How would a super capacitor effect your esc… I know from reading the rc forums multiple small high voltage/ low resistance caps are best for taming inductance induced spikes?
People saying the so called “super capacitors” would help, are not correct.
- Voltage sag: Voltage drop at battery connector due to drawing high current, occurs at every voltage, increases when battery depleted.
When adding a capacitor, you’re practically adding a battery with a high C rating, but with such small capacity that it won’t matter. In less than 250ms the capacitor would be at a to low voltage and battery current will rise just as if there was no capacitor. So unless you plan on accelerating for times less than 250ms, this idea is not viable.
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There are super capaciters that deplete their capacitance much slower than that…
You’re going to ask me for evidence but for the life of me I can’t find it! 
Trust me, there is…
Although this article is about Ultra-capacitors (which could still be used), they talk about using in EVs for sudden short bursts of current, such as this use case…
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Hmm, nice find.
Let’s say you get your hands on a 500F capacitor for 8S battery though. (Probably would cost you around €1000). Calculating this fast, would let me guess this would give you 1 minute 15 seconds of acceleration power, until the capacitor is depleted to a voltage level insufficient to let the motor spin at a decent speed. (As the motor’s speed is in direct relation to its voltage, unless it’s current is limited). If we calculate generously, we may say minute and a half. (This calculation is made for a current draw of 30A, which is what my board draws when acceleration full throttle.)
You would also need this time to charge it back to full voltage with a 30A current, although to prevent the voltage sag I suppose you want this lower than the amps you’re using the capacitors for, right? So let’s say 15A, which would require 3 minutes to charge the capacitor again.
No matter what scenario you write down, the time to charge the capacitor will always be higher than the time you accelerate, don’t you think? In the case the capacitor is depleted, the battery would be providing current to charge the capacitor + power the motors and would be limited by the charge resistor for the capacitor to the previously selected 15A. I suppose the motor would receive half of that (not quite sure).
Anyway, I don’t know enough about this to give a definite answer, but I can pretty much conclude for myself that this is a bad idea. For the price, you’d be better of buying good batteries with low voltage sag ;).
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You could always buy several smaller capacitors and parallel them…
Caps get charged very quickly, I think you’re underestimating the speed in which they charge back up. Also, if someone were to create a ‘smart’ battery, electronics could turn on and off the capacitor as and when it’s needed. You’re not going to hard accelerate for more than a few seconds at a time, when the draw goes over a threshold, in kicks the super cap, when it eases, switch back to the cells, all the while the cells are charging the caps up at the highest rate they can cope with without sagging… I’M A GENIUS!!! Someone needs to make these ‘smart, super-cap-ion’ battery packs!! lol
It’ll still be around the same price then, cause that’s the only option as far as I’ve seen. (And you’ll have to put them in series instead of parallel, as the voltage they’re built for is the issue. So your capacity will stay the same but possible voltage will be higher.)
And yes they do, but only in figure of speech (Well, they’re faster than batteries, but if it’s not faster than discharging then I’m not going to call it fast.). They charge as fast as they discharge, and because regular capacitors only have low capacity, they appear to charge very fast. In practice it’s 4-5 times the RC (Resistor to limit charge current X capacity) coefficient. Where after 1 x RC coefficient, it already reached 63% of it’s maximum voltage. But after 2 x RC it reached 86% then 95% and then 98%. This means that because the raise in voltage, the voltage difference between the battery and the capacitor decreases, resulting in a drop in charge current and slower charging the higher the capacitor voltage will be.
That’s why the calculated times in my previous post are so low - and probably still estimated to good -.
But to be honest, it simply won’t matter. The voltage drop on your battery will be significant once it’s nearly depleted. Look at this graph, at the start your voltage will drop quite significantly, then it’ll remain quite constant for some time and it’ll appear as if you’re barely losing charge. (For those with a % meter on their longboards, you’ll be finding yourself in the 80%-40% range, but suddenly, after dropping below 40% it seems like your batteries break 
and they suddenly get to 10% really quick! But it’s normal and putting capacitors in their won’t benefit this, it won’t matter.
But yeah, it’ll prevent that a sudden acceleration makes the battery drop a few % for a few seconds. But I do not see this as an issue as long as your cutoff voltage is set conservative and this issue decreases if the C rating of your battery is higher.
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But that’s the point. Most voltage sage issues happen under hard acceleration, perhaps on some kind of incline. A lot of them result in a cut out in power. This can be potentially dangerous for the rider as they get catapulted forwards (it’s happened to me!). This solution will effectively eradicate that issue.
The cap deals with the sudden draw of high current, then it peters out after a second or two where the normal battery resumes and has less current draw/load.
If that issue is so significant, then you should limit the current, your batteries are simply not up for the task. I don’t see any gains for developing a capacitor system if you could just spend less money, for a battery setup that works just as great. A battery should be chosen with a C rating, offering a current minimal double of the current you’ll maximum draw. My battery setup can deliver 125A and I’ve never had issues like this.
You’ll perhaps also want to measure the resistance between your battery and VESC if you had issues. Perhaps a bad soldering causes a high resistance connection. If the total resistance of the cable, connections would be lets say 0.05Ohm, it would cause another 1.5V voltage drop at full acceleration in my case.
But if you were to develop something like this, I do want to check it out 
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The difference between more cells in parallel could be as much as €100 depending on what cells you have. Some li-ion cells put out 42A but they’re mega expensive.
I believe smaller less expensive caps in parallel will make this a cost effective solution.
If your gonna do anything. Figure out a cap+TVS solution for going downhill and preventing over voltage during braking. Forget the cap for acceleration, get bigger/more batteries.