Cap banks - the pre-emptive answer

[jcald2000]

300 burst rated, subed on takeoff.
So, 6 caps series + parallel as shown?

[drwayne]

Mildly concerned of damage to esc caps.
Test the onboard caps, in circuit.
All will return same if ok.
If not same, the recommended bank is insufficient.

Enjoy !

[viper1]

Wayne;

Very informative thread, learned heaps, thanks for that !

A question: I've read -someplace I forgot-, that when adding a cap bank that (more) smaller caps were better than (less) bigger ones, assuming they both would add up to the same capacitance.
Had something to do with discharge speed but not sure?

Also does the wiring thickness make a difference at all on short lengths of say 2-1/2" / 6cm?
I found the wires quite thin on my 180 V3 for the cap bank, and thought about changing them, but looking at leads of the caps itself, all these little electron guys will still need to 'squeeze' through those tiny leads right? Your thoughts?
I understand the necessity on longer lengths.

Thanks in advance

P.S. 'Schutte' , Dutch heritage?

[ray schrauwen]

The capacitors are flattening the AC ripple current not the DC drive current so, that's how T180 v3 gets away with thin leads. I've used 14G wire before on a hot 6s2p setup and it's just fine.

[viper1]

But.. (don't you love starting replies with that....) I understand part of what you say, the part where the caps are not taking the full current, but now you brought up another question: how can it flatten AC current, shouldn't they be mounted on the output side (AC) -in this case motor leads- as the input is DC right? I thought (and apologies for using layman's terms, otherwise I wouldn't even understand my own typing) that the caps store energy -from-battery- and deliver extra during peak pulses when batteries can not deliver that quick to the esc.

[ray schrauwen]

My electronics theory is old but, the basic rule is that capacitors pass DC CURRENT but, block AC CURRENT.


Why block it on the input since you say it is connected to a pure DC source (lipos) ? Well Backemf is the reason I think?!

Thats not the best link for the information. Someone posted the correct explanation in an old thread of BL motor theory.

Basically when any winding is energized (pairs are energized at any given time on our BL motors) it forces the core armature to move until it is de-energized (shut off). When power is disconnected from the winding the magnetic energy field in the coil collapses and this collapse sends a BACKEMF voltage in the other direction back into the esc. This is (I think) is where/when the caps settle that returning ac waveform. This happens at a frequency that you set your esc to like the 8Khz or 16Khz, etc. This is a ac wave in the form of Pulse width modulation PWM, square wave.

I'll take any lambasting for any mistakes in here. I took my best shot. lol...

[kingwrench]

Dr Wayne as I told a youngster today I learn something new every day. Thanks again mate

[drwayne]

@Viper1 .. seems you missed the meat in sandwich.. read lower half of this post re ac/dc ripple
http://forums.offshoreelectrics.com/...127#post448127

@Ray. Shhhh. .. :) you have confused logic answering Viper1's misunderstanding

[drwayne]

The comment more small Vs large is/was mine ( dont remember where)
The T180 micro external cap bank has less joule return than a single 35V470uf used onboard that esc. The extra are fine for high freq ripple clipping, not more.
Leads.. if the caps have high charge/discharge, why starve them with low yield wires ?

[ray schrauwen]

@Viper1 .. seems you missed the meat in sandwich.. read lower half of this post re ac/dc ripple
http://forums.offshoreelectrics.com/...127#post448127

@Ray. Shhhh. .. :) you have confused logic answering Viper1's misunderstanding

Aaaaaaaaaaahhhhh!!!!!!

[ray schrauwen]

Dr. Wayne sums it up again. THIS is a fairly simple version also:

The way capacitors and resistors behave is totally different. While resistors allow a current to flow through them which is proportional to the voltage drop across the resistor, capacitors oppose a change in voltage across them by either drawing in or supplying current as they charge or discharge resp. The flow of current through a capacitor is thus directly proportional to the rate of change of voltage across it.

This is given by the relation, i = C* (de/dt) where de/dt is the instantaneous change in voltage.

As the voltage does not change in the case of DC, de/dt = 0 and the current that is allowed to pass through by the capacitor is 0. For AC voltage the voltage changes in a regular manner. Hence here de/dt is not 0 and a current is allowed to flow through by the capacitor.

[drwayne]

@Viper1
This thread discusses purpose, benefit and variants of capacitance buffering/filtering of the DC input to a brushless ESC ( DC->AC 3 phase inverter. )

Capacitance on the output side has merit, but will not be raised in this thread

ps. 'Schutte' is of German heritage.
Thyer, Schutze and Spier are some previous title holders of last remaining male of this bloodline !

[viper1]

@Viper1 .. seems you missed the meat in sandwich.. read lower half of this post re ac/dc ripple
http://forums.offshoreelectrics.com/...127#post448127

AAARgh, must have been reading to quick, missed that part, crystal clear, probably got distracted by the simple drawing above it...simple seems to attract me more

The comment more small Vs large is/was mine ( dont remember where)
The T180 micro external cap bank has less joule return than a single 35V470uf used onboard that esc. The extra are fine for high freq ripple clipping, not more.
Leads.. if the caps have high charge/discharge, why starve them with low yield wires ?

Pretty sure I got it from a Dutch forum, but covered more the esc's in general, forget the 180, I hear you. What I meant was that all the caps are smaller, but added up have same value as bigger uF's, less in quantity. ?

Re the leads; OK bigger is better, but has it benefits to go thicker than the solid wire coming out of the cap itself, when mounting directly against the ESC ?

@Viper1

ps. 'Schutte' is of German heritage.
Thyer, Schutze and Spier are some previous title holders of last remaining male of this bloodline !

Thought it sounded vaguely familiar for a 'cheese head'

[drwayne]

Pretty sure I got it from a Dutch forum, but covered more the esc's in general, forget the 180, I hear you. What I meant was that all the caps are smaller, but added up have same value as bigger uF's, less in quantity. ?

Factual data on capacitor performance is no mystery, however application in array form is not common knowledge amongst amateur electron gobblers.

Re: many small Vs few large equals same capacitance.
Charge/reply on a small cap is faster than a large.
Many small caps can buffer a ripple more efficiently than fewer large where their response is slower.

Schutte: from a long line of brewers, beer drinkers, engineers and all round good guys.

[viper1]

Factual data on capacitor performance is no mystery, however application in array form is not common knowledge amongst amateur electron gobblers.

Re: many small Vs few large equals same capacitance.
Charge/reply on a small cap is faster than a large.
Many small caps can buffer a ripple more efficiently than fewer large where their response is slower.

Schutte: from a long line of brewers, beer drinkers, engineers and all round good guys.

Thanks Wayne,

In different words that's what I remembered right then, discharge speed or as you called it response time.

I wouldn't have brought it up if I got it from a amateur

With the cheesehead comment I was refering to myself, to be honest, I would't mind the foamie stuff in the ancestry either.

Thanks again mate