Schematics Variable current 12v 60A to 0A

[Dazza]

I need a circuit that will allow me to continuously very the output current with a potentiometer.
I needed it to be able to.
Limit the maximum current.
Be very reliable.
Run continuously at maximum current.
The current value must be in the same position on the potentiometer when continuously adjusted.
It has to respond very fast.
When shutdown no power to output.(very important)
This is for my experiments with hydrogen power combustion engines. I will have 12v to 60A power supply from the alternator. this will be an isolated alternator from the existing electrics.
Will I need to use a battery, or can I set some think up with capacitors. because I will need an additional charge before the engine is started for a period of time say 7seconds approximately 12V 10A. which could be charged from the existing battery from the vehicle.  Any help would be appreciated.

[Ante]

Dazza,

Which is most important, the current or the voltage? If it

[Dazza]

Thanks for your reply Ante.  My idea of using existing battery for start-up.  When the ignition is switched to the on position, it will connect to the storage device to charge it as well as disengage the relay to the starter motor.  And when the unit is fully charged disconnect and reconnect the starter motor.  Yes I thought of using the alternator for the control. I don't feel this is going to be reliably accurate enough for the air fuel mixture.  As I can increase the production of hydrogen this must evenly vary between zero to the maximum. I can then reduce the fuel, gasoline, petrol accordingly.  Ultimately eliminate the need for the petrol.  I also have to know the combustible nature of this mixture, to be able to adjust the ignition timing correctly, as well as vacuum advance and also mechanical centrifugal advance. Now I am a little confused about the voltage amps.  With my experiments, I used the 0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL. that I built from electronic labs.  It has a maximum voltage of 19V. With my hydrogen experiment, I achieved 3.20A.   I used two metal plates fixed close together submerged in a salt water solution. I set the voltage to maximum and used the current control to increase or decrease the reaction.  So when I was at maximum current my voltage dropped down to about 7 V. So with the 12v system of a car if you start turning on headlights air conditioning etc, the voltage stays the same but the amps increase.  I don't really understand why, when I set my voltage at say 12v with my power supply, the voltage will drop according to the varying load. Also I don't think the voltage really matters as long as I can increase and decrease the reaction.  I hope you can make sense of what I am trying to do.

[Ante]

Dazza,

How about PWM, will it affect the hydrogen production efficiency? I think it can be done with PWM but then you should have a separate battery and alternator. A PWM circuit can be made with very fast response time, but isn

[Dazza]

I didn't know what PWM was. so I done a google search,for the applications it is being used for it seems like the way to go. Do you know of good schematics for my application.  So basically it turns the power on and off the faster the switching the more current it provides?.  What happens when the current is reduced to a minimum, is the switching duration still very fast.  I don't want irregular flow of hydrogen at idle.  Yes I think it will be a good idea to use a battery with the isolated alternator, keep it simple . I was just worried about the stress on the battery in drawing so much current as well as the bulkiness of adding an extra battery. There will be some lag but I think I can compensate for this with the Carby pump.  My first test engine will be a 3 and 1/2 hp 4 stroke lawnmower engine.  The ignition will have to be modified so it can be varied. A Turbocharged engine would be risky.  All so I will have problems with using a car alternator for the fact that it will need to draw current to charge the electromagnets. I think this will stop my little 3 and 1/2 hp engine in its tracks.  Maybe you could help me out with a way of modifying a DC brush motor with permanent magnets as a alternator, generator. It wouldn't need to produce as much current as I am using a small  test engine. they use this sort of thing in drag cars. Yes a knock sensor would be a good idea. but for now I think a little trial and error will be needed.  Yes the only Safeway, immediate combustion. Storage is a road that I'm not willing to go down.  That's where the Hindenburg is burning. The reason why why power supply only put out 19v, I used a recycled transformer from and old stereo, it has a 11v output and a 16v output I just used the 16v.  You said that the battery acts as the storage device (capacitor). If I was to disconnect the battery with the engine running, everything will function as normal, as the power will be drawn directly from the alternator.  The old-style generators which use to be used would put out a steady voltage,current to keep the battery in a high State of charge.  Does this sound right. (alternator AC current) wears its converted to DC through what is known as the diode pack and then the regulator. (the old generator) I am not sure of the difference?

[Ante]

Dazza,

A good schematic does not exist for an application like this, you have many factors in play and it have to be tailor made so to speak. A PWM system has a fixed frequency and a variable pulse length so yes the switching duration is the same. This parameter must be experiment with since different applications needs different frequency

[Dazza]

Thanks for sharing your knowledge with me  Ante.  You have help me fill in some gaps in my understanding of these things.  I have found quite a few PWM projects on the net, and have spent some time trying to understand how they work, I seem to be getting a grasp on it.  I found two projects that seem to be a good starting point for experimenting with (http://www3.telus.net/chemelec/Projects/PWM/PWM.htm )  (http://casemods.pointofnoreturn.org/pwm/circuit2.html ) I have some ideas of modifications however selecting the right components and values will be a bit of a guessing game for me.  If I can be a pest, and ask if you would be kind enough to have a look at the schematics and see what you think.  I will only need around 20A for experimenting with the 3.5 hp engine.  My plan has always been to use three separate units for producing hydrogen each around 20A.  The reason for this, two of the units will be in constant use and the third will automatically service itself.  I think there will always be  deterioration of the electrodes regardless of the material being used, and a buildup of gunk for lack of a better word, due to impurities in the solution.  There is going to be  lots of work involved in developing this system properly.  I may need to monitor hydrogen production, maybe an oxygen sensor as these are already use in fuel injection vehicles.  Yes hydrogen and oxygen is being produced two parts hydrogen one part oxygen as I am to understand.  In measuring the oxygen I can then calculate the hydrogen production.  I will also have to measure the conductivity of the solution and this will have to be maintained.  I also have an idea on the system to achieve this. also the temperature will need to be maintained.  I'm not the sort of person that get an idea and goes into it without looking at the big picture.  The hardest part for me is going to be the electronic side of things. hopefully the good people of electronic lads will be able to help me.

Thanks again Ante.

[Ante]

The PWM circuits can be

[Dazza]

Thanks again for your reply Ante.  I built the first circuit the one with the multiple MOSFETs.  It worked very well with a single MOSFETs and a small load. I'll add another MOSFETs and test it to its maximum in the next couple of days.  The MOSFETs that was available to me that seem to suit this application, in other words a bit of guesswork, is a (MTP3055E). I am unsure if the value of the resistor is correct to its Gates or even if this is what I should be using.  I have attached the datasheet.  I have an idea to add a transistor immediately before the 330 resistors and a trimport at the transistors Gates, to give me a start stop point.  Could you suggests a suitable transistor and the value of the trim port, if this will work. Yes a fuse would be a very good idea. I don't want everything going up in smoke, these things can be overlooked.  Yes it is possible to separate the oxygen from the hydrogen, this would make things very complicated.  The distance between the hydrogen oxygen being produced, and passed the Carby butterfly valve then where it will be safe.  Is very small as well as in volume, if it was to ignite the majority of the explosion would be directed to the intake of the engine. A relief valves can be used as a safety precaution two direct it away safely. I have an idea to stop the buildup on the electrodes. If I can continuously switch the power to the electrodes positive two negative this will keep them clean. do you have any ideas on how I can do this.

[Ante]

I

[Dazza]

The on-off point.  When I reduce the power to the minimum I still had power to the electrodes. This was something like less then one volt.  I was thinking a transistor at the base of the MOSFETs and a trim port at the base of the transistor. So when I increase the power to the electrodes as normal, power to the MOSFETs would only start when the transistor was turned on, and the trim port at the base of the transistor could be adjusted to give me the on-off point.  Yes the H-Bridge looks like the way to do it, although the P channel MOSFETs are a little hard for me to get hold of. I found a H-Bridge on the net that used only N channel MOSFETs (http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/h-bridge.htm) it looks a little complicated especially with having to have the voltage Doubler. The ICL7662 is the only component I am unable to get hold of.  Do you know of another voltage Doubler circuit that I can use for this.  I will also have to incorporate a circuit that will  continuously switch the H Bridge forward and reverse.  I have a circuit that is use for model railway for switching two LEDs on and off, a flip-flop. Do you think a flip-flop would be a good way of doing this, or is there another way it should be done.

Thanks Ante.

[Ante]

Is the residual voltage a problem; is the production of hydrogen greater than the idle consumption? So, the P-channel is hard to get at your location. The Blanchard site H-bridge has P-channel AND N-channel MOSFETs.  I agree this gets a bit complicated compared to an ordinary bridge. Maybe someone else reading this have a suggestion. You can use a 555 instead of the ICL7660 to create a low current negative supply if you need one. How frequent must the electrodes change polarity to keep nice and clean? I know this is answering questions with questions but I like to know as much as possible to give you the best answers I can come up with.        

[Dazza]

Sorry Ante I gave you the wrong Web address , this is the one I was referring to (http://www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/nch-brdg.htm) I've been battling the flu for the last few days, I'm not really with it .  I'm glad you're wanting more information, I was getting worried that I might be becoming a pest.  But for tonight I need to put my head on a pillow.

[Ante]

Yes, I figured that was the case after I looked around in the Blanchard place. You just rest for a few days and it will pass. Pour some good stuff in your tea or coffee and you will feel much better shortly. It