What Batteries

[jimbo385]

Hi guys,

I';ve got 4 3530 1100kv motors with the following specs;

Kv (rpm/v): 1100     
Power(W): 410     
Wire winds: 14     
Resistance(mΩ): 82     
Idle current(A): 1.5     
ESC(A): 30     
Cells Ni-Cd / Ni-MH: 6-12     
Cells Li-PO: 2-4     
Prop: 9*5 / 10*4.7     
Weight: 80g 

I';m running them on 30A SimonK esc';s with 3s batteries.

I';d like to get over 8 mins flying so I';d like to choose the correct batteries and C ratings.

So, my questions are;

1.)  What capacity battery should I get for around 8 mins flying?
2.)  What would be the minimum C rating
3.)  Is there a calculation that I can utilise to obtain the answer to the above so that I can use with other motors?

Many thanks.

[andythilo]

Hi

1. Max you can comfortably fit, recommend 5000mAh, or you could parallel 2 x 3000/4000
2. Get the highest you can afford.
3. http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en

[flybywire]

Don';t worry about the c rating too much, unless you aim to fly 3D heli';s!
I';m wondering why you';re not using 4 cell lipo';s with those motors?

Oh, as for calculations, i find the old schoolboy equation Amps X Volts = watts  seems to provide most of the answers for simple electrics, i believe it';s based around ohms law or some such?  You can then divide it up by the current capacity of your chosen lipo to get flight times, although from my experience the results should be taken with a sprinkling of salt, no sub for real world tests!

Andy

[jimbo385]

Thanks for the info guys.

In answer to a couple of questions, I don';t use 4s purely down to funding. I already had the following;

1.) Overlander Extreme 60c 2200mAh
2.) Turnigy nano-tech    25c 2650mAh

On my KK2 quad running Emax MT2213 and 9x5 props, I get 8 mins on battery 1 and 7 mins on battery 2

On my FPV550 Crius based quad running the 3530 motors 20A controllers and 10.3.8 props, I get 7 mins on battery 1 and only 3 mins on battery 2!

My conclusion is that I need the higher C rating for my FPV550.

So, my question is what';s the minimum C rating I need to run the 3530 motors as I don';t want to buy 30c and find that I really require 40c!

Cheers.

[flybywire]

Ok, I hear what your saying, but for the price of a couple of Turnigy 25c 4 cell 5000 mAh liopo';s you';d get much better flight times. (c. 10-12 mins).

N.B unless you';re using it as some kind of aerial ';hod carrier'; or ';beer lift'; that is!

[andythilo]

Oh and don';t bother with the Nano-tech batteries, the standard Turnigy blues are better.

Some of these would be your best bet : http://www.hobbyking.com/hobbyking/store/__26740__Turnigy_5000mAh_4S_25C_Lipo_Pack_UK_Warehouse_.html

$40 and 125A discharge, can';t be bad, plus they';re in stock in the UK warehouse so you can get them next day delivery .

[flybywire]

125A!  You can start a Fiesta with that. 

[dirtyharry]

Battery wise a 40c 5000mah turnigy blue is probably going to be your best/cheapest option with those motors on a hex. If you';re not silly with the throttle or use smaller props ( and its going to be a rocket with those motors) a 25c would do.

Calcs are as follows :-

Required battery c rating = (current pull of motor at max thrust x number of motors) / battery capacity in amps

so if your motors pulls 25 amps at max throttle  , and your using a 5000 mah battery on a hex

c= (25x6)/5

c= 30c (  add a bit to be on the safe side , but remember the higher the c rating of the pack the heavier and more expensive it is)

Good flight times are about weight + blade efficiency ( small efficient motors with low kv and big props) , not battery size and c rating,  unfortunately something you won';t get with those motors , you need something about 150- 200w output and 800kv with apc 10x4.7 props.

http://www.hobbyking.com/hobbyking/store/__10306__Turnigy_5000mAh_3S_40C_Lipo_Pack.html
http://www.hobbyking.com/hobbyking/store/__9183__Turnigy_5000mAh_3S_25C_Lipo_Pack.html

[flybywire]

As the legendry ';enry once said "A good big-un';ll always beat a good-little-un"!

[guest325]

I';m using 3S 2200 on a quad, flies about 7 mins on 25C and the same on 40C - only real difference is that the 40C';s make it more lively I.e. better throttle response.

[jimbo385]

That';s great guys.

I have found that my 2650 capacity 25c Nano Techs don';t last as long as my 2200 60c packs.

[dirtyharry]

prob because nano-tech batteries are pish , the one i tried didn';t last a year before losing a third of its capacity.

[guest325]

prob because nano-tech batteries are pish , the one i tried didn';t last a year before losing a third of its capacity.

+1 there Nanotechs are not as good as the normal blues, I';ve found zippy compacts the best so far - lighter and smaller for the same capacity!

[jimbo385]

Ok,

I';ve done some calculations and come up with the following. Hopefully, my maths is correct!

Motor Power (W)        = 410
Max Pack Voltage (V)  = 12.6

Max Amp Draw (A)      = 32.5       [410/12.6]

Number of Motors       = 4
Cell Capacity               = 2.2

Therefore Min C Rating = 59.2     ([32.5*4]/2.2)

If the above is right then I';d need the following;

3000mAh  45C
3500mAh  40C
4000mAh  32C
4500mAh  30C
5000mAh  25C

Cheers

[guest325]

It';s not quite that simple, what you have calculated is worst case which assumes the motors running full chat with the biggest props they will run.
This is very rarely the case in practice, without using a watt meter you don';t really know what is going on. If you are running on 30A esc';s of chinese origin I would guess you are probably never pulling more than 25A, if you are they would most likely go up in smoke! 
The smaller batteries are most likely being pushed hard but you should see that because they usually get hot if pushed too hard.
I see you only have 20A esc';s on your hex - if they handle the motors ok then your calculation is irrelevant because those esc';s will not handle 20A continuously.

[jimbo385]

Sometimes I hate my fingers! 

I';m actually running 30A controllers!

Having said that, I understand what you are saying and that what I have calculated is a max burst and not a continuous run.

Therefore, would it be reasonable to half that figure?

Cheers

[guest325]

Without using a watt meter it';s difficult to say but I usually rate at 0.6 of peak for safety, as I said before a good guide to batteries not having a high enough C rating is if they get hot or your model doesn';t seem as responsive to throttle as you expect it to.