jfetter
Posts: 321
Joined: 11/25/2003 From: MIRAMAR, FL, USA Status: offline
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quote:
ORIGINAL: BoneDoc 6S vs 8S depends on the amps. My TRex 600 batt can go to 2000 watts. Don't tell me that even if this plane comes at 10 lbs (doubt it since the numbers tell us that it'll come in around 8-9 lbs) 200 watts/lb is "not enough". But then again, only time will tell. Batteries are rated in volts and amps, watts express the amount of work done by a certain amount of electric current (amps) at a certain pressure (volts). The numbers you see when you measure the wattage (whattmeter I assume?) is input wattage, only partially related to the outout power as different motors, gearboxes and propellers can reduce efficiency to less than 50% in some cases. So when you say your battery is capable of 2000 watts, that does not equate to the motor producing 2000 watts of power at the propeller when you make your 200 watts/lb analogy. Take the 2000 watts measured by the whattmeter (input power, not power at the propeller), if you were running a 6S pack that would be a 90 amp draw on your battery, not exactly ideal when designing the ideal combination of battery, speed controller and motor. Yes, it is slightly less than the rated 20C (100 amps) continuous amperage draw the battery is capable of but not a good design if one were building this system from scratch and looking for the ideal combination of components to use. Change that battery to an 8S and you now have a more sustainable draw of 67 amps (your battery will thank you for this on hot days) and the ability to comfortably use a 75 amp speed controller. I say this not to say you are wrong BoneDoc, I have read your posts before and I know you are knowledgable, I say this only to prevent someone from assuming a battery is a battery and simply interchangeable from model to model. The single biggest change one can make to the power and performance of an electric plane is to change only the battery, for that reason I try and match them to the application. If you keep a battery well within its operating parameters it will last longer not to mention have the extra kick when needed... Jack
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