# Help needed with triangle wave circuit / Op amp mosfet driver.

#### RIKRIK

Joined Oct 11, 2019
107
Basically i am trying to replica a wave form from a research study paper. However the guy doing the study had a large waveform generator, hooked up to the mains , in which he tested 3 waveforms, square, triangle and sine, and came to the conclusion that a triangewave at 25/30khz yielded the best results. heres the paper https://drive.google.com/open?id=1H-N0w95-LL5lIIu_JSMPD8k4WF_NURfW

The circuit iv been working on,and somewhat failing , needs to be compact and run off a 12v battery, Maybe a split +6/-6 supply as the load im driving (represented by the lamp) can be made smaller for less voltage. however i do want to run about 5A through it. I have the circuit which is a wein bridge oscillator running at where i want it, and have also put together a circuit below, which is the final wave form im looking for, however its using a SCR, as thats the only component in the circuit simulator that seemed to work. but i am dubius its too good to be true as i have no experiance with that component. also the 1meg resistor linking 2 separate power supplies, it works, but id rather do it properly. so any advice would be great.

kind regards,
Rik

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#### ApacheKid

Joined Jan 12, 2015
157
Basically i am trying to replica a wave form from a research study paper. However the guy doing the study had a large waveform generator, hooked up to the mains , in which he tested 3 waveforms, square, triangle and sine, and came to the conclusion that a triangewave at 25/30khz yielded the best results.

View attachment 195947

View attachment 195948

The circuit iv been working on,and somewhat failing , needs to be compact and run off a 12v battery, Maybe a split +6/-6 supply as the load im driving (represented by the lamp) can be made smaller for less voltage. however i do want to run about 5A through it. I have the circuit which is a wein bridge oscillator running at where i want it, and have also put together a circuit below, which is the final wave form im looking for, however its using a SCR, as thats the only component in the circuit simulator that seemed to work. but i am dubius its too good to be true as i have no experiance with that component. also the 1meg resistor linking 2 separate power supplies, it works, but id rather do it properly. so any advice would be great.

kind regards,
Rik
Isn't that just a rudimentary AM modulator?

#### crutschow

Joined Mar 14, 2008
25,423
What's the purpose of the SCR?
It seems ill-suited to the task.

#### AnalogKid

Joined Aug 1, 2013
8,596
a triangewave at 25/30khz yielded the best results.
Best results for what? What you are trying to achieve is not clear.

What is the output waveform you want? A 25 kHz triangle wave that is amplitude modulated with a much lower frequency signal? Something else?

ak

#### ci139

Joined Jul 11, 2016
1,696

#### ci139

Joined Jul 11, 2016
1,696
mathematically speaking you got a double A of sine added to 0 for INP and the normal A·Sine for output
e.g. A·(Sin+1) → A·Sin /or simply Sin+1 → Sin
so ? trivial detect 2A divide by 2 subtract from src.
if the frequency is constant the slope of 3-wave gives you A also
... if fixed slope input , then you can likely achieve it with integrator of half the slope and or some ±balancing thingy

or a loose simple in Falstad

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#### RIKRIK

Joined Oct 11, 2019
107
Sorry for the late reply, and thankyou for your comments, basically its for a drone i am wanting to try to develop. the drone is lifted by hydrogen gas, so pretty much electrolysis, However iv found afew different papers online and one claim a triangular shaped wave at 30khz will give 74% efficiency. do i believe this is true, meh... but the promise of using a smaller battery and solar set up, out of harms way took my interest.

Heres the design without the SCR, my question is the pfet im using in the software is -2v Threshold Voltage . do i need any other drivers and do you know any good pfets which are close and can handle about 10a. The 1m resistor in the picture represents the load, I have to take into account the conductivity of the water with and without a electrolyte, making sure each of the plates, including neutral plates are getting no more that 2.5v per cell over 12v, any more is wasted heat. circuit link https://drive.google.com/open?id=1C_H2w03TK4WuvaNYV_wE_TNk853hFBtb @ https://lushprojects.com/circuitjs/circuitjs.html

#### AnalogKid

Joined Aug 1, 2013
8,596
There is no common reference potential between the opamp circuit and the FET circuit - no GND. I'm surprised the simulation program does anything.

There are three plots with resistance values above them, but no indication of which resistor is changing. Please consider adding reference designators to *every* component.

There are a total of six waveforms presented, with no indication of what any of them are.

Please describe in text what you want the waveform at the FET gate to be.

ak

#### ci139

Joined Jul 11, 2016
1,696
from water you will be producing both O₂ and H₂ in close proximity and in close proximity to high current source
... considering your drone will have AC background of 25kHz exposure to sunlight and mostly-capacitive coupling to usually negatively charged Earth . . .

. . . you have an interesting if not potentially explosive situation . . . where your distance from your experiment may have a key relevance . . .
blah, blah, blaah . . . .

#### Danko

Joined Nov 22, 2017
989
However iv found afew different papers online and one claim a triangular shaped wave at 30khz will give 74% efficiency. do i believe this is true
Every electron of current through electrolytic cell always frees one hydrogen atom.
So, efficiency of electrolysis always is 100%, regardless of current shape.
Using triangular shaped current, you will lower efficiency to 74...50%,
because of energy losses in electronic parts of triangular pulses generator.

#### AnalogKid

Joined Aug 1, 2013
8,596
Using triangular shaped current, you will lower efficiency to 74...50%,
I see that you took some time and made an effort to point out what was wrong. Perhaps you also could put some effort into suggesting what is right. What waveform is best for this application?

ak

#### RIKRIK

Joined Oct 11, 2019
107
okay maybe i should explain it better, heres the paper imworking off https://drive.google.com/open?id=1H-N0w95-LL5lIIu_JSMPD8k4WF_NURfW the 3 wave forms shown are from the same circuit on right, they are formed by changing the value of the resistor represented as the load of the water cell. its there to represent the relationship between the voltage and current. im pretty much doing things backwards, instead of designing a circuit for the cell, im designing the cell for the circuit. this device wont be on the drone, its more like a pump at a petrol station. hope this helps,

kind regards
Rik

#### ci139

Joined Jul 11, 2016
1,696
"... targeting the resonant frequency of the water electrolysis cell [12]. ..." the reference [12] Mazloomi, K., N. B. Sulaiman, H. Moayedi5, "An Investigation into the Electrical Impedance of Water Electrolysis Cells - With a View to Saving Energy" Int. J. Electrochem. Sci., 7, 3466 – 3481 (2012). → http://www.electrochemsci.org/papers/vol7/7043466.pdf
[13] https://www.tandfonline.com/doi/abs/10.1080/02533839.2014.912787
[14] https://pdfs.semanticscholar.org/340d/b389a137d90b5308ce3828a36e5d96ca7bda.pdf also (https://researchportal.port.ac.uk/.../a-concise-model-for-evaluating-water-electrolysis)
((a bit over my head , this stuff ...))
___________
Every electron of current through electrolytic cell always frees one hydrogen atom.
in favorable conditions ...
https://ocw.mit.edu/courses/chemical-engineering/10-626-electrochemical-energy-systems-spring-2014/lecture-notes/MIT10_626S14_S11lec23.pdf
by https://www.google.com/search?q=charge+diffusion+polarized+electrolytes , there might be more to it as ion clusters and the water structure influence
http://jes.ecsdl.org/content/165/14/A3299.full
http://www1.lsbu.ac.uk/water/electrolysis.html cite from : "Gas-containing cavities in liquid solution (often called bubbles) ..." F;·T

https://en.wikipedia.org/wiki/Fullerene#Quantum_mechanics versus https://en.wikipedia.org/wiki/Water_cluster

accounting the ↑soap↑ there may be a role of some frequency stimulus to the https://en.wikipedia.org/wiki/Dissociation_(chemistry) process (not that i know too much about it)

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#### Danko

Joined Nov 22, 2017
989
Using triangular shaped current, you will lower efficiency to 74...50%
What waveform is best for this application?
Straight line (DC current).
I see that you took some time and made an effort to point out what was wrong. Perhaps you also could put some effort into suggesting what is right.
As I said already, electrolytic cell efficiency is 100% by current (Faraday's law of electrolysis).
Only way to increase overall efficiency is decreasing voltage on cell.
Theoretical voltage on cell is 1.23V.
In reality (in my experiments) that voltage was 2.0...2.7V (depends on electrode material, electrolyte, current density etc).
Best way I found is mechanically cleaning electrodes from products of side reactions.
In designed device I used rotated silicon rubber wipers, with 0.5s cycle of cleaning.
Material of electrodes - iron steel, electrolyte - KOH solution.
Measured cell voltage was 1.7V at low current (about 50mA, for eliminate voltage drop on electrolyte resistance).
EDIT:
@ci139
What is, in reality, resonant frequency of water molecules? [microwave oven]
What is result of water molecules resonance? [microwave oven]
And ions can not resonate in electrical field, only bipolar molecules can resonate.
EDIT:
Abstract
"The energy efficiency of water electrolysis has been considerably improved in the presence of an ultrasonic field. This was demonstrated by measuring the cell voltage, efficiency and energy consumption of the generated gas from the electrolysis. These measurements were carried out in alkaline solution using linear sweep voltammetry (LSV) and galvanostatic polarization techniques. A large reduction of the cell voltage was achieved under the ultrasonic field, especially at high current density and low electrolyte concentration. With the same current density, the cell voltage difference with and without the ultrasonic field fell as the concentration of the electrolyte was increased. The efficiency of H2 generation was improved at a range of 5–18% at high current density in the ultrasonic field but the efficiency of O2 generation fell a little due to the difference in the behavior of the gas bubbles. The energy saving for H2 production by using the ultrasonic field was about 10–25% for a certain concentration of the electrolyte when a high current density was used. On the other hand, the energy consumption for O2 production with and without the ultrasonic field was almost the same."

Big question:
Are H2 and O2 in their experiment disproportioned????

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#### ci139

Joined Jul 11, 2016
1,696
it stays unclear how the ultrasound is exposed to the electrolyzer stcak

. . . but i . . . assume that the vibration pattern to plates that puts the bubbles to move along some grad field would be preferable . . . maybe (assumes flexy / ? piezo electrodes )

and i don't get the correlation in between electrical resonance and ultrasound misc. including the frequency . . . if its tangent to plates it'll further reduce the ion travel patterns at electrical resonance ??? ... misty

ok i missed that

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#### RIKRIK

Joined Oct 11, 2019
107
Well basically at 20/30 hz is when water starts to cavitate, these bubbles remove excess hydrogen off the plates, keeping the resistance down. Apparently.

#### RIKRIK

Joined Oct 11, 2019
107
Danko, i am wondering if you have any pictures of your cell, would be interesting to see, also you wouldnt know the resistance of your cell in water and electrolyte.

#### Danko

Joined Nov 22, 2017
989
Danko, i am wondering if you have any pictures of your cell, would be interesting to see, also you wouldnt know the resistance of your cell in water and electrolyte.
Electrolyte:
30% solution KOH (potassium hydroxide) [300g KOH + 700g of water].
Recommended working temperature 75...80°C.
Resistance of cell:
In water-
R_dist.water = 286000 * 2L / A [Ohm]
In electrolyte (30% KOH)-
R_at_15°C = 1.85 * 2L / A [Ohm]
R_at_80°C = 0.87 * 2L / A [Ohm], where
L is distance between electrodes, [cm]
A is total area of working surfaces of all electrodes, [sq. cm].
==========================
I do not have pictures at all (do not keep any documents).
Will draft sketch.

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