I definitely must be missing something; it could be a communication problem or even a language thing. I apologize and will stay out of it until the results of your testing are available to see what difference it makes.
cap on battery, influences charging?
- Thread starter ProDigit
- Start date
BatteryMooch
10 kW
You're correct. The battery voltage to the input of a controller does have a ripple in the waveform that is caused by pulling current from the battery in pulses. There are capacitors at the input controller that set the ripple at a point where it doesn't affect the controller. You can add lots of additional, very low ESR, capacitance to the input of the controller to reduce the input voltage ripple even more but the big question is, why? What will this do? A smoother waveform going into the controller will make almost no measureable difference as the controller was already designed with the existing ripple in mind.ProDigit said:
And those additional capacitors need to be mounted within a fraction of an inch of the other capacitors already there to have any effect. A design I'm part of now sets a 1/10" distance on the input capacitors (from the controller's circuitry). Any further away and the resulting inductance renders the capacitors almost useless.
Even if you just want to try and see what the caps might do, you need to figure out how are you going to mount them as close to the input of the controller's circuit as the existing caps. Mounting the caps anywhere external to the controller case won't help with the voltage ripple. It can help with voltage sag, but that's a completely different use for the caps.
There can also be high frequency electronic noise also coming from the input of a controller but you probably won't be able to suppress that with just capacitors. Typically, series inductors and capacitors to ground are used to create a low-pass filter than screens out the high-frequency noise. You'll also need to pay attention to how the cabling is run, etc., to prevent noise from "jumping over" the filter and back into the wiring. All this is only necessary if you find that the controller is interfering with other electronic devices (and you've narrowed down the problem to conducted, not radiated, noise coming from the input and not anywhere else) or need to control emissions from the controller to conform to particular gov't/industry regulations regarding emissions.
I apologize too! I don't mean to be rude, this forum is just sometimes hard to distinguish people who want honest conversations from people who're just spamming.amberwolf said:
Perhaps not for the controller, but perhaps the battery would benefit from it. Imagine if the battery instead of giving 10A continuously, is giving many pulses of 40A, about 25% of the time interval, then the battery would be providing the same power to the controller, only in one case the battery does not get stressed, and in the other it gets stressed multiple times per second!
I don't know what the extent of the voltage difference is, whether the controller is sucking out pulses of all of the battery's capacity, or if it's just causing small fluctuations on the power draw.
The fluctuations voltage wise may make less impact than amp wise.
I am not convinced that batteries are made to be treated this way (large powerdraws multiple times a second), and think the possibility could exist to extend battery life by installing a cap, that would dampen these power draw chops. If the controller already has caps installed, they are not that many, or big ones, because the controller itself is a pretty small device!
If the powerdraw of the controller goes in chops, internally on the battery, the cells must be generating heat waves many times a second, always heating up and cooling down, instead of staying at a steady temperature. Theoretically, on a microscopic scale, that could mean that the fibers within the cells are constantly expanding and shrinking (as material expands when it heats up and shrinks when it cools down), and thus rubbing on each other, generating more heat, and wearing out faster...
It's just a theory, until proven. Some say that the battery can handle this, but perhaps this is the reason why the battery only has 700 recharge cycles instead of more! Theoretically having a good cap on the battery, could extend it's life to 1000, 1200, or possibly even 2000 recharge cycles for the same battery.
But due to lack of knowledge, and practical experience, I can't tell if it would, or would not make a difference. I only suspect that the possibility is there for it to cause a difference; as it's ALWAYS better to have a constant flow of energy (which is natural), compared to a chopped flow.
In clocks, watches, remote controls, media players, cellphones, etc.. the voltage is also chopped, but the power draw is in the likes of milliwatts (microwatts in some cases even), and compared to the battery's size, it really won't affect the battery life much at all!
On a bike, we are talking about near to Kilowatts, and the battery has way less capacity compared to a watch when you measure powerdraw over capacity (an ebike can run for ~4 hours on a charge; a media player anywhere between ~14 and ~40 hours, a cellphone can run for ~4days, a watch can run for ~4 years; so voltage chops become more important the higher the power draw is over the total battery capacity).
It does not matter, electrically speaking, where the cap is installed, within the controller or within the battery, or anywhere between. They are connected by 2 large gauge wires; anywhere along the line is fine.
The noise itself is just a by-effect of the voltage chopping, and is harmless in most cases.
Also in most cases just installing a large sized cap can filter out any high frequency noise (voltage wise) on the battery, as well as lower frequency noises. The larger the cap, the larger voltage chops it will be able to smooth out.
high frequency noise can easily be eliminated by a $5 cap; but what's more important is the lower frequency pulses!
I'll give my input regarding capacitors with these brushless controllers.
I'm come form a RC background and my toys are far more abusive to LIPO's vs most ebikes.
Installing caps at the battery input does help a lot when you have high amp draws. My toys peak over 185A and drain 5000mah in less than 5 minutes running up and down the street. Without the extra caps I would kill my controllers. Heck I even installed extra TVS's on them, just so I can run at the near limit of the controllers.
I ran into an issue a while back when Castle Creations released a new firmware for their controllers. I was only able too use around 25% of my battery, before the car would loose it's acceleration power. The amp draw was just too high for the 40C lipo to keep up. To get rid of this problem, I installed additional low ESR caps onto the battery input and am able to have the same performance to 60% of my battery capacity.
Adding caps on a regular RC brushless setup helps out too with heat coming from the controller. The power is cleaner and you gain some time. Braking power is much more improved as well.
In RC drag racing, caps are a big thing and makes a big difference in your times. It doesn't matter how badass your batteries are, caps will gain you some more performance.
I had made a capacitor bank for my ebike a while back and see what it would do. I was hoping for a smoother throttle response with the extra caps and I did get it with everything else being the same.
I'm betting better performance for those that run 120% throttle with their sensored setups and running regen braking.
If caps didn't help improve performance in brushless controllers, none of the RC brushless manufacturers would offer extra cap banks/packs as an option.
This is the cap bank that I had build for the smoother throttle response. For max power, cooling and better braking, I would use thicker wires a put it closer to the controller input.
I'm come form a RC background and my toys are far more abusive to LIPO's vs most ebikes.
Installing caps at the battery input does help a lot when you have high amp draws. My toys peak over 185A and drain 5000mah in less than 5 minutes running up and down the street. Without the extra caps I would kill my controllers. Heck I even installed extra TVS's on them, just so I can run at the near limit of the controllers.
I ran into an issue a while back when Castle Creations released a new firmware for their controllers. I was only able too use around 25% of my battery, before the car would loose it's acceleration power. The amp draw was just too high for the 40C lipo to keep up. To get rid of this problem, I installed additional low ESR caps onto the battery input and am able to have the same performance to 60% of my battery capacity.
Adding caps on a regular RC brushless setup helps out too with heat coming from the controller. The power is cleaner and you gain some time. Braking power is much more improved as well.
In RC drag racing, caps are a big thing and makes a big difference in your times. It doesn't matter how badass your batteries are, caps will gain you some more performance.
I had made a capacitor bank for my ebike a while back and see what it would do. I was hoping for a smoother throttle response with the extra caps and I did get it with everything else being the same.
I'm betting better performance for those that run 120% throttle with their sensored setups and running regen braking.
If caps didn't help improve performance in brushless controllers, none of the RC brushless manufacturers would offer extra cap banks/packs as an option.
This is the cap bank that I had build for the smoother throttle response. For max power, cooling and better braking, I would use thicker wires a put it closer to the controller input.
snellemin said:
Cool cap bank, but most of those guys are just sitting there. Caps only really do anything when the ESR is lower than the battery, and with a big parallel chain like that, and such thin interconnects, most are idle.
This stuff needs to be as close to the controller as possible, otherwise the effects are negated. Inside the controller really is the best place, right on the FET rails if you can.
OP: I see several EE's saying over and over, caps on the battery are not going to gain you anything. It probably won't hurt, but its likely a waste of time, money, space and weight on a bike.
BatteryMooch
10 kW
Ahh, OK, I'm understanding better what you're trying to do.ProDigit said:
Yes, reducing the magnitude of pulsed loads to a battery (using a capacitor or a lower ESR battery) will help to smooth out the voltage from the battery and increase the efficiency of the system (because of reduced ESR-induced power loss, etc.). This can also help increase the effective capacity of the battery.
In the situation I was referring to, reducing RFI being emitted by the input of the controller, the connection location of the caps is critical, absolutely critical. In your application, which I'm now starting to understand, the caps still cannot be located anywhere (for best performance). Even with 2AWG wiring, you will have voltage drops. The caps should be mounted as close as possible to the controller as their "job" is to provide pulses of current that you don't want to have pulled from the battery. The closer the caps are to the battery (and not the controller) the more the caps will share the load with the battery. It's best to have the smallest resistance possible between the controller and caps so that the largest percentage of the current pulse comes from the caps.
That high-frequency noise is a HUGE problem in many applications and can interfere with any electronics mounted nearby. Just using a large cap, mounted anywhere, will do nothing. In fact, the larger the cap, the less it will do as its ESR typically increases with size (reducing its effectiveness). The frequencies that a capacitor can "swallow" increase with decreasing size/capacity for the cap. It's always best to use multiple, small, very low ESR caps mounted VERY close to the controller's circuitry to handle high-frequency noise.
However, to reduce standard voltage ripple on a controller's input, using a larger cap can work. But, it's effective resistance MUST be a LOT less than the effective resistance of the battery! This includes internal resistance, wire lead resistance, and resistance from the cap to the controller. Having a cap with an effective resistance greater than that of the battery will ensure that the cap only contributes a tiny bit to handling the voltage ripple. This is why the type of capacitor, its ESR, how it's mounted, and where it's mounted matters a LOT. Sure, just tossing any big cap on might help a bit. But with a bit of time spent on choosing a good cap, and mounting it properly, it can have a big impact on reducing voltage ripple.
How much reducing the ripple (i.e., minimizing the current pulses from the battery) affects overall system efficiency and battery capacity/life, I don't know. Perhaps an insignificant amount, perhaps a couple of percent, perhaps a bit more. Commercially, it's not worth the expense, time, and added weight/size. But for an individual looking to squeeze everything out of their setup...perhaps.
It will be interesting to see the results of your tests!Final note...
I should note that you can reduce the voltage ripple that's on the input of a controller to a very, very low level using tiny, very low ESR, capacitors mounted right at the controller. These caps already exist in every controller but they can be supplemented with added caps to "swallow" even more ripple. Since the ripple is caused by the huge current pulses from the battery dropping the battery's voltage, reducing the ripple to almost nothing will, I believe, also reduce to nothing the large current pulses from the battery. These tiny capacitor's are incredibly effective at supplying truly enormous amounts of current for the very short time that a controller needs it for each cycle. If you're comfortable playing with surface mount caps, I wouldn't discount trying to supplement these caps internally before going to a large cap external to the controller.
snellemin said:
ZOMGVTEC hit the nail on this one. That cap bank is utterly useless. As for your toys running 185A peaks, this doesn't say us jack shit if we don't know the other stats of your pack. It wasn't the caps that made the difference, it was something else. Caps on RC toys = poor use of weight. Take this from someone who calculated the bare minimum of copper wires to and from battery and motors of a quadcopter.
40C battery, please - it could have been worn or overrated, that happens all the time. Your words about better throttle response and whatnot are just bollocs.
Youre one of the spammers with your nonsense about battery, capacitors - not having a clue of what inductance is and what it does.ProDigit said:
ProDigit said:
That is why you need capacitors on the input - to smooth current ripple. Current ripple is a function of duty cycle, amperage draw, battery inductance and more.
Prodigit said:
This is electronics 101, OHMS LAW. U=RI. know two, calculate the last! Know ampere draw and internal resistance? woops, you have voltage sag! Know delta voltage unloaded and known ampere draw? woo, internal resistance calculated.
Voltage difference further depends on motor speed - and voltage difference determines rate of current climb. If you have a dead short - all of the batterys power are being sucked out. The controller makes sure the power draw is stopped before the motor acts as a near short. The motor is a inductor. Voltage leads current in a inductor, that means current starts to rise after voltage has been applied. NOT AN INSTANTANEOUS THING, also electronics 101.
Prodigit said:
No, no, no, no, no, no. The time constant for heating and cooling is WAY out of the possible idiotic "theorietically on a microscopic scale". It is theoretically not going to happen as you explain it to. Batteries, and also fets - have quite a time constant for heating.
"Theoretically having a good cap on the battery, could extend it's life to 1000, 1200, or possibly even 2000 recharge cycles for the same battery." - Show me the evidence and theory (not your mumbojumbo) that supports this statement.
Your understanding of electronics seems to be along the lines of this:
Go read a book.
liveforphysics
100 TW
You guys are just feeding the troll.
Controller caps need to be local to work. The battery doesn't care about ripple, and if the caps on the controller at good, it barely see's ripple anyways.
Controller caps need to be local to work. The battery doesn't care about ripple, and if the caps on the controller at good, it barely see's ripple anyways.
Kin
10 kW
^I loll'ed.
For what it's worth, LiPo batteries are kind of like capacitors. I used to say that jokingly because nanotech have mindblowing C ratings. But, actually. They're layer upon layer upon layer of slightly seperated charged particles. Maybe the membrane thickness is enough that they don't count usefully capacitors, but I think you can say they're capacitors in the same way you can make a stupid capacitor with paper and al foil :-D. Yeah, wait, is what I'm saying even making sense? I started BS'ing something that I think might be true. Is there any measurable amount of energy stored in LiPo because of their nature of layered separated charges? (course most is just electrochemical)
Sorry though, there is a LOT of troll feeding here. I am partaking right now >.< sorry.
Sooo...to improve your battery situation, I recommend the capacitor brand called "Hobbyking Nanotech."
For what it's worth, LiPo batteries are kind of like capacitors. I used to say that jokingly because nanotech have mindblowing C ratings. But, actually. They're layer upon layer upon layer of slightly seperated charged particles. Maybe the membrane thickness is enough that they don't count usefully capacitors, but I think you can say they're capacitors in the same way you can make a stupid capacitor with paper and al foil :-D. Yeah, wait, is what I'm saying even making sense? I started BS'ing something that I think might be true. Is there any measurable amount of energy stored in LiPo because of their nature of layered separated charges? (course most is just electrochemical)
Sorry though, there is a LOT of troll feeding here. I am partaking right now >.< sorry.
Sooo...to improve your battery situation, I recommend the capacitor brand called "Hobbyking Nanotech."
SamTexas
1 MW
A picture is worth what? Here are two gazillion words.
Seems like for every good post there are 3 or 4 trolls on the forum.
Usually the ones complaining about trolls are the trolls themselves, so I'll just skip reading their comments.
If it is true that a battery operates like a cap,then it is impervious that a cap be installed!
Because in the industry, caps tend to blow quite often; and they only blow because of layers continuously rubbing against each other, when heating up and cooling down. In this case we are not talking about a 250W hairdryer that operates on a 50 or 60Hz AC current. We're talking about a few hundred watts, to a kilowatt of chopped voltage, that could be fluctuating as much as a few thousand times per second!
I would like to see an oscilloscope reading on the battery output to see if the cap used in the controller is enough to bridge the current fluctuations!
The way I see it the cap inside the controller may do a wonderful work at zero power, or no load acceleration, but once we're talking about full throttle under load the graphs look much different!
And I can't believe any cap small enough to fit inside the controller is capable of bridging those chops!
As far as installing a large capacitor cap not filtering out high frequency noise, that's not really true.
The larger the cap, the more of the noise will be absorbed.
Try experimenting with audio gear, and you'll see I'm right. larger caps completely absorb high and even mid-frequencies, while smaller caps do only high frequencies.
Also, as far as the importance of a cap being placed as close to the controller as possible, I don't see any reason why.
At least, in my case scenario, the 2 wires I have installed in my bike are good enough for upto ~55A (2500W).
They carry all signals. There is no significant voltage loss or degradation over the cable (which is less than 3ft in length). Just for filtering the noise it matters not where the caps are installed, on the controller's side (which is harder, because I'd have to cut one of the wires), or on the battery side (which is easier to do, because of the connectors).
The idea of a cap bank is a good one!
Since it's quite hard to find a good cap operating on a high DC voltage, perhaps it is possible to use several lower capacity caps for 110V AC.
I could get a 600-6000V 4uF cap, which at lower voltages operates much like a large cap, but I'm afraid that the current losses are higher with higher voltage caps.
And since most caps are sold ranging from 12V to 24V, and then jump to 120V AC or higher, I don't really have a choice but to go for 110V AC caps!
Either use 2 caps of 24V in series, and have a low capacity, high priced cap bank,
or buy a few 120V caps, put them in parallel, for something like $10-15, and solder them onto the main power lines of the bike.
I see no reason why this should be expensive, nor why it should take up a lot of space or be heavy.
For one, I'm interested in this one:
http://www.amazon.com/110-125-Volt-Start-Capacitor-270-324/dp/B004NKXU28/ref=sr_1_2?s=electronics&ie=UTF8&qid=1340861365&sr=1-2&keywords=ac+capacitor
although the application is meant for AC, it may be able to be used in lower voltage DC applications as well! Perhaps solder 4 of them together...
Worst case take a pick on one of these deals:
http://www.amazon.com/s/ref=sr_nr_n_0?rh=k%3A120V+capacitor%2Cn%3A16310091%2Cn%3A!16310161%2Cn%3A306506011&bbn=16310161&keywords=120V+capacitor&ie=UTF8&qid=1340860785&rnid=16310161
Put 25 to 50 of these smaller ones in parallel, and they might be enough to filter out the noise! You just need to be able to solder them, and use a lot of electrical tape to keep them together, but if you ask me, the first one should do fine!
A cap bank of about 6x3x4in in size (rough guess, I can actually measure it tomorrow), can very easily be installed under the seat compartment (where all the controller wires are located). There's enough free space, as well the possibility to install the cap bank on the chassis.
Usually the ones complaining about trolls are the trolls themselves, so I'll just skip reading their comments.
If it is true that a battery operates like a cap,then it is impervious that a cap be installed!
Because in the industry, caps tend to blow quite often; and they only blow because of layers continuously rubbing against each other, when heating up and cooling down. In this case we are not talking about a 250W hairdryer that operates on a 50 or 60Hz AC current. We're talking about a few hundred watts, to a kilowatt of chopped voltage, that could be fluctuating as much as a few thousand times per second!
I would like to see an oscilloscope reading on the battery output to see if the cap used in the controller is enough to bridge the current fluctuations!
The way I see it the cap inside the controller may do a wonderful work at zero power, or no load acceleration, but once we're talking about full throttle under load the graphs look much different!
And I can't believe any cap small enough to fit inside the controller is capable of bridging those chops!
As far as installing a large capacitor cap not filtering out high frequency noise, that's not really true.
The larger the cap, the more of the noise will be absorbed.
Try experimenting with audio gear, and you'll see I'm right. larger caps completely absorb high and even mid-frequencies, while smaller caps do only high frequencies.
Also, as far as the importance of a cap being placed as close to the controller as possible, I don't see any reason why.
At least, in my case scenario, the 2 wires I have installed in my bike are good enough for upto ~55A (2500W).
They carry all signals. There is no significant voltage loss or degradation over the cable (which is less than 3ft in length). Just for filtering the noise it matters not where the caps are installed, on the controller's side (which is harder, because I'd have to cut one of the wires), or on the battery side (which is easier to do, because of the connectors).
The idea of a cap bank is a good one!
Since it's quite hard to find a good cap operating on a high DC voltage, perhaps it is possible to use several lower capacity caps for 110V AC.
I could get a 600-6000V 4uF cap, which at lower voltages operates much like a large cap, but I'm afraid that the current losses are higher with higher voltage caps.
And since most caps are sold ranging from 12V to 24V, and then jump to 120V AC or higher, I don't really have a choice but to go for 110V AC caps!
Either use 2 caps of 24V in series, and have a low capacity, high priced cap bank,
or buy a few 120V caps, put them in parallel, for something like $10-15, and solder them onto the main power lines of the bike.
I see no reason why this should be expensive, nor why it should take up a lot of space or be heavy.
For one, I'm interested in this one:
http://www.amazon.com/110-125-Volt-Start-Capacitor-270-324/dp/B004NKXU28/ref=sr_1_2?s=electronics&ie=UTF8&qid=1340861365&sr=1-2&keywords=ac+capacitor
although the application is meant for AC, it may be able to be used in lower voltage DC applications as well! Perhaps solder 4 of them together...
Worst case take a pick on one of these deals:
http://www.amazon.com/s/ref=sr_nr_n_0?rh=k%3A120V+capacitor%2Cn%3A16310091%2Cn%3A!16310161%2Cn%3A306506011&bbn=16310161&keywords=120V+capacitor&ie=UTF8&qid=1340860785&rnid=16310161
Put 25 to 50 of these smaller ones in parallel, and they might be enough to filter out the noise! You just need to be able to solder them, and use a lot of electrical tape to keep them together, but if you ask me, the first one should do fine!
A cap bank of about 6x3x4in in size (rough guess, I can actually measure it tomorrow), can very easily be installed under the seat compartment (where all the controller wires are located). There's enough free space, as well the possibility to install the cap bank on the chassis.
ProDigit said:
And after you are done, invent some more problems that need curing by adding a capacitor bank.
Think of yourself as a white man arriving on an island full of know-nothing savages. Somehow we've been running these brushless controllers for decades without problems. You just know a better way to do it, and when you clue us in, you'll be regarded as a god on this island!
BatteryMooch
10 kW
ProDigit said:
Caps blow for many, many different reasons...
-Exceeding their voltage rating.
- Exceeding operating temperature limits.
- Exceeding ripple current limits. This is what you incorrectly refer to as layers rubbing against each other. If you don't spec a cap with a good enough ripple current rating the cap's internal resistance causes excessive heating. No rubbing involved.
It is absolutely, totally true and a basic part of how caps work.ProDigit said:
You've obviously read something about audio caps and incorrectly interpreted it. A larger capacitance (NOT a "larger capacitor") can, if all else is set up correctly, smooth out a pulsating DC voltage more than a smaller capacitance. But smaller caps handle higher frequencies of noise better than larger caps...basic electronics.
Please, please read the data sheets and online tutorials for various capacitors. NOT from audio sites. The "science" discussed on these sites is often useless. The effective resistance of a capacitor typically increases as the size of the cap, or its capacitance, increases. This is a simple, basic part of what happens with caps. As the effective resistance increases, the ability to handle faster-changing signals decreases.
And I haven't even started with how you're going to have to calculate whether the caps you select can handle the ripple current going "through" them. etc.
You don't see why because you're not at all understanding how different caps work differently and, seemingly, don't want to learn more.ProDigit said:
Every law that exists regarding electricity says that there is degradation/loss over every single part of your cables, no matter how large the gauge is. How much that loss affects what you're doing depends on what you're trying to do and the frequencies. resistances, inductances, etc., involved. I've explained why it matters where the caps are located. Please, please do some additional research.
For low-frequencies, the cap location matters less than for high frequencies. If you're just trying to reduce the voltage ripple on the controller input lines then you'll see less of a difference due to cap location than if you're trying to reduce noise. You're explanations of what you're trying to do are very confusing because you're confusing terms that have very specific meanings.
But, no matter what the frequencies, mounting the caps closer to the controller means that the resistance between the caps and the controller is reduced and that will increase the cap's effectiveness. This cannot be changed or explained away. It sounds like you've chosen to mount the caps at the battery. This is fine, but it will reduce their effect because you're moving them farther away from the load. For your application, this may or may not be noticeable. But, since you haven't mentioned how you're going to test the caps' effectiveness, none of any of this might matter at all.
Caps are available in just about any voltage you can think of. Go to http://www.digikey.com and search for "Capacitors". You'll see that they have over 200,000 different types/values of capacitor.ProDigit said:
Why do you feel this cap is a good choice in your application? This is not a rhetorical questions, I'm asking this because I really want to know why you feel this is a good cap. Especially since you don't know if it's even compatible with your application?ProDigit said:
Why do you feel these caps would be a good choice? They are so completely different in what they'll do in your application than the other cap you mentioned. How are you coming to the conclusion that these might filter out the voltage ripple you're concerned about?ProDigit said:
Assuming 50 of these in parallel, you'll have a 0.006 microfarad cap. Even mounted directly at the input of the controller's circuitry, they'll almost no effect in your application....none.
I very, very strongly recommend that you purchase the caps (whichever ones you want to buy) and install them where you want to. Do your tests and get back to us with the results. How are you going to verify that the caps have made any difference though?ProDigit said:
I'm serious...how?
dnmun
1 PW
.
It would make sense, however practice has taught me that this is not true!
Larger capacity caps absorb more frequencies, including the higher ones!
The resistance only increases when the voltage handling of the cap increases. at low voltage handling, but large capacity, there's just more 'foil' in the cap; at a high voltage, low capacity, the cap has less foil in it, but the foil is separated further to prevent leakage. This is what causes lower capacity, and higher resistance as far as I know... Higher voltage caps may indeed absorb high frequencies less good; though I'm currently guessing a 1-3Farad cap can absorb most of the signals just fine.
Unfortunately 48V is not really an industrial standard. I've looked at the site you mentioned, and there are only 2 caps for 48V DC. Both of them are ridiculously large in size (one of them being 165Farad???)... Crazy! Anyway, it's hard to find a good cap on 48V.
1- Fits my budget
2- Is a cap
3- Is quite a large cap too
4- Is made for AC, but most caps work on DC too
I noted too late indeed that the caps where too small. It's more meant as a joke than a practical solution! No way will I spend time soldering 50 caps together, nor do I think anyone would!
LOL!
Unless someone wants to donate an oscilloscope, I guess the only way to verify, is drive around a lot, and see how the batteries react after 700 recharges! That'll probably be 3 to 4 years down the road!
emmmmm.......
Has anyone mentioned how some certain cheap and nasty controllers may benefit from a few good caps, although i think for a good controller it will help as much as using OFC cable.....
what will this do for people who run on SLA ..................
Has anyone mentioned how some certain cheap and nasty controllers may benefit from a few good caps, although i think for a good controller it will help as much as using OFC cable.....
what will this do for people who run on SLA ..................
flez1966 said:
It would if we had an actual problem of controller capacitors being inadequate. I've been reading this board daily for over 2 years and have never heard of such a thing - unless we are talking about cheap RC ESCs.
flez1966 said:
The answer to that question is covered within the first 2 pages of this thread.
BatteryMooch
10 kW
You're wrong.ProDigit said:
Reactance in ohms for any capacitor is inversely proportional to the frequency of the alternating current. Notice that there's no mention of the voltage rating anywhere in the equation. Different caps by different manufacturers have different reactances ("resistance") for different cap physical sizes but there's no rule that the reactance increases when the voltage handling rating increases. Sounds like you've adopted an audio web site over-generalization.
For example, reactance of a 100 uF capacitor:
Frequency (Hertz) = 60, Reactance (Ohms) = 26.5
Frequency (Hertz) = 120, Reactance (Ohms) = 13.3
Frequency (Hertz) = 2500, Reactance (Ohms) = 0.64
Higher resistance = less ability to handle current pulses without dropping voltage internally (i.e., adding ripple or "noise" as you call it).
Ahhh, you only want a 48V cap? Aha! Didn't know this, but perhaps you mentioned this earlier.ProDigit said:
165F is too large? But, you said larger was better so this should be an absolutely amazing cap! Why is selecting such an amazing cap considered crazy? This is very confusing.
You guessed that 1F to 3F might be good. OK, if we're not using the amazing 165F cap we can settle on a less effective smaller cap. The larger capacitance caps often come in lower voltage ratings. Have you considered placing caps in series? Four 12V, 10F caps would be just about in the middle of your 1F-3F, 48V requirement.
OK, now where getting even more info!ProDigit said:
1) What's your budget? Dollar-wise, size-wise, and weight-wise?
2) I'm confused. The 165F cap...umm...is a cap.
3) But, you have no idea of what the value (capacitance) of the cap is. What if it's a 165F cap?
4) Agreed
There are many, many applications that use lots of smaller caps instead of one big one. Since the smaller value caps handle higher frequencies so much better, they must use smaller ones. But, a certain total capacitance is often needed so dozens of caps are used in parallel.ProDigit said:
For a larger circuit board, there's just no way one big cap in the corner is going to handle the decoupling/bypassing ("swallowing noise") needs of that board! You need to spread out the capacitors to be as close as possible to each source of current use to be of any use. Mounting these caps even 1/4" away from the chips they're supposed to be helping out makes the caps almost useless at the higher frequencies they're needed and creates LOTs of electrical noise on the board as a result.
I'm confused. How is that going to test anything? You need another setup, without caps, to compare the cap results against. Otherwise you're not testing anything, just enjoying riding around with a setup with caps until you feel that the battery needs replacing.ProDigit said:
I don't know how much more either of us can contribute to this conversation as we disagree even on the most basic concepts of how a cap works. But, I wish you luck in purchasing and using your cap(s)! Hope you'll stop by in that 3-4 years and let us know how it worked out.
the 165Farad cap is just too large to fit anywhere on the bike; it's almost the size of my battery!
my budget is user friendly.
I don't care if I get a 1 or 4 farad cap, just as long as I can justify it's price for what I'm trying to accomplish.
If a good cap costs me $80, and two fairly ok caps costs me 2x$5, then the solution is quite obvious!
If I can get the job done for $2, my budget would be $2!
I don't like to work with budgets, as you always find out you get overcharged.
instead look around, and find same thing, only cheaper!
If a 48V cap costs me $40, but a similar 96V cap costs me $15, because it's more sold than a 48V one, and thus prices go down on the manufacturing, then I'll get a 96V one. If a 110V AC cap could do the job just as well, for a quarter of the price, it's silly to insist on a 48V cap, and create a budget around it.
my budget is user friendly.
I don't care if I get a 1 or 4 farad cap, just as long as I can justify it's price for what I'm trying to accomplish.
If a good cap costs me $80, and two fairly ok caps costs me 2x$5, then the solution is quite obvious!
If I can get the job done for $2, my budget would be $2!
I don't like to work with budgets, as you always find out you get overcharged.
instead look around, and find same thing, only cheaper!
If a 48V cap costs me $40, but a similar 96V cap costs me $15, because it's more sold than a 48V one, and thus prices go down on the manufacturing, then I'll get a 96V one. If a 110V AC cap could do the job just as well, for a quarter of the price, it's silly to insist on a 48V cap, and create a budget around it.
BatteryMooch
10 kW
That is, quite possibly, the most astounding thing I've ever seen in print. LOL, I'm absolutely speechless at its implications.ProDigit said:
If it works for you though, go for it!
Price is not a good determiner of quality.
I could buy a cap made out of plated gold costing $500, but if for my purposes don't need the (say: faster response time, or better cooling), but a $5 cap does about 95% of the golden cap, then obviously... you know...
You got to look around, and see if you can beat the budget price you've set for yourself; and perhaps some of those industrial $10 chinese caps, that are terrible quality to be used at the rated 600V ac, may be good enough for operation at 48V DC.
I could buy a cap made out of plated gold costing $500, but if for my purposes don't need the (say: faster response time, or better cooling), but a $5 cap does about 95% of the golden cap, then obviously... you know...
You got to look around, and see if you can beat the budget price you've set for yourself; and perhaps some of those industrial $10 chinese caps, that are terrible quality to be used at the rated 600V ac, may be good enough for operation at 48V DC.
shock
1 kW
Caps are already built into the controllers, so if you need some OCD reason to add caps, just upgrade the ones in the controller to solid state or something. I know guys I fly 700 class helicopters with, add external caps to the batt>ECS wiring to help with brownout condition to the servos during heavy collective pitch rotor changes (read 0.5 second 3d maneuvers). Honestly a proper built ebike , with properly sized battery and controller (math helps here) does not need any external caps, nor do I really see a benefit to adding caps vs. just adding more lipo. No one is saying adding caps won't work. IT WILL. But it will be of far less value than adding more battery amp hours.
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