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Power caps concern and questions

Power caps concern and questions

Old 02-15-2007, 01:17 AM
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Default Power caps concern and questions

Hi all

I just want your opinion :

Is it still worth to put power caps (low ESR and high ripple caps) attached to pos and neg battery lead on the latest ESC (ex. Sphere comp. 007, GTB, GTX, VFS-1, etc. ) ?


Thanks for you answer / comment ....
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Old 02-15-2007, 01:24 AM
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In a word.. YES

Can't speak for the others but the GTB in particular is designed to operate with a large 4700uf 10v cap in order to improve efficiency.

Actually, do to the high Amp draw of modern low turn motors, it's advisable to run caps in any situation to smoothen the voltage ripple that occurs during hard usage.

Novak recommends running the cap at all times, and even running a second cap wired in parallel for improved performance.
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Old 02-15-2007, 01:55 AM
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Originally Posted by AngryAsian
In a word.. YES

Can't speak for the others but the GTB in particular is designed to operate with a large 4700uf 10v cap in order to improve efficiency.

Actually, do to the high Amp draw of modern low turn motors, it's advisable to run caps in any situation to smoothen the voltage ripple that occurs during hard usage.

Novak recommends running the cap at all times, and even running a second cap wired in parallel for improved performance.
Thanks

So the more caps installed in parallel, the better ?
Ex. I added 10V 3300uf, so the voltage will stay and the capacitance will increase to 8000uF ....

By adding another caps, will the ESR decrease and ripple increase ?
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Old 02-15-2007, 02:36 AM
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I'm not sure about the ESR ratings to be honest...
All I know is that the lower the ESR, the better the cap is. Both in quality (as they are hard to produce), but also in terms of usefulness in a high frequency application. Lower resistance is a good thing!

As for ripple currents, I THINK in RC use, we're talking quite large ripple currents. So the applicable capacitor type is the electrolytic type. I don't see any other type of cap used in rc. Not sure what the effect it when used in series, but I think it's more to do with the application than anything else.

There is also a relationship between ESR and ripple voltage. The higher the ESR the higher the ripple voltage. The relationship is inverse (I think - can't remember).. So ESR impacts the operation in that regard. Big ripples are bad.. This is something that I don't really understand.

I think the general gist is: A cap is rated for a certain ripple. Ripple is bad as it "works" the cap harder.

Lastly: More caps = more better! The voltage dips experienced by the esc under high amp loads are quite large. More caps effectively adds to the capacity and I'd assume takes the same time to charge due to the parallel wiring.

**I'm not in any way an electrical engineer. So please take all of the above with a grain of salt. Internet forums! Bah!**
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Old 02-15-2007, 03:03 AM
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If you wire the capacitors in series then you will actually get less capacitance, but I would imagine you would be able to throw a higher voltage through it (pointless in R/C as the voltages are relatively low and we already have 10/16V capacitors that are sufficient).
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Old 02-15-2007, 08:09 PM
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Thanks for the info...

If I use it with silver can or tamiya sport tuned motor, does it give any slight difference than without the caps ?
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Old 02-15-2007, 09:18 PM
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Doesnt a mosfet or transistors efficiency go way down as voltage drops or when it dip significantly. The cap helps to combat the dip in voltage seen by the esc keeping the it cooler and more efficient.
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Old 02-15-2007, 09:55 PM
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Originally Posted by schmelme
Doesnt a mosfet or transistors efficiency go way down as voltage drops or when it dip significantly. The cap helps to combat the dip in voltage seen by the esc keeping the it cooler and more efficient.
Means caps protect ESC
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Old 02-15-2007, 09:56 PM
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Is there a chart or table somewhere that helps me match the right caps to the motor turns and winds, wire gauge, and esc?

thanks!
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Old 02-15-2007, 10:04 PM
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I think, it should be related to the internal resistance (IR) of the ESC rather than motor turn, winds and wire ....

The caps should have ESR near the IR of ESC ..... That's what I think ...

Any comments ?
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Old 02-16-2007, 12:13 AM
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Default About parallel power caps made by Straight Ltd., Japan

While searching for good caps, I have found out what's exactly attached to this ROK-90S4 Layer Capacitor made by Straight Ltd., Japan

Also for ROK-90V8 Layer Capacitor


According to the website, they are connected in parallel.
And you'll see on top of the caps, the ROK-90S4 use 680 uF (not sure about this 'cause I don't have the caps yet and the pics on their web is not so clear.. unless someone who has it can confirm about it) and ROK-90V8 use 220 uF (it's clear from the pic)

Both are using nichicon caps products, vertical chip-type capacitor, with the datasheet you can find here
(see the "UD" series on top of the caps).

My questions are :
1. Is it low ESR same with low impedance, cause I always see in the capacitor datasheet, they always refer to impedance not ESR

2. Looking at the datasheet tabel for 220 & 680 caps, the lowest impedance for 220uF is 0.17 at 25V/35V and for 680uF at 0.09 at 10v/16v
Some say (in other thread ) low ESR should be max. 0.05 ohm for ESC
If the caps put in parallel, the capacitance will be multiplied but will the total impedance (ESR) be divided (decrease / lower) ?

3. How about the ripple in parallel caps, will it be divided or multiplied or remain the same ?

4. What are the advantage and disadvantage of putting the caps in parallel ?

I hope someone could enlightenment....
Really sorry to ask this 'cause I'm not electrician or have knowledge about power caps....
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