Super Cap for High Amp Draw and lifepo4 battery in Parallel?

[evolution9]

Can I use a super capacitor bank in the same capacity (no pun intended) as car audio people use them for amplifiers that draw lots of amps RMS? i.e. use a 80V cap in parallel with a 80V Lifepo4 battery. to ensure that amp draw can keep up with controller? I just picked up a controller capable of drawing 150A+ and want to make a configuration for acceleration.

I was thinking the cap would allow the controller to draw the 150A required for acceleration and help stabilize regardless of the BMS attached to the batteries.

Has anyone done this?

Any idea how to calculate what capacitance would be required for the bank at 80-100 V at 150A ? I'm not looking for any sustained performance, just an initial boost.

B

 

[arkmundi]

Seems feasible, yes, but no, have not done, but would interested in those who have, or some experimentation by the intrepid among us. Best!

 

[evolution9]

I just ordered 4 super caps to do some testing http://item.taobao.com/item.htm?_u=q1q92q42d385&id=14947442968

where should I place them?

 

[TheBeastie]

I just ordered 4 super caps to do some testing http://item.taobao.com/item.htm?_u=q1q92q42d385&id=14947442968

where should I place them?

I have given this theory some thought in the past, cool to see someone trying some experimentation.

You would put them in parallel with your main battery, as if it was just another battery, its that simple.
The most important thing to do though is make sure your battery does not exceed the capacitors voltage rating, there wont be any leniency on this, the ultracap will likely just die if it receives 110v if its rated at 100v. I would give it as much as %20 head room if its a significant investment.

Also I think that to achieve this under reasonable budget the ebike battery probably should be around 48volts or less because amounts of voltage each ultracap can give.

I was thinking 3 of these would be great on an ebike, no doubt they would add bulk to the bike.
http://www.ebay.com.au/itm/15V-233F-Ultracapacitor-Engine-Battery-Starter-Booster-Car-Ultra-Super-Capacitor-/181238407263?pt=Battery_Chargers&hash=item2a32a6a05f&_uhb=1

Or these http://www.ebay.com.au/itm/15V-233F-Ultracapacitor-Engine-Battery-Starter-Booster-Car-Ultra-Super-Capacitor-/181238407266?pt=Battery_Chargers&hash=item2a32a6a062&_uhb=1
http://www.ebay.com.au/itm/1500-Farad-KIT-Ultracapacitor-Engine-Start-Booster-Battery-Eliminator-Car-Audio-/301059034609?pt=US_Motherboard_CPU_Combos&hash=item4618844df1&_uhb=1

Doesn't say anything about how much they weight though.

Looking at those caps on that taobao site it seems they lack high farad capacity which is Ah in capacitor speak.
The one you listed is only 100,000uf. uF stands for microfarads so its only got 0.1F, so you would need 10 of those capacitors to reach 1 farad of energy. Personally I consider getting into supercap/ultracap territory once you break 1 farad barrier.

The upside of those caps is they are high voltage and maybe having 10 in parallel could give a noticeable boost to the take off for the bike but I guess we would have to break out some maths to work that out.

I don't think there is a cheap way to add such booster support to the battery with out spending money on high farad capacitors. If ultra low C rate batteries that are low in cost become common on the market the supercap would be its best friend and would make it a common design due to the neutral costs and benefits.

Even with ultracaps at current prices I wouldn't be surprised that they would actually be worth their price now in increasing the length of life of a standard lithium battery due to offloading high C rate discharge and being able to handle all regen energy storage from DD motors. But its still a very much luxury item/design, just not something people "need", ideally there should be a market for those who are very concerned about battery waste to the environment and are willing to spare the extra costs of ultracaps.

 

[Teh Stork]

Can I use a super capacitor bank in the same capacity (no pun intended) as car audio people use them for amplifiers that draw lots of amps RMS? i.e. use a 80V cap in parallel with a 80V Lifepo4 battery. to ensure that amp draw can keep up with controller? I just picked up a controller capable of drawing 150A+ and want to make a configuration for acceleration.

Short answer: No. Buy more or better battery.

I was thinking the cap would allow the controller to draw the 150A required for acceleration and help stabilize regardless of the BMS attached to the batteries.

It won't for as long as you would like it to. Do the math.

Has anyone done this?

Trains do it as energy storage for short term delivery. Audio guys use it as decoupling. Some has connected capacitors in parallell with their batteries, a stupid measure in my opinion (And it has been discussed to death elsewhere here on ES).

Any idea how to calculate what capacitance would be required for the bank at 80-100 V at 150A ? I'm not looking for any sustained performance, just an initial boost.

Here you go.

I just want to say; NO. Abandon ship. Revise your plans. Again, do the math. Don't install those caps, the leakage current will probably bleed the battery down while you're not looking.

I'm a naysayer, and this is the end of the discussion from my part.

 

[evolution9]

http://www.technologyreview.com/news/415773/next-stop-ultracapacitor-buses/

In china they are using the configuration I just mentioned for initial starts. They have a bank of caps and lifepo4 batteries. Dont know how they do it tho!

Thanks, I'll keep you posted on my testing.

B

 

[dogman dan]

I see no reason this would not work, other than the caps might need to be bigger than you think. Bigger if the amp spike will last very long.

The controller will ramp it down quick, but I mean for a longer spike that is within the controllers max amps.

One question though, will the cap refilling cause an even more harsh spike? I don't doubt it can be made to work, it just might be easier and possibly even cheaper to get a better battery.

 

[TheBeastie]

Yeah any one who says it won't work doesn't have a clue because the "maths" is there, as I clearly stated in my post above I only consider it easily feasible for 48volts max or else your going to be carrying a fair amount of capacitors, or at least be buying very very expensive ultracaps.

The incredible storage in farads of ultracaps show they can start cars or ride electric scooters etc, yes the maths is absolutely there to get a "boost" as you have clearly stated you are after. Its been around 15 years since I sat in a lecture for capacitor maths so if you can't view youtube videos below of people riding around on ultracaps or starting up cars multiple times with ease then too bad, if your really interested then that should well send you on your way to work it out your self.

Hopefully someone useful on here on this forum will be willing to drop the detailed maths in for you if your interested in it at the engineering level.

As your article clearly states, they were able to save %40 energy by putting all the regen energy into the ultracaps, something lithium batteries can't do due to the small window of opportunity to absorb a huge amount of energy in such a short amount of time.
https://www.youtube.com/watch?v=z3x_kYq3mHM
https://www.youtube.com/watch?v=exwd-tswyzA

You just got to be willing to spend the money on the right ultracaps.

I will only ever move off geared ebike motors onto DD motors with regen ability if/when I have an ultracap setup because I believe regen into just lithium packs is a battery life killer, and I dislike the idea of dumping more batteries into the environment etc

 

[dnmun]

ok, show us the calculations then. if you did the math then show us how big the capacitor has to be to supply and extra 80A of current at 60V for 100 seconds to allow him to climb the hill or accelerate up a long incline.

what is a farad? what are the units? how much current at 60V does one farad deliver in 100 seconds. i used easy round numbers so you can do it off the top of your head.

if you wanna have a source of more immediate power you can add a lipo pack in parallel with the lifepo4 pack. the C rate of the lipo is so much higher that the lipo can deliver the current and the lifepo4 will slowly release enuff charge in between power spikes to recharge the lipo.

 

[evolution9]

http://mobile.maxwell.com/ultracapacitors/

I need some of these

 

[Punx0r]

Y'all need to remember what happens to the capacitance when you put dozens of those 1.2 ultracaps in series to make the voltage you need.

Also consider that the capacity is based on a discharge from 1.2 to 0V. You will only every be able to use tiny fraction of this. Say you have a 48V battery that sags to 40V. You're trying to reduce this load on the battery, say keep it above 44V. So your caps start at the no-load voltage of the battery (since the battery charges them): 48V and can discharge no lower than 44V.

If you're using 40 ultracaps (48V / 1.2V) that's a 4V range divided by 40 caps in series = 0.1V. So each capacitor will be discharged from 1.2 to 1.1V - that is your "usable" capacity.

The idea will work, but you'll likely need a small trailer to tow the capacitors behind your bike, and they'll likely cost many time that of a battery that could do the job properly in the first place.

If you must have a booster device for an existing, low C rate battery then considering just adding a few Ah of high-discharge LIPO...

Hopefully someone useful on here on this forum will be willing to drop the detailed maths in for you if your interested in it at the engineering level.

I'd say the starting point should always be the maths and engineering view. The only alternative is pissing in the wind!

 

[Chalo]

I'd say the starting point should always be the maths and engineering view. The only alternative is pissing in the wind!

The trouble with that is that looking at the situation with Ohm's law doesn't take into account what's happening at the waveform level. There can be big excursions of voltage or current that only measurement can find, and capacitors are typical of the remedies you'd use to correct them.

Caps can do a lot to keep your power clean when the load is as inductive and weird as a huge e-motor with a PWM controller.

As far as catching momentary peak loads (seconds rather than milli- or microseconds) to relieve the battery, I think you'd need more capacitor to do that than you'd want to carry.

 

[major]

Here's an Ucap/NiCad bike from a long time ago.



Six 2500 Farad 2.5V Maxwells in series wired in parallel with the NiCad pack. It stiffened up the battery but really wasn't worth it, especially if we would have had to buy the caps.

 

[parabellum]

Guys, ASS well do not forget, ultra caps use resistors in parallel to balance them selves in series strings (large and short), so there is a bleeding current non stop. :lol:

 

[dogman dan]

Mostly, I just felt that it was possible that the math on the cost didn't add up well compared to just buying a battery.

For example, a 5 ah 30-40c lico pack would stiffen a laptop cell pack a lot. For really cheap. It would work fairly similar, some low resistance cells can provide a nice relief from sag under an acceleration load. But in cruise, the weak cells keep partially charging the smaller pack of stronger cells. I've done it with several chemistry mixes, as have others, with good results.

It's like wanting a fuel cell, but realizing your car will be cheaper with a big pile of Limn of some kind. Sure, it might be good, but you can't always afford the best.

 

[evolution9]

i've changed my tone on this a bit. how about using a cap to reduce voltage drop as a result of heavy load?

 

[evolution9]

is that case would it be placed between the controller and the battery in series ?

any other things to consider? would that help with voltage drop?

 

[evolution9]

correction, cap between the battery and the controller, negative side going to ground.

 

[parabellum]

Yea, your drawing is strange. Cap in reasonable size will do next to nothing actually, super cap may do some noticeable effect but not that thing from the link in 3rd post, it is actually regular cap.

 

[wineboyrider]

Mostly, I just felt that it was possible that the math on the cost didn't add up well compared to just buying a battery.

For example, a 5 ah 30-40c lico pack would stiffen a laptop cell pack a lot. For really cheap. It would work fairly similar, some low resistance cells can provide a nice relief from sag under an acceleration load. But in cruise, the weak cells keep partially charging the smaller pack of stronger cells. I've done it with several chemistry mixes, as have others, with good results.

It's like wanting a fuel cell, but realizing your car will be cheaper with a big pile of Limn of some kind. Sure, it might be good, but you can't always afford the best.

ggoodrum did something like that with his golf cart and used lipos to help with the sla sag ....

 

[wineboyrider]

I've seen people use them to start their ice engines without batteries successfully, but then again people told the wright brothers they couldn't fly

 

[TheBeastie]

Been watching a few supercap vids on youtube, some are quite old and I guess they came about when serious farad supercaps became well priced. I guess the other thing about typical information on analog electronics on the net is its quite standard well established, its therefor quite outdated when it comes to the supercap component since this is a rather new advent in history of analog electronics when stuff probably doesn't change that much.
Anyway came across this one which is kind of hilarious what hes doing with his supercaps
https://www.youtube.com/watch?v=3LzcGXHjpdM

OK I found a youtube video of someone doing what you want to do from way back in 2008, thats 5 years ago now.. I see ypedal was active way back then, here is a guy going down the street on his pure Ultracap ebike.
https://www.youtube.com/watch?v=KW8PF5RiRnI
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=7511&start=25#p118675

No doubt he got more then just a boost out of it.
Well here is the math from the OP of the thread above, he got 0.75 or 1.2km of distance out of his pure no battery 48v ultracapacitor ebike (only 24volts usable due to LVC)
i = C dV/dt, so dt = C dV/i = (160 F)(24 V)/(20 A) = 192 s = 0.05 h
0.05 h * 24 kph = 1.2 km = 0.75 miles

Or maybe just wait for Graphene Supercapacitors http://www.technologyreview.com/view/521651/graphene-supercapacitors-ready-for-electric-vehicle-energy-storage-say-korean-engineers/
(video version https://www.youtube.com/watch?v=6nkzCfUHF_U

 

[Punx0r]

As far as I can determine from google, those things weigh about 400gm each. So 2kg total.

The TV ran for 159 seconds (0.0442 hours) at a load of, approximately, 100W. So energy from caps = 4.42Wh = 2.21 Wh/kg

And he benefited from a useable voltage range per capacitor of ~0.5V.

Lastly, if you check up on the how these "capacitors" work, you'll find they function more like a battery than a capacitor.

 

[Holocene]

Hi EV-9,

The fundamental problem with this approach is the mismatch in the Voltage/State-of-Charge relationship between supercapacitors and lithium batteries. Supercapacitors have a near-linear relationship between Voltage and their State-of-Charge.

So in a parallel arrangement with lithium batts, there will always be only a small portion of the total energy in a supercapacitor available to support the current generated by the Lithium batteries. The supercaps would sag quickly as their (already small) amount of energy is delivered. After that, they are dead weight on your EV, and their voltage must be supported by the lithium cells (further reducing their performance).

The problem is that, without a sophisticated BMS (read 'expensive, complicated, unavailable commercially'), the Supercaps will either overcharge the Lithium battery, or drain voltage from it. This is just a bad marriage, best to accept a quick annulment.

The basic research necessary to combine the characteristics of supercapacitors and lithium batteries is a hot topic right now. It may be helpful to read into the subject of hybrid supercapitors. Here's an interesting article from MIT Technology Review to get you started: "A Battery-Ultracapacitor Hybrid"

But there MAY be a way to bake your cake and eat it too by paralleling small, high-power LiPo batteries with larger, low-power LiFePO4 batts. For more on that approach, read on the 'sphere under the topic "Booster Pack"

Good luck with your project, and have fun! 8)

 

[Hillhater]

Lastly, if you check up on the how these "capacitors" work, you'll find they function more like a battery than a capacitor.

That is the relavent point. ...
Together with the fact that they are bigger , heavier, and a LOT more expensive than a half decent li battery.