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SUPER CAPACITOR STEP UP POWER SUPPLY

R

RealInfo

Jan 1, 1970
0
Hi all

In case I use some super capacitors with very high capacitance
like 10s of farads in parallel and those capacitors
can be charged to 2.7 volts max, how do I step up that low volt to constant 24 vdc , high currnet ?

The main problem is that the 2,7 volt decreases to almost zero gradually .

So how I keep a constant 24 vdc while capacitor voltage goes down ?

Thanks
Elico
 
B

Bill Sloman

Jan 1, 1970
0
Hi all

In case I use some super capacitors with very high capacitance
 like 10s of farads in parallel and those capacitors
 can be charged to 2.7 volts max, how do I step up that low volt to constant     24 vdc , high current ?

The main problem is that the 2,7 volt decreases to almost zero gradually ..

So how I keep a constant 24 vdc while capacitor voltage goes down ?

http://en.wikipedia.org/wiki/Cockcroft–Walton_generator

It's a bit tricky to get much current out. A transformer-based
inverter can work a whole lot better.
 
J

John Devereux

Jan 1, 1970
0
RealInfo said:
Hi all

In case I use some super capacitors with very high capacitance
like 10s of farads in parallel and those capacitors
can be charged to 2.7 volts max, how do I step up that low volt to constant 24 vdc , high currnet ?

What is "high current"? Your input current will be 10 times as high as
that, so consider if this is at all practical.
The main problem is that the 2,7 volt decreases to almost zero gradually .

So how I keep a constant 24 vdc while capacitor voltage goes down ?

You would need a "boost converter". Some of the products marketed as
"energy harvesting" work down to very low input voltages. You might be
able to find something that works in one stage, otherwise two cascaded
boost converters.
 
R

Robert Baer

Jan 1, 1970
0
John said:
Even 10s of farads at 2.7 volts won't last very long making 24 volts at "high
current." Have you done the math on that?

How high a current did you have in mind? For how long?
Maybe 10 mega-amps for 10 femtoseconds?
 
C

Cydrome Leader

Jan 1, 1970
0
Michael A. Terrell said:
How bad is the ESR of those caps?

some are pretty darn low.

I just got some maxwell 2 or 300F 2.7 volts caps, which are about the size
of a D-cell and called "D Cells" or something silly like that.

I shorted one with a multimeter lead and it melted the tip almost
instantly.

Interestingly, these caps sound like they're full of liquid, but are
extremely light.

there's no question they're dangerous and have an extremely low ESR. It's
quite the contrast from the standard memory caps which do nothing if you
short them out.
 
In case I use some super capacitors with very high capacitance
like 10s of farads in parallel and those capacitors
can be charged to 2.7 volts max, how do I step up that low volt to constant 24 vdc , high currnet ?

The main problem is that the 2,7 volt decreases to almost zero gradually .

If the capacitor would be loaded with a constant current load, the
voltage drop would be linear.

However, if you need a constant current on the 24 V side (i.e. a
constant power load), the current drawn from the capacitor must
increase as the capacitor voltage goes down. This will further
accelerate the voltage drop rate and thus, there is not much point in
trying to use close to zero capacitor voltages.
 
B

Bill Sloman

Jan 1, 1970
0
With some sort of step-up switching regulator, either a boost converter,
a flyback converter, or a transformer converter operating in buck.

If you start with 2.7V and if super capacitors have the same voltage vs.
charge behavior as regular capacitors, you'll have extracted 90% of the
available energy by the time you're down to 0.9V -- that's a considerable
range, but at least it's not "almost zero".

Second, what is keeping you from running a number of super capacitors in
series? With ordinary capacitors that would be a very tidy way of
increasing the available voltage, without changing the available energy
per capacitor. You would have to worry about things like equalization,
but it might make your circuit easier to design if you start with a
series capacitor bank that can store nearly 24V.

Putting capacitors in series works a lot better with tight-tolerance capacitors.

Typical electrolytics with tolerances in the range +80%/-20% can't be relied on to divide the series voltage equally. Three +80% tolerance parts in series with one -20% tolerance part would put 43% of the total voltage drop across the -20% part.
 
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