Forums

SUPER CAPACITOR STEP UP POWER SUPPLY

Started by RealInfo April 7, 2013
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



 




On 7 Apr, 21:56, RealInfo <therighti...@gmail.com> wrote:
> Hi all > > In case I use some super capacitors with very high capacitance > =A0like 10s of farads in parallel and those capacitors > =A0can be charged to 2.7 volts max, how do I step up that low volt to con=
stant =A0 =A0 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%E2%80%93Walton_generator It's a bit tricky to get much current out. A transformer-based inverter can work a whole lot better. -- Bill Sloman, Sydney
RealInfo <therightinfo@gmail.com> writes:

> 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. -- John Devereux
On Sun, 7 Apr 2013 04:56:27 -0700 (PDT), RealInfo <therightinfo@gmail.com>
wrote:

>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 >
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? -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On Sun, 07 Apr 2013 04:56:27 -0700, RealInfo wrote:

> 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
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. -- Tim Wescott Control system and signal processing consulting www.wescottdesign.com
John Larkin wrote:
> On Sun, 7 Apr 2013 04:56:27 -0700 (PDT), RealInfo<therightinfo@gmail.com> > wrote: > >> 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 >> > > 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?
Robert Baer wrote:
> > John Larkin wrote: > > On Sun, 7 Apr 2013 04:56:27 -0700 (PDT), RealInfo<therightinfo@gmail.com> > > wrote: > > > >> 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 > >> > > > > 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?
How bad is the ESR of those caps?
Michael A. Terrell <mike.terrell@earthlink.net> wrote:
> > Robert Baer wrote: >> >> John Larkin wrote: >> > On Sun, 7 Apr 2013 04:56:27 -0700 (PDT), RealInfo<therightinfo@gmail.com> >> > wrote: >> > >> >> 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 >> >> >> > >> > 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? > > > > 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.
On Sun, 7 Apr 2013 04:56:27 -0700 (PDT), RealInfo
<therightinfo@gmail.com> wrote:

>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.
On Monday, 8 April 2013 05:49:28 UTC+10, Tim Wescott  wrote:
> On Sun, 07 Apr 2013 04:56:27 -0700, RealInfo wrote: > > > > 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 ? > > 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. -- Bill Sloman, Sydney