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Old 08-26-2005, 01:21 AM   #181
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Quote:
Originally Posted by andsetinn

Well. You should read this thread from the beginning. I'll just say this. Capacitor that is connected to the battery does not store energy from the motor when you back of the trigger. The reason the punch changes is because the capacitor helps the battery to maintain voltage when the throttle is punched. The battery charges the capacitor.
You had the effect right, (larger capacitor = more punch (up to a point (it's not black or white))) not the cause.

I personally think the ESC software is badly designed if it "needs" capacitor, but that's my opinion.

Would you say then a car audio amplifier is poorly designed if it gains from the use of a capacitor? (A large one albeit, as in .5-1.5 farad)

ESC is basically an amplifier, using a very small current (from receiver) to controll a very large curren (from batt to motor) Only difference being the frequency stays the same with an ESC, whereas the frequency varies with music. By using more throttle, you are in effect turning up the volume.

It is also my understanding that using a capacitor will DECREASE your run time. Think about it, if the capacitor charges up while you are off throttle, then it is a load on the battery, then when you hit the throttle, the power from the capacitor is supplementing the power being delivered by the battery (in effect more power going to motor, otherwise whats the point right?) then the batteries are being discharged MORE over the course of a run, as more power is being delivered to the motor. You can not have an overall net increase in power delivered to the motor without a net decrease in charge of the cells.
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Old 08-26-2005, 03:38 AM   #182
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Quote:
Originally Posted by PitCrew
Would you say then a car audio amplifier is poorly designed if it gains from the use of a capacitor? (A large one albeit, as in .5-1.5 farad)

ESC is basically an amplifier, using a very small current (from receiver) to control a very large current (from battery to motor) only difference being the frequency stays the same with an ESC, whereas the frequency varies with music. By using more throttle, you are in effect turning up the volume.

It is also my understanding that using a capacitor will DECREASE your run time. Think about it, if the capacitor charges up while you are off throttle, then it is a load on the battery, then when you hit the throttle, the power from the capacitor is supplementing the power being delivered by the battery (in effect more power going to motor, otherwise whatís the point right?) then the batteries are being discharged MORE over the course of a run, as more power is being delivered to the motor. You can not have an overall net increase in power delivered to the motor without a net decrease in charge of the cells.
Yes, I would say amplifier is poorly designed if there is noise in the output that can be fixed by adding capacitor.

1st rule of energy. Energy is not used, it's converted. (Meaning it can't be lost. It can't vaporise. It's only converted into some other form of energy). Hehe, I love these simple natural truths that can be hard on the brain.
As you say yourself. "if the capacitor charges up while you are off throttle, then it is a load on the battery, then when you hit the throttle, the power from the capacitor is supplementing the power being delivered by the battery".
Energy has been stored in the capacitor, then taken out. It has not been wasted. Imagine it's like water system, water goes through the pipes into a bucket, and then it goes back into the pipes. It has not been poured out of the bucket. Therefore it has no noticeable effect on runtime.
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Old 08-26-2005, 04:14 AM   #183
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In terms of amplifiers, i wouldn't say its poor or good design because it needs a capacitor. There is no definitive answer. Its perspective dependent.

Using another analogy:
A computer that has ram is not always one that is poorly designed.

The user simply needs to draw information from the computer faster than what harddrives are capable of providing. That's why we have ram in a computer.

Perhaps it is good designed because it has served the purpose of the user, to access information at a high speed.

Ofcourse you can always arge that the harddrive in this case is poorly designed, hence the need for ram and cache. But if a better harddisk design is not avaliable due to various constraints, ram will always be a necessary part of a "good design".

A "good design" being one that accomplishes its purpose. (my definition in this case anyway.)


But I do agree with andsetinn that it will have no noticeable effect on run time. Theoretically, I agree with PitCrew, if greater acceleration is gained as a direct result of inserting a capacitor, then the battery has done more work versus the case of no capacitor.

Andsetinn has pointed out that you probably won't notice a runtime difference. The reason I think is because the there is still plenty of energy left in the battery after even when you dump your packs. The Energy used in charging the capacitor is insignificant this case compared to the energy your motor draws.

I will point out that the above is from my experience only. I have no numerical evidence to support my argument. If I am wrong, please come back with some hard numbers. I am all ears.
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Old 08-26-2005, 04:51 AM   #184
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Quote:
Originally Posted by rcnewb2004
But I do agree with andsetinn that it will have no noticeable effect on run time.


If you find that installing a capacitor decreases your runtime noticeably, then check your capacitor. It might be leaking.
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Old 08-26-2005, 11:08 AM   #185
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It can help to think of cells as small factories that convert chemical energy into electrical energy. The energy is stored by converting electicity into chemicals, it's released by converting the chemicals back into electricity.
Elecetric energy is be measured by pressure (Volts) and current flow (Ampers). Each cell has 1.2 Volt pressure and can store enough chemical energy for about 3.3 Amper current flow for one hour (3300 mAh cells).
To raise the pressure up to the 7.2 Volts we use, we use a battery of cells. A 6 cell battery.
Each cell has limited current output.
When the user asks for more current than the cell can supply the pressure falls.
Capacitors store electrical energy directly and can therefore work much faster than the cells.

When the user asks for current from the battery (for example by using the throttle) the current flows from the place where the pressure is highest, first from the cells or the factories, which start immidiently working full power to keep up the pressure. But when demand is greater than the supply from the battery the pressure falls. When pressure from the battery falls, the capcitor becomes the one with higher pressure so the current starts to flow from the capacitor, who's now acting as a damper on the pressure. The battery and capacitor work side by side.

PS.
Watts, the common energy measurement, is calculated by multiplying Volts with Ampers. Watthours is calculated the same except we also multiply by hours. 7.2 Volt 3300 mAh (3.3 Ah) battery is 23-24 Watthours, it can supply constant 23 Watts for 1 hour or 47 watts for half an hour, or nearly 100 Watts for 15 minutes.

PSS.
Since the capacitor does not convert energy but stores it directly it runs much cooler than the cells. If the capacitor warms up, the most likely reason is that lot of current is flowing into and out of it, could be because of old cells. Or that it's ESR is high.

Last edited by andsetinn; 08-26-2005 at 11:19 AM.
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Old 08-26-2005, 12:17 PM   #186
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Quote:
Originally Posted by andsetinn
Yes, I would say amplifier is poorly designed if there is noise in the output that can be fixed by adding capacitor.

1st rule of energy. Energy is not used, it's converted. (Meaning it can't be lost. It can't vaporise. It's only converted into some other form of energy). Hehe, I love these simple natural truths that can be hard on the brain.
As you say yourself. "if the capacitor charges up while you are off throttle, then it is a load on the battery, then when you hit the throttle, the power from the capacitor is supplementing the power being delivered by the battery".
Energy has been stored in the capacitor, then taken out. It has not been wasted. Imagine it's like water system, water goes through the pipes into a bucket, and then it goes back into the pipes. It has not been poured out of the bucket. Therefore it has no noticeable effect on runtime.
I made no mention of energy evaporating... My point was the same as yours, that energy is converted. In an RC car, its converted to heat and motion.

When you let off the throttle, if there has be voltage depression, the cap will charge to whatever the cells voltage is (it will only ever equal the voltage of the cells) when you hit the gas, the voltage drops due to the load on the cells, at this point the capacitor discharges into the circuit as well- thereby for a short period of time delivering MORE power to the motor than would otherwise had gotten there if no cap was used. This power has to come from somewhere- it comes from the batteries. Therefor, buy using a capacitor in an on and off demand, the net energy delivered to the motor is going to be higher than without using a capacitor. In looking at your simple laws, you can't get something for nothing. More power to motor in same time period with cap, then with no cap means the battery is discharging faster. Less run-time.

With the audio amplifier example I made, I was referring to a capacitor on the input power (12v) not the output. Maybe you are not familiar with high end car audio? They use HUGE caps mostly on the sub amps to maintain power under huge bass hits (big load). When big bass hits, its makes a big load, and can draw down the voltage. Then to maintain the same wattage, as most amps have circuitry to do this, they draw more amps. Then they get hotter, and have more distortion.
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Old 08-26-2005, 01:32 PM   #187
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Quote:
Originally Posted by PitCrew
It is also my understanding that using a capacitor will DECREASE your run time. Think about it, if the capacitor charges up while you are off throttle, then it is a load on the battery, then when you hit the throttle, the power from the capacitor is supplementing the power being delivered by the battery (in effect more power going to motor, otherwise whats the point right?) then the batteries are being discharged MORE over the course of a run, as more power is being delivered to the motor. You can not have an overall net increase in power delivered to the motor without a net decrease in charge of the cells.
I think this is good reason not to use too big capacitors, it decrease run time after all. For instances, there will be some left energy or charged ions left inside capacitor after you finished the race. Ideally, all electrical energy stored in battery should be out to motor during the race, right ? So the bigger the capacity, the more unproductive energy left in stored.

Capacitors is helpful to stabillized the volts under current draw or perhaps smooth out the current flow, but it doesn't make any motors go faster / produce more rpm.
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Old 08-26-2005, 01:47 PM   #188
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It doesn't increase overall speed, but they can help you have quicker acceleration.
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Old 08-26-2005, 01:56 PM   #189
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according to novak, the cap helps you get from point A to point B faster, sounds like more overall speed to me.
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Old 08-26-2005, 03:37 PM   #190
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I guess its definition then.

Were you stopped at point A then accelerated to speed to reach point B? Then yes, the caps would help.

If you were allready at full speed when you crossed the plane of point A, and stayed at the same speed to reach point B, then whether you had a cap or not, your top speed would be the same (obviously all other parameters being the same, and ignoring any weight difference that may affect the top speed).

I guess when I said overall speed, I should have said Top Speed.


But a decrease of run-time, to get more juice through the motor I think is probably a good thing with today's high capacity batteries. When was the last time you dumped in stock or 19t? (with a good pack)
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Old 08-26-2005, 09:46 PM   #191
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Hey guys, I am totally electronics illiterate. I would really appreciate it if somebody could could give me the stats of the best general capacitor such as volts, temperature, uf, and esr and more if i missed sumthin. I am hoping i will be able to place it on my TT-01R when i comes.
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Old 08-27-2005, 12:02 AM   #192
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Use the one that comes with your ESC, that is your best bet.

If non is avaliable, then you will have to tell us what type of track you race on to determine what's "best". There is no one right answer.
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Old 08-27-2005, 01:09 AM   #193
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Hi All,

JUST IMO,

I have read a thread which talking about the use of a cap of an ESC.

Why the current ESC need an BIG CAP? What does actually an CAP does and why not all kind of CAP will should for any ESC. The thread said:

When we pull our throttle full in a very short time. The ESC will trend to fully extract the energy from the battery. This is related to the working cycle(Frequency) of the ESC. But what the battery will be? In each start of the "on" cycle, the battery will experience a suddent drop of voltage which down to 2.x V/pack And then go up again. The drop of voltage bacause the suddent change of resistant from infinity to almost "0" on the Fets. The rate of change is too shape. Due to this large amount of energry suddent extracted. The output drain of the ESC will experience a low voltage at such very little of time. Within this little time the FETs inside the ESC will turn in to a stage called "ripple". In this stage the internal resistant of the FET will increase in a lot (out of the specification tells). And you all know what will it be. Heat up and deduce the efficiency. Event the time is so short but it does affect the performance. So if we parallel a cap which can compensate this voltage drop, the efficiency of the ESC can be kept. This is why not all kind of CAP is suitable. Most of the time we need twice the voltage and capable fast charge/discharge cycle (Close to the operation of the ESC).

A good software does handle the problem. Some popular brands would be Keyence and Tekin. What they do is recycling the fly back current from the motor any keep up the voltage of the battery in all the way. But this will take up more resource from the hardware and will become large in size. With such complicate software, higher grade hardware is need. If you open the case of a G10pro and a LRP competition 1. The PIC used in G-10 pro is almost double the power of LPR does. The drawback is it may restrict the motor go to top speed (around 98% using MMS to measure when compare to my SX-9). But in term of punch and efficient, the one which can go without an external cap seems to be the winner at the moment.
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Old 08-28-2005, 02:27 PM   #194
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I haven't read all this thread, so if this is repeating something that went before, I apologise. First a few facts...

Take any of the caps on the market, charge it up and connect it to your motor - absolutely nothing will happen! There is not enough energy in the cap to turn the motor over one comm segment, let alone provide any acceleration. Caps don't provide additional acceleration in that way.

As Pit Crew says, they use them on autos for the stereo system - but you need to see the size of them!!

Not all speedos are supplied with caps. Indeed, it wasn't until some speedos started supplying caps and recommending they were fitted, that we needed to talk about them. Which begs the question - why a cap?

MR4-tc sp's explanation is the one given many times before, and it is the only one that fits the facts. If the cap can't store enough energy to turn the motor, it must have another purpose. If it can store enough energy to keep a FET fired at its design voltage, that would explain why it appears that the car goes better under acceleration.

If the FET is not fed with voltage so it can perform its function, and if it heats up when this happens, there will be a drop in performance that we see as the car not accelerating very well. If it is true that fitting the cap gives a better performance under acceleration, then the cap must be doing something to improve FET (speedo) performance.

Now comes the crunch - if your speedo isn't supplied with a cap, then it isn't designed to need one. If it doesn't need one, fitting one will make no difference to your performance! If your speedo comes with a cap, fit it - if it doesn't, save money and weight!! HTH
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Old 08-28-2005, 11:09 PM   #195
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That's the best post following PitCrew's explanation since I've been following this thread... everyone else just seems to be regurgitating misinformation/misexplanations ... Thanks SlowerOne -JB
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