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Old 06-14-2005, 03:46 AM   #151
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Have you done the experiement ?

My tip : Buy Keyence Rapida or Novak GTX, and relax watching tv.

If you are Mac Gwyver style : Most Pentium 2 and Pentium 3 motherboards have very low ESR capacitors. They are located next to CPU area and you can easily read the marking like 16V 3300uF 105C Rubycon or Sanyo. Here is the catch, expensive computer use high quality components and vice versa. You need to pull out the caps from motherboard ( need 2 people and 2 solders + flux ).

You can download ESR number from its manufacturer. Electronics manufacturers have datasheet for each part they make.
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Old 06-14-2005, 05:59 AM   #152
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Quote:
Originally Posted by rcnewb2004
andsetinn:

Ok, see where I go wrong with this. Because your conclusion does not make sense to me.

I am a pre-service high school teacher so I will look at this like a highschool experiment.
I forgot to mention that frequency changes ESR.

Well here is a link to a ESR chart. Link. This is the same link I posted on page 3 in this very thread. It lists worst case scenarious for new capacitors.

Now, rcnewb2004. I want you to answer all the questions in your previous post using the data from this chart as a guideline. I want you to assume that all the variables that can affect ESR (age of capacitor, temperature and frequency) are the same. Wires and solder do not effect ESR, they affect resistance, but that's usually so little that you can safely ignore it, unless you're designing high frequency timing sensitive circuits.
I also want you to answer the last questions in your post, for the hardcore techies, using Google to look up the information.
If you were my teacher and handed me this experiment I'd never forgive you. Hmmm, you did hand me this experiment.
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Old 06-14-2005, 06:27 AM   #153
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Quote:
Originally Posted by asw7576
Honestly speaking, I can't tell the difference with or without power caps. The car is running neck to neck with big azz cap's cars. I just installed it because of trendy reason.

The reason I use 6.3V cap is faster charging to get full capacity of the cap. Using higher voltage rating cap such as 10V is good for long lasting life of the capacitor, but I'm not sure it will reach full capacity, especially if you accelerate and brake often ( technical circuit ).

If the cap gets hot it means it's working.
- Honestly speaking, I can't tell the difference with or without power caps....
Hello asw7576, personally I didn't mean that much more frequent running your M-Chassis and 540 motor is the reason that makes u can't feel the difference with/without caps brother... it its might be

but let me tell you that the only way you can feel difference is that if you run mods class car where every second counts... lot difference I mean in punch and run time parameter given on the same other equipment and car,,

pls read this, I'm sorry, no offense at all.. :
1. I just installed it because of trendy reason...
this is the funniest reason I ever read in this forum,
putting an Capasitor is not like a bling-bling or cheapo stickers...main function of capasitor is to smoothe the ripple voltage that occurs in an electrical circuitry (imagine its like a plenum chamber on turbo cars..), this the DEFINITION of CAPASITOR FUNCTION bro..

2. Selecting voltage rate is from the max-min ripple current on the occurs circuitry from the variable load on that motor on acceleration and feed back current from motor..
if you choose 6.3V cap from thingking it is faster charging, and 10V more prolong life sorry I have to tell u that choosing voltage rate is scientific think you could learn and study
trial and error is ol trick bro..

6.3V is then bad idea why.., coz current isn't just flow one way from batt (6.0-7.2V) to esc then motor,
sometimes on hard crash or heavy braking, reverse voltage occurs from motor return back to esc sometimes bigger that 12V in short pulse (spike shape) period, 6.3V can't withstand this, capasitor help this process A LOT.. This spike will be absorbed by this caps not directly convey to esc.. when accelerate hard and ciruitry voltage down below caps voltage caps release the charge back to circuitry to keep balance..

I have a tips here to share:

you dont have to dig in trash motherboard to get LOW ESR capasitor, In electronic shop rarely people understand what Low ESR capacitor is,
but if u just ask him or her for ORIGINAL NICHICON JAPAN 4700uF/16V Capasitor packaged shrinkwrap in gold color,

this the best replacement (instead original Part #: 5675 NOVAK one..same 4700uF) from my test on last year, i test this stuff on 2 esc, NOVAK GT7 and
LRP V7.1 on TC3 and XXX-SG+
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Old 06-14-2005, 12:03 PM   #154
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Quote:
Originally Posted by ratcar1
Ghostfit,
What are Centerline Batteries?
Not so much batteries but cars, think Yoke YR-F2 or Kyosho KY-One or HPI Pro3 or Losi JRXs !
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Old 06-15-2005, 09:39 AM   #155
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Quote:
Originally Posted by Red RSX
sometimes on hard crash or heavy braking, reverse voltage occurs from motor return back to esc sometimes bigger that 12V in short pulse (spike shape) period, 6.3V can't withstand this, capasitor help this process A LOT.. This spike will be absorbed by this caps not directly convey to esc.. when accelerate hard and ciruitry voltage down below caps voltage caps release the charge back to circuitry to keep balance..
Except for the fact that the capacitor should be placed on the battery side of the ESC. All the current that flows through a ESC goes from the battery through the transistors in the ESC to the motor. Transistor is a diode with a electronic switch to open it, current can't flow through it backwards, you need couple of thousand of volts to break the reverse treshold on most transistors. Therefore this spike from the motor can't reach the capacitor, unless it's couple of thousand volts and that would destroy the ESC much faster than the capacitor.
Only on ESCs with regerative circuitry (Tekin G9 is the only one I remember that has this feature) can this spike theoratically go through the ESC to the capacitor (I'm not sure if it can go through the G9, most likely the G9 limits the voltage through the regenerative circuit), unless the ESC has short circuit. If your ESC has short circuited then the capacitor is the least of your worries.

To prevent confusion. I'm not saying that everyone should buy 6.3 volt capacitors, in fact it's pretty hard to get 6.3 volt capacitors. I'm only saying that you shouldn't be afraid to try 6.3 volt capacitor should you be able to get one that has the same capacitance but is physically smaller than say 10 or 16 volts. If you have 2 capacitors that have same capacitance and same physical size you should buy the one with the higher voltage rating because he should have lower ESR.
Most likely if you have 2 capacitors (6.3 volts and 10 volts) that have same capacitance and same physical size then they are identical indside, the 6.3 volts would most probably be just a "rebadged" 10 volt capacitor.
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Old 06-16-2005, 03:31 AM   #156
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rcnewb, how is the experiment going.

A little hint about what ESR is. Current does not go through capacitor, it flows into it. The capacitor has nearly infinite resistance to current flowing through it but wery little resistance to current flowing into it.
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Old 06-16-2005, 04:15 PM   #157
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Quote:
Originally Posted by andsetinn
Only on ESCs with regerative circuitry (Tekin G9 is the only one I remember that has this feature) can this spike theoratically go through the ESC to the capacitor (I'm not sure if it can go through the G9, most likely the G9 limits the voltage through the regenerative circuit), unless the ESC has short circuit. If your ESC has short circuited then the capacitor is the least of your worries.
Regen inherent in ESC and not unique to Tekin, nor patented
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Old 06-20-2005, 04:03 AM   #158
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Quote:
Originally Posted by ProMaX
Regen inherent in ESC and not unique to Tekin, nor patented
yea, and perhaps only Tekin which use "regen things" as item on their ads. so some people will then refer "regen" is means "tekin".. good..
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Old 06-20-2005, 01:22 PM   #159
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Haven't done any experiemnting, but did do some reading.

Here's a good answer:
http://www.capacitors.com/picking_ca...s/consider.htm

My experiment previously listed is voided.
I think there is a whole series of things that affect ESR, not what i previously assumed (voltage and capacitance only).

Seems freqency, temperature also have a play in these things. I will have to read into this in more detail before I can relate this to RC.
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Old 06-20-2005, 01:53 PM   #160
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Hi Guys
just to clarify what someone has said earlier about the cap going to the battery side of the ESC.

My mtronik ESC has a power cap(large) which has to go on the motor positive and battery negative.OR
The smaller cap supplied is soldered entirely on the battery side.

Why the difference???

Cheers
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Old 06-20-2005, 02:20 PM   #161
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Quote:
Originally Posted by rcnewb2004
Here's a good answer:
http://www.capacitors.com/picking_c...rs/consider.htm

I will have to read into this in more detail before I can relate this to RC.
Isn't it wonderful how complicated those simple things are? A capacitor is just 2 plates of metal, almost touching each other. How can it be so complicated?
The advice I was given when learning about electric components (all those many, long, long, years ago and I'll admit I've forgotten too much about it) was find what matters to the task at hand and ignore the rest, follow the KISS rule. By the way, that advice is useful in every aspect of life.
In RC capacitors are used to reduce ripple current and for a few valuable milliseconds to act as secondary battery. For that we need high capacity ((uf) to store lot of power) and low resistance ((ESR) to release that stored power fast and without heating the capacitor too much). We also need small physical size. The other parameters for capacitors don't really matter, the voltage we use is too low (4.8 to 7.2 volts) to matter, almost all capacitors can handle that with ease. The heat you can't control, etc.
You might gain a little performance if you buy capacitor that has low ESR on the exact same frequency as your ESC, but it's very unlikely that you'll notice that little performance difference.
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Old 06-20-2005, 08:44 PM   #162
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At least I got some of my answers now

The resistance from the solder joints will not be able to affect the power reaching the motor.

From the derivations, higher frequency (i still need to understand where this frequency thing comes in and whether it is related or not to RC) means lower ESR.

Lower Voltage rating = smaller physical size.
Lower ESR = less heat generated and more current flow.

Indeed that's good advice andsetinn. However, I do not know enough to tell "what matters to the task at hand" so I do not want to be oversimplifying. I want make things simple, but no simplier. If there are simplifications made, I want to know where and how they are being made, and see justification for it.

(I hope I am not offending anyone by saying this, but that's sorta my way of making sense of the world.)

My last question remains though... (which I guess I will read up on unless someone has some answers handy.)

2x 5000uF capacitors in parallel vs 1x 10000uF capacitor, which will have the lower ESR? assuming all other parameters being the same.
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Old 06-21-2005, 12:37 AM   #163
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I am going to say that in your 2 vs 1 example, all other parameters being the same, that the net ESR value will be the same in this application.

I say this simply because the ammount of current available to charge the caps is limited by the internal resistance of the cells. Therefore, there is a given time period for the cells to begin the chemical reaction to produce the current to charge the caps. Since the overall resistance of the capacitors in the discharged state is basically 0, you are basically dead shorting the battery untill the capacitor is charged, which happens VERY quickly at the levels of amperage quickly produced by the cells. As the caps charge, their resistance (to charge) goes up dramatically. That is why a discharge cap, when place across the battery will spark, but a charged cap will not spark.

As far as discharge resistance goes, this happens almost instantly, regardless. I cannot speak for the difference of the 2 vs 1 scenario in regards to discharge speed (cause thats what were after here, faster is better right?). However, I can say with certainty that 10,000 micro farad of capacitance from either one or two caps is going to deliver a fairly strong jolt when discharged regardless of whether from 1 or two caps. In fact, when looked at as a function of time in relation to current discharged from cap, I think its really pointless to try to determine whether one is better than two or vice-versa. It happens so fast, that all things considered, it probably makes no difference in the RC application due to other parts of the system trying to catch up. I am making reference to the time it takes to acctually accelerate all the moving parts in the drive train, let alone the whole car.

In thinking about this, I would like to point out that for every revolution of the motor, each pole is switched twice. Thats six switches for the motor for every revolution. Figure at 30,000 rpm, that 180,000 switching cycles the motor goes through in a minute. Just a thought.

As a note, I don't even run a capacitor on any of my cars (except for the spektrum receiver). My car is at least as fast as anybody else running comparable motors. I would have to say the only time the cap may make any significant impact is starting from a dead stop. While on the track, the voltage depression due to driving limits the caps ability to gain any advantageous charge, as the current is being drawn directly to the motor, and the current again is limited by the cells ability to produce current- which there is a delay in time from placing a load to current production. Batteries are like electron pumps, in a sense. Electrons are everywhere, on all things. They just don't have an impact untill they start moving.

My fingers hurt now.
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Old 06-21-2005, 10:55 AM   #164
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Quote:
Originally Posted by rcnewb2004
The resistance from the solder joints will not be able to affect the power reaching the motor.
If you have cold solder joint it will affect the power reaching the motor.

Quote:
Originally Posted by rcnewb2004
2x 5000uF capacitors in parallel vs 1x 10000uF capacitor, which will have the lower ESR? assuming all other parameters being the same.
5000 uf capacitors are not manufactured so you'll have to use 4700 uf.
Under normal circumstances you get about equal ESR from both setups, the difference is almost unnoticable. The 2 capacitor setup would have lower capacitance.
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Old 06-21-2005, 06:43 PM   #165
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agreed.

the 2x 5000 uf was just a theoretical round number i was using to pose my question

anyone have any real esr numbers to compare just for the sake of argument?
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