how to measure the energy in capacitor

[studystudystudy]

i have an question, how to measure the energy stored in the capacitor?

i doing the piezoelectric energy harvesting.

then i try to used a simple circuit to harvest the energy.

the piezo is an input of my circuit with following information
piezo is AC voltage, with maximum voltage 80V and the current is 2.5uA

please see the attachment and give your opinion.

 

[karesz]

Hi,
I would say:Energy=~80Vx2,5uAxtime(half pulsewidth)...
1,
But I dont know these diode & dont understand the data because over web are types coming for 25A as 1N1200c or 1N 36116 as cross type...
2,
The load as 1K seems me to be too low!
I think the 80V/2.5uA measured not with the drowed circuit!?
K.

 

[studystudystudy]

eii. the data is actually the piezo data, when piezo under pressure, the voltage is 80V and the current is 25uA.

the diode is actually using UF4007 ultra fast switch, the purpose of this diode is to rectifier the AC to DC.

the higher resistor is better?

i try to get the energy as high as possible.

thanks for your guide and opinion. thank you very much

 

[karesz]

Study,
A 1KOhm is practically a short for a source they delivers on some uAmps - measured (I think your probe/DMM) on 10MOhm load!?
Dont worry_ I know over 40 years, that a diode in so a cicuit is to rectify some input signals _ I didnt understand only your "KW type" in a vibration harvester :-(...
Ok, is the current yet 2.5 or 25 uA pls?
What kind of load optimal is: depends of your vibration & trancducer(piezo)_ you must measure the characteristic your piezos for your art of vibrating energy!
I mean, try a application typical exiting, hold it stabil & measure your outputs with a diode+ C & diverse loadresistors, than change some component, i.e. other diode try repeatedly your measurements & change other component too as storage C`s Type & value & so on.
So will you have a data collection/validation of your energy converter elements in system_its a small diss work..
Than is as next step to Know how is the full energy converter if you yet will change the exiting vibration in energy/frequency & / or spectrum...
BE CARE pls: your mechanical outlet must be unchangaed for valid datacollection...
Lot of work, but only so can you have a knowlidge; is some changed in vibrating= I have to do these or that in my circuit...
If you have characterized your piezo (similar as by photo voltaic: you have to find a maximum output power for best efficiency of harvested energy (calculataed from U/I outs by diverse loads)= you will see what is the best load value for your concret piezo in the concrete environment.
K.

 

[studystudystudy]

A 1KOhm is practically a short for a source they delivers on some uAmps - measured (I think your probe/DMM) on 10MOhm load!?

because my input current very low. To harvest it, i need low resistor isn't it?

I didnt understand only your "KW type" in a vibration harvester

i don't understand this sentence. i didn't used vibration to harvest the energy, i just foot step on the top of piezo disk, then the piezo disk under compress and amount of voltage produce. then i get the energy. my aim is to stored that energy when continuous foot step on piezo disk.

is the current yet 2.5 or 25 uA pls?

my measurement is 2.5 uA, but this is not a constant value. it may change, sometime even lower or even higher.

If you have characterized your piezo (similar as by photo voltaic: you have to find a maximum output power for best efficiency of harvested energy (calculataed from U/I outs by diverse loads)= you will see what is the best load value for your concret piezo in the concrete environment.

i did do it, but hahahah, very funny result. because my Vin is using piezo disk as the sources. then i go step it using foot. i though there will have amount of energy stored in the capacitor, in fact no!!.
i try use DMM to measure the energy stored in the capacitor, but DMM doesn't have this function, how to know whether the energy is increase in the capacitor??
then i try to measure the voltage in the load resistor. strenght result. no voltage!

thanks again your kindly and effort to guide me and lead me to success.
really really thank you

 

[karesz]

Hali,
1, Yes, Iin is small, but you must find the optimal load/working point for your concrete piezo element, its no matter if its energy is coming from a vibrating or a pressure by your walking; than thiese is a kind of vibration too , only cyclings frequency is at tenth of second!... Take a characteristisc befor makes some things, these is A & O.
2,
"KW" type = your diode in the attachements circuit was a kilowatt type-sorry!
If you will give a circuit knowed, it should be with real/concret components drowed! It makes only wast time for others, than only you can know what reality is...
3,
clear is 2.5 uA variant-than your pressing isnt standardized, these was the reason if I wrote for you: "apply pls a standard mechanical outline by the characteristics measurements" (or was similarly)...
4,
I think - your electrolytic has higher leck current as the produced/harvested one...
5,
do forget to first your storage C, make only the rectifying & diverse load resistors check....
And even, the DMM has a 10 MOhm load too!
I would take a resistor of i.e. 1.1Mohm and measure the voltage across that, than is your Rload= 1.1Mohm parallel10Mohm=> 1MOhm real,your measured Voltage divided with 1Mohm=> the delivered current,than calculate the power, i.e. ca. 20uW, than change the resitor to residual 0.4/0,1/ 5 & 10 MOhm & calculate every time the output power!
Because your system is a litlke bit statistical, all measurements are i.e. 10 times to do & take a middle yalue from all... I sayd: its a lot of measuremet to do_is a small diss. lem: an super clear writing and consequent, clear documentation of all your details/parameters!!
Its surly better if you change the test set up & not you will walk, bit regularly apply a presure force to the piezo: otherwise it will be never exact and repeatably_sorry...
Anyway, for the starts its surly OK by walking too...
K.

 

[karesz]

Hali,
Some info to read
K.

 

[karesz]

I think, you can read some interesting sides here: https://www.ioxus.com/applications.html]

Design-Aid Calculators: **broken link removed**
Really good web side: https://www.EnergyHarvesting.net
K.

Sorry,I found the first collection only in German, but a part of them was originally in English...
"Bewegungsenergie lädt Akkus auf"=~ca, Movements energy charge batteries...

 

[studystudystudy]

thanks again keresz

now i try to used a very simple circuit to harvest the energy, i used Vin connect series with UF4007 fast switching diode and series with the 1000uF, 10V capacitor.
but i no used resistor as the load.

i measured the capacitor voltage using DMM, the voltage of capacitor icrease . ^^ very good news for me

a few question

1. the capacitor is 1000uF and 10V capacitor, what is the meaning of 10V, is that the maximum voltage can be pass through the capacitor?

2. the capacitor is 1000uF, how many maximum energy can be store? i understand that the energy is in term of joule, how to calculated

3. the voltage of capacitor increase when the Vin apply to in, but why the capacitor voltage will degrade after remove Vin?

4. is the resistor as the load necessary, can i straight away measure to the capacitor voltage?

thanks, this few question make me headache all the time

Thank you for your kindly reply

 

[keith1200rs]

10V is the maximum voltage you are allowed to put on the capacitor.

The energy stored in a capacitor is 0.5CV^2

One problem with electrolytic capacitors is leakage. When you remove the voltage source they will slowly discharge on their own. Even a battery does that. A large ceramic capacitor may be better, but you will not be able to get such a large value.

Keith

 

[karesz]

...One problem with electrolytic capacitors is leakage. When you remove the voltage source they will slowly discharge on their own. ..Keith

Hi,
Tnx Keith.
Exactly, as I wrote it before too, but for that are the proposed/said "super (or Gold) Caps" developed & proposed...
K.

 

[keith1200rs]

Hi,
Tnx Keith.
Exactly, as I wrote it before too, but for that are the proposed/said "super (or Gold) Caps" developed & proposed...
K.

Very true. I was assuming he was using an electrolytic.

Keith.

 

[FvM]

I was assuming he was using an electrolytic.

Yes, obviously 1000 uF/10 V is electrolytic. Good ones can be expected to have < 1 uA leakage current at 25 °C
(after some equilibration time). The DMM input current (assuming Rin = 10 MOhm) will be higher.

 

[studystudystudy]

10V is the maximum voltage you are allowed to put on the capacitor.

The energy stored in a capacitor is 0.5CV^2

One problem with electrolytic capacitors is leakage. When you remove the voltage source they will slowly discharge on their own. Even a battery does that. A large ceramic capacitor may be better, but you will not be able to get such a large value.

Keith

hi keith

isit you mean the capacitor maximum storage is 10V?

The energy stored in capacitor is 0.5CV^2, how to get the velocity value. sorry

is there any capacitor will no have leakage? super cap and gold cap?

 

[keith1200rs]

The energy is 0.5CV^2 where C is the capacitance and V is the voltage. So the maximum energy you can store is 0.5 * 10u * 10 * 10 = 500uJ.

As Karesz mentioned, supercaps and gold caps have a lot lower leakage. You can get around 100uF or maybe a bit more in ceramic but not in high voltage.

Keith.

 

[frankliner]

You need a higher voltage rating on the capacitor, or a zener in parallel to protect it.

Did you look at the time required to charge this cap?

 

[karesz]

Hi,
I think, the reverse current of Zener will be light/rash higher as the piezo`s harvesting capacity
(similar problem as with practically all electrolytics :-()...
K.