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Old Jun 28, 2013, 02:08 AM
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billisfree's Avatar
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Question
What burns up first?

Lets say we have a 20amp motor, 20 amp ESC and a 20 amp battery.

IF we go to a 40 amp motor... will the ESC or Battery be damaged?

Likewise:

IF we go to a 40 amp ESC will the motor or battery be damaged?

IF we go to a 40 C (amp) battery will motor or ESC be damaged?

-------------------------------------------------------------------------------------

I supposed one is supposed to program the Xmitter to limit the amps?
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Old Jun 28, 2013, 02:22 AM
Registered User
Staffs, UK
Joined Nov 2003
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First thing....there's really no such thing as a "40amp motor". The actually current is controlled by the motor plus the load on it (i.e. the prop). A motor which might be safe at 40A will still only take 10A, 20A etc if it has a reasonably small prop on it. And if the motor is taking less than the ESC and battery are capable of there is never a problem.

If the motor is TRYING to take more the battery or ESC are capable of then either:
a) the battery may not provide all that's being asked for (which may damage it) or
b) the ESC may be damaged because there's too much current going through it

One is actually supposed to choose components that will work together. Relying on programming the Tx to make incompatible components sort of work is not a good idea .

Steve
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Old Jun 28, 2013, 02:27 AM
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Kilsyth, Victoria, Australia
Joined Oct 2003
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Essentially, you can forget the battery because IF the propeller to which is attached to the motor does not cause the system to draw in excess of 20 amps then battery capacity doesn't matter providing it is has sufficient capacity or has a high enough 'C' rating to handle a 20 amp system.

Going to a 40 amp motor means nothing. It is only the motor AND the prop which is fitted that draws any current other than a very small draw when running free.

Same with the ESC and even the battery. The prop is what cause the system to do the work.
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Old Jun 28, 2013, 03:10 AM
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Letchworth, Great Britain (UK)
Joined Jul 2004
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Quote:
Originally Posted by billisfree View Post
...IF we go to a 40 C (amp) battery will motor or ESC be damaged?

-------------------------------------------------------------------------------------

I supposed one is supposed to program the Xmitter to limit the amps?
As others have said, you don't limit the amps using the transmitter; you limit the amps by the prop you put on the motor. In theory, if a certain prop is making a "20A" motor draw 20 amps, then when it's on a bigger "40A" motor, it will still only make that motor draw 20 amps with the same battery voltage.

"40C" on a battery doesn't mean it can deliver 40 amps: To find out how many amps a battery can comfortably deliver you multiply its Ah capacity (that's mAh divided by 1000) by its C number. So, for example, a 2200mAh 30C pack should be capable of delivering 66 amps (2.2 x 30) comfortably. In practice you should sometimes take the manufacturers' C numbers with a pinch of salt though.
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Old Jun 28, 2013, 03:32 AM
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You guys answered my question pretty good.

Now... I assume a motor with no prop attached will reach it's rated kv (like 1400kv) and draw very little current? Correct?

AND if a motor has big prop so that it is unable to reach it's rated kv... then there's a heavy current draw??? Such that the motor will overheat?

So now... if motor overheats... the smart move is to find a smaller prop?
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Old Jun 28, 2013, 03:49 AM
Glow 😡 no no no
Australia, SA, Evanston Park
Joined Mar 2010
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Originally Posted by billisfree View Post
You guys answered my question pretty good.

Now... I assume a motor with no prop attached will reach it's rated kv (like 1400kv) and draw very little current? Correct?

AND if a motor has big prop so that it is unable to reach it's rated kv... then there's a heavy current draw??? Such that the motor will overheat?

So now... if motor overheats... the smart move is to find a smaller prop?
Smart move is to get a wattmeter in the beginning and avoid future problems.

Something like this, http://www.hobbyking.com/hobbyking/s...=6380&aff=3664 I know guys with these and they work well.
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Last edited by aeromaniac; Jun 28, 2013 at 03:56 AM.
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Old Jun 28, 2013, 04:20 AM
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United States, OR, The Dalles
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Yes, current draw will likely be small if no prop is installed. Current draw will be large with a large prop. If something prevents the prop from spinning, current draw will be very high.

If you overload an ESC, or don't provide adequate cooling air, it can fail suddenly or burn up. If the ESC is also providing power to the reciever and servos via a built in BEC, you will loose control of the plane.

If you run recommended components things will likely be fine. Otherwise use a power meter to check amps and watts and make sure everything is within spec.
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Old Jun 28, 2013, 06:13 AM
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Aberdeen
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Originally Posted by billisfree View Post
So now... if motor overheats... the smart move is to find a smaller prop?
Simple answer... yes
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Old Jun 28, 2013, 06:31 AM
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Staffs, UK
Joined Nov 2003
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Quote:
Originally Posted by billisfree View Post
Now... I assume a motor with no prop attached will reach it's rated kv (like 1400kv) and draw very little current? Correct?

AND if a motor has big prop so that it is unable to reach it's rated kv... then there's a heavy current draw???
Just to be clear, as soon as you put any load on a motor it will turn at less than the theoretical rpm (V x Kv) and the current will increase over the minimum no-load current. The way we use our motors it's quite rare to run at much more than about 80% of V x Kv.

Steve
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Old Jun 28, 2013, 11:36 AM
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What burns up first?
...my money.
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Old Jun 28, 2013, 12:25 PM
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United States, TX, Fort Worth
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The most overstressed component is most likely to fail first.
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Old Jun 28, 2013, 03:48 PM
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USA, GA, Marietta
Joined Aug 2005
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Quote:
Originally Posted by aeromaniac View Post
Smart move is to get a wattmeter in the beginning and avoid future problems.

Something like this, http://www.hobbyking.com/hobbyking/s...=6380&aff=3664 I know guys with these and they work well.
Best answer of the bunch.

Glen
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Old Jun 28, 2013, 04:20 PM
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United States, AK, Fairbanks
Joined Aug 2009
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Quote:
If you run recommended components things will likely be fine. Otherwise use a power meter to check amps and watts and make sure everything is within spec.
A very important note on "recommended components" is that motors will often have a couple different recommended prop sizes and battery cell counts. You might see a 10x6, 8x4, and 6x5 recommended for the same motor, and it might be rated for 2-4S batteries. Going off this info, you might try to run 4S with a 10x5 prop... and the motor would smoke instantly. The unseen rule is that the bigger props ALWAYS go with the lower voltages.
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Old Jun 28, 2013, 04:22 PM
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United States, NJ, Frenchtown
Joined Mar 2003
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If you goto a place like adamonerc web calculator . He has a pictorial graph that shows ALL the data you are looking to juggle around & get the best speed power & duration with any combinations.
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