Battery losses

[Flydigital]

..Not sure if that's the correct term for what I'm experiencing.
I charge a 3s battery to 12.6v. Once it's off the ground the levels are immediately into the 11.x range. I have a 1st warning beep set on my Tx of 10.6v and 2nd set at 10.4v.
Within a couple of minutes I start getting beeps when I go full throttle up. So it may be at 11.2v at hover then drop down to 10.2 on a major thrust then recover back above 11v.
Is this a sign of poor quality batteries? They have been used about 20times max, each battery.
(Turnigy Flight Max 3s 500maH on a F550) - correction 5000mAh
Thanks for any help here..

 

[eskil23]

Are you really using a 500 mAh battery or are you missing one 0?
If you are using a 500 mAh 20C battery you have definitely exceeded the C-rating.

 

[Flydigital]

Yes, sorry typo. It's 5000 mAh.

 

[eskil23]

That's more reasonable.
500 mAh * 20C = 10 A
5000 mAh * 20C = 100 A

Now I don't know what motors or ESCs you are using, but I think a good guess is DJI 2212 motors with 15 A ESCs. With 10x4.7 props they max out at about 15 A each at full power which is what the ESCs can hande, but you still get a total of 90 amps. That is close to the C-rating of that battery. If you have larger ESCs or motors you will exceed the C-rating at full power.

 

[Benjamin Kenobi]

Sounds normal to me. The lipos should recover after you reduce power. Alas lower quality lipos do have a large voltage drop under load so just lower your limits a bit and check how many mah you're putting back in after each flight (you should be putting back in no more than 4000mah into a 5000mah lipo).

 

[Flydigital]

Now I don't know what motors or ESCs you are using, but I think a good guess is DJI 2212 motors with 15 A ESCs. With 10x4.7 props they max out at about 15 A each at full power which is what the ESCs can hande, but you still get a total of 90 amps. That is close to the C-rating of that battery. If you have larger ESCs or motors you will exceed the C-rating at full power.

Yes it's standard DJI motors - 2212 / 920Kv but the ESCs are 30A, supplied as standard. The 5000mAh battery. I think it's 20c.

 

[Flydigital]

check how many mah you're putting back in after each flight (you should be putting back in no more than 4000mah into a 5000mah lipo).

Thanks for that. I've actually just started keeping a log. A couple of them are over the 4000mAh when charging. I would have assumed that if you drain to 9.9v on 3s (which is the point the stop flying) then fully charging would stick 5000mAh back in. Is that the general principle?

 

[PeteDee]

A 5000mH pack should only ever need 4000mH put back in, if you are putting 5000mH you are going far beyond the 20% rule, never deplete your LiPo's below 20% left or you will damage the pack.

 

[Flydigital]

Ok but 20% of what exactly?
The voltage on take off is 12.6v and will drop down to say 10.4v. Are you saying I should only use 20% of the battery? So 80% remaining would be 10.1v. I have been told don't go beyond 9.9v. If I'm wrong can you explain the 20% thing. Thanks!

 

[Flydigital]

Update. Should have googled first '20% lipo rule'. Interestingly from what I read people seem to fly until their lipo alarms go 3.3v? But then once back on the bench the resting voltages recover up to 3.7v or so.
This is actually my experience but have only just started monitoring charging mAh and see 1 or 2 batteries going over the 80% charge. Maybe cheap batteries but I'll get a better sense of them the more I continue to log and more accurate figures.

 

[eskil23]

All batteries have "internal resistance" that causes the voltage to drop under load. How much depends on the size and quality of the cells. The C-ratings are a good measure for lipos.

 

[fltundra]

Update. Should have googled first '20% lipo rule'. Interestingly from what I read people seem to fly until their lipo alarms go 3.3v? But then once back on the bench the resting voltages recover up to 3.7v or so.
This is actually my experience but have only just started monitoring charging mAh and see 1 or 2 batteries going over the 80% charge. Maybe cheap batteries but I'll get a better sense of them the more I continue to log and more accurate figures.

I never fly lower then 3.6 ever under load (17 amp hover, 3 axis with 600mw tx and strobes) and can reach the 80% mah mark before hitting that voltage. 4s8000mah readymaderc.
You need to at least be able to measure IR or else it's a shot in the dark as far as pack C rating goes.
Here's a tool I've used that will give you current, and C rating knowing you have IR measurements.
http://www.soko-heli-tools.com/en/lipo-battery-calculator/lipo-battery-calculator.html
Also, get a good charger. Icharger, or Cellpro, only two I own and would ever purchase again.

 

[Benjamin Kenobi]

Update. Should have googled first '20% lipo rule'. Interestingly from what I read people seem to fly until their lipo alarms go 3.3v? But then once back on the bench the resting voltages recover up to 3.7v or so.
This is actually my experience but have only just started monitoring charging mAh and see 1 or 2 batteries going over the 80% charge. Maybe cheap batteries but I'll get a better sense of them the more I continue to log and more accurate figures.

Good man. There's lots to learn and we all made errors in the beginning. Do do some reading around lipos as they are way more dangerous than you first think they are.

Each setup is different so just spend some time flying and seeing how the lipos behave and how much you put back in. You should also be using a timer to time your flights. Start with 5 minute flights and then see how many mah you're putting back in. Adjust accordingly.

And have fun!