Ultra Caps?

[recumpence]

Does anyone have any information on what Maxwell Technologies Ultra capacitors (Boostcaps) sell for? I have been looking into them for RC applications for a while now. I understand their benefits (if run parrael with a typical battery pack) for providing high current while the lower discharge capable battery pack provides voltage thus reducing high amperage induced sag for accelleration bursts. However, I have been unable to find a price for them. All suppliers list them with a note "Email us for quantity pricing and to become a distributor". Hmm, I just want 18 of the C size cells to work with.

Anyone have any information on what these things would cost and where I could buy just a handfull of them?

Matt

 

[paultrafalgar]

These people claim to sell on line, I don't know anything about minimum quantities etc.
http://www.tecategroup.com/ultracapacitors/ultracapacitors.php

 

[recumpence]

Thanks for the link.

Hmm, $400 for the caps I would need. I will have to think about that. Heck, for that amount of money I can double my AH lipo pack.

Bummer. Man, I would really love a set of these, though. I have read alot about using large ultracaps in electric cars for accelleration. They keep the voltage from dropping. My pack is 49 volts when fully charged (settles to 48 volts shortly into the run). Under hard accelleration, it can drop to 44 or even touch 43 volts. I am sure it drops further than that in tiny dips too short for my display to read. Ultracaps would keep the voltage up at 48 volts constant unless I was pulling huge amperage for a relatively long time (8 seconds or longer). But, typically, if I am really hammering my bike, I pull large current for 4 to 5 seconds to accellerate. That means I would have 10% more power on tap. Of course, I already have tons of power.

But, like I said, I could double my AH with more lipos for that price. :?

Matt

 

[eP]

Thanks for the link.

Hmm, $400 for the caps I would need. I will have to think about that. Heck, for that amount of money I can double my AH lipo pack.

You have to spend $2000+ for ultracaps you need i'm afraid.
Look at that :http://www.tecategroup.com/store/index.php?main_page=product_info&cPath=18_20_39&products_id=18

Bummer. Man, I would really love a set of these, though. I have read alot about using large ultracaps in electric cars for accelleration. They keep the voltage from dropping. My pack is 49 volts when fully charged (settles to 48 volts shortly into the run). Under hard accelleration, it can drop to 44 or even touch 43 volts. I am sure it drops further than that in tiny dips too short for my display to read. Ultracaps would keep the voltage up at 48 volts constant unless I was pulling huge amperage for a relatively long time (8 seconds or longer).

You are wrong Matt. 160F/48V bank ( 18 pieces 3000F each in serial ) will discharge at rate 0.5V/s at 80A load, so after 8 second you will see 4 volts less.

But, typically, if I am really hammering my bike, I pull large current for 4 to 5 seconds to accellerate. That means I would have 10% more power on tap. Of course, I already have tons of power.

But, like I said, I could double my AH with more lipos for that price. :?

I think you don't need double your AH, but i'm sure you need 50% more volts and 50% more rpm to get 6kW power out efficiently that you need.
So adding 6 more LiPos + a bunch of caps before ESC is much less expensive than $2000 bank of ultracaps which are still pretty heavy .

 

[recumpence]

I don't mean to argue with you, but it would not be $2000. It would be $400 for the caps I would use (the C size cells). You are looking at the wrong cells. Also, you are calculating voltage drop of the caps without any battery at all, merely capacitors alone. All I am looking for is a helping boost, not to power the whole bike. They are also very light weight for their size.

My lipo pack would still be putting out the majority of the current the motor would be pulling. The caps would merely help out with the peaks.

Again, I am not married to the ideA. I am just intrigued by it. Lastly, I cannot run 50% more voltage. My controller won't hanle it, nor would my motor. My efficiency is decent for the power output I have and the weight. I am just sort of thinkihng out loud with this. I have seen these used in car and motorcycle applications as an added boost to eliminate voltage drop under load with great success.

Matt

 

[tostino]

I don't mean to argue with you, but it would not be $2000. It would be $400 for the caps I would use (the C size cells). You are looking at the wrong cells. Also, you are calculating voltage drop of the caps without any battery at all, merely capacitors alone. All I am looking for is a helping boost, not to power the whole bike. They are also very light weight for their size.

My lipo pack would still be putting out the majority of the current the motor would be pulling. The caps would merely help out with the peaks.

Again, I am not married to the ideA. I am just intrigued by it. Lastly, I cannot run 50% more voltage. My controller won't hanle it, nor would my motor. My efficiency is decent for the power output I have and the weight. I am just sort of thinkihng out loud with this. I have seen these used in car and motorcycle applications as an added boost to eliminate voltage drop under load with great success.

Matt

I'm really not too sure how this would work, so would you mind explaining it?

With my limited understanding, do you plan to wire the cap bank up in parallel with your batteries?
If that's the case, would the batteries keep the cap bank charged at all times, and then just share the load with it?

How efficient is charging up a cap? If you lose a lot of power doing that, wouldn't it just cancel out any gains you may get?
-Adam

 

[eP]

I don't mean to argue with you, but it would not be $2000. It would be $400 for the caps I would use (the C size cells). You are looking at the wrong cells.

Don't hesitate to argue with me Matt - i like your opinions.
But i'm sure i'm looking at the right cells for your needs.

Also, you are calculating voltage drop of the caps without any battery at all, merely capacitors alone. All I am looking for is a helping boost, not to power the whole bike. They are also very light weight for their size.

Once again i'm sure you are wrong. 80 A load is a mean value. It is 160 at begining and zero at the end (8 seconds later).
You now have heavy load 120+ A at accelerations, so i'm sure after such pricy upgrade you should have 160 A available at least.

But if you still sure i'm wrong, so show us your calculations - and related explanations - Matt.

My lipo pack would still be putting out the majority of the current the motor would be pulling. The caps would merely help out with the peaks.

If this would be the case, than ESC would see majority of the voltage sag.
If you want eliminate majority of the sag at peaks than supercaps cannot merely help out - they should help out as much as they can. This is what you paying for at least.

Again, I am not married to the ideA. I am just intrigued by it. Lastly, I cannot run 50% more voltage. My controller won't hanle it, nor would my motor. My efficiency is decent for the power output I have and the weight. I am just sort of thinkihng out loud with this. I have seen these used in car and motorcycle applications as an added boost to eliminate voltage drop under load with great success.

Matt

I'm also not married with ideas . But i'm sure you need much more than 40V (at ESC) if you need 6kW power out or even more .
If your controller won't handle 50% more so try 35% more.
If your motor won't handle 50% at heavy load than you should consider to use another one.
High efficiency and high rpm limit is what you paying for.
If motor Rm hot is close to 80 mohm than you need much more than 40V at 200 A load if you need 6 kW power out.

Best regards

 

[recumpence]

I don't mean to argue with you, but it would not be $2000. It would be $400 for the caps I would use (the C size cells). You are looking at the wrong cells. Also, you are calculating voltage drop of the caps without any battery at all, merely capacitors alone. All I am looking for is a helping boost, not to power the whole bike. They are also very light weight for their size.

My lipo pack would still be putting out the majority of the current the motor would be pulling. The caps would merely help out with the peaks.

Again, I am not married to the ideA. I am just intrigued by it. Lastly, I cannot run 50% more voltage. My controller won't hanle it, nor would my motor. My efficiency is decent for the power output I have and the weight. I am just sort of thinkihng out loud with this. I have seen these used in car and motorcycle applications as an added boost to eliminate voltage drop under load with great success.

Matt

I'm really not too sure how this would work, so would you mind explaining it?

With my limited understanding, do you plan to wire the cap bank up in parallel with your batteries?
If that's the case, would the batteries keep the cap bank charged at all times, and then just share the load with it?

How efficient is charging up a cap? If you lose a lot of power doing that, wouldn't it just cancel out any gains you may get?
-Adam

Yes, they would be parrallel with the battery pack. Normally capacitors just charge themselves according to how much current can be sent into them. Theoretically they have an unlimited recharge speed, though in practice they can only pull power from a battery just so fast.

Basically, an ultracapacitor bank would give out huge current for a few seconds to aid the battery with huge current spikes that would be drawn from it. The battery pack would not see such a huge amp draw, thus drastically reducting the amount of voltage sag seen under load.

In my setup, I lose about 10% (maximum) voltage under the hardest accelleration. The capacitor bank would release the huge amperage needed at those times, thus allowing the battery pack to remain up at full voltage level. This reduced (nearly eliminated) sag would result in more votage to the controller and, therefore, 10% more power.

As I said, I am not married to the idea. Heck, I would rather buy another 10AH of lipos for that money which would reduce voltage sag a bit as well by sharing the amp load among twice as many cells. I was just thinking out loud and trying to get some pricing information on these cells.

I will put my position on it this way;

From what I understand and from what I know these caps would cost me, I would only add them if I already had all other issues worked out in my bike and had plenty of range available with my batteries. Since I don't have those parameters met, I am not buying any ultracaps. As far as what the future holds, who knows?

I think if I were building a hot e-sprotbike adn money were no object, I would definately bite the bullet and add a large bank of ultra caps to it.

Matt

 

[recumpence]

I don't mean to argue with you, but it would not be $2000. It would be $400 for the caps I would use (the C size cells). You are looking at the wrong cells.

Don't hesitate to argue with me Matt - i like your opinions.
But i'm sure i'm looking at the right cells for your needs.

Also, you are calculating voltage drop of the caps without any battery at all, merely capacitors alone. All I am looking for is a helping boost, not to power the whole bike. They are also very light weight for their size.

Once again i'm sure you are wrong. 80 A load is a mean value. It is 160 at begining and zero at the end (8 seconds later).
You now have heavy load 120+ A at accelerations, so i'm sure after such pricy upgrade you should have 160 A available at least.

But if you still sure i'm wrong, so show us your calculations - and related explanations - Matt.

My lipo pack would still be putting out the majority of the current the motor would be pulling. The caps would merely help out with the peaks.

If this would be the case, than ESC would see majority of the voltage sag.
If you want eliminate majority of the sag at peaks than supercaps cannot merely help out - they should help out as much as they can. This is what you paying for at least.

Again, I am not married to the ideA. I am just intrigued by it. Lastly, I cannot run 50% more voltage. My controller won't hanle it, nor would my motor. My efficiency is decent for the power output I have and the weight. I am just sort of thinkihng out loud with this. I have seen these used in car and motorcycle applications as an added boost to eliminate voltage drop under load with great success.

Matt

I'm also not married with ideas . But i'm sure you need much more than 40V (at ESC) if you need 6kW power out or even more .
If your controller won't handle 50% more so try 35% more.
If your motor won't handle 50% at heavy load than you should consider to use another one.
High efficiency and high rpm limit is what you paying for.
If motor Rm hot is close to 80 mohm than you need much more than 40V at 200 A load if you need 6 kW power out.

Best regards

Gotcha.

I am still seeing a good 44 volts under load. So, 44 volts at a maximum of 200 amps (though normally about 150 amps for most hard accelleration situations) would be a maximum of 6,600 watts being drawn from the pack. I realize there are losses. But you can see the wattage output is still quite high.

Anyway, like I said, my voltage sag is really not that bad. I am just trying to look into any peice of technology I can.

My controller is rated at 50 volts max. The manufacturer of my motor insists I should not exceed 50 volts. So, that is where I am staying.

I have to say, I do not need any more power. However, I like to push everything to its absolute limit. Cost is a factor, but not the only factor in these decisions.

At this point, I am probably going to double my AH to 20 AH rather than my current 10 AH by purchasing more lipo cells. That will reduce my sag and double my range at the same time, all for $435 (the price of the C size caps). I just figured, heck, if those caps would be $150 or so, I would try them. But, the cost is more than the benefit would be for me, it looks like.

Matt

 

[dirty_d]

charging a cap from a constant voltage is only 50% efficient average from start to end if the cap starts at 0V. if you have a capacitor that starts at 24V and charge it with a constant voltage source(like a battery) to 48V, then the instantaneous charge efficiency is 24.0/48.0=0.5(50%). you can easily prove this, you have a 48V source, and a cap already charged to 24V, say the capacitor ESR plus all the other resistance is 0.5ohms, the current will be (48.0 - 24.0) / 0.5 = 48A, the losses from resistance are then 48^2 * 0.5 = 1152W, the total power going into the capacitor and resistance is 48V * 48A = 2304W, so that means that out of the total 2304W, 2304-1152 = 1152W is being stored in the capacitor, 1152/2304=0.5. that means when the cap is already charged to 24V and the applied voltage across the cap is 48V the instantaneous efficiency is 50%. thats only the instantaneous efficiency though, what you really want to know is the average efficiency going from 24V to fully charge at 48V, when the cap is at 48V and the applied voltage is also 48V the efficiency is 100%, so for that case the average efficiency is (24.0/48.0 + 48.0/48.0) / 2.0 = 0.75(75%).

so if you make this deal and it only drops 4V under a heavy load or something, then when you back off the throttle and let it charge back up the efficiency will be (44.0/48.0 + 1.0) / 2.0 = 0.96(96%).

 

[recumpence]

charging a cap from a constant voltage is only 50% efficient average from start to end if the cap starts at 0V. if you have a capacitor that starts at 24V and charge it with a constant voltage source(like a battery) to 48V, then the instantaneous charge efficiency is 24.0/48.0=0.5(50%). you can easily prove this, you have a 48V source, and a cap already charged to 24V, say the capacitor ESR plus all the other resistance is 0.5ohms, the current will be (48.0 - 24.0) / 0.5 = 48A, the losses from resistance are then 48^2 * 0.5 = 1152W, the total power going into the capacitor and resistance is 48V * 48A = 2304W, so that means that out of the total 2304W, 2304-1152 = 1152W is being stored in the capacitor, 1152/2304=0.5. that means when the cap is already charged to 24V and the applied voltage across the cap is 48V the instantaneous efficiency is 50%. thats only the instantaneous efficiency though, what you really want to know is the average efficiency going from 24V to fully charge at 48V, when the cap is at 48V and the applied voltage is also 48V the efficiency is 100%, so for that case the average efficiency is (24.0/48.0 + 48.0/48.0) / 2.0 = 0.75(75%).

so if you make this deal and it only drops 4V under a heavy load or something, then when you back off the throttle and let it charge back up the efficiency will be (44.0/48.0 + 1.0) / 2.0 = 0.96(96%).

Umm, yeah, what you said...........

Matt

 

[dirty_d]

which caps were you looking at by the way? what voltage and capacitance?

 

[recumpence]

I do not have the link handy, but they were Maxwell Technologies Boostcaps, "C" cell size 120 farad caps. I would need at least 18 in series for 48 volts. So, 48 volts, 120 farads.

Matt

 

[dirty_d]

if you only need 18 i guess those are the 2.7V ones, keep in mind that when you combine caps in series the capacitane gets divided by how many you have, so its 48V 11F. im checking this stuff out in a simulator too see how it really performs.

any idea what the internal resistance of your pack is?

oops i mean 48V 6.66F

 

[dirty_d]

hmm, for that 48V 6.6F bank, if the controller draws constant 100A, then the cap will go from 48V to 40V in 0.532 seconds. not too good. i could be wrong though, the way i calculated it was that at 48V the capacitor bank stores 48.0 * 6.66 = 319.68C, at 40V it stores 40.0 * 6.66 = 266.40C, the difference in charge from 48V to 40V is 53.28C. at 100A 100 coulombs of charge passes a point in one second so 53.28C / 100A = 0.532 seconds. i think you need bigger caps.

if you want to calculate what voltage a cap will be after a certain discharge at a constant voltage you can use (Vstart * C - t * I) / C = Vend, so like for that situation (48.0 * 6.66 - 0.532 * 100.0) / 6.66 = 40.01V

 

[recumpence]

OK, gotcha. I didn't know the farad capacity dropped when run in series. That kind of kills the whole thing from my perspective.

I will just double my AH capacity with more lipos and be happy.

Matt

 

[dennis]

Do you mean something like this? http://www.afstrinity.com/xh.htm.
Aptera.com seems to be working on a similar powertrain using ultracapacitors for regen braking and power boosts during acceleration. This seems to be the best solution to prolong the useful life of the batteries.

 

[recumpence]

Yes, that is basically what I am talking about.

Matt

 

[Jay64]

That setup sounds like something I was thinking of doing with my final race bike. Ultra caps for regen and then a short burst during acceleration out of corners. I like how that website refers to lithium-ions as a low-cost battery pack. :lol:

 

[recumpence]

No kidding. There is nothing cheap about lithium, no matter what flavor you are dealing with.

I still love the idea of using these. But, for the cost and space, I will double my lipo cells.

Matt

 

[dirty_d]

yea, good call. i could see if they were cheaper than batteries, but these ultra caps are just so damn expensive.

 

[Jay64]

Would it be possible to wire up a button actuator to get the short burst of power from Ultra caps to boost your acceleration, or would it have to be done by a computer and stuff?

 

[recumpence]

The boost just happens naturally. When the electrical system demands current, the caps naturally discharge into the system. The bank of caps would merely be wired parrallel with the pack.

Matt

 

[Jay64]

yes, with that setup. However, I would like to make a way to have it only come on when I wanted it to. At high performance levels you don't want a big burst of power while leaned over in a corner. I want to have it wait until I have the bike more upright and then hit hard to bring the speed up and then switch back to battery only to maintain speed.

 

[dirty_d]

its not really a boost, the voltage just doesnt sag as much, if you want a boost have the caps stay in parallel with the pack, then press a button to switch the caps into series with the pack to get double the voltage for a few seconds ,