Amperage is the amount of electrons flowing by a curtain point so wouldn't that be the quantity. As voltage is the potential difference or the push / pressure of a circuit.
Posted by Monte L Fullmer (Member # 2797) on 12-26-2009, 01:39 AM:
Guess, we can use the analogy of a garden hose to this topic then:
the inside diameter being the voltage and the flow of water out of the hose being the current.
-Monte
Posted by John Hawkinson (Member # 1135) on 12-26-2009, 09:25 AM:
Err...voltage and current are inexorably linked. You can't really change one without the other changing.
When we say "Xenon lamps are current-controlled" what we really mean is that there is a very small voltage variation for a rather large current variation. Change the voltage by a little, and the current can change a lot. Change the current by a little, and the voltage change is almost imperceptible.
So really it comes down to how you think about it. You can think about the rectifier changing its output voltage to change the lamp's applied current. This tends to make sense to me, but it's not the only legitimate interpretation.
It is true that you can't really think about the current without knowing the characteristics of the load (the lamp), whereas its easy to think about the voltage without the load. But of course, the load characteristics of the lamp are radically different before and after striking...
Monte, switching power supplies do not switch at 60 Hz. They switch a thousand times faster (in the kHz), and then that switched voltage is filtered to look like smooth DC, but there is always some ripple (just as there is with traditional high-reactance power supplies).
--jhawk
Posted by Randy Stankey (Member # 64) on 12-26-2009, 10:08 AM:
Generally speaking... If you are talking about electricity going through a transformer, changing the ratio of primary windings to secondary windings (AKA: "Taps") will vary the voltage coming out of the secondary, assuming the voltage going into the primary is constant. Current generally obeys Ohm's Law.
Now, if you have a regulated power supply there are many kinds of components which can be used to ensure the output stays within a certain range, it is possible to regulate current. Some of those power supplies can be very complicated.
When a power supply is built, regardless of the type, it will engineered from the ground up to supply voltage and current within certain ranges. Therefore, in operation, resetting the taps will vary the voltage and the current according to the laws of physics/electronics but, if the device is operating the way it is supposed to, you should not see current or voltage go outside the limits that the xenon lamp can handle.
Posted by Louis Bornwasser (Member # 3063) on 12-26-2009, 10:10 AM:
For years I have hoped (given that we measure both voltage and current on the meter board) that we could get a direct reading in WATTS. Should be simple with the addition of only one chip. We already have the digital display and the volt/amp switch.
Further, a limit could be preset internally to turn off the power if current exceeded a certain level, depending on the bulb and power supply. (For example 2200 watts on a 2000 watt bulb.) Louis
Posted by Steve Guttag (Member # 268) on 12-26-2009, 10:19 AM:
Irem does that on their "EX" series switch mode supplies.
Posted by John Hawkinson (Member # 1135) on 12-26-2009, 10:29 AM:
Louis, why is a display of watts useful?
A reasonably wide display of voltage is helpful in diagnosing striking problems (is the no-load voltage sufficient to strike?) and once you've struck, as long as the voltage is near the nominal operating point (e.g. 28V for a 2k), it's not very interesting.
Current is what the bulb is actually rated in, and is what matters for ohmic heating of components (I^2*R) and I think is also what the luminous flux is proportional to. It's what the bulb datasheet rates the bulb in terms of.
As the bulb ages, the cathode tip erodes (from striking), and that causes the operating voltage of the lamp to rise. If you maintained constant-current as this happened, then the power draw (watts) of the bulb would grow without the brightness growing. (Of course, that's not what actually happens. Since the rectifier probably tends to maintain constant-wattage output, meaning as the bulb's required voltage increases its current draw changes and it's necessary to adjust the rectifier's current control to get the same current through the bulb...; and of course there's also the fact that the same current will produce lower brightness from a bulb as it ages...blackening? not sure what the mechanisms there are...)
So why do you want watts? Sure, it's the product of volts*amps, but if, e.g, your voltage is at 28.0V and you are running at 80A, that's 2240W, but still perfectly OK on a 2k bulb. And if your voltage rises to 30.0V and you're still at 80A, that's 2400W, but it's still within the current-control range of the bulb. On the other hand, if your current rose to 85A (the maximum by the datasheet) and your voltage was still at 28V, then your power would be 2380W, but you would *not* be ok (redlining the bulb). So 2400W could reflect a reasonable current with a high-but-acceptable voltage, which is fine. But it could also by a normal voltage with a too-high current, which is not fine.
I guess cooling capacity of the lamphouse is measured in watts, but one would think that a reasonably-designed lamphouse would deal adequately with the full range of a 2k lamp (famous last words...)
--jhawk
Posted by Mark Gulbrandsen (Member # 72) on 12-26-2009, 12:39 PM:
Actually the latest version of the Strong switcher is based on a 60khz oscillator. Although I repair a gob of these I've never bothered to look at the exact switching frequency with a scope...
Mark
Posted by John Hawkinson (Member # 1135) on 12-26-2009, 02:10 PM:
60 kHz = 60 Hz * 1000
not exactly the same...
Posted by Kenneth Wuepper (Member # 1174) on 12-26-2009, 05:08 PM:
Monte,
I just have to clarify your hose analogy for the sake of future readers of this thread.
In Ohm's Law, Current equals Voltage divided by Resistance. (I=E/R)
To use the garden hose analogy, The pressure of the water is the Voltage, The cross section area of the hose is the Resistance and the water flow is the Current.
This is an easy analogy to use if the components are properly identified.
I hope this is helpful.
KEN
Posted by Randy Stankey (Member # 64) on 12-26-2009, 05:39 PM:
I often use the "cars traveling down a freeway" analogy where the number of cars passing a given point every second equals "current", the average speed of the cars passing that point equals "potential" and the number of lanes on the freeway is resistance.
Posted by Kenneth Wuepper (Member # 1174) on 12-26-2009, 06:53 PM:
The problem with the hose analogy is that the bigger the hose the LESS resistance to flow so it has an inverse relationship and that is where the analogy breaks down.
KEN
Posted by Monte L Fullmer (Member # 2797) on 12-26-2009, 07:01 PM:
Whoops, I forgot to put the "k" in the "60" kilohertz thingey ..(my bad on that one) - why John had to make the correction.
Thx Ken, I knew that I was missing something with that analogy. Even though I knew of the "PIE" formula to get the wattage.
-Monte
Posted by Tim Reed (Member # 137) on 12-26-2009, 07:45 PM:
I was going to suggest Monte probably meant 60 KHz. ![[Smile]](smile.gif)
The relationship of voltage, current, and resistance is often difficult to comprehend at first blush. Especially if you are someone like me, who never took algebra in high school. I know I had a heck of a time understanding exactly what current is. I kept thinking two-dimensionally (for lack of a better term), as if current were an "applied" value rather than the *result* of the voltage and resistance/reactance.
Once I "let the current flow as it may" in my head, it all came together for me and I could visualize that eternal relationship.
Posted by Steve Guttag (Member # 268) on 12-26-2009, 08:01 PM:
I'm guessing you never got transistors, then ...you know current-controlled current-sources (ICIS).
Posted by Tim Reed (Member # 137) on 12-26-2009, 08:41 PM:
Okay, Steve. Back to your corner.
Posted by Steve Guttag (Member # 268) on 12-26-2009, 08:53 PM:
I guess Jhawk was right (inside comment)
Steve
Posted by Sean McKinnon (Member # 612) on 12-29-2009, 10:48 AM:
I was told one by a nuclear physicist (sp?) that there is no such word as "amperage" and that you don't measure "amperage" you measure "current" with the measurement of "amperes" so according to him you should say "how does the power supply regulate the current..."
I don't know if he was correct as I see a LOT of people (electrical engineers etc...) use the term "Amperage" but now everytime I see or hear it it drives me crazy and makes my brain hurt!
Can someone help me out here and settle wether or not "Amperage" is really a word? If so is it more correct to say "Measure the current" or "measure the amperage"?
Thank you in advance!
Posted by Stephen Furley (Member # 1277) on 12-29-2009, 11:32 AM:
I would say current. Certain other comparable terms are used, mileage, footage and tonage for example, but you measure the flow of water, not the gallonage. You don't seem to hear this sort of usage with S.I. units either, but somebody will doubtless think of an example of it.
To 'measure the Amperage' seems to mean to measure some unspecified property of something in Amperes; since the only thing measured in Amperes is current, and the only unit current is normally measured in is the Ampere, the two terms mean pretty much the same thing in this case.
If you ask somebody to measure the footage of a reel of film you're asking them to measure some property of it, presumably the length since you wouldn't normally measure the width or thickness of it that way, in feet. If you asked them to measure the length of it then they might give you an answer in metres, for example, or if they felt like being awkward, in furlongs, chains, cubits, or whatever.
If you just asked somebody to measure the film you could mean to measure any property of it, the weight for example, or the optical density of the base. You might not normally do this, but if you'd just been discussing the density of various film bases with somebody, and you handed them some film and said 'measure this piece', they would probably interpret this as meaning measure the density, not the length.
Posted by John Hawkinson (Member # 1135) on 12-29-2009, 11:39 AM:
Sean, amperage is a word.
Many people like the word current better, but amperage is a fine choice. The OED (Oxford English Dictionary) says it has been around since 1894. It is in no way ambiguous. Often when people are particular about words, it is because the choice of word matters, and some people mean one thing with one word, and another thing with a different word, and mixing them up can cause confusion. That is in no way the case here.
It's a lot like "megahertz" versus "megacycles." Or maybe "pop," "soda," "tonic," to refer to carbonated beverages like Coca-Cola -- regional variation. (And, if you're in some strange parts of the US, they refer to all such drinks, including Pepsi, as "coke." I think this is in the South, but I'm not 100% sure.)
Please note, seperately, that ampacity is yet another word, which means something different entirely ("current-carrying capacity of a conductor"), and has no convenient short substitute.
Some people may prefer to use amperage because they like to honor André-Marie Ampère, who was active in the discovery of electromagnetism theory; that seems a fine reason. Probably most people do it because that's how they were taught, but that's absolutely OK as well.
Stephen: There are plenty of other units people use for current. You might argue it doesn't count since it's just a prefix change, but plenty of people measure current in milliamperes and nanoamperes, especially when dealing with circuit design. I think some physicists who are big on CGS units measure current in Fr/s (Franklin/second)... But yes, among normal people the ampere pretty much rules the day.
--jhawk
Posted by Mark Gulbrandsen (Member # 72) on 12-29-2009, 11:59 AM:
It's back to Wikipedia for some of you as well as Sean's Physicist friend! Or perhaps to say Current and Amperage are the same thing...
Posted by Steve Guttag (Member # 268) on 12-29-2009, 11:59 AM:
It would be tough to allow voltage and not allow amperage. You are comfortable using the word current since it is a nice neat word. For voltage, you have "electro-motive force" and "Potential Difference"...neither neat so Volts or Voltage it is. And with that, you have to accept Amperage. Personally, I use current.
Posted by Randy Stankey (Member # 64) on 12-29-2009, 12:12 PM:
The word "Amperage" is like the word "Yardage."
"Yardage" refers to a quantity of distance, measured in yards.
"Amperage" refers to a quantity of current, measured in amps.
While I would prefer to use the word "current" or, if speaking in terms of a quantity of electric current measured in amps, simply saying "amps," I often accept the use of the word "amperage" if the person is speaking in non-specific terms.
For instance, when working on the stage, you'll often hear people discussing their lighting rig and the amount of electric current being used in terms of "amperage."
e.g. - "That's way too much amperage for those cables!"
However, when speaking in specific things I expect people to use the word "current" or simply "amps."
e.g. - "How much current can those cables handle?" OR "Those cables can only handle 20 amps."
Posted by Stephen Furley (Member # 1277) on 12-29-2009, 12:29 PM:
Fair point Steve; you're right of course. I don't have any objection to Amperage, but I would tend to say current. I suppose the most complete way would be to specify both the property you want measured, and the unit that you want the answer in, 'measure the current in Amperes' or 'measure the Amperage of the current', but that sounds a bit odd, and in this case is redundant, since by specifying either the property or the unit the meaning is clear and unambiguous; you don't need both.
As to the SI units thing, we have the exception here of course; the Ampere is an SI unit. It does seem to be the exceptio though, I've never heard of litreage, metreage, kilogrammeage for example.
Voltage is rather like the 'Auditoria' vs 'Auditoriums', which comes up here from time. I would never say 'auditoriums'; to me it sounds awful, and it's a horrible word to say, whereas 'auditoria' sounds fine, and is easy to say. The problem of course is that somebody then brings up the example of 'forums', which sounds fine to me, while 'forua' just sounds wrong. I don't really know why.
How on Earth did I ever manage to learn to speak English, without even having the benefit if knowing another language first in which things could be explained to me? I find it almost impossibly difficult to learn another language now.
Posted by Monte L Fullmer (Member # 2797) on 12-29-2009, 12:34 PM:
Yet, it's interesting that Mike C. has never came back in on this thread to see if his question has been answered, which was would be the answer to his question?
Don't you love threads like this when one person starts a thread, but never returns?
-Monte
Posted by Mike Croaro (Member # 3123) on 12-29-2009, 06:31 PM:
Hi Monte; Folks:
I've been letting the various answers accumulate. Thank you everyone for your various explanations.
So if I undertsand all the answers the knob controls the amount of voltage supplied the lamp.
STEPHEN WROTE:
"I would never say 'auditoriums'; to me it sounds awful, and it's a horrible word to say, whereas 'auditoria' sounds fine..."
I can';t stand it when people call the auditoira "rooms". I.E. "We saw Avatar in the large room". "What room is Indiana Jones playing in"?
Mike
Posted by Ken Lackner (Member # 1002) on 12-29-2009, 06:55 PM:
I never heard auditoriums (sorry, that's the way I've always heard it and said it) referred to as "rooms" until I moved to Los Angeles. I found it quite common out there. It never bothered me, and if fact, I started using it myself.
For example: "I need to tune this room." (My personal favorite. ![[Big Grin]](biggrin.gif)
)
Posted by Monte L Fullmer (Member # 2797) on 12-29-2009, 07:10 PM:
I'm a "house" guy - "What house is that movie playing in..?"
Posted by Ian Parfrey (Member # 5122) on 12-29-2009, 07:42 PM:
I like "screen"...as in "What screen is that playing in?"
For Drive-ins, my preference is "field"...as in "Avatar-The Director's Cut, 573 mins- is playing on Field 2".
Aint personal preferences wonderful?
Posted by Tristan Lane (Member # 1169) on 12-29-2009, 08:44 PM:
It must be a Nampa thing...I call em' houses too.
Posted by Monte L Fullmer (Member # 2797) on 12-29-2009, 09:40 PM:
Posted by Sean McKinnon (Member # 612) on 12-30-2009, 11:37 AM:
Thanks for all the replies! I can now finally stop from cringing every time I hear someone say "Amperage"
On a side I did ask why "Voltage" was ok and was told it's because voltage is another term for "electromotive force" as well as a measurement but that "Ampere" is purely a measurement. However, I am not going to argue with the oxford english dictionary! Thanks JHawk for settling this one, it's been driving me nuts for years!
Posted by System Notices (Member # 2357) on 03-03-2011, 11:13 AM:
It has been 427 days since the last post.
Posted by Bill Yacey (Member # 6102) on 03-03-2011, 11:13 AM:
I realize this is an old post, but I thought I might have something to add here. In a simple electric circuit with a fixed resistance (load) value, current will increase or decrease in a linear manner as the voltage goes up or down. The resistance is the constant.
Arc lamps which are a variety of lamp that operates by ionizing the gas between the electrodes. Neon and other gaseous filled lamps operate on the same basic premise of ionization. One of the important characteristics of this type of lamp is that it tends to self regulate the voltage applied across the electrodes once the arc is struck. In trying to increase the voltage across the lamp, the voltage will not increase in a linear manner, in fact it remains for all intents and purposes a constant.
Most of the deviation from this constant is due to electrode erosion which changes the gap length as the bulb ages during use, and also by contamination withing the bulb envelope changing the characteristics of the arc conduction.
However, upon trying to increase the voltage, the current will readily increase, utilizing more power and generating more light output yet the arc will still clamp the voltage and prevents it from rising.
Early voltage regulator circuits actually used neon or other ionized gas bulbs for a constant voltage reference prior to the introduction of zener diodes in electronics.
As an example, if the voltage across the bulb is 24VDC after the arc is struck and stabilized, and the current measured is 68.5 Amperes, using ohms law we come up with a resistance value of the arc at .35 ohms. 24Vdc divided by x resistance in Ohms equals the current in Amperes.
In the real world according to Ohms Law, something has to change before the current can change if the voltage is constant. This only leaves the resistance value. By increasing the current, this causes the ionized gas resistance to lower, or conversely to go up in resistance as the current is decreased.
I hope this helps to explain the current vs voltage theory regarding lamp supplies.
Posted by Robert Minichino (Member # 3495) on 03-03-2011, 12:42 PM:
Any power supply is built specifically to attempt to hold its output to a particular range of voltage, current, and/or power.
Most familiar power supplies are approximations of voltage sources, which mean they try to hold their voltage constant as the load changes by varying current. Arc lighting power supplies (and welders) are approximations of current sources, which mean they try to keep their output current constant as the load varies by varying their voltage. A constant-power supply is somewhat exotic, but attempts to supply a constant power into the load by varying voltage and current together.
For the simplest cases, Ohm's law says that the voltage drop across a load is proportional to the current through it, with the scale factor being a fixed property of the load called resistance. Ohm's law doesn't apply in every case, but it is useful even where it doesn't strictly apply. We can use Ohm's law in a case where the resistance isn't constant by specifying the resistance at a given current.
The resistance of most real devices changes, usually with the current passing through the device. A wire, a simple resistor, and an incandescent light bulb will all have a higher resistance as they gets hotter, and they get hotter with more power dissipation, which generally means more current. This results in somewhat non-linear behavior, but it's self-limiting, since a higher resistance with a common voltage source means that less current flows (back to Ohm's law here).
As Bill explained above, Xenon bulbs, and other arcs, aren't ohmic devices, and their resistance actually decreases with increased current. This means that as you pass more current through the arc it becomes a better conductor. If you hook an arc up to a voltage source, it will draw more and more current until the voltage source is maxed out. This seems to be an application crying out for a current source, particularly since lamp brightness is related to current, and we want to keep the brightness constant.
A voltage source "likes" an open circuit (infinite resistance), because it doesn't need to supply any current to get the desired voltage across its terminals, and it "hates" a short circuit (zero resistance), because it would need to supply infinite current to get the desired voltage across its terminals. Non-ideal voltage sources (i.e. real ones) vary from this behavior because they 1) can't supply infinite current; and 2) let the voltage vary a little as the load varies. We generally represent the first shortcoming as a specification sticker slapped on the supply (5V @ 3A), and the second we represent as an ideal resistor in series with an ideal voltage source.
A current source "likes" a short circuit because it doesn't need to produce any voltage difference between its terminals to get a given current to flow, and it "hates" an open circuit because it needs to supply infinite voltage to get a current to flow. Here, current sources fall from the ideal by 1) not being able to supply infinite voltage, and 2) allowing the current to vary a little as the load changes. We represent the first shortcoming as the current source's open-circuit voltage, and the second as a resistor in parallel with an ideal current source.
In an arc power supply, the open circuit voltage is the striking voltage, and the voltage drops as the arc starts, because the load resistance drops with the higher current.
A really neat trick is that a non-ideal voltage source can be implemented as a non-ideal current source, and vice versa. A 10A current source with a 50V open circuit voltage can be represented as a 50V voltage source in series with a 5 ohm resistor. When this current source is shorted, you get 10A. Of course, if the resistance is higher, the current is actually lower, so this is not an ideal current source, but it can act like a current source for a given range of loads.
This is exactly how the current was regulated in the old motor-generator days with carbon arcs. Large rheostats were placed in series with a DC generator (which is a very good approximation of a voltage source), and the resistance was varied until the arc current was approximately correct. The high-reactance supplies were way better, because instead of wasting a lot of power in the rheostat, they used a specially-wound transformer that had a lot of "virtual" resistance that didn't result in actual power dissipation. Even better are the newer switching power supplies that use transistors and feedback to monitor the output current and vary the output voltage based on the current set point. These use transistors that are either on or off, so very little power is dissipated in them (if they're on, there's little voltage across them, so P=0*I = 0, ideally, and if they're off, no current flows P=V*0 = 0), and an inductor smooths the pulses into a nice constant flow. Since the transistors switch at a very high frequency, the size of the magnetics are much smaller than the 50 or 60 Hz transformers.
But all the power supplies work on the same principle: they try to keep some aspect of their output constant as the load varies.