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Old Nov 12, 2008, 05:01 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,923 Posts
Careful!
too long battery wires will kill ESC over time: precautions, solutions & workarounds

I have copied (parts of) useful posts in this thread into this opening post.

... therefore, lengthen the motor wires if possible, not the battery wires.

Contents
  • Problem
  • Solution
  • Rules of thumb
  • Capacitor type
  • Capacitor polarity!
  • How to add extra capacitors
  • Expert/manufacturer opinions, rules of thumb, installation
  • Explanation/theory
    References
  • Measurements
  • DIY pictures
Problem
Conclusion from the links below, all controller manufacturers say the same:
Too long battery wires will kill your ESC over time!
The standard input capacitors (large cylindrical thingies in thin shrink wrap) will be destroyed over time because they get warmer/hotter. Using thicker wire will not help, it's mainly a wire inductance problem, not a resistance problem.

This goes for all makes, they all use the same principle (except Sinus controllers, they use sinusoidal commutation instead of trapezoid, they tested 70 meters without capacitors). However, lengthening the motor wires may lead to radio interference. Give the three of them a twist to prevent this.

Solution
Lengthen the motor wires, not the battery wires. That's hardly critical because there's already a lot of wire in the motor itself. If the motor-ESC wire eventually gets too long, it will not harm motor and/or controller. May cause interference though, give the motor-ESC wires a twist. Always a good idea to do that anyway.

Rules of thumb
If you have to lengthen the battery wires, for whatever reason, add extra electrolytic capacitors in parallel with ESC, never in series with ESC. As a rule of thumb, for every 4inch/10cm extra length/distance between battery and ESC, add an 220uF extra capacitance near the controller (electrolytic condensators, voltage the same as the capacitors already installed, low ESR type) (Ludwich Retzbach, German e-flight author&editor, the 'R' in LRK).
Better to use several smaller caps (in parallel) instead of one biggie. Smaller caps can shed more heat and total inductance will be lower (inductance per cap is lower and those inductances are paralled to boot ). See attached pictures below.
Also keep the positive and negative wires as close to each other as possible, eg. by twisting and/or taping them together. If the wires are close to each other then the series inductance will be reduced, because the current is going in opposite directions in each wire (and therefore producing opposite polarity magnetic fields which cancel out). For example, 13AWG wires separated from each other by 1 inch have about 4 times higher inductance than if they are bound together. (Bruce Abbott in www.rcgroups.com/forums/showthread.php?p=11594609#post11594609)

Extra capacity based on current and wire length (spreadsheet)
www.rcgroups.com/forums/showthread.php?t=952523&page=58&pp=10#post24486468

Capacitor type
The main spec you need is low impedance and low ESR(equivalent series resistance). I think the only thing you will find at radio shack will be general purpose caps, not low ESR. The ESR of a cap won't be printed on it, you will have to look up the manufacturers spec sheet. The Rubicon ZL series mentioned in the Schulze instructions is a good one and is available from newark/farnell. The Panasonic FM series is another good low impedance cap and is available from digikey
www.farnell.com/datasheets/2161.pdf
industrial.panasonic.com/www-data/pdf/ABA0000/ABA0000CE108.pdf
PS You would want the voltage rating on the caps to be significantly higher than the battery voltage. Same voltage rating is the installed caps. Higher rating is no problem. (thanks jeffs555, from www.rcgroups.com/forums/showthread.php?p=11971048#post11971048)
If you try it with longer wires and no extra low esr caps it may work for a while, but the longer wires put an extra load on the original cap. The extra load shortens the life of the original cap and it will eventually fail, probably catastrophically. (thanks jeffs555, from www.rcgroups.com/forums/showthread.php?p=11996840#post11996840.

Capacitor polarity!
Electrolytic capacitors, like batteries, have a (+) and (-) lead! Solder them in the wrong way and they will got hot, pop open or even explode. Nasty fumes and the liquid stains. Don't ask how I know

How to add extra capacitors (English and German)
www.matthias-schulze-elektronik.de/guide/gfutc-de.pdf (English)
YGE controllers, extra capacitors and their location, nice pics, click to enlarge:
www.yge.de/caps2.php

Expert opinions, rules of thumb, installation
Schulze controllers and battery lead length
www.matthias-schulze-elektronik.de/guide/gfutc-de.pdf (English)
Castle Controllers about battery lead length
www.rcgroups.com/forums/showpost.php?p=1537846&postcount=28
www.rcgroups.com/forums/showpost.php?p=4833040&postcount=5
www.rcgroups.com/forums/showpost.php?p=1531363&postcount=25
www.rcgroups.com/forums/showthread.php?t=1095329
Bob Boucher (Astrobob, www.astroflight.com) on long battery leads
www.rcgroups.com/forums/showpost.php?p=2988042&postcount=32
Hacker on long battery wires:
www.hacker-motoren.de/images/Master-manual-Engl.pdf (English)
-> Safety and operating instructions
www.hacker-motoren.de/images/MASTER-Manualgerman.pdf (German)
-> Sicherheits- und Betriebshinweise
Novak
www.teamnovak.com/tech_info/power_caps/power_caps.htm
Paul Daniels
www.rcgroups.com/forums/showthread.php?p=11297012#post11297012

Explanation/theory
First a watery analogy, water running in a pipe and through a tap. Now turn off the tap quickly. You'll hear a loud knock/shock sound in the pipe. The water wants to continu flowing but it can't, for a moment the water pressure is much higher than the static water pressure. It's the same for a current that's switched off, because of the inductance it wants to keep on flowing, voltage gets higher. This is also what causes sparks (brush fire) in a brushed motor.

The controller is like a watertap that's switched off (and on) very fast (8,16, 32kHz PWM) to get the desired current. Turning off the current, in combination with the battery wire inductance, causes voltage spikes because the current wants to continue on its course (ref. inertia of the moving watercolumn). Those voltages are higher than the battery voltage. The input capacitors (cylindrical) takes care of these spikes (they reduce the wire inductance). The longer the wires, the higher the voltage spikes induced in the wires, the harder on the input capacitors. They will get warmer, heat up and explode. This is caused by the wire inductance, not by wire resistance. Therefore, using thicker wire will not help much, it's not a bad idea either, but extra capacitors are the solution, thus reducing/compensating the wire inductance. Or longer motor wires instead of long battery wires.

www.s4a.ch/eflight/reglerleistung.pdf (German)
-> Akkukabellänge und seine tödliche Auswirkung
The coils switching off create the high voltage spikes in the battery wires:
www.rcgroups.com/forums/showthread.php?p=10940134#post10940134
In depth discussion
www.aerodesign.de/peter/2001/LRK350/SPEEDY-BL_eng.html
www.aerodesign.de/peter/2001/LRK350/Warum_dreht_er_so_eng.html
www.rcgroups.com/forums/showpost.php?p=10028325&postcount=2661
www.rcgroups.com/forums/showthread.php?p=1518827#post1518827

References
1) hyperphysics.phy-astr.gsu.edu...indeng.html#c2
Shows that energy stored is proportional to inductance, L, and proportional to current squared, I^2
2) www.ee.scu.edu/eefac/healy/indwire.html
Shows that the inductance of a straight wire is proportional to the length of the wire times the natural log of the length of the wire ...which is close to being linearly proportional.
(References thanks Panther3001, post #685)

Measurements
By RCGroups user Peter D Rieden
www.rcmf.co.uk/4um/index.php/topic,50366.msg569630.html#msg569630

Vriendelijke groeten Ron van Sommeren
brushless motor building tips & tricks
diy brushless motor discussion group
Drive Calculator download & discussion group
int. electric fly-in, Nijmegen, the Netherlands


DIY pictures
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Old Nov 12, 2008, 06:58 AM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
Odd that in the industrial drive world we use input reactors to assist knocking the spikes from the incoming line. I've yet to see this on any ESC, but I have seen it on servos and BEC's.

Is there any manufacturer who adds or suggests a torroid on the input lines?
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Old Nov 12, 2008, 08:58 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
10,923 Posts
That would only increase the problem because induction in the lines causes the spikes. Industrial controllers are AC voltage fed, our controllers convert DC current to 'AC'.

What are 'input reactors'?

Vriendelijke groeten Ron
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Old Nov 12, 2008, 10:23 AM
Reduce the drama...
rick.benjamin's Avatar
USA, OR, Damascus
Joined Apr 2004
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Here's a PDF from a manufacturer
http://www.ab.com/drives/techpapers/...%20Drives1.pdf
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Old Nov 12, 2008, 10:25 AM
Reduce the drama...
rick.benjamin's Avatar
USA, OR, Damascus
Joined Apr 2004
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And a presentation here
http://www.mtecorp.com/tutline/reactors.pdf
Says they are essential for proper operation of Variable frequency drives
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Old Nov 12, 2008, 10:27 AM
Reduce the drama...
rick.benjamin's Avatar
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And finally one more article
http://www.idscontrols.com/publicati...ansformers.htm
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Old Nov 12, 2008, 07:10 PM
Registered User
United States, NJ, Frenchtown
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Industrial drives are used on 3 phase usually.The rest are usually AC of some kind.

Ours are DC. That may be the change point. Chopping DC into the 3 phases.

Industry is trying to stop excessive inrush currents. Use a inductor.

DC.... capacitors...... slow down a voltage rise on the cheap drive parts used.
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Old Nov 13, 2008, 03:25 AM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
16,632 Posts
Quote:
Originally Posted by cyclops2
DC.... capacitors...... slow down a voltage rise on the cheap drive parts used.
Which a series inductor would do, along with the capacitor across the input... An 'L' filter.

In a VFD, most large drives use a DC choke / reactor in series with the bus capacitors to help filter the bus voltage ripple and reduce the reflected voltage notching on the incoming line due to current pulses.
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Old Nov 14, 2008, 06:35 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
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The RCGroups links were dead, fixed it.

Prettig weekend Ron
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Old Nov 14, 2008, 09:22 AM
aka: A.Roger Wilfong
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Depends on how you look at it. There are different ways to look at how capacitors and inductors work.

Generally, capacitors resist changes in the voltage across them. But they can also be thought of as passing AC current but blocking DC. Used as a filter as across the input to an ESC, the capacitor(s) acts to resist changes in voltage - both up and down.

Inductors resist changes in current flowing through them. In other words they pass DC and block AC. Inductors used in traditional power supplies are used to block AC caused by changes in the input voltage. This is normally ripple, as in a 50/60 Hz mains power supply, or switching spikes from a switch mode supply. The inductor works by storing energy in a magnetic field at high current portions of the cycle and releasing the enery during low current portions. Wires are also inductors (inductors are simply wires wrapped in circles or around ferrous material to increase the magnetic field and interaction between the fields created by adjacent turns. But a straight wire also has inductance. The longer the wire, the greater the inductance.

With our ESCs, the traditional use of inductors as filter is turned on its head. In a traditional power supply, the load is constant relative to the supply. That is the variations in supply voltage are at a much higher frequency than changes in the load. So, the filters (particularly the inductor) are reacting to changes in the input.

With an ESC, the source voltage is constant relative to the load. That is, the load is changing at a much higher frequency than the supply. This causes large changes in current flow through the inductor (the leads). Since inductors resist changes in current, the result is that the voltage at the ESC end of the wires drops as the as the ESC switches a coil in the motor on and the current instantaneously increases. The capacitors can only compensate for so much voltage sag - which doesn't have a negative effect on them, but can cause the electronics in the ESC to reset or glitch. The problem with the capacitors failing occurs when a coil is switched off. The instantaneous drop in current flow causes the magnetic field in the inductor to rapidly collapse, resulting in a voltage spike into the ESC. The capacitor absorbs this spike by passing the current - passing current causes the caps to heat up shortening their life. But if the spike is too large, it can exceed the voltage rating of the capacitor. This can cause the capacitor to internally short. In either case (heat or short) the cap is going to eventually fail.

Adding more caps in parallel distributes the does two things. First it increases the capacitance limiting the change in voltage - reducing the posibility of a short. And, second it distributes the current from the spikes across several capacitors - reducing the heating.

In short - follow the manufacturer's recommendations on battry lead length.

- Roger
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Old Nov 14, 2008, 09:32 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
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Excellent Roger, I added a link to your post to my first message, for copy/pasting the text in the future.

Prettig weekend Ron
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Old Nov 14, 2008, 04:26 PM
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Quote:
Originally Posted by Ron van Sommeren
This goes for all makes, they all use the same principle (except www.sinusleistungssteller.de , they use sinusoidal commutation instead of trapezoid, they tested 70 meters without capacitors).]
Ron: The MaxCim line of motors [unfortunately no longer in production ] did not have any known limitation on battery-side wire length. Whether the fact that they are sensored makes that difference, I don't know. But for this reason, I'll never part with any of mine. Tex.
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Old Nov 15, 2008, 07:08 AM
Crash Master
Gene Bond's Avatar
Indianapolis, IN
Joined Sep 2001
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Well put Roger.

I know we fight the 'distributed inductance' of long line and load leads with AC-sourced VFD's routinely. The typical 1st level solution is to concentrate a large inductance close to the drive, thus limiting the current change... but again, this is for AC. In the DC section, an inductor is used in conjunction with the capacitors to limit ripple currents.

But, of course, AC and DC circuits have different problems and solutions
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Old Nov 15, 2008, 07:16 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
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Quote:
Originally Posted by Sabrejock
Ron: The MaxCim line of motors [unfortunately no longer in production ] did not have any known limitation on battery-side wire length. Whether the fact that they are sensored makes that difference, I don't know. But for this reason, I'll never part with any of mine. Tex.
The switching (coils off) causes the problem, this is not influenced by sensored or sensorless.

At WOT, life is much easier on the ESC and the input capacitors, than at mid-range. There's not so much switching (PWM chopping) going on in the ESC.
http://www.rcgroups.com/forums/showp...postcount=2661
http://www.aerodesign.de/peter/2001/...DY-BL_eng.html
http://www.aerodesign.de/peter/2001/...er_so_eng.html

Prettig weekend Ron

ESC output at WOT


ESC output at partial load
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Old Nov 23, 2008, 01:54 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
The Netherlands, GE, Nijmegen
Joined Feb 2001
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Hacker on long battery wires:
http://www.hacker-motoren.de/images/...anual-Engl.pdf (English)
-> Safety and operating instructions
http://www.hacker-motoren.de/images/...nualgerman.pdf (German)
-> Sicherheits- und Betriebshinweise

Vriendelijke groeten Ron
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