Supercapacitors: The Future of High-Performance Energy Storage?

[sam charlton]

Hello,

what is the consensus on using super capacitors to power a 500w electric bike motor.

cheap and innovative alternative to li-po batteries or explosion between thighs waiting to happen?

the plan is to create something like this:


i will use a 24V motor (http://www.ebay.co.uk/itm/ZY1020-Electric-Motor-24v-500w-Brushed-E-Bike-Scooter-24-Volt-500-Watt-6mm-Chain/192391102611?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649)

The super capacitors will have a volt meter assigned to them and when they drop to a certain voltage, i will charge them using 2X 12 v batteries and a switch.

I am by no means wise in this area, just trying to find my to fun with electronics, so any advise from those who know will be very much appreciated.

Thanks, Sam.p.s. I can draw a terrible diagram if anyone is still unclear, but be warned, i have very limited knowledge and so a diagram from me may not be too enlightening!

 

[NascentOxygen]

Bear in mind that with a capacitor, once you have drawn off, say, 33% of the stored charge, the voltage has likewise dropped by 33%. So your 24V charged capacitor is delivering just 16V, i.e., probably next to useless. In practice the terminal voltage under load will be significantly less than this, due to resistance.

Are 24V super capacitors available? Are they cheap?

 

[anorlunda]

What research did you do on your own before posting? I found the following in just seconds.

As of 2013 commercial specific energies range from around 0.5 to 15 Wh/kg. For comparison, an aluminum electrolytic capacitor stores typically 0.01 to 0.3 Wh/kg, while a conventional lead-acid battery stores typically 30 to 40 Wh/kg and modern lithium-ion batteries 100 to 265 Wh/kg. Supercapacitors can therefore store 10 to 100 times more energy than electrolytic capacitors, but only one tenth as much as batteries.[

 

[sam charlton]

hi,

thanks for the telling off.

i have no doubt an afternoon on Wikipedia could provide me with something close to a B-Tech, but i was simply interested to hear if anyone has real world experience with super capacitors. Some people say they are hand grenades so don't touch them, others use them to power their cars. Now i want to hear from the people of physics forums. unless I'm mistaken, your wikipedia page doesn't have a section called "common mistakes people have made in the past".

Thanks again,

Sam x

 

[Merlin3189]

Your 500 W 24 V could draw about 20 A using 30 kJ/minute, but even at a more sensible 100 W it uses 6 kJ per minute

I found an automotive battery using supercapacitors rated at 16 F, 16.2 V. That stores $E = \frac {1} {2} CV^2 = 2.1 kJ$
So for this battery alone you could not run for more than 3 minutes at 100 W.
(But note Nascent's comment. His idea is correct, even though in dropping from 24 V to 16 V, you have used 5/9 of the stored energy, rather than 1/3. You may be able to utilise the SC battery to even lower voltage through a suitable boost regulator, but you won't get it all.)

That battery is less than 30 pounds sterling, so you could buy maybe 8 or 10 for the price of an 8 Ahour Li battery, giving you no more than 30 minutes at 100 W.
The 24 V, 8 Ahour Li battery stores 690 kJ, giving nominally 115 minutes running at 100 W (though I doubt it will yield all its energy either.)

The 16 F SC battery is only 235g, so 10 would be 2.35 kg which is comparable to Lithium batteries of this size.
Charge cycle life I expected to be better for the capacitor, but both types seem to claim around 1000 cycles.

I only did a brief survey, assuming the SC batteries would be outclassed. But they may not be so far off the mark as I thought. It may be worth more careful research.
I would expect capacitors to have a much lower charge time and better ability to deliver peak loads, if those were wanted.

Edit: I see you wanted real experience. This is not that!

 

[gleem]

what is the consensus on using super capacitors to power a 500w electric bike motor.

Not practical.

Individual SCs come with maximum voltages of about 2.5 to 3V , a capacitance up to more than 3000Farads ,and weight up to 0.5Kg. You need 24 volts so you need to connect 9 to 10 Sc in series. But this reduces the net capacitance of this arrangement by at least a factor of 9 or 10. You can boost the capacitance back to the original of the individual SC by connecting the 9 or 10 series arrangements in parallel. But now you could have 80 to 100 SCs which could weigh up to 50 Kg and occupy more than one cu ft. To store the charge you need to run your bike you need 3150 Farads of capacitance and that only enough for you to run about 15 minutes if you motor can still perform adequately at 18V.

innovative alternative to li-po batteries or explosion between thighs waiting to happen?

Put the battery in a sturdy metal case.

others use them to power their cars.

I would like to see that. they need at least 50 time more power than you do.

 

[sam charlton]

I would like to see that. they need at least 50 time more power than you do.[/QUOTE]

i mean normal car batteries, not power the entire car haha, sorry

 

[anorlunda]

i mean normal car batteries, not power the entire car haha, sorry

You can use supercapacitors to start the car. That doesn't need much energy. But you want more than start you bike moving; you want it to keep going.

In post #2, I told you that batteries store 10 times as much energy per kg as supercapacitors. Why would you want supercapacitors anyhow?

Check back in 5 years or 10 years. The answer might change.

 

[sophiecentaur]

@Sam charting
You still seem to be resisting using your own fact finding. Just do some searching for “super capacitor applications” and cut out the PF middle man. Then ask some well informed questions. PF delivers excellent answers to such questions.

 

[Windadct]

The reason there is not much practical experience in doing what you want - is technically it is not practical from the get-go... in general the "consensus" does not build, test and evaluate systems that are inferior.

E> Highlighted I am referring to the system, not Supercaps per-se.

 

[sophiecentaur]

The reason there is not much practical experience in doing what you want - is technically it is not practical from the get-go... in general the "consensus" does not build, test and evaluate systems that are inferior.

"Inferior" may be a bit harsh.
One of the few good uses for a Supercapcitor would be for a Camera (or other Flashgun) or even just a hefty spark generator. The non linearity of the load would ensure that pretty much every Joule of energy in the Capacitor would get used.
Most conventional loads need a steady supply voltage and only half the energy capacity of a Capacitor is available down to 70% of the start voltage. Having said that, modern circuitry can make meaningful use of the stored energy, even is a Capacitor with low volts remaining.
I do feel that the present honeymoon period with SuperC's may not last as battery technology improves even further.

 

[donpacino]

I would like to see that. they need at least 50 time more power than you do.

They are used in some hybrid vehicle applications. When you have a series system electrical motor drives the drive-train, powered by battery, with an alternate supply charging the battery such as a diesel motor or hydrogen power supply. In this case you can replace the battery with a supercapacitor, there are some drawbacks (ex youll need to charge the supercap before you can move), but if those don't matter for your application you're fine. Think of the supercap or battery as a load balancer. It allows the energy source to operate at maximum efficiency, you don't NEED a battery over a supercap.

 

[donpacino]

Also to the people talking about supercaps only being a few volts, many battery types are only available in low voltages and current capabilities as well. It is putting these cells in parallel and series that they can achieve the desired results.

Please note: yes battery cells are put in parallel, but that doesn't not mean you can do it at home and achieve good results. you need to truly understand the chemistry and the battery controller (often a customer battery controller is required).

 

[nitsuj]

as far as i know the "super" in super capacitor means more capacitor capacity, not more "battery".

A supercap is something you want in a high performance race car for accelerating and decelerating quickly. It's stored in a field so cause and effect happen pretty quick and likely with much less loss to the comparatively slow chemical type of longer term storage.

From lamborghini website

The sports car of the future uses electricity instead of gasoline. Electric systems generate high efficiency and offer several interesting characteristics like the possibility to recover kinetic energy and to deliver huge peaks of power. In order to take the most from the opportunities offered by electrification, the accumulation system must be power-oriented and symmetrical, to allow high performances and the greatest energy recovery possible. To harvest this opportunity, today’s batteries are not enough and a big leap forward is needed: Lamborghini aim is to develop an innovative supercapacitor able to close the gap with conventional batteries in terms of energy density, preserving an outstanding power density.

Lamborghini gets it lol