What are the Adavantages of High Amperage?

[Pharrahnox]

What are the advantages of having high amperage? By the way, I'm rather new to electronics.

I know that having high-voltage reduces the energy loss through the wire, and you don't need as thick a wire. But I cannot find the advantages of high amperage on the internet. This may be due to my bad wording of the question, or due to my lack of knowledge on the subject, however I still would like to know.

Thanks for any help, in advance.

 

[phinds]

One example of where it is advantageous (a necessity really) to have high current (and very low voltage) is in electronic welding.

It would be very dangerous to provide welding-level power using very much voltage, so typically (as I recall) welding is done with 3 volts and hundreds of amps.

 

[Drakkith]

High currents are usually needed to provide high amounts of power to something. I don't really know if there's an "advantage" or not. I always thought of current as simply the consequence of your voltage and resistance.

 

[Pharrahnox]

Thanks for the fast replies.

Why is it dangerous to have high voltage in electronic welding? Is it so that the arc cannot travel far, or doesn't want to go through your body?

 

[marcusl]

It's not so much a safety thing (welding is already plenty dangerous) but a property of the welding arc, which has very low resistance. Producing high power to melt the metal with a low resistance naturally requires high current and low voltage.

 

[Drakkith]

Thanks for the fast replies.

Why is it dangerous to have high voltage in electronic welding? Is it so that the arc cannot travel far, or doesn't want to go through your body?

I believe a higher voltage would increase the current even further.

 

[marcusl]

I believe a higher voltage would increase the current even further.

Yes but there is an optimal current for each welding job. Factors include the type of metal to be welded and its thickness, the type of filler metal, the thickness of the filler rod, and the weld process used (e.g., TIG). Increase the current too far for the conditions and you produce lousy welds and/or melt too much of the metal. 50 - 200A are commonly used.

 

[Studiot]

The magnetic effect is proportional to the current, not the voltage so any application that depends upon the magnetic effect such as electric motors and induction cookers and furnaces are controlled by current.

Electrochemical processes are current controlled so not only resistance welding but aluminium smelting, electroplating, battery charging etc.

 

[Pharrahnox]

The magnetic effect is proportional to the current, not the voltage so any application that depends upon the magnetic effect such as electric motors and induction cookers and furnaces are controlled by current.

Electrochemical processes are current controlled so not only resistance welding but aluminium smelting, electroplating, battery charging etc.

Oh, I didn't know that the magnetic effect relied on amperage. I thought it was just a higher charge in general, but this helps, as I have been interested in increasing the power of my solenoid.

 

[mfb]

If you want to generate magnetic fields with coils, current (and geometry) is the important quantity. Voltage is just a nasty by-product required to power the coils, unless they are superconducting.
As an example, the LHC uses superconducting coils with some kiloampere current in the cables. They produce a magnetic field of up to ~5T (design value is something like 9T).

 

[Caio Ferrari]

For transmitting energy, high amperages are a very bad idea due to joule effect.

The advantage is generating a large amount of magnetic filed around it.

 

[Andrew Mason]

The main reason for higher current is the need for lower voltage. For a vehicle even 100 volts would pose a significant safety hazard. The Prius uses just under 300 volts but only for the drive train functions which are heavily protected - the rest of the car uses 12 volts. If Henry Ford had used 100 volts in the Model T there would have been a lot of dead Ford owners who would not be coming back to buy another one.

AM

 

[jartsa]

What are the advantages of having high amperage? By the way, I'm rather new to electronics.

I know that having high-voltage reduces the energy loss through the wire, and you don't need as thick a wire. But I cannot find the advantages of high amperage on the internet. This may be due to my bad wording of the question, or due to my lack of knowledge on the subject, however I still would like to know.

Thanks for any help, in advance.

If the advantage of high voltage is that no thick wires are needed, then the advantage of high amperage should be that no thick electric insulation is needed.

 

[Pharrahnox]

The main reason for higher current is the need for lower voltage. For a vehicle even 100 volts would pose a significant safety hazard. The Prius uses just under 300 volts but only for the drive train functions which are heavily protected - the rest of the car uses 12 volts. If Henry Ford had used 100 volts in the Model T there would have been a lot of dead Ford owners who would not be coming back to buy another one.

AM

Why is high voltage more dangerous than high amperage?

 

[Andrew Mason]

Why is high voltage more dangerous than high amperage?

It is not. It's the amps that kills you. But in order to get high current to pass through you, you need high voltage. It is just Ohm's law. I = V/R.

Study Ohm's law first and you will understand how voltage and current are related.

AM

 

[phinds]

If the advantage of high voltage is that no thick wires are needed, then the advantage of high amperage should be that no thick electric insulation is needed.

While it is true that low voltage/high amperage wires require less insulation than the other way round, that is irrelevant to the reasons for USING them --- it's just a side effect.

 

[phinds]

Why is high voltage more dangerous than high amperage?

If you have a 10volt potential that is capable of delivering 1,000,000 amps, it will not hurt you at all to grab the leads, because low voltage won't actually USE much at all of that current capabiltiy on your high-resistance body.

If you have a 10,000 volt potential that is capable of delivering a tenth of an amp and you grab the leads, it will most likely kill you because the high voltage will push enough current through your body to do so.

 

[Drakkith]

If you look at Ohm's law, you will see that the current is determined by the voltage and resistance. When the resistance is very very low you can get a high current from even a low voltage source. However many things, such as the insulation around wires and human skin don't have low resistance. When you crank the voltage waaaay up it stars to have the ability to discharge through even high resistance objects. Once this happens you get very large currents through things that shouldn't have them. As Phinds said, a 10 volt source will not push a large current through your hands if you touch the leads, while a 10,000 volt source will.

 

[cabraham]

If you look at Ohm's law, you will see that the current is determined by the voltage and resistance. When the resistance is very very low you can get a high current from even a low voltage source. However many things, such as the insulation around wires and human skin don't have low resistance. When you crank the voltage waaaay up it stars to have the ability to discharge through even high resistance objects. Once this happens you get very large currents through things that shouldn't have them. As Phinds said, a 10 volt source will not push a large current through your hands if you touch the leads, while a 10,000 volt source will.

Only if the power source is constant voltage. With a constant current source, voltage is determined by current & resistance, but CCS is not how batteries & generators are designed. Insulators are very good, while conductors are not, so it is better to source constant voltage, i.e. the voltage is always full value, and the current varies from 0 to 100%, depending on loading.

When current is determined by voltage & resistance, that is a man made condition. It's not Mother Nature. We could design the power grid so that I is constant, V varies with R. We don't for a good reason, but we could. Voltage does not "push" the current. I don't wish to be pedantic, but I feel this needs to be mentioned.

Claude

 

[mfb]

Well, the constant current source, attached to a human body (with high resistance), would have to deliver a high voltage. And, as stated before, this is bad for humans.

 

[Drakkith]

When current is determined by voltage & resistance, that is a man made condition. It's not Mother Nature. We could design the power grid so that I is constant, V varies with R. We don't for a good reason, but we could. Voltage does not "push" the current. I don't wish to be pedantic, but I feel this needs to be mentioned.

Claude

I'm not sure what you are getting at. A circuit with a constant current must have V vary with R, as Ohm's law states. Just as a constant voltage must have I vary with R. As to voltage "pushing" current, I don't know enough about electronic circuits to be certain, but I thought that was exactly what happened.

 

[phinds]

When current is determined by voltage & resistance, that is a man made condition. It's not Mother Nature.

That seems to be saying that Ohm's Law is just some made up words that have no bearing on reality. Surely that's not what you mean?

 

[russ_watters]

No, cabraham is saying that we make voltage the independent variable and amperage the dependent -- that that is an arbitrary choice and it could just as easily be the other way around.

I beg to differ: I don't think a passive constant current source is possible. We didn't choose constant voltage supplies arbitrarily, we chose them because they are what happens naturally.

 

[Pharrahnox]

I have not read into Ohm's law much, so I never thought of current as a byproduct of volts and resistance. Does this mean that a 100 volt power source could vary its current simply by adding a thick wire to get less resistance?

 

[Studiot]

Does this mean that a 100 volt power source could vary its current simply by adding a thick wire to get less resistance?

Yes this is true.

You need to understand what is meant by a voltage source and a current source. Both of these have precise meanings so if you do not understand these meanings you can easily draw false conclusions.

A source of electrical energy is either a current source or a voltage source.
It cannot be both and in general you cannot have both in the same circuit.
Both are actually idealisations never achieved by real world components - although some are better than others.

A voltage source maintains the voltage it presents between its terminals, at a predetermined level, regardless of the current drawn from it by the circuit.

A current source maintains the current through itself regardless of the voltage the circuit imposes on its terminals.

 

[cabraham]

No, cabraham is saying that we make voltage the independent variable and amperage the dependent -- that that is an arbitrary choice and it could just as easily be the other way around.

I beg to differ: I don't think a passive constant current source is possible. We didn't choose constant voltage supplies arbitrarily, we chose them because they are what happens naturally.

Not possible? Are you serious? Take an ac generator used by the utility company. It is spun at constant speed so as to produce constant voltage. If it were spun at constant torque, the result would be a constant current source. The power company could just as well deliver to us a power source with constant current, & voltage that varies with load.

It isn't done because conductors have higher losses than insulators. A CCS generates, & transmits at full current all the time. A CVS produces ful voltage all the time, which is less lossy.

Which one is independent vs. dependent is indeed arbitrary. It could be either way. Batteries can be produced as CCS, but the performance is inferior. Nuclear batteries OTOH, are more suitable as a CCS. Search using key words "nucell", "nuclear battery".

Because CVS works better, generators & batteries are optimized for CVS operation, but this is man made. A capacitor, however, tends to maintain CVS operation. This is Mother Nature, not arbitrary. Likewise an inductor has a natural CCS modus operandi, not arbitrary.

Claude

 

[Integral]

I have not read into Ohm's law much, so I never thought of current as a byproduct of volts and resistance. Does this mean that a 100 volt power source could vary its current simply by adding a thick wire to get less resistance?

Sound like it is time for you to go read up on Ohms Law. Without knowledge of that most of what has been said in this tread is meaningless.

 

[Andrew Mason]

Not possible? Are you serious? Take an ac generator used by the utility company. It is spun at constant speed so as to produce constant voltage. If it were spun at constant torque, the result would be a constant current source.

The power company could just as well deliver to us a power source with constant current, & voltage that varies with load.

The only way this could occur is if voltage and power output decreased as load increased. That would not be very practical for a system that is supposed to provide more power if load increases.

For example, suppose you have a generator producing 100 watts of power at 100 volts and 1 amps current supplying a 100 w. lightbulb. If you added another 100 watt lightbulb in parallel, thereby doubling the load, the voltage would have to drop to 50 volts in order to keep the current a constant 1 amp (1/2 amp for each light bulb). This means the power supplied to each lightbulb would decrease to 1/4 of its previous value.

It isn't done because conductors have higher losses than insulators.

What does this statement mean?

I have to agree with Integral that you need to learn about Ohm's law before we can have a meaningful discussion here.

AM

 

[willem2]

The only way this could occur is if voltage and power output decreased as load increased. That would not be very practical for a system that is supposed to provide more power if load increases.

For example, suppose you have a generator producing 100 watts of power at 100 volts and 1 amps current supplying a 100 w. lightbulb. If you added another 100 watt lightbulb in parallel, thereby doubling the load, the voltage would have to drop to 50 volts in order to keep the current a constant 1 amp (1/2 amp for each light bulb). This means the power supplied to each lightbulb would decrease to 1/4 of its previous value.

The only way it could work, is if all your appliances and outlets were in series. To switch something off, you'd have to short-circuit it. A 100 W lightbulb would have twice the resistance of a 50 W lightbulb. An outlet would always have both sides connected, only to be broken, if you inserted a plug.
Instead of a fuse that procected against too large currents, you would have to have a fuse that protected against too large voltages and short-circuited if the voltage became too large.

 

[cabraham]

The only way this could occur is if voltage and power output decreased as load increased. That would not be very practical for a system that is supposed to provide more power if load increases.

For example, suppose you have a generator producing 100 watts of power at 100 volts and 1 amps current supplying a 100 w. lightbulb. If you added another 100 watt lightbulb in parallel, thereby doubling the load, the voltage would have to drop to 50 volts in order to keep the current a constant 1 amp (1/2 amp for each light bulb). This means the power supplied to each lightbulb would decrease to 1/4 of its previous value.

What does this statement mean?

I have to agree with Integral that you need to learn about Ohm's law before we can have a meaningful discussion here.

AM

Dude, I hate to tell you, but you are the one in need of studying. I am in the final stage of the Ph.D. in EE, & I am in my 34th year as a pro EE. You're lecturing me on what's what, so how much education do you have. BSEE, MSEE, Ph.D.?

With a CCS operating mode, the lamps are wired in series. The switch which turns the lamp on & off is placed across the lamp (in parallel). With both switches shorted, both lamps are off, since the constant current goes through the 2 switches. Opening switch A results in constant current through lamp A. Lamp B remains off since the constant current is diverted through switch B. If the lamp is a 100 ohm value, and the CCS is 1.0 amp, we get 1.0 amp always, & the voltage is 100 volts. Total power is 100 watts.

If we wish to turn on lamp B, we open switch B. Now there are 2 lamps in series, with a 1.0 amp constant current. The voltage is now 200 volts, & the power is now 200 watts. Constant current can be made to work very well, but there is a problem with it.

In the miles of transmission lines from the power plant to the home, there are insulator losses, & conductor losses. The insulator loss is V²G, & the conductor loss is I²R. It so happens that insulator loss is way smaller than that for the conductor. If we generated at transmitted at full current all the time, & variable voltage depending on load, loss is higher than the CVS method.

It's less lossy to generate & transmit at full voltage all the time with current depending on load. This is why we do so. In addition we get another benefit with CVS operation. Constant voltage is a result of constant turbine speed. A side benefit is constant frequency. Since the CVS bus is also CF (constant frequency), synchronous motors can be used for applications where fixed speed is needed. Clocks are a great example.

In addition, it pays to use transformers to raise V & lower I reducing I²R loss further. In doing so we increase V²G loss, but that loss is so tiny in comparison, it's worth it. All of these issues have been thoroughly examined for over a century. Many people do not have a need to know this, but if you have never dealt with power, sources, energy conversion, etc., how can you tell an old pro that they got it wrong?

As far as my needing to learn Ohm's law goes, all Ohm states is that the relation between V & I is R. The V/I ratio equals R. That doesn't explain the pros & cons of CVS vs. CCS operation. What I explained above requires more than Ohm's law gives us. I don't mind people asking for clarification, but I advise all reading these posts to be careful before telling someone they are wrong.

A person w/ limited technical education should think twice before rebuking someone. Learning this stuff takes many years of very intense study. Very few know this topic as well as they would like to believe. Nothing personal.

Claude

 

[truesearch]

cabraham: 'current is determined by voltage and resistance, that is a man made condition. It is not mother nature'... what do you mean by that, what physics principles are you using?
How does 'mother (father?)' nature sort this out, are we close to understanding?

 

[cabraham]

What I said was that our power sources, batteries, ac wall outlets, bench top lab supplies, car alternators, etc., are intentionally designed, built, & optimized for CVS operation. The terminal voltage is monitored & regulated to a constant value. A load placed across this CVS terminal pair has the fixed voltage value impressed upon it. The current is then computed per Ohm's Law, I = V/R.

If V is fixed, & R is fixed, then we easily can compute I per Ohm. It's pretty simple. But we need to remember that V being independent & I being dependent is so because the utility company intentionally holds the line voltage as the fixed value. It could work the other way. The power plant could configure their turbines so as to output a fixed value of current, i.e. a CCS. If our wall outlets were CCS instead of CVS, then a load plugged into an outlet would have a fixed current impressed upon it, and with a resistance value of R, the voltage is given by Ohm as V = I*R.

In the CCS case, I is independent, & V is dependent. It's a man made condition. The CVS mode is preferred because conduction loss is way lower than insulation loss. Not only is CVS used, but the value of said fixed voltage is stepped way up with transformer to great values in order to decrease the values of current. This greatly reduces conduction loss even further.

Anyway, that is my point. The notion that "V is fixed, I varies inversely with R", is a man made condition, not Mother Nature. As I said earlier, however, inductors behave like a CCS, whereas capacitors behave like a CVS. That is not man made, but that is Mother Nature. Did this help? I will elaborate if desired.

Claude

 

[truesearch]

As I understand it you cannot have a current without an emf but you can have an emf without a current. I think that power supplies are 'intentionally designed' to generate an emf rather than a current, a current needs a complete circuit... what if no one connects!...It then seems natural to design electrical appliances to operate on a constant voltage rather than a constant current.
Could a power company generate a 'constant current', waiting for consumers to connect? Are their any examples of such a thing?
I think I am also correct in saying that a constant current source has a very high (infinite) effective output resistance. A constant voltage source has a very low (zero) effective output resistance.
Look forward to enlightenment

 

[mfb]

As I understand it you cannot have a current without an emf

Superconductors can do that.

but you can have an emf without a current.

This is a good approximation.

It then seems natural to design electrical appliances to operate on a constant voltage rather than a constant current.

I think so, too.

 

[truesearch]

I just knew that some one would say superconductors... we are all here !

 

[Darwin123]

Thanks for the fast replies.

Why is it dangerous to have high voltage in electronic welding? Is it so that the arc cannot travel far, or doesn't want to go through your body?

One advantage of high amperage with low voltage is that long electric arcs are suppressed. If the voltage is small, unwanted arcs over large distances of air are suppressed. In fact, long arcs through any sort of insulator is suppressed by small voltages. The waste caused by heating of the wires is offset by the safety from long electric arcs.
A high voltage difference between any two points in the air can result in an electric arc between the two points. If the electric field strength (volts/meter) is very large, then a large electric current can be generated between the two points. If a person is between the two points, he can be electrocuted or burnt alive by the electric current. Since the distance between two points can't always be increased, electric engineers choose to decrease the voltage.
The issue concerns the electric field strength necessary to produce an arc in the air. The magnitude of an electric field is the electrical potential difference between two points divided by the distance between the two points. A commonly used unit for electric field is volts per meter.
Air is an insulator for electric fields with small magnitude. However, air becomes a conductor for electric fields with high magnitude. Ordinarily, air is an electric insulator. The current density through air is very small if the electric field is very small.
Air has a threshold electric field where the neutral molecules break down into ions. When the electric field in air exceeds this threshold, the air becomes an electrical conductor within a few milliseconds. Before it becomes an electrical conductor, the electric current can be very small. When air becomes an electrical conductor, the electric current density through the air can suddenly become very large. This produces what is called an electric arc. The electric current through the air becomes very large.
In fact, any insulator becomes a conductor when the electric field in the material becomes large enough. If the voltage divided by the distance is large enough, an electric current can go through any material.
Note that a fixed voltage difference can produce a small arc instead of a big one. In arc welding, the user wants an arc between two electrodes placed a small distance apart (say 0.01 meter). However, the user does not want an arc to pass from one electrode to the plumber pipe (ground) on the other side of his head (about 5 meters). So he wants the average voltage small enough so the electric field strength between the two electrodes is above breakdown threshold but small enough so the electric field through his head is small.
The electric current through the small gap between electrodes has to be very large in order for the arc to get hot enough to melt steel. So here is an advantage of high amperage with small voltage.

 

[Darwin123]

As I understand it you cannot have a current without an emf but you can have an emf without a current. I think that power supplies are 'intentionally designed' to generate an emf rather than a current, a current needs a complete circuit... what if no one connects!...It then seems natural to design electrical appliances to operate on a constant voltage rather than a constant current.
Could a power company generate a 'constant current', waiting for consumers to connect? Are their any examples of such a thing?
I think I am also correct in saying that a constant current source has a very high (infinite) effective output resistance. A constant voltage source has a very low (zero) effective output resistance.
Look forward to enlightenment

Yes, you can buy electric current sources. There are power controllers (sometimes called power supplies) that keep the electric current constant while changing the voltage.
Photomultiplier tubes are a type of light detector that often acts as a constant current source. When a photon hits the cathode of a photomultiplier tube, an electron is released. The electron is copied through a cascade process. So a sizable electric current can be caused by one electron hitting the photocathode. Typically, a million photons get released for every photon that hits the cathode. The number changes, but is not important.
For a fixed flux of light, the electric current generated by the photomultiplier is constant. The electric current in electrons per second is proportional to the flux of the light in photons per second. So for constant power from a light source, the electric current from the photomultiplier is constant.
Therefore, the photomultiplier is effectively a source of constant electric current. No matter what resistors that you place in the electric circuit, the photomultiplier in a steady light produces the same amount of electric current. The voltage may change as you change the resistance, but the electric current will remain the same.

There are off course caveats to what I just said about photomultiplier tubes. They do have an upper limit to the amount of current they can produce. The current is linear with light flux only over a specific range. PMTs can burn out! However, a PMT under steady light conditions should be considered as a constant current source to first order. One can make serious mistakes by assuming that the PMT to first order acts as a constant voltage source.
I want to go slightly off the topic, since you are interested in constant current sources. "Bare" photoemission devices in steady light act as sources of constant electric current. However, electrical engineers and scientists are more comfortable with constant voltage. So scientists use terminating resistors to force the photoemission devices to act as constant voltage sources.
One makes the PMT act like a constant voltage source by adding a low terminating resistance. In other words, a low resistance should be placed in parallel to the PMT if you want it to act as a constant voltage source. However, such a resistor effectively makes any constant current source into a constant voltage source.
It took some time to learn how the terminating resistor of a PMT works. It also is useful in suppressing the capacitance of the PMT, which is a related problem.
Photovoltaic devices act as constant voltage sources and photoemission devices act as constant current sources.

 

[Studiot]

As I understand it you cannot have a current without an emf

Thermionic current?

 

[Andrew Mason]

Dude, I hate to tell you, but you are the one in need of studying. I am in the final stage of the Ph.D. in EE, & I am in my 34th year as a pro EE.

Sorry about that cabraham. I was thinking I was responding to the OP who is admittedly not familiar with Ohm's law. My mistake.

AM

 

[cabraham]

No problem, apology accepted. Best regards.

Claude

 

[truesearch]

Thermionic current?...OK.. I go with that and I would even add photoelectric current

 

[cabraham]

As I understand it you cannot have a current without an emf but you can have an emf without a current. I think that power supplies are 'intentionally designed' to generate an emf rather than a current, a current needs a complete circuit... what if no one connects!...It then seems natural to design electrical appliances to operate on a constant voltage rather than a constant current.
Could a power company generate a 'constant current', waiting for consumers to connect? Are their any examples of such a thing?
I think I am also correct in saying that a constant current source has a very high (infinite) effective output resistance. A constant voltage source has a very low (zero) effective output resistance.
Look forward to enlightenment

If the power company delivered CCS instead of CVS, the customers are always "connected". The loads are stacked in a series loop, and the "circuit" is always complete, i.e. a closed loop. Each load has a shunt switch across it. To turn on, the switch is open, to turn off, switch gets shorted.

With CVS a short is a fault, so a series circuit detects overcurrent and opens. With CCS, an open is a fault resulting in overvoltage. A shunt circuit "maker" closes when this happens.

With CCS, you have to flip your thinking. Loads are in series instead of parallel, switches are in parallel instead of series, switches and circuit makers open for ON, closed for OFF. These are the opposite of that with CVS. They are analagous.

Again, CCS works just fine with any load. We just have to make mental adjustments. At stall, a motor is a near short. With CCS, the synchronous motor would not work. A CCS system has variable frequency, so other means, such as servo control using a frequency reference, would be needed to maintain constant speed. Likewise induction motors would run at varying speed.

If speed does not need to be fixed, CCS works. Like I said, we have to adjust our thinking from a Thevenin system to Norton. That gives many trouble.

Claude