Post by: plasma on September 19, 2020, 07:54:41 PM
At present it just making a li5le amount of gas, but will build up the Farads.
Put a 9Vac source across 330ohm resistor and the salt gap, measured 87ohms for the salt gap. I moved the electrodes closer and now get sprays of water out after I short the gap.
Post by: Zipdox on September 21, 2020, 09:18:53 AM
Also that's not going to work very well since you need to heat up the entire water mass to 100 degrees before any water can start boiling. Read up on how smoke machines work.
My suggestion is heating a mass of metal and pulsing the water instead with a pulsed pump or something.
Post by: plasma on September 21, 2020, 09:49:57 AM
Still testing it at the moment.
Thanks for the feedback. ;)
Post by: klugesmith on September 21, 2020, 07:11:30 PM
At that point none of the water has vaporized. You need an additional 2.5 kJ for each mL of water turned to vapor.
I made a water resistor for calmly discharging a 10 kJ 22 kV pulse duty capacitor. About 150 mL in a plastic bottle with two sheet-copper electrodes, and enough copper sulfate to get about 100 ohms. When connected to capacitor charged to 1 kJ, there's no sound. Kilovoltmeter reading drops to zero, the water warms up slightly, and one of the electrodes turns black.
Post by: HiVi on September 21, 2020, 08:30:22 PM
Maybe use only spark gap in distilled water so you do not have any byproducts from salts?
If such high voltage is not possible, resistive heater is also good idea. With preheated water and insulated container.
What is the idea/application? Steam engine as in thread subject?
Post by: plasma on September 21, 2020, 11:21:28 PM
NaCl at the moment, but ammonium sulphate it disovoles better ,lower ohms.
Destilled water could work, but I'm trying to keep the voltage lower to minimize surface tracking.
I'm using the water as reaction mass for jet type thing, well what started the idea.
A resistance heater would defiantly work, if the above doesn't work I'll fall back to that, but the pressure for size will be lower.
Post by: klugesmith on September 21, 2020, 11:58:09 PM
Here's a contemporary engine that uses vaporized water as a propellant, with Isp around 100s, at a scale suitable for cubesats.
https://aurorapt.fi/2020site/wp-content/uploads/2020/08/AURORA_Single_Resistojet_Thruster_V3.pdf
Post by: plasma on September 23, 2020, 12:53:49 AM
Installed more capacitor, making 45uF 9J it arcs inside the water between the electrodes with a blue colour.
Going to look at Scr the screwdriver switch will be maxed out soon.
Post by: plasma on September 27, 2020, 02:32:14 PM
Trying to get the resistance as low as possible, the 2mm gap is around 25ohms, it quickly climbs when expanded, making a punny crack when shorted.
Next couple of days should get some more capacitor taking it up to 60uF.
Post by: plasma on October 04, 2020, 08:56:40 AM
Got some more capacitor taking it up to 60uF. At present it takes 4 shots to remove all the water in the salt gap, most of it gets blown out.
Later when I've sorted out the water injection I'll get a SSR traic and 555 to switch off the charging circuit then switch on the Scr.
This Wednesday I'll pickup two more capacitor.
Tried putting a magnet under the salt gap, it wasn't as energetic.
Post by: plasma on October 05, 2020, 03:52:38 PM
The DMM reads 510V across one of two 1W 10Mohm voltage divider.
Post by: plasma on October 14, 2020, 05:06:54 PM
NaCl solution was put in the gap, measuring the voltage across the 47ohm gave 9.28V from 10.4V, about 6ohm for the salt gap.
NH4SO4 solution gave 9.6V ,4ohms.
The ammonium sulphate solution gave a burn smell when fired.
At higher resistance solution give larger bangs.
1000V cap bank into 4 ohms might be to much for solid state components, might have to think about mechanical.
Post by: Twospoons on October 15, 2020, 09:37:29 PM
1000V cap bank into 4 ohms might be to much for solid state components, might have to think about mechanical.
You have a way to go before abandoning solid state switching - all that changes is you have to be a bit more rigorous with your design.
Think hockey-puck thyristors, with appropriate drive.
Post by: plasma on October 16, 2020, 08:36:35 AM
Post by: davekni on October 17, 2020, 04:15:07 AM
The issue that will need care with thyristors is the parameter called "critical rate of rise of on-state current". It's often about the same for large thyristors as for small, in the 50-150A/us range. It may require an inductor in series to limit current rise rate.
Post by: plasma on October 17, 2020, 06:17:07 AM
It says the gate current is 55mA max,min 15mA at 6V if I keep it at 40mA will it work(haven't used one before)
The voltage on the cap bank I was meaning it can still supply holding current if the resistance is less than 1kohm.
At 100A/us does that mean in 4us it will be at 400A, afte how do you size the inductor as after 1Tc more current will flow?
Thanks
Post by: davekni on October 17, 2020, 09:05:37 PM
Holding current is 100mA or less per spec., so could be say 50mA. As long as your charging circuit is switched off, or is charging with well less than 50mA, then the thyristor will turn off after discharging the capacitor.
Gate trigger current is specified at 55mA max (80mA max at -40C). That's the worst-case needed to trigger. So, you need to supply at least 55mA of gate current. 200mA would be fine, or even 2A for a short trigger pulse. Higher gate currents help a bit with current rise rate handling.
Current rise rate is voltage/inductance. For 1000V, 7uH would give 1000V/7uH = 143A/us. 7uH is reasonable to achieve with an air-core coil of wire. Then you don't need to worry about core saturation at 250A peak current. If you need to use a smaller inductor for some reason, then high gate current may allow operation up to 300A/us (3.3uH inductor).
Surge current rating is 340A for 10ms with 150C junction. For your short pulses, currents up to 700A (or even more depending on frequency) should be fine. 1000V/4ohms = 250A, so no issue for CS30-16io1.
Post by: plasma on October 17, 2020, 09:42:50 PM
Checked out foumlas, I think you use I'll=1/0.000007*(1000*0.000001) =143A
Nice post cheers.
Post by: plasma on October 25, 2020, 09:50:03 PM
I'm going to have to minimise the salt gap electrodes, thinking maybe 0.25mL with two shots a second.
The power supply will be a 4-8kW petrol generator, well the boundary I'm working in
Having minimal water in there makes a more reactive shot, I'm guessing the energy is more constructed.
Added 136mH between the charging circuit and cap bank, I started blowing diodes when firing.
Selected a better Scr 1200Apk in case the resistance of the gap drops to 1ohm.
Post by: davekni on October 26, 2020, 12:51:33 AM
A charging series-inductor is a great idea. That can double efficiency compared to resistive charging. However, it can double voltage. If starting at 0V on the capacitor, connecting to a DC supply through an inductor makes a series-resonant circuit. Analog simulation (LTSpice or one of the other free tools) would be a great way to experiment with charging circuits without frying parts.
Post by: plasma on October 26, 2020, 01:48:58 AM
Ive got ltspice will check this out just in case, each capacitor of the cap bank is 450Vac, 320Vdc about.
Cheers
Attached sicmatic, the green is across inductor.
Post by: Twospoons on October 26, 2020, 04:39:41 AM
With a specific heat of 4.2J/g/K its going to take ~84J just to heat from room temp to 100C.
Then to turn that into steam, the latent heat of vaporization is 2260 kJ/kg, or 2260 J/g, meaning another 565J to turn 0.25ml of 100C water into 100C steam.
That's over 3000uF at 640V.
And that's assuming 100% efficiency too, so your cap is going to have to be bigger still.
Did you run the math before you started this project?
Post by: plasma on October 26, 2020, 11:35:48 AM
There's also increase in pressure with no volume change which gets converted to heat.
Is it local or global heating, all at 100 degrees or local pockets at 300.
Its not exactly easy.
Post by: plasma on November 05, 2020, 01:20:33 PM
This is the component used https://www.digikey.co.nz/product-detail/en/vishay-semiconductor-diodes-division/VS-70TPS16PBF/VS-70TPS16PBF-ND/2632107 .
The inductor measures about 3uH , the two resistor equal 44ohm with a diode just in case anode shorts to gate.
The salt gap makes about the same noise as before.
Post by: plasma on November 07, 2020, 03:28:14 AM
vthroat =sqrt(2*k/k+1*R*Tthroat) =395m/sec
R =461 for water vapor
Tthroat=300
k=1.3
V1 =R*T1/p1 = 0.27
p1 = 505000
Vthroat =V1*(k+1/2)^1/k-1 =1.10
Athroat =mVthroat/vthroat = 2.78mm2 for the size of the hole, the chamber will be 20mm ID with the inner electrode 12mm. I plan to fibreglass one end of the pipe, and weld flat bar over the other.
I'll be getting more caps next week, the Scr and resistors don't get hot, I was worried that I might exceed the wattage of the gate, did notice when I got a good contact to switch the Scr on, it resulted in a larger shot.
The sounds a mulfed but a blue arc can be seen inside.
Changed my cap bank to 2 in series 4 in parrellel given 60uF 30J at 1000V.
I added the salt water read 4 ohms across the gap and fired it, it made a small pop sound.
I think that I can measure the resistance across the gap to get approximately the mL in the chamber. The chamber has a slightly larger ID than the previous but should work with more energy.
Post by: plasma on November 10, 2020, 10:35:41 PM
I've moved back to the pic attached, it has 0.5mL and I plan to modify it so I can inject water into the gap.
I upgraded the wiring on the cap bank, its getting to the stage were ear muffs are compulsory.
The last picture is the injector idea, gravity feed at first, but a slow continuous flow from a pump should work.
I'm thinking that maybe 4 of the above feeding into a central tube might be better than one large chamber and a lot of energy.
Post by: plasma on November 12, 2020, 04:01:47 AM
The back pressure when fired delays the topping up, but after a shot it froths at the exit between electrodes.
The third picture shows the froth, a lot of small bubles. Upgraded the charging circuit by parrellel more capacitor, it now takes 2 seconds to reach full charge on the bank.
The latest shot must have cleared a blockage, the water flows quicker into the gap.
Post by: plasma on November 20, 2020, 07:08:27 AM
The Scr seems to be turning off prematurely, there's still 200 V on the cap bank, I though that would be enough to supply 150mA holding current?
I thought that maybe the charging circuit was raising the voltage on the cap bank, but increase to 4uF doesn't seem to change the value.
I probably should have noticed it early, it charges to -536V then after the discharge goes to 106V, this is with a 50% voltage divider.
I tried adding a diode after the choke for the Scr but didn't do much, its probably the choke between charge circuit and cap bank.
Post by: davekni on November 21, 2020, 01:56:26 AM
Post by: plasma on November 21, 2020, 07:04:51 AM
If I increase the size of the capacitor bank it should lower the reverse voltage?
My DMM can't read inductor that low but it should be about 5-6uH, with 75uF I get 0.28ohms for impendence at 8217Hz and last I checked the salt gap should be 3-5ohms, would that be accurate for 200V?
Post by: davekni on November 21, 2020, 08:09:25 PM
Your calculations look good. The salt gap resistance is clearly dropping during the discharge, perhaps forming an arc. Resistance must be dropping to ~0.28 ohms. The effect of more capacitance is hard to predict, as that will also change the salt gap resistance during the discharge.
Post by: plasma on November 22, 2020, 05:00:19 AM
About 8 years ago on www.4hv.org there was a thread were someone had Ali foil in a barrel with a little water, the video showed a lot of reaction out the non closed end.
I tried rolling up small Ali balls and placed them in the chamber, the Ali turned to AlOH after a shot and aloud noise.
I have patched up the chamber to fix leaks and a slightly larger volume, guessmate 2mL.
I should be getting some more caps to take it 90uF 45J and some 6A diodes.
The Gibbs free energy of water is 237kJ/mol 13.1kJ/g which is a lot for a small amount, hoping other elements or salts can lower the input.
I'm going to try some different salts, and look at Ali foil more.
Post by: plasma on November 28, 2020, 04:36:08 AM
The Ali foil makes it more vigorous with the smell of burnt Al, not sure if its from air trapped or oxygen from the water. Al2O3 has 1532kJ/mol on formation, with 30g/mol for Al, its twice the mole mass, but 4 times the energy of water. Finding a way to pump it between the electrodes is going to be a problem.
The water getting sprayed out I think is the sudden production of hydrogen and oxygen, I don't think its local effects of water turning to steam.
I've added diodes across the Scr but it didn't have any effect to reverse voltage on the capacitor bank which has stumped me.
Post by: Twospoons on November 28, 2020, 06:04:33 AM
I've added diodes across the Scr but it didn't have any effect to reverse voltage on the capacitor bank which has stumped me.
Not surprising at all. By the time the current goes to zero the caps will have some reverse charge, and a lot of the water in your gap will be gone leaving an open gap full of mist. Any arc will rapidly extinguish once the current is low enough - the plasma will cool rapidly with all that atomised water. At that point there is no longer a conduction path for the caps and they will retain their reverse charge.
What you need is a reverse diode across the caps - that way the residual energy in your inductor will end up dumped in the water gap, rather than cycling back into the caps.
Post by: davekni on November 28, 2020, 06:35:48 AM
As Twospoons said, the salt gap must be non-conductive at the end. With the diode across the SCR, the remaining reverse cap voltage is also across the salt gap. Even a relatively-small conductivity in the gap would discharge the caps before long.
Diodes across the caps is likely what you want given the salt gap's lack of conductivity. The diodes will conduct a bit more current for longer placed across the caps, but there's likely still plenty of margin in their 10ms surge rating.
Post by: Twospoons on November 28, 2020, 11:03:54 PM
Hydrogen and oxygen production is insignificant compared to heat/steam.
There may be a fair bit of hydrogen produced by the reaction of aluminium with water. The discharge is likely stripping the oxide off the foil, and probably also atomising some of the foil, leading to a large reaction surface.
Post by: davekni on November 28, 2020, 11:56:04 PM
Yes, perhaps. I'm a bit skeptical, unless significant amount of aluminum is atomizing. Think of the reaction of dropping solid sodium into water. Rapid, but not so much compared to the <millisecond of this discharge.
Post by: Max on November 29, 2020, 11:51:37 AM
Assuming you're using copper electrodes and no chemical reaction with the electrodes takes place, Twospoons (https://highvoltageforum.net/index.php?topic=1241.msg9433#msg9433) is entirely right. The fact that some or even all of the water dissociates and recombines doesn't add any energy. The reason is that it takes exactly as much energy to dissociate the water than it takes to recombine. Anything else would violate the law of conservation of energy and allow you to create infinite amounts of energy (You could just continuously dissociate and recombine water to gain more and more energy).
You mention pressure, too. However, that pression doesn't magically form. Since you're not adding any mass to the system, any pressure change can only arise from two things: change in temperature and change of the state of aggregation (solid/liquid/gas). In other words, water does not vaporize because of an increased pressure. Rather the pressure increases because water has been vaporized in first place.
The other way around you would again create a perpetuum mobile. Take any sufficiently robust enclosure and fill it with let's say 1l water. now create a minuscule spark. Just enough to locally rise pressure and temperature such that some water vaporizes. If you were right, this would make the water around vaporize, too. And because this would rise the pressure further, the temperature would increase further, which would vaporize even more water. See where this is going? your minuscule spark would vaporize any amount of water. But it doesn't. You get a blip, and an overall increase of temperature that wouldn't even be measurable.
Same thing for your steam engine. You don't get any more energy out of the thing than you put into it. If you use reactive electrodes, that's additional energy you're going to put into it. However I'm assuming that's not what you want (otherwise you may start looking into explosives which are far better sources of "rapid" chemical energy than corroding aluminium electrodes). So I think it is safe to assume that you want to vaporize water with the electric energy only. And that leads without mercy or "escape" to the values quoted by Twospoons. 334J/g to get from 20°C to 100°C and an additional 2260J/g to get vapor. Add a couple tens to hundreds of Joules for losses to the environment, cables, etc. The law of conservation of energy is hard and doesn't know exceptions for hobby or free energy projects.
Rounding those values leads to 3kJ per 1 gram of water that you want to get from 20°C to fully vaporized. Sure, with only 1kJ you'd still get a decent bang and "steam". But that "steam" would be 2/3 atomized water (fine droplets of liquid water flying around), not vaporized water.
Kind regards,
Max
Post by: plasma on November 29, 2020, 03:04:07 PM
I added the diodes across the capacitor bank, more energy seems to go into the discharge, 200V, it drops to 1.2V Vfd.
I'm still looking at other salts, as I think they can add to the gas/vapour.
The 2-4kJ was expected, and within the 4-8kW Genny boundary.
The Al seems to work better in air, but apart from some wire feed system like a Mig welder, I'm not sure.
I think a salt that can lower resistance of the salt gap, will produce more I^2R heat in the water due to more current but less resistance.
Post by: plasma on December 03, 2020, 01:12:03 PM
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Thinking of using ZnCl2 its highly dissolved and I think it will lower resistance, just worried about by produced.
Post by: plasma on December 07, 2020, 03:30:28 AM
This is with Ali wire at 95uF 1kV
The video is hard to make out, but it looks like in the centre ,molten metal is moving away.
F =I*l*B
If current is 200A the length 0.05m and the Tesla 0.12 ,it works out at 1.2N of force.
The thing with wire, I can have multiple wires, with salt water its just one channel.
I have two magnetic separated with the wire going through. Fired it ,it is leaving 440V with the same polarity as the capacitor bank, I think its harder to form a plasma/melted channel. Blow the reverse diodes on the bank, I'll try 47ohm resistor to limit it to 6ish amps.
Post by: plasma on December 11, 2020, 03:39:10 PM
I plan to get a blender and put tin foil and water to make fine powder and mix that with salt water.
The reaction of the wire moving isn't notable the magnetic themselves don't move.
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Post by: plasma on December 26, 2020, 01:38:42 PM
The pulse duration is about 200uS, longer pulses should help, as well as some Neo magnetic which should triple the current force.
When the pulse length Reach's 1mS I'll parrellel a second wire with its own 2ohm and Scr.
I'm planning on using thin wire to melt, but not so quickly as to not impart force.
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