4S Battery High Voltage Sag?

Hi guys,

I’d like to know how to tell if my voltage sag is within normal parameters.

When my quadcopter is at 50% battery (4S, according to my FlightDeck script on Taranis) I’m getting 14.5V. This is while in auto mission & moving forward.

I have a 680mm Quad frame with 2kg AUW. It’s running on 4S 5200mAh (35C/70C Burst) from Lumenier. I’m swinging 15"x5.5 props and four T-Motor MN3508-380kv. I’m using Mauch Power modules.

Off the bat: I know my quad is heavy for the thrust on 4S. Also my batteries are slightly puffy, I’ve never had batteries puff so I can’t discern the gravity of the swelling.

Thanks in advance!

log file: https://www.dropbox.com/s/7v5kebof0g2bq1o/2019-05-09%2015-37-02.bin?dl=0

online host log file: https://plot.dron.ee/68Qy

What brand and C rating are the batteries?

4S 5200mAh (35C/70C Burst) from Lumenier

Thanks, I see that in your original post now. I must have read it too quickly the first time…
I don’t have a program to review logs on this computer to see how much current you’re using at the time.
But, I have not had great luck w/ Lumenier batteries, and think what you’re seeing sounds about right. Especially if your batteries are puffy… They’ve usually lost some capacity at that point.
All my lumenier bats eventually puffed… So did my ‘Zippy’ batteries. My graphene batteries have been great! I can abuse them, run them dry and no problem. Accidentally charge as lihv to 4.35v per cell, no problem. They’ve never puffed on me.

I’ve got Tattu brand I can buy as well, any suggestions on those? Dealing with HobbyKing is always so slow.

People generally consider them high quality. They’re still just standard lipo’s though… Probably will puff if you pull too much power or over discharge them,etc. The graphenes really are special. But the Tattu should hold up better than the lumeniers.
You’re only discharging them at about 5C…
I usually drain my batteries to about 3v per cell under load. So I’d consider them empty at 12v. Then the voltage should recover a bit on the ground to 3.3 or 3.5 per cell.

You should be running a 6S battery.

With a 1555 and 4S you are getting 430 grams of thrust per motors at 50% throttle. That comes out to 1620 grams total. The aircraft is under powered and that causes high current and significant voltage sag. I’d guess hover throttle is around 60%. That’s not “bad” but you are cutting into the amount of throttle you have left for attitude control.

If you run 6S, at 50% throttle each motor will make about 820 grams of thrust for a combined total of 3280 grams and the aircraft will be overpowered. To get closer to a hover throttle of 50%, go with a 1344 on 6S. You will get 550 grams per motor for a combined 2200 grams (2.2Kilos) of thrust.

To get a better handle on this we need to know what the DRY (no battery) weight is. Then we can play with battery weights and give you recommendations that will give you the most flight time using the 1555 props. My thinking is a 6S 10000mAh.

I have a slightly stretched Tarot 650 Sport. I’m running 350Kv motors on a 10000mAh LiPo swinging 1655 props:

Aircraft Dry Weight (No Battery) (g) 2085
AUW (with Battery (g) 3305
Battery Capacity (mAh) 10000
Number of Cells 6
Battery Weight (g) 1220
Battery energy density (Wh/kg) 181.9672131148
Number of Motors 4
Thrust per Motor (g) 826.25
Motor Efficiency (g/W) 7.87

Expected Flight Time 31.7181240545 minutes
Flight Time with 20% Reserve 25.3744992436 minutes

																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																				Tarot 650 Sport Stretched to 662mm																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																																															

Pixhawk w/GPS
3DR 915mHz Telemetry
XT-Xinte 5010-350Kv Motots
1655 CF Props.
Tarot Retracts
FlyTron Navigation Strobes
Craft&Theory Telemetry
6S +12 volt BEC
6S +5 volt BEC
OLED Display
3 Axis Gimbal w/ STorM32 Controller
GoPro Hero 3+ Black
Tarot “Carbon Look” Canopy
MavLink OSD running MWOSD
200mw FPV Video Transmitter
RHCP Clover Leaf Video Antenna

Excellent response, thanks so much for sharing your build and knowledge! I knew that 6S would be a better match. What would be the benefit of going for shorter 13" props?

My dry weight is 2200g (with my Sony A6000 on it)
My lumineer 4S 5200mAh is 486g
My LiHV 6S 5500mAh is 580g

If you look at the motor data chart, swinging 1344’s on 6S 5200mAh puts the motors right in the throttle “Sweet Spot” of 50%. The “extra” 200 grams of thrust makes up for the 200 or so grams added by the 6S battery. Based on the data you gave me, you’re looking at a 29+ minute flight time using 80% of the battery capacity.

Another added bonus is that because the props will be spinning faster, attitude control response will be more “lively.” The aircraft will have lesser tendency to “wallow” in roll and pitch, yaw will be crisp and more precise, and landings will be smooth and easy to control.

If you go with 1448 props on 6S 5200mAh battery you have about 200 or so grams of “extra” thrust at 50% throttle making the aircraft a tad over powered. This isn’t particularly “bad” from a performance stand point, but is does tend to have a negative impact on handling and pilot control. The reason being when you are overpowered, the hover throttle is below 50%. This shortens throttle stick throw between low and hover throttle so you end up loosing resolution which can cause landings to be “exciting.” The real upside to using 6S is you can use longer props and a bigger battery.

For example, if you use a 6S 10000mAh battery that weighs 1200 grams like I do, your AUW would go up but you could run your 1555s and get a flight time of about 34 minutes give or take.