery issue.
Of course this assumes that there is nothing else like a poor connection somewhere that is simply making a poor contact.

By far the easiest way to diagnose this sort of problem is by substituting each component in turn one at a time with ones that do work. This of course assumes you have access to spare bits.

 

[Boiii]

Oh, I forget to mention that it was about -1degree cesius.

 

[Tench745]

Oh, I forget to mention that it was about -1degree cesius.

This is important information. Lipo batteries won't be able to deliver as much current when they get cold. The colder it is the worse this gets. 5 minutes seems like a reasonable time for this setup in cold weather.
As others have said, the Low Voltage Cutoff is a safety measure, it is the absolute minimum a battery wants to be discharged to. Typically you want to stop flying before you get to that voltage. Personally, I don't like to discharge my batteries below about 3.4v per cell at the lowest, it is easier on battery and keeps it healthier over time.