Originally Posted by
drwayne
Words Vs pictures
remember these numbers ... ...
C= 470uf cap, low ESR, rated voltage ~ 25% above your pack voltage
2 in parallel c1+c2=940uf
2 in series offers C1xC2/(C1+C2) = 235uF !!!!!!
series (-)---[C1]---[C2]---(+)
That series pair in 3x parallel array offers 705uf
(-)---[C1]---[C2]---(+)
(-)---[C1]---[C2]---(+)
(-)---[C1]---[C2]---(+)
Initial charge of the 6 caps is same as if all were individually charged
OMG Ive written and rewritten this a few times and each time I start expanding on referenced detail that loses most people.
simply..
In this circuit, the charge/discharge speed is 8x the std , thus smoothing the DC line ripple more effectively ... even though the energy return availability is 705/2820 ( std6 caps ) .. it presents 8x speed of charge/return into of those original individual 6 caps.. gives us twice the total energy available, at a far higher return rate than std. ( 705 x 8 / 2820 )
In the 15S300A5698/910 example I used a total of 1410uF as detailed here, and logged ripple <0.19Vdc.
Unfiltered, ripple measured >1.6Vdc .. but I didnt enjoy the lacklustre performance so I went home...
I use cap banks as detailed to cover both yield(battery recharges the caps) and reply(esc demand on power system) needs of the system.
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I read above .. What is DC ripple ? . When the esc fires a phase, it draws energy from the 'energy sump' .( DC batteries ).. this causes a sudden voltage drop evidenced by a blip on the voltage display of your oscilloscope.
Each 3 firings ( a rotation of the motor ) makes 3 tiny blips ..... eg at 30,000rpm there are 90,000(at least) tiny blips.. a ripple .. an induced frequency.....EMF inciting ESR .....
This ripple.. creates an AC that is not usable by the DC-AC inverter (ESC) thus the esc now sees lower voltage...V x Kv - zoomzoom
Capacitor banks reduce the size of that ripple, the esc sees higher nett voltage = more fun.
If the cap bank is too large, it will induce it's own ripple as it recharges.
Would I recommend this type of cap array if asked .. depends on your application.
Im sure to edit this once Ive seen it in a fullscreen.. and read it as a mini-novel.
W