F550 battery problems (again) - Help needed please :-)

[domx]

Hi All,

First post for a while, so be gentle :nevreness:

I've read everything I can find on the forum on this topic, but I'm still unsure why I'm getting such bad flight times from my rig. Here are the details:

DJI F550 with stock motors and ESC's
Naza GPS
Aeroxcraft landing gear
Brushless gimbal
Go Pro Hero 3
OSD
5.8GHz FPV transmitter
Graupner 10" E-Props

It's a pretty heavy setup now (1950g without a battery). That said, the flight time until the red flashing light comes on is getting worse all the time. This evening I did 3 test flights with the following results:

4250mAh 14.8V 30C packs - 2 mins 40 secs
6000mAh 14.8V 35C pack - 3 mins 45 secs

The weight of the rig with the respective batteries is:
4250mAh - 2340g
6000mAh – 2490g

I have to confess, I had the whole rig built for me so I've no idea how to check the voltage level at which the red light starts flashing, so that may be part of the issue.

I use this balance charger: http://bit.ly/1urir2C and at the end of the charge cycle for the 4250mAh packs it showed a charge of 1024 in the bottom right hand corner of the display. Does this mean that it's only partially charged the pack?

Apologies for the 'dumb' questions, but I'm still very new to electric flight and multi rotors generally, so I'm on a steep learning curve! :tennis:

Any advice or help much appreciated.

Thanks,
Dom.

 

[SJBrit]

The charger is telling you how much energy it put back in the battery, so you are only using about a quarter of that battery before the red light starts flashing. You shouldn't drain a battery past 80%, so working the numbers:

• You used 1024mAh from a 4250mAh pack.
• You CAN use 80% of 4250 mAh = 3400mAh
• So you used 1024/3400 = 30.1% of your available battery capacity
• You could therefore have flown for 2min40s/30.1% = 8mins 51s

So, that's your real max flight time - just under 9 mins. Is that more like what you were expecting?

 

[Gary Seven]

[MENTION=9934]domx[/MENTION]; think about it. At the end of your charge cycle you put back 1024mA which means you used about 24% of the battery's capacity! There may be lot's of things going on at once here, but first and foremost you MUST check and calibrate your "Low Voltage Alert" settings in your Naza Assistant. Or better yet, disable it and do some test runs, timing them each time (start with a 5 min. run, then say, 7 min., etc.). After your battery has cooled down take a reading, check each cell, and then charge it to see how many mA's it takes. Be methodical but careful.

If you were to follow the "80% rule" which I've heard repeated so many times on various forums, then 4250 x 0.8 = 3400. That's about how many mA your charger should put back in after a good discharge. How many cycles have your batteries experiences, anyway?

 

[domx]

Thanks SJBrit… that explains a lot and is definitely more like what I'd like to see from the batteries!

I now need to figure out how I change the point at which the red light starts flashing. I have an EZ OSD system which allows me to see the voltage on the Black Pearl screen. Do you happen to know what voltage I should let the batteries drop to before landing?

Thanks,
Dom.

 

[domx]

Thanks SJBrit… that explains a lot and is definitely more like what I'd like to see from the batteries!

I now need to figure out how I change the point at which the red light starts flashing. I have an EZ OSD system which allows me to see the voltage on the Black Pearl screen. Do you happen to know what voltage I should let the batteries drop to before landing?

Thanks,
Dom.

 

[domx]

Thanks for the feedback Gary… much appreciated.

I'll follow your advice and do some testing of the battery packs I have. I've got 3 of the 4250mAh packs and 2 of the 6000mAh packs. They're about 1 year old and have had approximately 30 charge cycles in that time.

Do you happen to know how I go about changing the "Low Voltage Alert" settings in the Naza Assistant? Having had the rig built for me I've no idea where to start with that one, embarrassing as it is to admit!

Thanks,
Dom.

 

[SJBrit]

Have a look on page 17 here: http://download.dji-innovations.com/downloads/nazam-v2/en/NAZA-M_Quick_Start_Guide_v1.26_en.pdf. It's a bit involved, but it does work. The main thing I test is how much battery I've used when it goes into auto-land - you want that to be at the 80% point. Do what it says in the manual, then hover with a fully charged battery until it auto-lands. Recharge it and have a look at how much energy gets put back in. Adjust the threshold voltage up or down depending on the result until you have it dialed in. Using the method in the manual works pretty well.

 

[domx]

Thanks… will give this a go.

The only issue might be that we only have Mac's in our house and it looks like the Naza Assistant will only run on Windows. A challenge to overcome I guess :nevreness:

Dom.

 

[SJBrit]

Thanks… will give this a go.

The only issue might be that we only have Mac's in our house and it looks like the Naza Assistant will only run on Windows. A challenge to overcome I guess :nevreness:

Dom.

There's a MAC version of the Assistant - that's what I use. If you look closely you'll see that the screenshots in the manual are off a MAC! That always makes me laugh to know that DJI uses MACs and that they have so little support for them

 

[domx]

There's a MAC version of the Assistant - that's what I use. If you look closely you'll see that the screenshots in the manual are off a MAC! That always makes me laugh to know that DJI uses MACs and that they have so little support for them

Tried the Mac version and it just crashes as soon as I open the application, so back to the drawing board on that one :upset:

I spoke to the people I bought the batteries off today and they're suggesting that I've wrecked the batteries by occasionally leaving them fully charged. They think that, as soon as I take off, the voltage is dropping enough to trigger the low voltage red light and, when I land and switch off, the voltage on the batteries rises back up again. Basically, it's drawing too much power when in flight.

Does this sound feasible or likely given that the batteries have had relatively little use? I did some tests today with the following results:

4250mAh 14.8V pack 1:
Red light on at 1 min 30 secs.
5 mins flight time – 2070 mAh re-charge
6 mins flight time – 2414 mAh re-charge

4250mAh 14.8V pack 2:
Red light on at 2 mins.
No 5 min flight
6 mins flight time – 2388 mAh re-charge

4250mAh 14.8V pack 3:
Red light on at 2 mins 12 secs.
No 5 min flight
6 mins flight time – 2385 mAh re-charge

Any thoughts welcome :nevreness:

Dom.