# Ultra capacitor Boost potential



## Brute Force (Aug 28, 2010)

In order to have a useful power dump, you need some actual power to dump. The 650 farad 2.7 volt capacitor, fully charged, has enough energy to "dump" 2.3 horsepower (1755 amps x 2.7 volts = 2738 watts, 748 watts per HP) for one second. This is a first order approximation: you can't draw current without the voltage dropping. How many of those $65 capacitors do you need to be useful? You do the math.

Wire in series to increase voltage, parallel to increase current.


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## major (Apr 4, 2008)

Pyroim said:


> The math behind it is:
> 
> "A capacitor's storage potential, or capacitance, is measured in units called farads. A 1-farad capacitor can store one coulomb (coo-lomb) of charge at 1 volt. A coulomb is 6.25e18 (6.25 * 10^18, or 6.25 billion billion) electrons. One amp represents a rate of electron flow of 1 coulomb of electrons per second, so a 1-farad capacitor can hold 1 amp-second of electrons at 1 volt."
> 
> ...


Hi Pyr,

You start out saying "dump all power" but then get into charge. Charge (or current) is not power. So taking charge from a capacitor is different than from a battery considering the energy (or power). As you discharge a capacitor its voltage decreases. With the battery, voltage essentially remains the same. So I suggest you base your application of capacitors versus battery based on energy and power rather than charge. I think you'll find that although the large current seems impressive from the capacitor, the low voltage and short duration are game spoilers. 

Regards,

major


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## Pyroim (Sep 19, 2011)

I was referring to it as kind of a NOS Button for EVs not some sort of long term use item, and because of the how fast the caps accept a charge ( hopefully im using the right terminology now  ) and the bonus that they are self balancing and self regulating they could ideally be refilled in a matter of seconds each recharge or simply plugging in to the wall for a few moments. 

Im going to do a bit more digging but the capabilities for short term use for a high torque / high acceleration seems promising

maybe even use them for ONLY acceleration so the batteries do not have to cope with the higher amp draw.


And as for you major sorry my terminology was off i'm still new to the EV game and im just looking at every possibility i can.

speaking of digging... more digging brought me to a Cheaper Chinese model of a 2400F-3000F 2.7V for dirt cheap which comes out to ~8000 Amps boost for 1 second, with proper wiring this could be very very very potent, and as for how mnay, well assuming a Netgain 144V motor

144V / 2.7= 53.3333 continuing, in series 

and according to Brutes watt to HP calculation the bonus would be a staggering 1540 HP for 1 second and once again properly wired possibly small sets of two ( in parallel) Then each set wired in series this power could be granted for 2 seconds which may not seem like much but the acceleration could be massive and possibly too much for most motors and drive trains to handle.

BUT on the nice side of things it could be used for things like entering the freeways , gaining speed even up hill and a few other useful scenarios 


Cheap 2400F 2.7s link right here even at the max price tag 500$ aint to shabby for a 1500 Shot of nitrous 

http://www.alibaba.com/product-gs/492585265/2400f_large_capacity_farad_capacitor.html


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## major (Apr 4, 2008)

Pyroim said:


> And as for you major sorry my terminology was off i'm still new to the EV game and im just looking at every possibility i can.


It's just not the terminology; it is your grasp of the physics behind the concept. This has been discussed previously on this board. Use the search feature on the forum toolbar for ultracapacitor. I have used them and posted about it. I like ultracaps. But you have some to learn about them. Keep at it


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## Pyroim (Sep 19, 2011)

Ah apparently it did not like me when i put a space between the ultra and capacitor, i got some readin' to do now, thanks for your input


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## JRoque (Mar 9, 2010)

Hi. I'm not sure about the use of ultracaps in this application. I guess the advantage of an ultracap is it's ability to take repetitive charge/discharge cycles. But they are very expensive, carry relatively low total power and many of them actually have higher ESR than Lifepo4 cells. IGBT switches in many quality DC controllers are already >97% efficient so bypassing them won't gain much in terms of short term oomph. 

If what you're looking for is maximum current delivery by going around your switches, I'd say you can install a handle similar to those found in racing cars. When pushed, it disconnects the controller and applies the pack to the motor. Your motor will speed up until it explodes and your battery pack will melt down or catch fire. But you will go fast for a little while.

JR


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## MN Driver (Sep 29, 2009)

Capacitors are expensive, large, heavy, and have too many limitations and dangers for what they do when it comes to using them in an EV application. I'd go with Lithium Polymer or a higher powered LiFePO4 battery than add capacitors. Even with a relatively low power capability battery if you add more voltage your sag doesn't matter as much because you started higher and as long as the cells can handle the amperage draw you are fine. With little 5Ah cells that can have a pulse draw of 450 amps, I'm just not seeing the point to go with caps anymore. Caps have their own balancing issues because their self-discharge, which is quite fast is not usually as consistent as you'd want/need it to be. Extra complications when that weight and volume could be filled with more batteries to the same result.


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## Brute Force (Aug 28, 2010)

Pyroim,

1540 hp? I calculate 53 capacitors x 2.3 hp as 122 hp.

That number is an oversimplified estimate. If you could pull the full current out at a constant rate from the capacitor (which you can't), the power would start off at 122 hp then decrease linearly to zero by the end of that second. As the charge is drained out of the capacitor, the voltage drops proportionally. Full charge, full voltage, half charge, half voltage, no charge, no voltage. And since power is volts times amps...


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## bjfreeman (Dec 7, 2011)

MN Driver said:


> Capacitors are expensive, large, heavy, and have too many limitations and dangers for what they do when it comes to using them in an EV application. I'd go with Lithium Polymer or a higher powered LiFePO4 battery than add capacitors. Even with a relatively low power capability battery if you add more voltage your sag doesn't matter as much because you started higher and as long as the cells can handle the amperage draw you are fine. With little 5Ah cells that can have a pulse draw of 450 amps, I'm just not seeing the point to go with caps anymore. Caps have their own balancing issues because their self-discharge, which is quite fast is not usually as consistent as you'd want/need it to be. Extra complications when that weight and volume could be filled with more batteries to the same result.


LOL Don't tell Maxwell Caps about this. They have a Cap box for use in hybrid buses.
The advantage of the Ultra caps is over a million charge.discharge cycle compare to about 50 thousand for Lithium
Based on the subject of this thread, They are used to for regen and Boost starts. The are capable, when configured properly of dealing with 1,000 amp for 10 Sec at 450VDC.
A bank that would provide this with some extras is about $20K. However that is a life tme compared to lithium that have 6-10yrs life.


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## Rational (Nov 26, 2011)

For an energy dump you might also search 

flywheel "magnetic bearings" vacuum energy power

With modern materials these things can spin at 100,000 RPM without flying into pieces.


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## dtbaker (Jan 5, 2008)

power dump is one thing... sustaining it for any length of time (energy) is another. 

a big cap bank MIGHT be good for capturing a 'braking event', and then dumping it on the next accelleration.... but the size, cost, and weight looks prohibitive compared to current energy density of lithium.

Maxwell has one unit that looks big enough for a braking event in a small car... but it is big, heavy, and expensive.....


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## Kerensky (Jul 8, 2011)

formula 1 racers are using a system like what pyroim is asking about. KERS or kinetic energy recovery system. my unerstanding is imperfect but the jist is ... regenerative drivetrain braking stored in capacitors which can then be used to provide aproximatly 80bhp boost for a few seconds... f1 guys generally use it when exiting a corner as opposed to "nos bost" passing gear, but yes pyroim the basic principle is sound ...... implimentation of said principle may prove to be prohibitivly cost ineffective for road vehicle use however (means its probably gonna cost a ton)


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## dtbaker (Jan 5, 2008)

Kerensky said:


> fimplimentation of said principle may prove to be prohibitivly cost ineffective for road vehicle use however (means its probably gonna cost a ton)



exactly. the unit I found for car size 'stopping event' was about 1x1x3 feet, weighed #150, and cost $9000.

now.... if you were stop/starting a taxicab, bus, or mail truck all day it might start to be worth it in the long run as a range extender to get back up to speed using the captured stopping energy.


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## Outtasight (Dec 8, 2011)

And another thing...

Putting humongous caps on the output of the controller or switching into the motor or battery may cause all kinds of mayhem. When there's a big difference in a cap's voltage and the thing you're connecting it to, it looks almost like a short circuit.

I've used a pair of old car audio 1F caps in series to make a 0.5F 24V cap on a small demo solar system. It used a couple of tiny 7Ah lead batteries to run a 1kW inverter so that the small batteries with the caps could deliver surges to the inverter.

Problem was that I couldn't just throw the 40A breaker on the battery to start up the inverter because the cap takes a massive current to charge up from flat. It keeps popping the breaker as if there's a short circuit (there is - it's the cap).

Instead you have to use a resistor and a second switch to pre-charge the cap before throwing the main breaker.

As mentioned, a lot of the energy of a cap can't be used as a cap's voltage is proportional to its stored energy (state of charge). Unlike a chemical cell that can hold a somewhat steady Voltage during its discharge.

You could extract more of the stored energy if the cap was charged to a much higher voltage. Say you need 12V for your load. If your cap is charged to 12V, you'll get almost no energy from the cap, as it will discharge to below 12V as soon as you take any energy from it and your load may cut out at 10V. But charge the same cap to 24V and you can extract all the energy that would have been released if you discharged the cap from 12V to zero by discharging it from 24V to 12V. 

Trouble is, your load won't like being hit with 24V and you need to be charging the cap to 24V when connected to the 12V load...

Caps work well for loads that have intelligent DC-DC converters in them already - so something that can run on any DC voltage from say 3V to 12V can make use of the energy in a big cap feeding it. A current limited LED would work well... But that's not gonna make your car go faster 

The electric KERs used by most (but not all) F1 teams is the Magnetti Marelli developed system that uses a 60kW liquid cooled brushless DC motor generator and a small lithium ion battery pack made by Saft. The regulations limit constructors to 60kW (about 80hp) for 6.67 seconds per lap (total energy limit is 400kJ or 111Wh).

http://www.gizmag.com/formula-one-kers/11324/

The FIA rules allowed teams to increase the battery size to 800kJ / 222Wh this year (2011) and will allow 4 wheel drive (or front wheel regen and rear wheel drive) of 200kW and 1.6MJ / 444Wh in the 2013 season.


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## Jan (Oct 5, 2009)

Just placing them in parallel with your pack gives such a limited voltage difference, you'll be happy if you can use 10% of their capacity.

To make really use of a capacitor bank, I think this is the only way to do that:

http://www.metricmind.com/audi/line_art/_0002_capacitor_concept.gif

And that DC-DC converter is the big problem. I don't know of a converter that can handle more than 2-300 amp. And if so, I wonder how much it will cost.

No, I don't see any use for a capacitor bank, considering the power modern batteries can deliver.


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## Jan (Oct 5, 2009)

Outtasight said:


> The electric KERs used by most (but not all) F1 teams is .... a small lithium ion battery pack made by Saft.


F1 preferring batteries above caps, is pretty convincing.


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## Kerensky (Jul 8, 2011)

ok hold up now... dont everyone start baggin on the power caps. I have personally used 32v 2000 farad cap banks to power roller coaster av/security systems.... the ones on the trains.... and they work for more than 15 minits between charges... hell ive seen 600watts of amp and 24 car speakers, 6 cameras, and a full blown computer network, not to mention the lighting. I do agree some form of regulation is necessary for cap bank systems but its not as impossible as is commonly beieved.... just expensive.


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## Jan (Oct 5, 2009)

Your examples are all caps only. For an EV that's only conciderable for drag racing. Maybe. In all other cases it is only concidered as a additional feature, in a hybrid setup. A buffer for peaks, or to make the batteries last longer. And in that case, it's not only expensive, but also pointless.


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## ElectriCar (Jun 15, 2008)

Has anyone here ever used caps on the input of a controller? I removed a 10,000uf bank from mine today and I swear it seems to have taken a hit on instantaneous power, ie when I first hit the throttle it seems to have lost the jolt it had before. 

I run a Curtis 1231C with a racing mod in which the accel rate has been shortened to about a half second or so and it's rated at 1000A but will do more than that for a short time.

Before removing the bank, if I hit the throttle a little too hard it would lurch forward and chirp the tires. Now it seems to be a lot more lethargic. I was going to sell them but now I'm going to do some testing and may not sell them.


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