Battery life... 45C is too much?

[frviana]

I have a F550 with 8"props and 3000 4S battery with a gopro mounted with its case on the bottom... everything is perfect except that the battery seems to last 2-3min.

Battery is brand new and I have a 2nd one that is the same thing... I thought in running them in parallel but I think the extra weight will make things worst.

My question is: Is 45C too much and the rotor drains them faster? Should my flight time change when I replace the props with the Graupner 10"?

 

[Elliott000]

about how much does the copter weight, i was burning 850 mah a minute but on a heavy lift copter... are you using the built in cutoff? if so i suggest setting it to off and flying an average flight on a full battery for 3 minutes since you havent gone more than that. After, charge it up and divide how many MaH you put in by 3 and youll know what you are burning off. giving you a rough max flight time, on those i figure a stock f 550 would see 4 - 5 minutes

 

[Tomstoy2]

Wow! You have something wrong. You should be getting at least 4-5 minutes I would think.

45c isn't too large. Think of it like a fuel line on your car. A larger fuel line doesn't mean that you are going to consume one more ounce of fuel, just gives you the ability to supply fuel to a larger engine.

Personally, I wouldn't go over 30c for something in a 550 range, save some bucks.

Your problem lies elsewhere.

How are you charging them? Have they gone below the 20% rule of thumb?

I suspect that if they are fully charged and drain that fast that you have a bad cell. When you plug in your charger what does the voltage read?

 

[frviana]

Can't be a bad cell because the same happens with both batteries. They are both same brand and both 3000mah but bought a month apart.
I charge all the way up to 16.8v and run it down to about 13.9v
I charge them normal (not fast charge). I've checked and all cells are balanced.

I haven't weighted the F550 yet, I will try doing that and will post here and will also do the calculation suggested by Elliot000 and post here the results.

Thanks for the comments

Wow! You have something wrong. You should be getting at least 4-5 minutes I would think.

45c isn't too large. Think of it like a fuel line on your car. A larger fuel line doesn't mean that you are going to consume one more ounce of fuel, just gives you the ability to supply fuel to a larger engine.

Personally, I wouldn't go over 30c for something in a 550 range, save some bucks.

Your problem lies elsewhere.

How are you charging them? Have they gone below the 20% rule of thumb?

I suspect that if they are fully charged and drain that fast that you have a bad cell. When you ug in your charger what does the voltage read?

 

[frviana]

Flying weight: 1737 grams, 1.73kg, 61.27oz, 3.82lbs

 

[kloner]

Can't be a bad cell because the same happens with both batteries. They are both same brand and both 3000mah but bought a month apart.
I charge all the way up to 16.8v and run it down to about 13.9v

Your killing the battery. they both do it cause you killed em both. Try discharging so it sits with no load at 14.8....... after the first time you took it past that, you damaged it. every flight after just kept driving the nail in the coffin.


Your batteries are all fried. if you have a icharger you can read the Internal resistance to confirm it, but honestly, there gone

 

[frviana]

This is the first time I ran till that point. Before it was cutting at 14.9 but I thought the flights weren't lasting long and I reduced to 14.10... when I plugged on my charger it showed 13.9 and in 2 seconds changed to 14.20...
Thanks for letting me know... I will adjust the cut-off point back to 14.8. Hopefully it didn't damage much as it was only once that I run it down that much.

 

[kloner]

now your talking about two different voltages. in a voltage cutoff setup, it is under load and the voltage would sag depending on the ir and the c rating. you want your battery no lower than 3.7 volts a cell when you put it on your charger.

none the less, 2 minutes? if you charged a pack all the way, ran it till you had 3.7 amps a cell when you went to recharge it and the time was really 2-3, it's a gonner. if the votage sag is making the battery drop in voltage so low it is shutting down when it shouldn't, that is internal resistance damage

this is a good video to watch

 

[matwelli]

a quick and dirty calculation http://multirotor.files.wordpress.com/2011/03/multirotorcalc1.xls (based on 170 watts per kg to hover - good multis hover at 120-140) and 80 % battery capacity

1750 grams ( frame = 1388 grams battery = 362 grams) has a flight time of 7 minutes and 10 seconds (at 170watts/kg)

if its a bit more efficient (Ecalc will tell you) , say 140 watts per kg (modify the cell B12 from 170 to 140 ) then its 8 minutes and 42 seconds

do as above, just fly it for 3 minutes, then put back on the charger and actually measure the amount of mA that get put back in , from a 3 minute run, you would expect about 1000 mah to go back in (at 170 watts per kg)


3.7 volts per cell (14.8 volts total) is about 20% capacity left, but expect a sag of say 0.2 to 0.5 per cell under load, your multi is drawing about 20 amps or 6.7"C" from those cells, so allow say 0.8 volts all up, so in flight (14.8 - 0.8 =4 volts) try running untill the voltage hits 14 volts under load.



so , if you do the testing, fly it for 3 minutes and put about 1000 mAh back in, but the cell voltage dropped very badly in flight, then either, as stated above both are damaged, OR have a look at your wiring, multiple connectors, thin wires and not-so-good solder all add to the voltage drop under load. is your in-flight battery monitor rigt at the battery (on the ballance tap) or further down the line ?