Supercaps...

[flash....]

Just a question... I have lots on new toys (kids) that now use supercaps.
Everything from little Zip\Zap RC cars to even an RC plane.

My question is this... would any of these have use in an LS or 5mm LED light??
Seems like a nightstand light would be a good fit. You can charge a Supercap in about a min or so for pretty good high current return or low power drain longevity.

Has anyone used Supercaps in their designs??

 

[INRETECH]

It all depends on the current draw and for how long, thoselittle Zip/Zap cars don't run long

Here is my SuperCap

http://www.inretech.com/pictures/cap4000f.gif

 

[Kram]

I've used the supercaps (1Farad, 5.5 volts - sold as memory backup capacitors) and found that they are really quite useful in driving a 5mm LED. I have used up to four of these in parallel and usually put a resistor in series with the LED to limit the max current (I usually go for 5ma at 5 V). What I found is that the group of 4 of them is plenty to keep an LED lit all night, albeit at a fairly low level. I have noticed significant variation depending on the brand. Some of them apparently have more charge leakage than others.

My applications have been in association with hand-crank generator lights that I've built using salvaged stepper motors. Being able to crank up a charge in 30-60 seconds that will provide some amount of light all night just appeals to me. As the voltage drops off (following an exponential discharge curve), the LED becomes more efficient, thus discharging the cap more slowly.

What appeals to me about the use of the supercaps is that they can handle hundreds of thousands of charge/discharge cycles and thus are inherently more reliable than any current rechargeable battery technology.

By the way, I have also used constant current circuits with these to drive LEDs, but found that the overall lighting time from a full charge was dramatically reduced (to something like 20 minutes) vs. several hours.

These things are fun to experiment with!

Mark

 

[flash....]

Inretech... Now, thats a super cap!! I was referring to something a little smaller. heh.

Kram... thanks for your input!! it is the long possibility and really short charge times that attract me as well.
Generator lights seem to be a good place to start...
I have also made generator lights from stepper motors and this seems perfect.
Where did you get yours and do you know of any good suppliers?
I want to experment with some as well.

 

[Kram]

I got my latest couple of batches from Mouser. These are Elna. Unfortunately, not very cheap. Here is the link to the catalog page:

http://www.mouser.com/catalog/616/436.pdf

I've used others (larger height, same diameter) that actually seem to leak charge much less (sorry, don't recall the brand), but these are nicer for many applications because they are smaller. I've also noticed supercaps on Ebay from time to time (for somewhat more reasonable prices). I think I would try there first.


Mark

 

[INRETECH]

Its a different product for a different use

A rechargable battery will have a higher power/weight ratio, but as we know the number of charge/discharge cycles causes the internal chemicals and structure of the battery to break

A SuperCap on the other hand has virtually an unlimited number of charge/discharge cycles since there is no chemical reaction taking place

The shake/flashlight is an excellent use for the SuperCap, since it can sit for months/years in storage, and then be used in a few seconds of shaking - but, it will not have the operating time * brightness that a comparable rechargeable battery would have

 

[Doug Owen]

[ QUOTE ]
flash.... said:
Just a question... I have lots on new toys (kids) that now use supercaps.
Everything from little Zip\Zap RC cars to even an RC plane.



[/ QUOTE ]

Are you sure?

For sure the electric plane and zip/zap cars I have are NiMH (the cell for the plane even says so). It's a 270 mAh, 1/3 AA 1.2 V cell made in China.

And several of the cars (and both tanks) have 'turbo charge' that is you can push a button and charge the cell in the car even more, something not possible with caps.

If they were supercaps (or any cap for that matter) they would be constantly slowing down, right?

Run the numbers. A one Farad cap charges (or discharges) a Volt per second per Amp This means for any but the most modest loads run times will be very short.

Doug Owen

 

[LEDependent]

I can second the fact that ZipZaps use NiMH. However, several cheapo clones DO use capacitors. I believe they have circuitry that regulates the decreasing output of the cap.

 

[gewe]

</font><blockquote><font class="small">Als antwoord op:</font><hr />
Kram said:
...
My applications have been in association with hand-crank generator lights that I've built using salvaged stepper motors. Being able to crank up a charge in 30-60 seconds that will provide some amount of light all night just appeals to me. As the voltage drops off (following an exponential discharge curve), the LED becomes more efficient, thus discharging the cap more slowly.
...


[/ QUOTE ]

Would it be possible to use a supercap as a backup for a bicycle light? Normally the light is driven by a dynamo. The supercap could make the light stay on when you are waiting for something like a traffic light.

Are there any circuit diagrams for applications like this?

 

[Harrkev]

It depends upon the current required. It might be possible to get a few seconds with a bright light.

All you have to do is:

1) Be sure that your dynamo outputs DC.

2) If the output is AC, then you need a full-wave bridge rectifier to convert AC to DC

3) If the output is DC, then add a single diode to keep the cap from dumping its contents back INTO the dynamo

3) Add cap in parallel with the bulb and go.

Note that caps can be VERY PICKY about their maximum voltage. DO NOT EXCEED THIS NUMBER. Also, note that with any sort of generator, the peak voltage can be close to twice the average voltage.

You also want a diode with as low of a voltage drop as you can get. Also, make sure that it can handle the current. A germanium diode should be more efficient than a silicon model.

 

[Jarhead]

charge(Coulombs) = capacitance(Farads) * voltage(Volts)
1 Coulomb = 1 Amp * 1 second
Energy = 1/2 C*V2
10 Farads * 2.3V = 23 Coulombs

or 1 amp for 23 seconds

For fun I did a *quick* mod with a NESSCAP 10uf 2.3V supercap to one of those el cheapo cars, as a "external gas tank", now it will run about 30 times longer, and it can be charged *real* fast

http://www.molalla.net/~leeper/carcap.jpg

Whats nice about the newer super caps, is you can discharge/charge them at really fast rates, like 100A, do it 100,000 times, and see only a 20% change. Some are much better than this.

Here is one manufactuers part: http://www.nesscap.com/prod/prod.htm

Really good article on them here:
http://www.nesscap.com/prod/Articles/PowerElectronics_310PET23.pdf
Especially see this part:
"A 54-V/175-F NESSCAP ultracapacitor bank module and 6-kW cycling data for 42-V vehicle application."

In electrical vehicle applications, ultracapacitors permit faster acceleration, increased range, and extend battery
life by freeing it from stressful high-power tasks. In addition, ultracapacitor technology now can do load-leveling to extend the life of EV (Electric Vehicle) batteries and provide the high power essential for EV acceleration. For example, a vehicle might use this power burst to accelerate and climb a steep hill. Ultracapacitors also can absorb regenerative braking energy and thus limit the otherwise very high charging current to the battery.

 

[Mark_Paulus]

[ QUOTE ]
gewe said:
[ QUOTE ]
Kram said:
...
My applications have been in association with hand-crank generator lights that I've built using salvaged stepper motors. Being able to crank up a charge in 30-60 seconds that will provide some amount of light all night just appeals to me. As the voltage drops off (following an exponential discharge curve), the LED becomes more efficient, thus discharging the cap more slowly.
...


[/ QUOTE ]

Would it be possible to use a supercap as a backup for a bicycle light? Normally the light is driven by a dynamo. The supercap could make the light stay on when you are waiting for something like a traffic light.

Are there any circuit diagrams for applications like this?

[/ QUOTE ]

Actually, there already is a generator/dynamo built on this principle. However, it's quite pricey from what I remember, and I think it's only available in Europe.

LightSPIN

Generator

Regulator Circuit Design

 

[Bandgap]

Would it be possible to use a supercap as a backup for a bicycle light? Normally the light is driven by a dynamo. The supercap could make the light stay on when you are waiting for something like a traffic light.

Asked Gewe.

That is what is in read 'standlights'.

 

[Bandgap]

Just a note on supercaps...

Some, mostly the memory back-up types, have high internal resistance.
Resistance is up to a few hundred Ohms, 30 is about average.

These cannot deliver high currents or charge in a couple of seconds.

For fast charge and discharge, there are plenty with a few Ohms, or under an Ohm, of internal resistance.

Steve

 

[Kram]

[ QUOTE ]
gewe said:


[/ QUOTE ]

Would it be possible to use a supercap as a backup for a bicycle light? Normally the light is driven by a dynamo. The supercap could make the light stay on when you are waiting for something like a traffic light.

Are there any circuit diagrams for applications like this?

[/ QUOTE ]

Actually, if you're using an incandescent light (which most bicycle lights are), the supercaps wouldn't have enough storage capability to really be practical as a backup power source. They are more suitable for lighting a single 5mm LED at a fairly low current.

As to a circuit, the preceding comments are accurate. In particular, you would want to be careful about making sure that the input voltage didn't exceed the rated voltage of the capacitor by much. You could do this with a Zener diode of the proper voltage. However, I have found that when the capacitor isn't fully charged, voltage spikes generally don't happen from small generators because the cap "sucks" them down. The real hazard is when the capacitor is fully charged.

As to the posts about how quickly they discharge, the calculations are correct. They don't, however, really show you what a direct drive 5mm LED (with current limiting resistor) can do. The "shake" generator lights use, I believe, a .22F supercap. Larger capacitor values would lenghthen the duration of light output. Also, please note that I've found that the 5mm LEDs still put out useful (a very subjective measure ;-)) light at very low currents. Indeed, the PALight 9V flashlight produces it's standby light at (supposedly) about 0.1ma.

It all just depends on what you want to do with the supercap as to whether it's suitable for your application.

Mark