Charging a supercapacitor using higher voltage

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lynx

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Hi

can i charge a 2.7V/350F supercapacitor up to 2.5V by applying 5 or
more volts from the power source without damaging the cap?

also if i short circuit the supercapacitor and make it hot but touchable..
does that degrades it? or it behaves like a normal capacitor and stays fine
as long as i don't exceed the rated temperature?

and one more thing.. on the cap it states 0.4Wh means it could output
2.5V/160mA for an hour? do you think it could sustain a steady output
for an hour?


thank you
 
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lynx said:
Hi

can i charge a 2.7V/350F supercapacitor up to 2.5V using 5 or more
volts from the power source without damaging the cap?
Click to expand...

I would expect the capacitor to be destroyed once it charged above 2.7V.

also if i short circuit the supercapacitor and make it hot but touchable..
does that degrades it? or it behaves like a normal capacitor and stays fine
as long as i don't exceed the rated temperature?
Click to expand...

No idea, but certainly the super capacitors I've seen in VCR's etc. don't seem to last very long before they die.

and one more thing.. 0.4Wh means it could output 2.5V/160mA for an hour?
Click to expand...

No, check the discharge curve for capacitors, the voltage falls quite rapidly.

Generally almost every thread on here about super capacitors seems to imagine they are a replacement for a battery - and in almost every case they are far inferior, and often unusable.
 
hi thanks for you reply!

yes that's what i also think.. probably it wont be able to widthstand
even 2.7V without deterioration, but let me explain my first question,
what i want to do is to use higher voltage e.g 5V and then monitor the
charging so i can stop it when the cap is at 2.5V. higher voltage = higher
current goes to the cap.

So there's issue when you apply higher voltage to a supercapacitor (
say because of high surge current) or only when you're trying to charge
it above it's rated voltage?

about rapid voltage drop i believe it can be fixed with a smart and efficient
DC-DC step up converter, do you agree?
 
hi ronv thanks for the PDFs especially for the second one..


ronv said:
You need to limit the current to the caps value in it's spec sheet.
Click to expand...

so there is issue using higher currents... by the way where's that detail written so i can also
search it for my cap "BCAP0350" model is it refered as "maximum continuous current"?


what about the other thing i said, do you think a dc-dc step up converter could be
useful so i can keep the voltage output constant long enough?

check this out
https://www.electro-tech-online.com/custompdfs/2013/08/22234B.pdf
 
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Sounds a risky and unreliable process.

So there's issue when you apply higher voltage to a supercapacitor (
say because of high surge current) or only when you're trying to charge
it above it's rated voltage?
Click to expand...

Presumably if you exceed the voltage it will rapidly due, as modern electrolytic capacitors do.

about rapid voltage drop i believe it can be fixed with a smart and efficient
DC-DC step up converter, do you agree?
Click to expand...

No, use a battery - far better and far cheaper

Why do you specifically want to use a super capacitor?.
 
Nigel Goodwin said:
No, use a battery - far better and far cheaper

Why do you specifically want to use a super capacitor?.
Click to expand...

no it's not...chemical power storage always was a problem..so the future is the capacitors unless if something else gets invented..

i need it for its fast recharge properties

have you seen the pdf of the dc-dc from the link i gave? sophisticated enough..
i guess the developers had in mind the joule thief when they did that

i think i dont agree with WTP pepper because he speaks in general about the dc-dc converters while im thinking about the specific one i've posted
 
More information would be far more helpful here.

What exactly are you powering and what are its input voltage current and run time demands?

Also what are you planning to charge them with and how fast?
 
lynx said:
no it's not...chemical power storage always was a problem..so the future is the capacitors unless if something else gets invented..
Click to expand...

I hope you enjoy your delusion

Chemical storage might be a problem, but capacitors aren't the answer - far too expensive, large, limited, and unreliable.

What we need is someone to invent a 'shipstone' - for those of us who like SciFi.
 

I'm not exactly sure how to interpret the curves for your cap, but from another source I found it suggested limiting the maximum charge current to the capacitor voltage divided by 5 times the ESR. That would put yours at 150 amps or so. When I look at your curves it would appear to depend on the duty cycle (which makes sense). I just can't figure out how you get 100% duty cycle. Maybe someone else can read the curves. In any case it looks like you can do whatever you want at 20 amps and a single event at almost 300.

The boost or step up converter will get you more useful output for a longer time, but I think what the guys are saying is that it is not a battery replacement in the classic sense. For example one time constant for the cap at around an amp is about 6 minutes while an AA battery would be 2 hours. But the cap has a lower internal resistance so if the current is very high, but short, the cap may be better.
 
ronv said:
For example one time constant for the cap at around an amp is about 6 minutes while an AA battery would be 2 hours. But the cap has a lower internal resistance so if the current is very high, but short, the cap may be better.
Click to expand...

The current capacity of a NiCd battery is pretty damn high as well - I can't see any common need for more than NiCd capability (which is already dangerously high), or that a supercap wouldn't soon expire if you tried to draw massive current from it?.
 
@ronv thanks for the valuable infos! me either i cant get the meaning of
some details from the datasheet, but from what i can understand the cap
can be charged and discharged at very high rates (more than what is needed
for what im interested to use it.)

so its likely..i could apply 5V or so and monitor the charge until it
gets up to 2.5V and then stop, but somewhere the datasheet states
something about voltage surge 2.85V which is one of the things
i dont understand

@Nigel i guess you are not aware of graphene capacitors
generaly as far as i know supercapacitors tend to get smaller in
size and higher on capacitance
 
Here is a link to the newest developments in graphene based supercapacitor development.

https://arstechnica.com/science/201...ene-capacitors-on-par-with-lead-acid-battery/

It would appear that in the lab they are getting them into the range of being equal to LA batteries on the physical size VS power density aspect.

Here is a guy starting a car on a set of 350 farad super capacitors similar to yours.

https://www.youtube.com/watch?v=z3x_kYq3mHM

Personally I am thinking that we may not be very far away for seeing capacitor based power density numbers that are in the power ranges of most common batteries. That is capacitors measured in Ah numbers instead of farads.

so its likely..i could apply 5V or so and monitor the charge until it
gets up to 2.5V and then stop
Click to expand...

I am not following the logic here? Given the very low ESR numbers you would need some sort of a current limiting system in the design. Without it just putting 5 volts into a 2.7 volt super cap could result in momentary amp draws of multiple hundreds of amps with charging times of fractions of a second to get to the 2.5 volt level.

What 5 volt power source are you wanting to use?
 
WTP Pepper said:
Unlikely. If you use a DC-DC to output a constant voltage, then as the input voltage falls to it, the input current will increase causing the input voltage to fall quicker. The DC-DC convertor will also heat up in the process wasting more energy.
Click to expand...

lynx said:
i think i dont agree with WTP pepper because he speaks in general about the dc-dc converters while im thinking about the specific one i've posted
Click to expand...

Pepper's statement, though general, DOES apply, because it is true of ALL power conversions, including the part you are looking at.

Converters do not increase POWER, they only convert between different voltage and current ratios, but the output power can never be greater than the input power. Input power will always be the output power plus the inefficiency of the conversion.

So, if the output voltage and current load of your converter stays the same, then the input power required will stay the same. If the input voltage from your supercapacitor is falling, then that means that the input current will need to increase to maintain the same input power.

Next you need to look at the conversion efficiency, and how it changes with different operating conditions. For that, let's refer to the chart on the bottom of page 2 of the datasheet you posted. I don't know the output voltage and current you need, but I'm going to pick 100mA @ 3.3 volts for the sake of this discussion.

While the voltage at the cap is 2.5V, the efficiency is about 92%, which is pretty good. But as the cap voltage falls to 1.2V, the efficiency is down about 78%. The next line on the chart (Vin=0.8) doesn't go out to 100mA, so your system would probably shut down when the cap voltage is someplace not far below 1.2V. And, as the efficiency drops, the converters operating temperature will increase, since that is where the heat of the inefficiency is dissipated.



Nigel. Yes, we do need Shipstones to power our world. To bad Robert was a great writer, instead of an engineer. May he Rest in Peace,
 
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lynx said:
so its likely..i could apply 5V or so and monitor the charge until it
gets up to 2.5V and then stop
Click to expand...
You can´t put a voltage supply across the cap without some current limiting. The cap looks like a few miliohm resistor right across the supply, and not many can withstand that safely. You need a current source, not voltage source.
 
You also need to consider the self leakage of a super cap. Like it or lump it, you won't get something for nothing. Adding a 100% efficient DC-DC convertor won't magically give you more out than you put in.

Supercaps are only really useful for providing short bursts of energy in a cycle with low energy usage. Hence their popularity in boy racer car amplifiers (every boom that blows your ears off has a quiteish period of recovery before the next boom add nauseum).

They are of little use in a constant power source scenario without external charging like you seem to think.
 
I think he knows he has to charge it since the original questions were how fast he could do that.

Where they shine is where the short currents are very high. For example try to draw 10 amps from a couple of aa batteries in series and the voltage would drop to 0.5 volts immediately while the cap would take 75 seconds to drop to the same voltage. Burst current is the application.
 

yeah...because there's no logic on it! look what happend...

when i did my experiments i was using a switching power supply regulated at 3.30V together with a power diode which
dropped the voltage at around 2.58V the current at the early stage of charging was around 700mA and then falling more
when the cap was close to full, which was too weird.. so i speculated my switching power supply limits the output because
of the low resistance load.

in fact what really happend and i didn't noticed right away, was a cable problem! my cables were introducing some resistance
to the charging circuit >2ohm so the current was limited and also my diode got saved from frying.

so what i asked about charging it at 2.5V by applying 5V was pointless concerning the decrease of charging time, but it's very
important it case somebody wants to try because it gets more versatile if you can use many different voltages.

i'll ask again for confirmation... it is possible right??


i guess you mean output power.. yes i know all these though thank you for explaining it
in more detail.


kubeek said:
You can´t put a voltage supply across the cap without some current limiting. The cap looks like a few miliohm resistor right across the supply, and not many can withstand that safely. You need a current source, not voltage source.
Click to expand...

agreed...but as you can read it was already done "all natural" and i didn't knew it.

WTP Pepper said:
You also need to consider the self leakage of a super cap. Like it or lump it, you won't get something for nothing
Click to expand...


i think the leakage is too few..atleast for the cap i got..

by the way noticing again what i was initially asking...seems pretty novice or maybe nonsense!
but since ultracapacitors are somewhat different than the usual capacitors...then i had to ask all these things hope you don't mind
 
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