[ssw422]

Hi,
I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
Any suggestions will be greatly appreciated!

EDIT: its for an EV the size of a child's toy (or smaller), also Its a competition so we have in total 10 minutes to 1) charge the vehicle(no energy in the vehicle at start) And 2) Let it move autonomously in the remaining time

 

[major]

Hi,
I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
Any suggestions will be greatly appreciated!

Hi ssw,

I suggest you read this thread. http://www.diyelectriccar.com/forums/showthread.php?t=49583&highlight=mining This should explain what to expect from generation by hand, or foot as it were.

Capacitor or battery, either way, you have to crank a lot to get enough stored to move a vehicle of any size very far or for very long.

Regards,

major

 

[Sunking]

I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.

At first I thought this was a joke, but after thinking about it I can see you are serious.

OK that hand crank generator maximum output is 25 watts. So with 10 minutes full output = 25 watts x .1666 hours = 4.16 watt hours.

So what size vehicle are we talking about here? Unless we are talking a child's toy car, you are not going to go anywhere with 4 watt hours. Crank it for 24 hours you get 600 wh about enough to go a mile or two.

 

[ssw422]

Yes, I forgot to mention its for an EV the size of a child's toy (or smaller). I was wondering what capacitance and circuit that I should look up.
Thanks for the replies!

 

[major]

Yes, I forgot to mention its for an EV the size of a child's toy (or smaller). I was wondering what capacitance and circuit that I should look up.
Thanks for the replies!

You're welcome. And you just have to do the math. Figure how much energy you need and then use E= ½CV². Figure at least 25% more, maybe twice the energy in the caps because it is very difficult to use all the energy as cap voltage approaches zero. A reason you may want to consider batteries.

major

 

[Sunking]

Charge efficiency of caps is not good.

 

[major]

Charge efficiency of caps is not good.

98-99% is not good Charge efficiency (and discharge efficiency) of capacitors is excellent due to the low ESR. Much better than batteries, even Lithium. That is the one outstanding attribute of capacitors. Of course it depends on the load, type of cap, etc, but in general, efficiency is great.

 

[dtbaker]

Hi,
I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
Any suggestions will be greatly appreciated!

you need to re-think.

a human on a very efficient bike (using very strong legs) can output a steady 250watts for an hour if they are very fit, with sprints up to maybe 800+ watts for 30 seconds if they are great. a hand crank will be WAY less than that.

most average people will struggle to output above 100-150 watts for an hour.

the typical EV takes 200 whr to move it a mile.

do the math.

 

[icec0o1]

I would suggest staying away from capacitors. Just do the math on how much energy you can crank out for the required amount of time (9 minutes?) and store that into the appropriately sized lipo battery. Supercaps aren't good for energy density and are usually used for very high current storage/dissapation. Hand cranking isn't going to give you high current.

 

[ssw422]

So i should look at lithium batteries? In less then 10 minutes, i need to charge it quickly using only manpower

 

[Ziggythewiz]

What is the contest? Furthest movement in 10 min? Fastest?

If you're only limited to human power, and have the resources, do a bike generator. You can sustain 10X the power you could with hand crank.

if you can do 200 watts (quite doable for 10 min) that's 33 watt hours, enough to mathmatically (who knows the practicality) move an actual EV over 1/10th of a mile.

A toy car should be able to drive out of sight.

Another idea would be to crank a slingshot for 10 min...then let it fly.

or use a trebuchet...are those against the rules?

 

[dtbaker]

So i should look at lithium batteries? In less then 10 minutes, i need to charge it quickly using only manpower

type of battery is not relevant. what is relevant is that 'man-power' is limited to maybe 300 watts for a ten minute sprint for a GOOD cyclist.... yielding a max around 50 wHr, which might move a small car about 1/4 mile on the level.

thats using both legs at a gut-busting 10 minute sprint... not a one-hand crank.

... I just re-read though, and since you are not trying to move a real car, the plan changes...

capacitors tend to be big, heavy, and expensive compared to batteries, BUT have the advantage of quick charge and quick discharge without damage. You could also go for a sprint or flywheel, but have issues regulating the start and power output of a purely mechanical system.

Part of your decision is going to be how 'empty' does your power supply have to be and how do you prove you are not starting with a pre-charged battery? Or, how about a guy on a bike with NO motor; could go close to 3 miles!

 

[icec0o1]

type of battery is not relevant. what is relevant is that 'man-power' is limited to maybe 300 watts for a ten minute sprint for a GOOD cyclist.... yielding a max around 50 wHr, which might move a small car about 1/4 mile on the level.

thats using both legs at a gut-busting 10 minute sprint... not a one-hand crank.

Type of battery is relevant... I wouldn't want to charge a lead-acid battery with a hand crank. And 50wHrs would be enough for 2 miles for an electric bycicle. I think it'd be enough for at least a mile for a toy car traveling less then 10mph where you're only fighting friction and not air density.

 

[GerhardRP]

Do you have a link to the rules of this contest?
Get a wheelchair marathoner to crank for you.
Gerhard

Hi,
I want to find the best way to store energy from a hand crank, something like this http://store.pasco.com/pascostore/showdetl.cfm?&DID=9&Product_ID=53272&Detail=1
I was thinking of a supercapacitor because I need to charge a vehicle and it has to move autonomous all within a 10 minute period.
Any suggestions will be greatly appreciated!

EDIT: its for an EV the size of a child's toy (or smaller), also Its a competition so we have in total 10 minutes to 1) charge the vehicle(no energy in the vehicle at start) And 2) Let it move autonomously in the remaining time

 

[ssw422]

The device has to be completely empty of energy at the start of the competition. The time start when we recharge the vehicle (only man power is allowed). We must leave the device we used to charge the vehicle on the vehicle.
The whole point of the competition is to build a vehicle that will recharge and go as many times back and forth (about 40 inch forward and 40 back) under 10 minutes.

 

[ssw422]

Do you have a link to the rules of this contest?
Get a wheelchair marathoner to crank for you.
Gerhard

PM was SENT

 

[frodus]

Why not use air and a tank.

 

[Duncan]

Why not use an elastic band?

Its not as silly as it sounds an elastic band or spring system would give you your motor and generator in one piece

 

[icec0o1]

I would definately go with lipo. Find a battery that's at least 6C charge so you can get all of the energy in in 10 minutes. Try to find a hand crank that has like 100 watt max output or something like that. And most important, if you're going back and forth only 40 inches, make it as light as humanly possible because innertia is your enemy.

Depending on your mechanical/electrical abilities, I'd probably use only one motor and have a high gearing system that also works as a hand crank. Like put a hole in one of the wheels (if they're made of plastic) and screw on a handle to charge it up. If you only use one motor, it'll save on weight and it'll be far more powerful than the 25W hand generator in your link.

 

[Tesseract]

ssw422 - if you had only provided the details a little sooner I, at least, wouldn't have dismissed your post as from yet another... ahem... crank.

Sounds like a cool little contest, and an excellent engineering exercise.

Duncan - a spiral wound spring is reasonably efficient but rubber/elastic bands are less so. I don't recall the efficiency off the top of my head, but I do know that a fair amount of the kinetic energy put into an elastic band is converted into heat as it is tensioned. Batteries/capacitors might just be superior in this regard.

icec0o1 - I think you've got the right idea, but given the distance to be traveled and the requirement that the vehicle start with zero energy stored, capacitors would be a much better choice of storage medium

Anyway, ssw422, a shunt wound motor might be the best choice of motor/generator here. Personally I'd like to see a bidirectional buck/boost converter in between the motor/generator and capacitor bank but that might be best reserved for if you are the returning champions next year and facing stiffer competition

Not going to work out all the relevant equations, but being familiar with the capacitor energy storage equation will serve you well: the energy stored in a capacitor in watt-seconds (Joules) is 0.5CV²