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Old Jun 11, 2012, 06:49 PM
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United States, MN, Minneapolis
Joined Mar 2012
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Discussion
High Voltage Low Amp Esc

Does anyone know of a 5-6S Esc that would only give 15-30 amps or one that could be programmed to.
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Old Jun 11, 2012, 07:18 PM
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pilotpete2's Avatar
The Northeast Kingdom, Vermont
Joined Jun 2004
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ESC's don't "give" amps, the load, in this case a motor, draws the current.
The only penalty for using n ESC with a much larger current rating than needed is the extra weight.
Pete
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Old Jun 11, 2012, 07:25 PM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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Judging from your other thread, I am afraid that you are going about this in the wrong way. First of all, an ESC does not "give" current, it only serves as a conduit that passes the current that the motor demands. The actual amount of current that passes through a power system is controlled by the load on the motor. Read that as the speed and diameter of the propeller. If a motor has a load that pulls 30 amps then only 30 amps will go through the ESC even if the ESC is rated for 100 amps. As such, any ESC that is capable of handling a 6s battery and will pass at least 30 amps will fit your criteria.

Secondly, you can't just arbitrarily decide to use any high voltage, low amp power system on just any airplane. The voltage and current levels have to be tailored to the type of aircraft and the way it is to be flown. One way to look at it is that voltage controls RPM, or speed, and current controls torque. As such, a high voltage, low amp system is good for turning a high speed, small diameter propeller such as would be found in a pylon racer or scale fighter. On the opposite end, a low voltage, high current system is good for turning a low speed, large diameter propeller such as would be found on a trainer or on many vintage scale designs.

I am guessing from the nature of your posts that you don't have a whole lot of experience with RC planes, especially electric powered RC planes. The bottom line, you don't pick a power system and assume it will work with just any airplane. You pick the airplane first, and then design the power system to fit it.

Larry
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Old Jun 12, 2012, 09:51 AM
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Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
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E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
http://www.theampeer.org/framesefo.html
-> Electric Power Basics
and this e-book
-> Everything youw wanted to know about e-flight (Ed Anderson)
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Old Jun 12, 2012, 10:16 AM
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Joined Jul 2009
159 Posts
Sheesh people, dont pound the guy over the head for asking a simple question.

Patrick, have a look at the E-flite pro ESCs. I have a 40a pro lite that handles up to 6s. E-flite might make a 30a that also will do 6s, just have a look at the specs.

Also to find the right motor kv rating for your 6s application, just take the kv rating for a 3s motor that works and divide by 2.

Say you have a motor that does 3500kv on 3s and you want to use a 6s motor to power the same aircraft. Your target kv would be around 1800kv which is a little more than half of the kv rating for the 3s system.

What kind of aircraft is this for? Going 6s on a heli is easy since motors are already made for this kind of thing. The 6s motor with the lowest kv rating that I know of is for the mini protos. I think its around 1300kv.

Get ready to find a gearbox, 1300kv on 6s will probably burn the motor on a direct drive system.

I dont know whats available in terms of gearbox ratios since I fly mostly helis.

6s motors are also available in 1630kv, 1700kv, and 2010kv all in the hyperion/scorpion brand except for that 1700kv which is made by outrage.

Tarot helis also has a 6s motor which I think runs at 1860kv.

Hope this helps.
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Old Jun 12, 2012, 01:17 PM
jrb
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Edina, MN, USA
Joined Oct 1999
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I prefer to get W from V rather than I .

1st -- it lets me get longer flight time from smaller batteries; i.e. A123s.

2nd -- I^2R losses.

And I always go for a lower Kv motor and bigger prop too!
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Old Jun 12, 2012, 01:38 PM
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7oneWo1f's Avatar
United States, MN, Minneapolis
Joined Nov 2011
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If you don't mind an external BEC, here is a 50 amp ESC that can do up to 7S.

http://www.hobbyking.com/hobbyking/s...dProduct=18006

Suggestion based on numbers, I haven't used that.
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Old Jun 12, 2012, 02:00 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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I recall someone who found a very, very low-Kv motor (I think it was one of those weird pancake ones used for multicopters) and decided to use it on a big Zero. Extremely high voltage (fourteen cells) and super low current swinging like a 13" prop. He was hitting about 2400W at just a 54A draw while running weak old packs. I don't know if he found any specific advantage to it, and that's about as extreme as you're gonna get in that department.
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Old Jun 12, 2012, 03:04 PM
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Going with a 6s setup on my blade 400 stretch (360mm blades) gives me much better flight times and very cool motor/esc/lipo temps.

On brand new 1300ma 30C 6s blue lipos I could easily get 7 or even 8 minute flights. Compare that to only 6 minutes with brand new 2200ma 30C nano tech lipos.

I know a 1300 6s pack compares better to a 3s 2600 but the weight is not much different. The important part is not losing power to all the heat on a low voltage setup.
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Old Jun 13, 2012, 11:56 PM
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United States, MN, Minneapolis
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So from what you are saying, would a motor with a prop connected straight to a battery only draw the amps needed to turn the prop????
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Old Jun 14, 2012, 12:02 AM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
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Quote:
So from what you are saying, would a motor with a prop connected straight to a battery only draw the amps needed to turn the prop????
Yep, unless it's a brushless motor connected directly to a battery. Then it'll just draw current equal to (Vbatt / Rphase1).
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Old Jun 14, 2012, 01:48 AM
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Hastings, New Zealand
Joined Jan 2001
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Quote:
Originally Posted by C₄H₁₀ View Post
Yep, unless it's a brushless motor connected directly to a battery. Then it'll just draw current equal to (Vbatt / Rphase1).
Depends on whether you connect the third wire or not.

Either way it will draw enough current to fry the motor and battery, so don't do it!
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Old Jun 14, 2012, 03:53 AM
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United States, MN, Minneapolis
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Quote:
Originally Posted by PatrickRC View Post
So from what you are saying, would a motor with a prop connected straight to a battery only draw the amps needed to turn the prop????
The voltage applied to a brushless motor is switched on and off by an ESC even at WOT (wide open throttle). If you change props, the current demanded would change at WOT. Connecting the wires of a brushless motor directly to a battery won't perform the commutation that the ESC does. If you skip the ESC, the inductor would saturate, heat up, and your battery will be damaged if the inductor wires don't open quickly enough.
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