Good deal

OK, something else I failed to research The MUR420G will be grossly inadequate to handle the current from the inductor. It's only rated for 6A, and you'll be pushing almost 3x that through it.

I suggest that you replace it with something like a STTH60P03S; it's rated for 60A continuous - or perhaps a Fairchild RHRP3060, 30A 500V. I've been poking around looking for a suitable Schottky barrier diode, but most of them are rated for < 15A. Those that have a higher rating are dual diodes, and that's not likely to work well in this application; one will get hotter than the other, thus will conduct more of the current, which makes it hotter - thermal runaway is not your friend.

ST Microelectronics' STPS20L15D/G might be worth a look. 20A, 15V, 0.33vF max. The very low Vf is attractive, but the 15v reverse voltage would be a problem if your alternator were putting out >15v.

 

How much current is likely to flow in the MUR420Gas there is only parasitic inductance in the original design?
What about the IN6097 it is rated at 50A

 

How much current is likely to flow in the MUR420G as there is only parasitic inductance in the original design?

In the original design, you wouldn't likely get very much; as you said, just the minimal parasitic inductance from the wiring. The addition of the inductor changes that significantly; now D1 becomes a real "flywheel" diode, providing a path for the relatively large inductance to discharge across the cell.

The lower the Vf of D1, the more of L1's stored energy gets dissipated in the cell, where you want it to be expended.

What about the IN6097 it is rated at 50A

That would work well - if you can actually find a few somewhere.
1N5828 (30A 40V), 1N6095 (25A 30V), 1N6391 (25A, 45V) would also work pretty well. It's finding them that's the problem.

This might actually call for a P-ch MOSFET to be switched by a comparator that looks at the Vds; if the drain voltage gets higher than the source, then the MOSFET needs to be turned on. That's getting rather complicated though, and switching times will be a problem.

In an emergency, you could actually use an N-ch MOSFET that has a Schottky body diode with the gate wired to the source and a rating of at least 20A. However, it likely won't be as efficient as a discrete Schottky diode.

 

Thanks I have made a note of the toroid details, I have installed the LTSpice and found models for the op-amp and power transistor; the next step will be to capture the schematic of the full circuit and simulate with a typical range of currents.

This is good stuff. We will help you with this if you publish your findings.

For bench testing I have removed the regulator from my PWM - it is running cooler with the higher Vgs.

That was really quite predictable. Instead of a 10v regulator, the circuit needs a 15v clamp to ensure that the circuit voltage never rises above that. Resistor, Zener diode, and relatively large capacitor.

I might see if the magnetic field from the toroid has any impact on HHO production – I am always skeptical about what I see on the internet as there is a lot of BS.

I very sincerely doubt that the "magnetic field" from the toroidal inductor will have any positive effect on "HHO" production. It will not matter where it's physically placed in the circuit overall; just the electrical placement is critical. Your benefit will be realized by the continuous current provided by the inductor; gas production will continue even when the current is not flowing through the MOSFET.

The load on your MOSFET will be greatly reduced when you add the inductor. You may need to need to "throttle back" the current limit setting significantly.

I do suggest that you reduce capacitor C4 to 10uF, which will make that portion of the circuit much more responsive. Note also the changes I made to the gate circuit; decreasing R9, increasing R13 and swapping their position. It's still not ideal, but better than it was. Adding a small cap (around 0.047uF) across R9 would definitely improve response on the gate.

And yes, there is a lot of BS floating around on the Net about this stuff.

Risking my neck here we as a whole would like to see some verifiable results from what you've been tinkering with. If things worked out favorably, tell us how you arrived at your results. If things did not work out favorably, tell us that as well.

What we've seen is ambigous and heresy claims of increased economy. That just doesn't sit well with any of us. We want to see (as a whole) a definite mileage improvement that is repeatable across at least a few vehicles.

Is that too much to ask?

 

Thanks once again - I will update the MK1 version with your suggestions. I have captured the schematics for both versions, I am currently limited with ballpark values until we finalize on a cell design, when this is done I will tune the components for optimum performance.
I was concerned with the loop stability - and saw some issues when I was running a couple of simulations, see attached JPEG.
With regard to measurements I will post them when I have the data - I have a friend who has been methodical with his measurements over a few months using a "brute force" cell and gets 15 to 20% improvement.

 

I see that!

Try changing the balance between R17 and R16.

Try increasing R14, and placing a 1uF capacitor across it. This should help reduce the wild swings a great deal.

We need a better electrical model of the cell.

At low voltage levels, it will likely act more or less as a "leaky" capacitor. That's a function of the plate area vs distance between the plates, and the dielectric constant of the electrolyte solution. Water is somewhere between 45 and 70, depending upon temperature (colder = higher dielectric constant).
Here's an online capacitance calculator:
http://www.daycounter.com/Calculators/Plate-Capacitor-Calculator.phtml

Once the voltage across the cell is somewhere between 1.5v and 2v, it should start producing gas, depending upon what your plates are made of and the electrolyte solution. Also at that point, the cell will probably act more or less like several forward-biased diodes in series. Attempting to raise the voltage across the cell will result in a great deal more current flow, but the actual voltage drop across it will likely remain fairly constant. Unless your cell wiring is very heavy duty, you'll probably see a significant voltage drop across the cell leads.

1 foot of AWG 10 wire has a resistance of just under 1 milliOhm. If you passed a 1A current through the wire, you would see just about 1mV difference between the two ends; 80A = 80mV.

It would help a great deal if you could take measurements on your existing cell and let me know if I'm in the ballpark. It would help a great deal if you had a variable bench supply capable of 0v-5v with a high current output.

 

The issue is the time constant of R10 and C2, I have changed C2 to 1uf and you can see the difference.
I would like an accurate model for the cell - I will probably go with some diodes and a resistor. The capacitance of the tubes are quite low and is effectively shorted out by the electrolyte.
I have limited resources at the moment - no variable power supply
The other concern I have is the low sense voltage 1.5mv/Amp - which could vary in the range form about 20- 60mv, I need to consider the car environment which is electrically noisy.

 

Well actually, one of the big differences is that your simulation is running at about 550Hz. Try reducing R2 to about 10k Ohms; since LTSpice doesn't have pots in the library you just have to change the resistor value. With the pot I had set to 12k, I was getting around 1.8kHz; dropping it to 10k gives me right around 2kHz.

Increase your R11 to around 900 Ohms. That's your current threshold.

C2 should actually have a reasonably steady voltage on it. Well, it does on my simulations. Try increasing it back to at least 10uF. Having the oscillator portion running at 2kHz should help a great deal in stabilizing that.

 

Thanks I have made a note of the toroid details, I have installed the LTSpice and found models for the op-amp and power transistor; the next step will be to capture the schematic of the full circuit and simulate with a typical range of currents.
For bench testing I have removed the regulator from my PWM - it is running cooler with the higher Vgs.
I might see if the magnetic field from the toroid has any impact on HHO production – I am always skeptical about what I see on the internet as there is a lot of BS .

How did you rewire the system when you removed the Volt Reg?

Where can I get a 15v Clamp to use instead of the 7810? Or can I just use a 555 Timer instead and if so how would I wire that in?

 

Your regulator has a fixed dropout voltage. 78xx series regulators have about 2v dropout. This means with 14.5v in, the most you could hope to get out of it is 12.5v.
....................
As I mentioned before, even an inexpensive 555 timer would make for a huge performance enhancement.

The circuit is variable from 0%-100% PWM duty cycle. Note that bypass caps are not shown.

How would I wire in the 555 Timer instead of the 7810?

 

Good deal

OK, something else I failed to research The MUR420G will be grossly inadequate to handle the current from the inductor. It's only rated for 6A, and you'll be pushing almost 3x that through it.

I suggest that you replace it with something like a STTH60P03S; it's rated for 60A continuous - or perhaps a Fairchild RHRP3060, 30A 500V. I've been poking around looking for a suitable Schottky barrier diode, but most of them are rated for < 15A. Those that have a higher rating are dual diodes, and that's not likely to work well in this application; one will get hotter than the other, thus will conduct more of the current, which makes it hotter - thermal runaway is not your friend.

How about a 1N6300A, KBPC6010 or S60SC4M

 

OK, I'm falling way behind So many projects, so little time...

Worked up a variation on a theme with the LM324 circuit, instead using more modern opamps and a comparator with a 150mA power driver for the MOSFET gate; the latter could be replaced with a suitable voltage follower. The Schottky diodes I'm using are right at their limit (25A) but I didn't have a model for a more capable diode.

D1 thru D4 and R20 (upper right corner) are my rough concept of a cell. D5 is a flywheel diode for L1; provides a current path for L1 to discharge back through the cell, maintaining a relatively constant current.

U1A's output is a square wave. R3 represents a 5k rheostat at minimum resistance, which gives a frequency range from around 19kHz to 31kHz. Oscillation frequency with R3 all the way down as shown is 31kHz.

U1B's output is a triangle wave ("saw" took fewer characters though)
R12 & R13 represent a 10k pot that sets the initial comparator trip level. When power is first applied, PWM duty cycle is 55%-60%. As C2 charges via R16 and R15, the threshold set by R9 & R10 is exceeded, causing Creflev (comparator reference level) to decrease, which decreases PWM duty cycle. R10 should be a 1k pot, connected as a rheostat. Selecting a close initial setting for the R12/R13 pot helps minimize overshoot during start-up.

In the initial "n2freepower" schematic, C2 was 47uF. However, that circuit was limited to a couple of kHz due to the opamp used. 0.68uF allows this circuit variation to much more quickly respond to the actual current through the MOSFET; hence the current in L1 and the cell. U5, the LT1007A, has far more gain than the LM324; feedback was reduced to compensate.

R17, the current sense resistor, was doubled. 3 milliOhms is quite a small amount of resistance; a short length of suitably gauged copper wire (eg: 3' of AWG 10) would be sufficient. If the wire were AWG 10 stainless steel, you'd only need 0.68".

For a decent compromise on start-up times vs overshoot, the pot represented by R13/R14 should be turned down to minimum (ie: minimum voltage on Creflev), then R10 maximized (ie: high voltage on vrefi).

Then R13/R14 should be increased until about 10% more than the maximum desired current is flowing through R17. R10 should then be adjusted to fine tune the current to the desired level.

The simulation was done in LTSpice, available as a free download from Linear Technology's website. It requires a good bit of time to run just 5mS worth of simulation on a 2.5GHz processor with 1GB RAM running Win XP Pro.

The last file is the schematic in LTSpice format.

 

How did you rewire the system when you removed the Volt Reg?

Where can I get a 15v Clamp to use instead of the 7810? Or can I just use a 555 Timer instead and if so how would I wire that in?

Hi Cat3rn,
Not ignoring you; just fell behind. I can't devote all of my time to this topic, or I'd never help anyone else.

A Zener diode can be used as a voltage clamp, also known as a "shunt regulator". In this case, we just need to make certain that the voltage doesn't exceed the limits of the device. A resistor can be used to limit current from the electrical system (battery, alternator) and a Zener diode used to ensure that the voltage in the circuit doesn't rise above a certain level. The trick is to balance the resistor in series with the supply to the current requirements of the circuit. Just using a plain Zener diode as a regulator isn't very efficient.

In this case, our OP would have been much better off to use a 7812 regulator. The system shouldn't be on anyway when the engine isn't running; accumulation of H2O2 is a very un-good thing. When running, the alternator will put out somewhere between 13.8 and 14.5V, so the dropout voltage of the regulator would almost always be satisfied - if the battery would ever get charged. However, with the additional load of the H2O2 cell on top of the typical electrical load, that's not very likely.

 

How would I wire in the 555 Timer instead of the 7810?

Well, the 555 timer circuit was intended as a replacement for the whole thing. However, that circuit doesn't have current regulation; which the LM324 circuit, despite all of it's shortcomings, does.

I re-designed the LM324 circuit using more modern opamps, a comparator and an inductor to keep the current constant. That was an intermediate stage; using components how they were designed to be used instead of outside of their normal operating parameters (ie: using an opamp in open-loop mode; a no-no).

The next step is to move towards more economical components that are readily available.

 

How about a 1N6300A, KBPC6010 or S60SC4M

1N6300A is a 136v 1500W Zener diode for transient suppression. Vf=3.5 @ 100A, which would not be good in this application. Can't find specs for Vf at lower current. It's not designed for duty cycles above 20%. Besides, nobody carries it.

The KBPC6010 is a 6A full wave bridge rectifier. I fail to see how that could be useful here.

The S60SC4M is a dual 30A diode;nobody carries it.

 

The S60SC4M is a dual 30A diode;nobody carries it.

I was able to find 10 of these - S60SC4M 60A 40V Schottky Barrier Diodes from a friend. Would they work?

 

I was able to find 10 of these - S60SC4M 60A 40V Schottky Barrier Diodes from a friend. Would they work?

A diode has only 2 wires this one has 3. How would one wire it? Is the middle connection - common ground?

You can find a datasheet for them here:
http://www.alldatasheet.com/view.jsp?Searchword=S60SC4M
They are dual diodes with a common cathode; the center pin and the tab. Those would be good candidates for this application.

 

DigiKey has the STTH60P03S available for only 3.36 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=497-4416-5-ND

My HHO Cell has 25 plates all 316L SS. 3 positives and 2 negatives with 5 neutral plates in between each one for an approx voltage across each plate of 2.3v.

 

DigiKey has the STTH60P03S available for only 3.36

The trouble is that they aren't Schottky diodes, and have a relatively high Vfp and Vf.
In very general terms, the lower the rated PIV for a Schottky diode, the lower the Vf will be. The lower the Vf, the less power will be dissipated in the diode as heat; that power is then useable by the load.

I have some STTH6004W ultrafast 400V 60A diodes that also have too high of a Vf for me to consider using for a project like this. The S60SC4M your friend has would be much better for this project. Take a look at the datasheet.

My HHO Cell has 25 plates all 316L SS. 3 positives and 2 negatives with 5 neutral plates in between each one for an approx voltage across each plate of 2.3v.

I don't quite understand how they're connected; your description is a tad vague. Could you post a diagram? Perhaps draw something up in MSPaint, or sketch and scan something?
Wait, I think I get it - something like this:
+ ||||| - ||||| + ||||| - ||||| +
where the "+" is a positive plate, the "-" is a negative plate, and "|" is a plate that has no physical electrical connection. That does make a good deal of sense. You will need to have the electrolyte paths fairly well sealed off so that the + and - plates can't directly pass current between each other. Still, you'll need a means to replenish the water taken from the electrolyte.

Since you basically will have numerous cells in series, the PWM circuit I posted may not help you very much. You're already dropping most of the system voltage across the multiple cells. If the flywheel diode has much of a Vf, very little power will be transferred to the multiple cells. My modifications to the original n2freepower schematic were to change a simple low-frequency PWM w/pseudo current regulation into a 'buck'-type converter that was actually current regulated; providing a relatively constant current to the cell. In order for yours to be able to work with that circuit, you may need to remove one of the intermediate plates from each +/- combination, or use something more like a buck-boost or flyback current supply.

[/QUOTE]
Interesting - what did you make the container out of?

I realize this is at an intermediate building stage. I don't see a provision for the gas flow out, anti-flashback device (bubbler), water replenishment, etc. Care to post the drawings you're working from?

 

Each plate with the exception of the + & - are 3" w by 7 1/2" h
The plates are 316L .020 gauge SS seperated by, of all things, wire ties.

Around the setup is 1/8" Lexan (acrylic plastic) held together (for the moment by rubberbands) until the marine adhesive dries. The Lexan is only around the sides and maybe a little at the bottom and top to make a convection-like flow of the gases.

Yes the setup is +|||||-|||||+|||||-|||||+

The 3 "+'s" will be connected by a stainless steel bolt with the upper "tabs" bent over in a fashion that will allow 1 SS bolt to be placed upwards through my HHO cap. The same will be done to the 2 "-" "tabs". Around the "tabs" is going to be large shrink wrap to maintain the electrolysis inside the cell.

I am using 4" ABS with a end cap on the bottom and female screw in top cap. Inside the top cap I am going to use 1" thick SS Mesh to keep the HHO foam from entering the tubing. The foam will dissipate when it hits the SS mesh.



The fill tube seen on the side is 3/8" ID with 90 deg barbed fittings and clamps.



The top has a pressure relief valve built using the parts seen in the exploded photo. The parts are arranged in order of assembly. R>L



The top also contains a 3/8" HHO out barbed fitting (Right) and a 1/4" inlet (Left side) for the Electrolyte (10 gms K+Phos per 1.5 liters) & distilled H2O.

My bubbler is simply a house H2O filter with the filter taken out. It works perfect for the setup because the inlet is down the middle (thru the PVC pipe bubbler) and the outlet is thru the other side but it is capped off and the gases go out thru the top 3/8" barbed outlet. There is also a 1/4" barbed fill inlet with a check valve on it. In case the bubbler gets low also.

Fittings attached as seen and down the center is 3/4" pvc with couplers at each end. The holes are drilled at the bottom to allow the bubbling to take place.

I have a 1 gal reserve tank with a 12v H2O pump on it to switch on and fill each tank (via relay) seperatly if needed.

I am only allowed 6 images so here is a link to the H2O reserve tank.
http://farm4.static.flickr.com/3019/2931093990_5924cb1994.jpg?v=0

On the top of the HHO Cell container and the bubbler are check valves purchased at www.usplastic.com

3/8" PP Liquid/Gas Check Valves

http://www.usplastic.com/catalog/va...ory_name=45&product_id=15641&variant_id=64049

1/4" PP Liquid/Gas Check Valves

http://www.usplastic.com/catalog/va...ory_name=45&product_id=15641&variant_id=64048