Lipo Batteries Voltage

[nicnac]

I have a prototype build of a quadcopter with 4 times 40 Amps brushless controller and 4 times 980kV motors (http://shop.lindinger.at/product_info.p ... id=9700063). They are 13A max permanent and 17A max burst (15sec) current. Burst power of 200W.
So in my eyes this totals (without bursts, wich I guess are not there at 1/2 throttle) to worst case 4*13 A = 52A.
I have a 2,2Ah LiPo pack with a C rating of 30 (50 burst). So to my eyes this should total in 2,2Ah/52A = max theoretical time for worst case = 2,5 min.
But there is no worst case, since I'm experimenting still and never gone to full throttle! So I'm dumping arround without takeoff and still got just 1:14 min motor time. The battery falls from 10,5 to 8,4 Volt in this time. And then single motors stop or all just stop. Is 8V allready drawn low?

Is there a logic mistake in here, did I crash the batteries? And for a 3 Cell pack rated 11,1V is 10,3-10,5V full charged (I only used a cheap balance charger)?
And/Or do you have any advice on how big the batteries have to be to fly arround 5-10min max? 5min with a little confidence.

[tovrin]

http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en

[jhitesma]

10.3-10.5v is nowhere near charged. Fully charged on a 3cell pack is 12.6v or 4.2v per cell. 10.3 is 3.5v per cell and that's the point I have my warning beeper set to go off at (though I usually land before that if I remember to set my TX timer which goes off when I'm around 3.6-3.7 per cell.)

[treym]

A few seconds after you landing .. each cell of your battery should be at 3.7v .. more or less ( depending of the overall expected battery life , 3.7v is a conservative value )

As pointed by tovrin , you might just have a very wrong weight/props/motor/battery ratio .

8v for a 3s battery = dead battery

[nicnac]

Thanks. And no - the whole thing weighs 518g with battery and I saw far heavier things.
The problem is probably my "Balancer". It was 20 bucks and is not worth a cent. Today I'll try a Graupner Charger wich I get access to and see if I can rescue anything.

Read so many numbers allready - thanks for the clear statements! I'll keep in the boundaries from now on.

[tovrin]

good call nicnac, i spent $100 on my charger because i know how crappy cheap chargers are!

[nicnac]

Yep, that was the problem!

Allways get decent stuff - nobody wants the bottleneck of his hobby to be a burning battery pack or wild props flying arround.
I had to learn this the hard way (batteries probably allready suffered)!

Please learn from my example

..fly on

[linuxslate]

Don't be too quick to knock cheap chargers.

I have one of these:


http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=36906

US$ 9.xx ...and I think it is awesome.

I bought it to charge my Video batteries (2S) and the 2S batteries in my son's V262 and a small brushless Quad, but now I often use just this instead of my main LiPo charger even for my main flight LiPo's. It's simple, faster to connect (since there is no main battery lead), and not prone to settings errors (there are no settings).

I am using it with a 1.5A, 12V wall-wart, and that is sufficient for up to 3S batteries (4S batteries may need a beefier power source).

As advertised, it is accurate to +/- 0.01 Volt, as verified with a separate LiPo checker, and a trusted Digital Multimeter.

It also works in the field as a LiPo checker.

I probably would not recommend it for charging anything really big. It gets pretty hot charging my 3S flight batteries, and of course charging anything over about 3000mah is going to take many hours, but for 2S or 3S, unless I needed a really fast charger, I would be perfectly happy if this were my only charger.