Hi All,
First, I am not at all knowledgeable about electronics, I don’t know if this can be done or if its basic knowledge but here goes…
I need to be able to take a 12 volt current and reverse the positive to negative in pulses automatically.
Can this be done and if so how?
Thanks
CB

 

It would help if you would explain more about your application.

Is it to operate a DC motor in forward and reverse directions?

How rapidly do you need the changes in polarity to occur?

How much current will be involved at 12v? If you don't know the current, how about power in Watts?

If the changes are slow in frequency, you could use a pair of single-pole double-throw relays to reverse the current flow through a motor.

You could also use an all-electronic circuit known as an "H-bridge", which consists of four transistors or MOSFETs and associated drive circuitry.

But we need to know more about what it is that you are trying to do.

 

Yes, but how much current do you need? A 555, capacitvly coupled to a negative output half-wave V doubler will give a neg output of around 50 mA, pure guestimate.

 

It would help if you would explain more about your application.

Is it to operate a DC motor in forward and reverse directions?

How rapidly do you need the changes in polarity to occur?

How much current will be involved at 12v? If you don't know the current, how about power in Watts?

If the changes are slow in frequency, you could use a pair of single-pole double-throw relays to reverse the current flow through a motor.

You could also use an all-electronic circuit known as an "H-bridge", which consists of four transistors or MOSFETs and associated drive circuitry.

But we need to know more about what it is that you are trying to do.

Experimenting with electrodes and hho production.
12v DC 18amps
Pulse Width modulator
If I could change electrode polarity at frecquency this could possibly slow down cathode degeneration while still maintaing production.
Maybe I wrong I don't know?
BTW Thanks for the quick reply!

 

HHO production.

Doesn't work, unless you want to make Browns Gas for welding.

 

Experimenting with electrodes and hho production.
12v DC 18amps
Pulse Width modulator
If I could change electrode polarity at frecquency this could possibly slow down cathode degeneration while still maintaing production.
Maybe I wrong I don't know?
BTW Thanks for the quick reply!

H-Bridge
“The H-Bridge arrangement is generally used to reverse the polarity..."
http://en.wikipedia.org/wiki/H-bridge

-Adam-

 

Doesn't work, unless you want to make Browns Gas for welding.

Pardon me for not understanding your response but what doesn't work and if I'm not mistakin, Brows Gas and HHO are one in the same.
Not tryin to be rude, just tryin to understand.
CB

 

Are you trying to run your car on HHO?

 

Are you trying to run your car on HHO?

No, nothing like that, although it would be nice.
Just tryin something different.

 

You might want to read this
http://www.aardvark.co.nz/hho_scam.shtml

 

Oh boy, here we go again.

If you are talking about a single "electrolyzer" cell (or whatever they're calling them nowadays) the voltage across the cell will be around 1.5v to 2.7v, depending upon the electrolyte used in the water, and it's concentration. Be warned, some of the chemicals being used can cause poisonous gas to be emitted along with the hydrogen and oxygen gas. Also, some can be quite corrosive.

Getting back to the 1.5 to 2.7v drop per cell, attempting to limit current by PWM alone will be futile, as you will either have maximum current flow, or zero current flow. During maximum current flow (perhaps 80 Amperes or so), the excess current would simply heat your electrolyte solution. During zero current flow, no gas is produced.

So, you would have a 25% ON duty cycle where some gas was produced and the electrolyte solution was heated, the remaining 75% duty cycle no gas would be produced.

You would actually need a high-power Buck type, sepic type, or flyback current regulator to regulate the current in a somewhat efficient manner. If multiple cells were used in series, then a Buck type current regulator could be used. You would have to do your own research on that. I really have no interest in fruitless endeavors.

Switching 18A-20A current back and fourth quickly is a non-trivial matter, particularly at higher frequencies; after a certain threshold you expend a lot of power simply turning gates of MOSFETs on and off.

We seem to get someone inquiring about these hydrogen/oxygen generation things at least once a month. There are some people making a lot of money from it; those who are selling plans and equipment to hopeful experimenters who believe the hype of fuel mileage increases of up to 70%.

The facts are that only a very few actually receive any actual increase in fuel economy, and much of that is achieved by different driving habits, tire inflation, and tuning of the engine.

There are a far greater number of people out there who have had very expensive repair bills for blown engines, burned valves, cracked pistons, broken rings, engine fires, and other disasters. They're out both the time and money expended on their project, and many times their vehicle as well.

 

You might want to read this
http://www.aardvark.co.nz/hho_scam.shtml

I understand how you feel and you have made your point, but…
Again, I am not trying to run my car on HHO although you may want to check this out.
http://www.youtube.com/watch?v=jhIYHemOCNE
I can however produce enough on demand HHO to heat a 1000 sq ft at 450 watts with that welding torch you were talking about.
http://www.hhohhu.com
I’ve always been a firm believer in the old sayin, “Can’t Never Could Do Nothin”!
Now that we have that out of the way, can you or anyone answer the original question?

 

Oh boy, here we go again.

If you are talking about a single "electrolyzer" cell (or whatever they're calling them nowadays) the voltage across the cell will be around 1.5v to 2.7v, depending upon the electrolyte used in the water, and it's concentration. Be warned, some of the chemicals being used can cause poisonous gas to be emitted along with the hydrogen and oxygen gas. Also, some can be quite corrosive.

Getting back to the 1.5 to 2.7v drop per cell, attempting to limit current by PWM alone will be futile, as you will either have maximum current flow, or zero current flow. During maximum current flow (perhaps 80 Amperes or so), the excess current would simply heat your electrolyte solution. During zero current flow, no gas is produced.

So, you would have a 25% ON duty cycle where some gas was produced and the electrolyte solution was heated, the remaining 75% duty cycle no gas would be produced.

You would actually need a high-power Buck type, sepic type, or flyback current regulator to regulate the current in a somewhat efficient manner. If multiple cells were used in series, then a Buck type current regulator could be used. You would have to do your own research on that. I really have no interest in fruitless endeavors.

Switching 18A-20A current back and fourth quickly is a non-trivial matter, particularly at higher frequencies; after a certain threshold you expend a lot of power simply turning gates of MOSFETs on and off.

We seem to get someone inquiring about these hydrogen/oxygen generation things at least once a month. There are some people making a lot of money from it; those who are selling plans and equipment to hopeful experimenters who believe the hype of fuel mileage increases of up to 70%.

The facts are that only a very few actually receive any actual increase in fuel economy, and much of that is achieved by different driving habits, tire inflation, and tuning of the engine.

There are a far greater number of people out there who have had very expensive repair bills for blown engines, burned valves, cracked pistons, broken rings, engine fires, and other disasters. They're out both the time and money expended on their project, and many times their vehicle as well.

OK, Thats enough!
It seems that on every forum there is always a know it all, rude person who wants to voice thier opinion regardless of whether it is requested or not!
I asked what should have been a simple question and I am now berated by the forum bully. I didn't ask your opinion of HHO and of using it to fuel cars or anything else.
Thanks anyway!

 

I am now berated by the forum bully

No, not at all. The majority of SgtWookie's response was informative. This last part -

We seem to get someone inquiring about these hydrogen/oxygen generation things at least once a month. There are some people making a lot of money from it; those who are selling plans and equipment to hopeful experimenters who believe the hype of fuel mileage increases of up to 70%.

The facts are that only a very few actually receive any actual increase in fuel economy, and much of that is achieved by different driving habits, tire inflation, and tuning of the engine.

There are a far greater number of people out there who have had very expensive repair bills for blown engines, burned valves, cracked pistons, broken rings, engine fires, and other disasters. They're out both the time and money expended on their project, and many times their vehicle as well.

- was simply stating our extensive experience with such questions and the usually intended application.

As you say your interest is not in mileage increase or overunity electrolysis, why do you feel bullied? None of the commentary seemed to be aimed at you.

One fact you might be interested in, though - the conversion of electricity to heat is very nearly 100%. The efficiency of hydrolyzing water and later burning it returns less than 80% of the energy expended. The mixture of gaseous hydrogen and oxygen is quite explosive, as well. Any failure in whatever protective mechanism you may have devised and you and your house go into low orbit.

If you want to try electrolysis, make a cell such that the hydrogen and oxygen gas produced can be collected separately. It's too much like cooking up nitroglycerin on you stovetop, otherwise.

Follow this link - http://forum.allaboutcircuits.com/showthread.php?t=28067 - and you will see why we do not approach new thread on the subject with open arms.

 

OK, Thats enough!
It seems that on every forum there is always a know it all, rude person who wants to voice thier opinion regardless of whether it is requested or not!
I asked what should have been a simple question and I am now berated by the forum bully. I didn't ask your opinion of HHO and of using it to fuel cars or anything else.
Thanks anyway!

Gee, I wasn't attempting to bully you at all - just giving you the facts as I understand them.

You asked how to reverse the flow of electricity, and I mentioned two methods that could be used:
1) Relays, for low frequency switching.
2) H-bridges, for higher frequency switching.
3) And if you want to go even higher, you could use (a) transformer(s). You'd have to wind your own, though - using a toroidal core would likely be the most efficient. Transformer design and construction is in itself a pretty specialized field.

You mentioned that you wanted to limit current to around 18A using PWM. I gave you the reasons why that was a bad idea, and gave you several alternatives, all of which will require research.

I also warned you about possible dangers of poison gas generation and corrosive electrolytes some use, without mentioning specifics.

Generating hydrogen and oxygen via electrolysis is not very efficient. At the very best, you'll get 70% power out for power in. If you're burning the hydrogen and oxygen gases to heat a room, you probably wouldn't notice the difference in efficiency over using a typical room heater, as either way all the power expended will remain in the room as heat. However, the addition of hydrogen and oxygen gases represent a potentially explosive combination, particularly if generated in large quantities.

If you want to explore more efficient methods of obtaining hydrogen, look at the methane steam reformation process; it's currently the most efficient method.

[eta]
More about changing polarities during electrolysis;
Hydrogen bubbles appear on the cathode (negatively charged plate), and oxygen bubbles appear on the anode (positively charged plate).

If you are using DC for the electrolysis, it is a relatively trivial matter to keep the two gases separated. However, if you start alternating the polarity of the anodes/cathodes, you will wind up with mixed gases; and there will not be an easy way to separate the two. Allowing the mixed gases to accumulate in even small quantities can be extremely hazardous.

There ARE valid reasons for on-demand hydrogen/oxygen generation. Off the top of my head, welding would be the best one. Sure, it's nowhere near 100% efficient; but it sure beats driving down to a gas sales place and getting tanks filled.

 

What frequency do you need? Hz, kHz, MHz, GHz?

 

Pardon me for not understanding your response but what doesn't work and if I'm not mistakin, Brows Gas and HHO are one in the same.
Not tryin to be rude, just tryin to understand.
CB

OK, so Brown's gas and HHO are the same. What is HHO?

John

 

I say go for it;

commercial fuel cell development has slowed in the past due to a declining call for alternative fuels, as have other hydrogen consumptive techniques.

Energy recovery of Fuel Hydrogen, derived from electricity is a poor efficiency investment, unless it is immediate and closed loop. This generally means that much work is required to bring it into consumers laps.

On the horizon is large scale hyrdogen rich fuels. We need to be ready to put them to use.

Answering the OP, you can manipulate the current/ voltage almost infinitely.

 

OK, so Brown's gas and HHO are the same. What is HHO?

It's a stoichiometric mix of hydrogen and oxygen gases. Two parts hydrogen, one part oxygen.

When "HHO" is mentioned I always think of Marvin the Martian saying,
"Where's the Kaboom? There was supposed to be an earth-shattering Kaboom?"

 

We all look forward to the new guy who will beat the law of conservation of energy. Nobel prize here they come ( unless it turns out to be the Darwin award ) I appoligize for the snarky nature of the above.