HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 03, 2014, 10:40 PM
Registered User
Joined Oct 2014
37 Posts
Discussion
General explanation of electronics

Hi guys,
I am having trouble really grasping the max current that you can put through a motor. Would it work to run the Sunny Sky 2204 2300kv motors with kiss 18 amp esc on a 4s? If anyone could explain to me how it all works I would really appreciate it. Does the esc step the power down enough to make that plausible? Im good on the vast majority of all things involving multirotors besides the electrical aspects.
Thank you so much
tdilwo is offline Find More Posts by tdilwo
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 03, 2014, 11:58 PM
Registered User
Wintr's Avatar
USA, MO, Florissant
Joined Nov 2010
1,849 Posts
Motors usually have two ratings: maximum continuous current, and maximum continuous Watts, both of which are there to keep the motor from overheating, and damaging itself. While these are related, they are not generally equivalent. For example, a motor limited to 10 Amps could only develop a bit over 120 Watts on 3S, because a 3S battery, at full charge, is 12.6V, and the volts drop some when current is drawn. That same motor, drawing 10 Amps on 4S would develop a bit over 160 Watts, because that battery might hold ~16 Volts at 10 Amps. However, assuming that same motor is rated at 140 Watts, you have to reduce the current some to keep it from overheating; in this example, that would be about 8.75 Amps. But, you can still get about 20 more Watts from it on the higher voltage. There are motors that cannot reach anywhere near the maximum power rating when the current rating is reached on a lower voltage, and the only way to reach it is to use a higher voltage.

A warning, before randomly increasing your battery voltage: the motor will try to go up in rpm by the same proportion as the increase in voltage, so it will try to spin 33% faster on 4S over 3S. The power to turn a prop goes in proportion to the cube of the rpm increase, so going from 3S to 4S, if the prop is not changed, the power will try to increase by 2.37 times. You have to change prop size (or whatever other load the motor is driving), to take this into account, and, to verify this, a good Watt meter is required. There is also a limit to the safe rpm of a motor, which is why you often see a rating for voltage, as well, often expressed as the cell count of the battery that may be used. A 2300kV motor is going to spin really fast on 4S; assume about 75% of 2300 times 16, or 27,600 rpm.

Oh, and the ESC doesn't step anything down; it will try to provide as much power as the motor needs to reach the rpm that the Voltage wants it to turn; if it can't, it melts.
Wintr is offline Find More Posts by Wintr
Reply With Quote
Old Nov 04, 2014, 03:43 AM
Registered User
Staffs, UK
Joined Nov 2003
10,768 Posts
Quote:
Originally Posted by tdilwo View Post
Hi guys,
I am having trouble really grasping the max current that you can put through a motor. Would it work to run the Sunny Sky 2204 2300kv motors with kiss 18 amp esc on a 4s?
You've missed out the critical factor. The amount of current that will be used depends on the PROPELLER SIZE.

I don't know that particular motor but I'd guess that any 2204 size 2300Kv motor on 4S could only handle about a 4 or 5" prop before exceeding it's maximum current or power ratings.

Steve
slipstick is online now Find More Posts by slipstick
Reply With Quote
Old Nov 04, 2014, 07:01 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,924 Posts
Quote:
Originally Posted by tdilwo View Post
... If anyone could explain to me how it all works ...
  • Motor/battery-current wants to go up with voltage squared and with Kv cubed. Way more than one would expect.
  • A motor's Kv constant says nothing about max.power, max.current, efficiency, rpm, quality etc.
  • The Kv constant is not a rating, not a figure of merit, it's just a characteristic. More windings will give lower Kv, less windings will give higher Kv, that's all there is to it. No big deal, anyone can do that.
  • Motors have just one Kv, not e.g. 1450Kv. It is physical quantity (length, weight, time, current, ..,.), not a physical unit (meter, kg, s, ampère ).
    Therefore: Kv = 1450rpm/volt.

For a rainy day(s)
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:
The Ampeer
-> Electric Power Basics

followed by
The Ampeer
-> Everything youw wanted to know about e-flight (Ed Anderson)
Table of Contents
  • Things To Check On a Ready-To-Fly (RTF)
  • What You Need To Know About Receivers
  • What function goes on which stick?
  • Battery Basics
  • Amps Versus Volts Versus C
  • Lithium Battery Chargers
  • Balance chargers versus external balancers
  • Extending Flight Times While Maintaining Balance (proper CG)
  • Understanding the Electronic Speed Control (ESC)
  • he Low Voltage Cutoff Feature (LVC) Of Your ESC
  • The Role of the Battery Eliminator Circuit in Your ESC (BEC)
  • Sizing Power Systems for Electric Airplanes
  • Prop Versus Amps
  • What Do the Kv Numbers On Motors Mean?
  • Who Needs a Wattmeter/Power Meter?



www.scriptasylum.com
-> RC calculations
-> electrical
-> system wiring
respectively ...
-> LiPo pack wiring
respectively
-> chargers (2 menu items)
The other menu items and demos are also veeeeery handy/instructive for e-folk, add site to your favourites?

www.ezonemag.com
-> FAQ

Vriendelijke groeten Ron
Ron van Sommeren is offline Find More Posts by Ron van Sommeren
Last edited by Ron van Sommeren; Nov 04, 2014 at 07:14 AM.
Reply With Quote
Old Nov 04, 2014, 07:10 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,924 Posts
Quote:
Originally Posted by tdilwo View Post
... Does the esc step the power down enough to make that plausible ...
Controller chops battery voltage to lower rpm, Pulse-width modulation (PWM)

Click to enlarge. Pictures from
www.aerodesign.de/peter/2001/LRK350/index_eng.html
-> Speedy-BL diy brushless controller.

PWM chopping


No chopping at WOT
Ron van Sommeren is offline Find More Posts by Ron van Sommeren
Last edited by Ron van Sommeren; Nov 04, 2014 at 09:21 AM.
Reply With Quote
Old Nov 04, 2014, 09:06 AM
Registered User
Joined Oct 2014
37 Posts
Thank you to everyone that has responded! It has been an enormous help!
tdilwo is offline Find More Posts by tdilwo
Reply With Quote
Old Nov 04, 2014, 10:14 AM
Registered User
Joined Oct 2014
37 Posts
Just one more thing. I was just looking at the assembly that Soma does for his warpquads and he uses the SS2204 motors but he only uses a 12 amp esc. How does he not destroy the esc? here is the data sheet for the draw with different propellers
http://www.rcgroups.com/forums/showthread.php?t=2112708
tdilwo is offline Find More Posts by tdilwo
Reply With Quote
Old Nov 04, 2014, 11:35 AM
Registered User
Staffs, UK
Joined Nov 2003
10,768 Posts
There are plenty of entries in that chart that draw less than 12A e.g. GF5030, HQ 6x3 etc. If he used one of those propellers what's the problem ?

Steve
slipstick is online now Find More Posts by slipstick
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion In general, is it better to use 5V electronics instead of 12V? Rockworthy FPV Equipment 21 Oct 09, 2014 05:12 PM
Discussion In general, are 5V electronics better to use than 12V? Rockworthy Power Systems 2 Jul 08, 2014 01:53 AM
Question Link to basic electronic explanations? TyFlies Beginner Training Area (Aircraft-Electric) 5 Mar 09, 2010 09:32 AM
Discussion ELECTRONICS general thread Chris Nicastro Venom 5 Apr 17, 2009 02:58 AM