too long battery wires can kill ESC over time: precautions, solutions & workarounds
I have also copied (parts of) useful posts in this thread into this opening post.
... therefore, lengthen the motorwires if possible, not the battery wires.
However, if you cannot but extend the battery wires ...
Conclusion from the links below, all controller manufacturers say the same:
Too long battery wires will kill your ESC over time!
Voltage spikes higher than battery voltage will destroy components and/or the standard input capacitors (large cylindrical thingies in thin colourfull shrink wrap) will be destroyed over time because they get warmer/hot. Using thicker wire will not help, it's a wire inductance problem, not a resistance problem. See Lenz's law. Inductance is what makes sparkplugs spark, 15-25kilovolt.
This goes for all makes, they all use the same principle (except SLS controllers, they use sinusoidal commutation instead of trapezoid and tested 150m extension without extra capacitors). However, lengthening the motor wires may lead to radio interference. Give the three of them a twist to prevent this.
Keep battery wires short, lengthen the ESC-motor wires.
That's hardly critical because there's already a lot of wire in the coils 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.
And on the motorside wire-inductance is a good thing, together with flyback diodes it smoothes the current thus reducing noise/interference.
Motorside: voltage chopping and currentsmoothing
Some ESC manufacturers advise against lengthening the wires motorside, that's only because motor wires have a tough insulating varnish/resin coating that has to be removed before soldering. Use the aspirin trick mentioned in opening post:
Sticky: (Re)winding and building motors
But what if you can not extend the motor wires?
Solution II & rules of thumb, calculation spreadsheet
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 by taping them together (twisting the wires will give extra length!). When 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)
Remove insulation of one of the wires???
Extra capacity based on current and wire length, calculation spreadsheet
Influence of ESC max.current rating on choice of capacitance
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 value of a cap is not 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
You would want the voltage rating on the caps to be significantly higher than the battery voltage. Same voltage rating as the manufacturer installed caps. Higher voltage rating is no problem. (thanks jeffs555).
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 (orientation)!
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 liquid stains. Don't ask how I know
How to add extra capacitors (English and German)
All capacitors as close as possible to ESC, not distributed along the battery wires!
YGE controllers, extra capacitors and their location, nice pics, click to enlarge:
Capacitor & pack suppliers
Expert opinions & their rules of thumb
They all say the same ...
Explanation, water hammer/knock analogy, 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 (voltage spike) in the pipe (wire). The water (current) wants to continu flowing but it can't, for a moment the water pressure (voltage) is much higher than the static water pressure (voltage). 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 on and off very fast (8,16, 32kHz PWM voltage chopping) 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). These voltage spikes are higher!!! than the battery voltage. The input capacitors (cylindrical aluminium 'barrels') take 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 and the rest of the controller will feel the full brunt of the voltage spikes. 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.
More on voltage spike and switched inductive load
PWM chopping - Wikipedia
Lenz's law - Wikipedia
Flyback diode - Wikipedia
1 - Full throttle, no PWM 2 - Part throttle, PWM chopping
Click to enlarge. Scope traces from
→ Akkukabellänge und seine tödliche Auswirkung
The coils switching off create the high voltage spikes in the battery wires:
In depth discussion
www.rcgroups.com/forums/showthread.php?p=32830073#post32830073 (added 10-2015)
Shows that energy stored is proportional to inductance, L, and proportional to current squared, I^2
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)
www.rcmf.co.uk/4um/index.php/topic,50366.msg569630.html#msg569630 (RCG user Peter D Rieden
Vriendelijke groeten Ron
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cap caps capacitor capacitors heat heating overheating hot hotter pop popping burst bursting melt melting molten
ImagesView all Images in thread
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?
That would only increase the problem because induction in the lines causes the spikes. Industrial controllers are AC voltage fed, our controllers convert DCinto some kind of AC by chopping. The chopping is the cause of the long battery wire problem.
What are 'input reactors'?
Vriendelijke groeten Ron
United States, NJ, Frenchtown
Joined Mar 2003
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.
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.
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.
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
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.
Prettig weekend Ron
ESC output at WOT
ESC output at partial load
Hacker on long battery wires:
-> Safety and operating instructions
-> Sicherheits- und Betriebshinweise
Vriendelijke groeten Ron
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