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Old Feb 04, 2013, 08:23 PM
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United States, MD, Clear Spring
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Question
KV power question

Will a plane rated for a motor that has 800kv fly correctly with a motor that is rated at 540kv, or can you simply add more voltage? (cells)
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Old Feb 04, 2013, 08:32 PM
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With the same prop, Kv=800 motor on 4 cells will turn similar rpm as Kv=540 motor on 6 cells, assuming both motors are of similar size and quality. The 6S setup will be similar power but 2/3 the current.

If you don't add voltage or increase prop size when you decrease Kv that much, you will drop power a LOT.
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Old Feb 04, 2013, 08:35 PM
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bookmark this site
http://www.ecalc.ch/motorcalc_e.htm?ecalc

It'll help guide you through questions similar to what you are asking.

And buy a wattmeter
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Old Feb 04, 2013, 08:35 PM
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thanks for the reply scirocco. I assume that I would have to up the esc as well then?
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Old Feb 04, 2013, 08:39 PM
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Originally Posted by ironace View Post
thanks for the reply scirocco. I assume that I would have to up the esc as well then?
Actually, re-read what he said. Expect the amp draw to be less with more voltage (once the correct prop is mated to the motor for the voltage increase).
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Old Feb 04, 2013, 08:42 PM
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my shortcoming. Thanks Ben
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Old Feb 05, 2013, 11:47 AM
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Quote:
Originally Posted by ironace View Post
thanks for the reply scirocco. I assume that I would have to up the esc as well then?
If the ESC you have is rated for 4 cells, yes, you'll need an ESC that will handle more voltage.

If the increased voltage is within the ESC's specs, then you're good to go with the same ESC - it'll just be loafing on the lower current.

- Roger
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Old Feb 06, 2013, 04:41 AM
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I think it has to do with Watts, which is a unit of work. voltage x amps = watts. So a high voltage setup will draw less amps to get the same amount of watts as a low voltage high amp system. The more amps you draw the more heat you build up and deplete your battery faster.
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Old Feb 06, 2013, 07:23 AM
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Watts is power which is work over time so watt-hours would be work. But yes, less amps = less heat and lower battery pack draw.
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Old Feb 06, 2013, 06:52 PM
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Note to the OP... all the posts here are based upon the idea that you change the prop to match the new output of the motor.

If you leave your relatively large diameter prop on the motor but increase the voltage, you'll draw a heck of a lot of amps and be spinning the motor far below its efficient range.
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Old Feb 06, 2013, 09:29 PM
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Sounds like you're pretty new to this. The answer to your question is technically "yes", but it's a very, very conditional "yes". For right now, let's just pretend that the answer is "no".

Let's try going at it from a more sensible direction and worry about the particulars later: What plane are you trying to power, and what motors are you looking at? Links are helpful pretty much required.

Learning the technical stuff behind power system selection is important and you'll definitely want to know it eventually, but for now it's easier to just skip to the end and get your plane up and running with a good solid power setup. There are quite a few variables involved in your question, and this really is one of those "if you have to ask..." type things.
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Old Feb 06, 2013, 09:35 PM
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Quote:
Note to the OP... all the posts here are based upon the idea that you change the prop to match the new output of the motor.

If you leave your relatively large diameter prop on the motor but increase the voltage, you'll draw a heck of a lot of amps and be spinning the motor far below its efficient range.
Not really. The question was about a using a different motor (decreasing Kv) and increasing voltage. As Scirocco pointed out, the RPMs will be about the same with the 540Kv motor on 6S as with the 800Kv motor on 4S. Assuming the motor chassis and prop are constants, the current will actually drop quite a bit for that given RPM level and power will remain approximately constant as well. The input to the motor is "changing shape" somewhat, but the output at the shaft ends up pretty much the same.
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Old Feb 06, 2013, 09:49 PM
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Originally Posted by C₄H₁₀ View Post
Not really. The question was about a using a different motor (decreasing Kv) and increasing voltage. As Scirocco pointed out, the RPMs will be about the same with the 540Kv motor on 6S as with the 800Kv motor on 4S. Assuming the motor chassis and prop are constants, the current will actually drop quite a bit for that given RPM level and power will remain approximately constant as well. The input to the motor is "changing shape" somewhat, but the output at the shaft ends up pretty much the same.
I must have misread something.
I thought he was sticking with one motor and wanting to goo up in voltage.
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