Quote:
Originally Posted by ReV:-O
yeah thanks man i fully appreciate all your help. i think u've more or less steered me away from maxamps now! lol.
when working out the continuous current, dont you do amps x C rating?
so VintageMA, how can you say 25C is more than u'll ever need? because that depends on the mAh. like you can have a 4000mAh 25C lipo, but that would only be 100A continuous (4 x 25 = 100), so this isnt good enough for any Neu motor. i still think the 5000mAh 25C flightpower pack will be cutting it real close because it will be only 125A...
or am i still missing something lol
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There are many things you need to take into account when figuring out the current that you will draw. The kv of the motor, the size of the motor, the gearing, the weight of th vehicle, the size of the tires, etc. None of them are exactly the same and none of them will be exactly consistent from one setup to another.
When you look at the max. continuous amp rating of a motor, that in NO WAY specifies how much current the motor will actually draw. And it only specifies the amount of current the motor can handle at the max rated voltage.
Let's take the values for the motor that you are talking about
: 1515/1y:
Specifications:
2200 RPM/Volt
volts: 7-25
Max Amps: 110*
*30 sec. at max. voltage. Otherwise, =Watts/your voltage.
Efficiency: 90%+
Rm (ohms) 0.006
IO: 2.5
1500 Watts Continuous
2700Watts - 30sec
Max rpm: 60,000
Stator Dia. 1.5"
Magnet/rotor length 1.5"
Shaft: 5mm
Shaft length: .75"
Weight: S-340g, F-360g
Dimensions 2.7"L x 1.56" dia.
The max amps is specified for 110A at the max voltage of 25volts. This is calculated using the power equation P=VxA. So P/V=A. For a 4S setup the max amps the motor can handle is 2700/14.8= 182.4Amps for 30 sec. On a 6S setup it is 2700/22.2 = 121.6Amps.
Looking at this rating doesn't really mean too much for battery selection though because it doesn't mean that your truck will draw 120 Amps for the period of the full run - even with a good 8000mAh pack it would last for 3 minutes runtime. Your Amps peak at startup and at full throttle, but most people will see an average over a 15 minutes period runtime of anywhere between 15 - 25Amps.
This is where the cont. and burst ratings for the packs come into play. At 25C a 5000mAh pack can put out 125 continuously (with decent air flow cooling) and in small bursts (ie: startup acceleration) can put out 50C = 250Amps. This is why I saw it is more than you will ever need.
And with the better quality packs you will be able to hold higher voltages ~3.4-3.5 volts/cell at these higher Amp draws; whereas, with the MaxAmps packs you will see that at such a high amp draw your voltage may drop down to 3.0-3.1 volts/cell.
Any of the Enerland packs people are talking about are really good quality cells.
I personally use the ThunderPower eXtreme V2 packs because all of my charging and balancing equipment is setup for the TP balancing jacks.
As an example of current draw, I am running the 1515/2.5D (1700kv) in my e-Revo with a 6S 5000mAh pack and my max power draw is around 1500watts which comes out to ~70 Amps max. The pack voltage always holds above 3.5 v/cell and I've yet to run down the packs fully but I estimate about 30 minutes runtime for this setup.
You also have to remember that a model of a certain weight generally take a certain amount of power to move around regardless of the number of cells you use. My XB8 takes about 1200 watts to move around so whether I use 4S 5S or 6S it still draws about 1200 watts max, it's just that at 4S it has to draw more current to reach that power than it does at 6S with the higher voltage.
I think a 6S - 5000mAh pack will be more than enough to push any 1/8 MT around happily.
IMHO - I think it's silly to stick 8000+ mAh packs into a 6S setup as all you are doing is increasing the weight of the vehicle and making it draw more current. With 5000mAh you will have plenty of runtime and a more efficient vehicle.