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[SOLVED] Using Capacitor as a power source

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Mithun_K_Das

Mithun_K_Das

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Hi,

I'm having an idea. If we can use capacitors as a power source, will this be a good or not?

I'm planning to use around 25 capacitors in parallel and then change this and use this energy stored in these caps when power is off. Super capacitor is not available in my local market (Dhaka), so I want to use HV caps.


Make a suggestion....plz
 

Standard capacitors store very little energy per unit volume as compared to batteries. And the output voltage of a capacitor decreases linearly as you remove the energy while the battery voltage remains fairly constant until it is discharged. .

What do you plan on powering?
 

Super capacitors are used in some applications like real time clock power. I once calculated if I could use a super capacitor to drive a phone screen for a few minutes, and it turned out I'd only be able to keep the screen on for some amount of microseconds before it lost all of its energy. This is something like a 1 farad cap at 3.3V. So, even capacitors designed to be power sources are very limited in their applications.
 

Mithun_K_Das said:
But a battery have little charging-discharging cycle than the capacitors. This is the point.
Click to expand...
Well, I didn't know the "point" of why you wanted to use capacitors for a power source until you told me. ;-)

What do you intend to power with the capacitors and for how long?
 

You would need an enormous amount (hundreds or thousands) of ultracapacitors to meet that spec.

How much power do you intend to draw? Keep in mind ultracapacitors typically have energy density of ~1J/cm^3. Standard HV electrolytics will have less.
 
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For example, for a 10V drop in the capacitor voltage at the end of the 10 minutes at 5A would require 150 Farads (150 million µF :!:) of capacitance.
 

Voltage from caps should be in some usable range, I supose 0,15V will not do the job. This will lower usable time.
 

what I really planning for, I'll take 22-28V input, and then convert it to 90VDC and charge some capacitors as (15,000uF/100V)X25. This will charge the capacitors. And then again there will be a buck converter to convert this voltage(90V-25V or so) to provide a 24V output. and the load current will be regulated. backup time will depend on the load.


look here what they made: http://www1.elfa.se/data1/wwwroot/assets/datasheets/2410-10_eng_tds.pdf
 

Capacitors cannot hold electricity on longer time, self discharge is high. For example if you have bank of caps which represent with capacity one supercapacitor, charged now, tomorrow is complete empty.

Supercaps are used in lots of situations, but generally when you need high current discharge in short time. Maybe for you is better to use two or three Lead Acid batteries in serie.
 

from the product you linked above, i can tell that this product is intended for very short time operation, like glitch in mains. or some accidental switching, or something like that.
i m sure that this product would power the load for very short amount of time, may be some mili seconds or tens of mili seconds.. not more than that.
 

Calculating the cap stored charge is simple: t*I=C*U.
t in seconds, I in amperes, C in Farads and U in Volts.
You have 0.375F capacitor block and about 70V of alowable voltage drop. So You can get 26.25As of charge on capacitor side. This will translate to about 50-60As on 24V side. So you will be able to source 1A for about 1 munute.
 
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    FvM

    FvM

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capacitors wiil not feed full amperes for 1 minute. as their charge will decay as current is drown.
Click to expand...
I presume, you didn't understand the suggested design and not check the calculation.
 
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    tpetar

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Calculation stands as it is! Voltage decrease was taken into account.
 

Agreed. 25 * 15000uF capacitors charged to 90V holds about 1.5kJ stored energy. That can provide 1A @ 24V for about a minute (with an efficient converter).

Expensive solution though - about $1500 USD for the capacitors from what I can see online. Using a car battery seems like a better option to me.
 
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    FvM

    FvM

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One additional thing should be taken in consideration, that is allowed voltage of capacitor. Usually bigger capacity capacitors rated for higher voltages can be very big, several of these and you have cumbersome device.

- - - Updated - - -

Cooper Bussmann manufacturer send samples.

See this 200F-400F 2,7V (to increase voltage put more caps in serie):
**broken link removed**
 
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    FvM

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Thanks all for your respond. Lets discuss more.


What the product "C-TEC2410-10" is used just to support the loads for 10ms-1min only. Its an industrial product, made by German company. The main purpose of this device is to provide clean power to the load. The factory have 5generators(4Runs,1rest). And after few hrs the rested generator starts and another sleeps. In this moment the voltage varies around 5-15V, also when they changes the main line in demand. As the machines are sophisticated, so they need a clean power. So they use this product to supply a clean power supply of 24V/10A.


So the backup time is very little but current is high. Also as the line voltage always varies (Due to heavy load on/off) so they don't want to use batteries. Because batteries have less charging-discharging cycle than capacitors.


In this case, what can be the right decision?

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If lithium-ion batteries are used, will the system be stable and long life?
 

What I see, this is job for lead acid batteries, or if they have lots of money Lithium based batteries.

Is there some special reasons why they dont want to use batteries?

This is true "Because batteries have less charging-discharging cycle than capacitors. ", but also they should take in consideration all advantage and lacks of both.



Mithun_K_Das said:
If lithium-ion batteries are used, will the system be stable and long life?
Click to expand...

Long Life thermin is discutabile, but for start we should define life duration variable or to use usual life time. Also way and conditions of usage is very important and can affect on life time.
 

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