Getting to grips with AC

Greetings All
I'm trying to get to grips with regular household AC. I understand the
basics from a electronics and DC understanding, but never got to grasp the
AC side of things. Thus I'm seeking your input and clarity if at all
1] Regular power supply from a utility company is at 120 V AC, does the
current then vary, based on the number of devices or appliances that
are running or is this fixed also?
2] One can use a transformer to increase or step up voltage from 12 to 120
1:10, what does this do to the current, keep it the same step it down
or what? If it loses current, then how can one create or induce
additional current, in order to increase the wattage (Volts x Amps) in the
3] AC was chosen was the standard means of electrical supply due to
transmission length. Yet most appliances convert this to DC. Can one
effectively convert all incoming electrical supply to DC, and yet still
connect the appliances or would the appliances have to be modified?
For example we can call our appliances computer, monitor and printer?
4] How does Watts, WattHours and Joules all relate to each other?
Thank you in advance, I look forward to your replies
Reply to
Barry Fawthrop
Loading thread data ...
--------- It varies (similar to DC case at fixed voltage as in a car) ----------
---------- In an ideal transformer V*I on one side =V*I on the other side --volt-amps constant. Real transformers are close to ideal. In your step up12/120 V case, 1 A at 120 V would produce a current of 10A at 12V (plus a smidgeon due to this being a non-ideal world). --------------
The choice of AC for transmission is due to the ease of changing voltage levels to those optimal for the purpose by use of transformers. Also AC motors and generators are cheaper, simpler and require less maintenance than DC machines. If you want to tie together a variety of sources and loads- AC is used. An interconnected grid such as we have is not feasible with DC. However there are length limits with AC so that nowadays there are high voltage DC lines in the limited cases where they provide economic or technical advantages. If you want to transmit (point to point)2000MW over 800miles- then HVDC is generally the best choice (at say +/- 600,000V to ground). If you want to connect two systems which may not be at the same frequency or run long underwater cables- DC is beneficial. THe HV DC is prodced using AC and rectifier/ inverters so does depend on AC systems.
Most appliances do not convert to DC. Motors in your home, lamps, heaters, etc are AC. For these, conversion to DC would be a waste of time, money and energy. Only the electronic loads require conversion to DC-generally at a lower voltage. ---------------------------------
what about refridgerator, stove and heaters/air conditioners? These take more energy. -----------
Power is in watts and is the rate of change of energy (1 watt=1 Joule/second) Energy is in Joules or watt-hours (1 watt-hour =3600 Joules)
You're welcome
Reply to
Don Kelly
The current supplied to (say) your house varies. Not sure re the USA, but in the UK up to about 80A @ 220V.
You can't. Essentially x Watts into the transformer, x Watts out. Full stop. (In practice a bit less due to losses in the transformer.)
Eg. 120V into the primary of a 10:1 transformer gives 12V out of the secondary.
If the secondary current (load) is 10 A (ie 120W ) he primary current will be 1A (also 120W, ignoring losses).
In general, yes they would need modification. Some may be OK on DC.
Depends on model- I've seen some Laptop PSUs that will accept AC or DC.
The Watt is a measure of Power.. Power in an electrical circuit is Current x Voltage.
WattHours is energy, power consumed over a period of time. In this case, at the rate of 1W per hour.
Joule is also energy, 1 Watt = 1 J / s
Reply to
Brian Reay
Thank you to Brian and Don for you clarification to my questions It really made sense, Thank You
I understand that a battery creates Voltage, but what can be used to create Amps ?
I understand what was said on the transformers Watts in = Watts out So if Voltage Increases the Amps have to decrease by the same ratio.
Are there any options where you can increase Voltage and yet keep the same Amps or increase Amps also ?
Thank you
Reply to
Barry Fawthrop
a battery stores energy
but what can be used to create
a load (i.e. resistance) connected to a power source.
current is the movement of electrons through a conductor. 1 amp of current is 1 billion electrons flowing past a point in one second. (i wonder who counted them first?)
voltage ( also known as electromotive force or EMF ) is what pushes them little babies along
you get one volt across the load when one amp is pushed through a one ohm load.
minus losses in the transformer
it is better to think "backwards" in this case. lets say a battery charger is supplying 10 amps AC before rectification at 10 volts full load. the transformer is outputting 100 watts. now if we are in Japan using 100 volts input what is the current? hint: P / V the input current will actully be a bit more than that in a real transformer with the 'lost' energy mostly being converted to heat.
no, you cannot obtain more power out of a transformer then what goes into it.
(unless you are a South American genius who just downloads the extra power from the ionosphere) ...
you can get more current from the secondary by obtaining a bigger transformer that has bigger wires and consequently can handle more current and more power without burning itself up.
Reply to
One 'Coulomb' worth of electrons, not one billion. 1 Amp = 1 Coulomb / second. 1 electron carries (if I recall) 1.67e-19 Coulomb of charge. Therefore that's about 6 billion billion electrons per second.
Reply to
operator jay
I don't like "creates Volts". A battery (or cell to give its correct name) is a energy storage device- energy is stored chemically, waiting to be released (or actually converted). When you connect a conductor (eg a wire or circuit that will allow electrons to flow), the chemical reactions can proceed.
In simple terms, there is a reaction at the -ve end of the cell that releases electrons, which flow through the wire/circuit to the +ve end where another reaction is waiting to absorb them. This potential to "release electrons" gives rise to a Potential Difference (measured in Volts).
In a primary cell, the reactions are non-reversable but in a secondary (or rechargeable cell), you can reverse them and recharge the cell.
The electrons flow -ve to +ve but, following from misconceptions in the early days, conventional current is still said to flow +ve to -ve.
That breaks the laws of Physics- you what more energy for nothing.
Having said that, I' sure some snake oil salesman will sell you one ;-)
Reply to
Brian Reay
"Barry Fawthrop" wrote in message news:LJU6d.36393$
understand the
got to grasp the
if at all
AC, does the
appliances that
You need a clue on basic electricity as well...Ohms law etc. the current is not *provided its DRAWN... whats provided is the potential to provide the current...surges can be 10,000 times what the designed for draw is.
... that is defined as the utility company line size, transformer size, and service feed size. the homeowners electrician fits a service panel as the home owner sees fit. (if its too big for the feeder wire, the utility company must place larger wire)....
so you have all this sitting there with no current draw at all, until you energise an appliance or whatever..then the appliance based on its internal resistance to electric current flow (reisistance) allows current to flow from the utility company under pressure of the applied voltage to the limit of resistance in the entire system....surge currents can be very very high...explosive even. So the question is not what the utility company provides as much as it is what your gismo's draw....and that is solely a function of thier internal resistance (lights and heaters) and impedance (produced by motors, a more complex issue).
A dead short in a 200 amp panel could draw 10,000 amps for a fraction of a second... enough to ruin yer entire day.
Look up Ohms law and study that and you will gain a clue... lacking that you are looking at the situation backwards...its doesnt work that way...
also with AC there is no unidirectional 'flow' of current as with DC and water hoses....its an ocilation of the same electrons in a piece of wire, at 60 times a second in the US... 50 times a second in the EU..... except in the case of a dead short, line to ground... then voltage (pressure) forces an abundance of electrons (amperage, a discrete number of electrons per amp) to ground in one direction. sort of like cutting a high pressure hose on a closed circuit hydraulic line....circulation ceases...the fluid goes to the ground under pressure.
Your first step is to read up on ohms law and learn what the terms are...lacking that its hopeless endeavor to understand what you are asking...
from 12 to 120
step it down
You have a bogus notion on what current is created by... you think it supplied... and thats true to some extent...but there is only flow if there is a path of conductance and the resistance in that path determines how much flow for the most part...(the transformer only limits the max flow, due to its own internal resistance, depending on the size etc)
a 120vac tranformer rated at 10 amps on the 120 side, will be good for 100 amps on the 12vac side... since the net power, wattage, is a function of volts x amps.
The wire size on the low voltage side will have to be large enough then to carry the 100 amps, that is 10 times the electrons as on the 120vac side, but at 1/10th the pressure (voltage).
Same net power (wattage) though on each side.... minus a few percentage points for loss in the transformer (usually over 95% efficient)
Watts = volts x amps
I =E/r were I=amperage, E= voltage and R = resistance (or ohms)
thats Ohms can mash that equation around 9 different ways to solve for any missing factor of the three factors.
This applies to AC or DC as far as the math and current etc are concerned.
AC differs from DC primarily in its occilations at 60hz.... and of course DC and AC motors are different animals etc.
DC is a lot more dangerous than AC as well... the higher the voltage and the heavier the wire the more dangerous.. Electric test equipment is rated for use near heavy wire or not... one way to die young is to use a cheapie unrated voltage test meter on heavy wire close to a line voltage transformer (we are talking wire larger than one of your fingers and voltage over 230 volts... 480 on heavy wire can be very dangerous... 600 volts on heavy wire can be even more dangerous..... 300' away, at a 110vac duplex outlet.. with size 12 wire feeding it... the resistance is so high as not to support such a dangerous spike in current flow.
Breakers and fuses need to be sized to blow or trip as fast as possible in the event of a short circuit.... one time buzz fuses work well on resistance loads, lights for example..and can be sized very close to the load, offering good protection.
Motors draw a heavy surge on startup so the fuzes in those circuits have to be oversized somewhat for the surge load, and time that in the event of a short to ground though ones sorry ass... the surge can be fatal... sizing these is a compromise.
So be careful around large high voltage motor circuits.... shorts in these applications can explode with the force of dynamite..... a 600 vac, 600 hp motor presents a wide range of absolutely dangerous issues, not seen in smaller motors, say 240 volt 2 hp motor...still dangerous... but the 600vac 500hp motor supply wiring and transformers provide enough potential to drop half of the states wiring grid into your lap.
See the excellent post a few days ago on the issues of Arc Flash....thats a very key and well written piece for anyone wishing to understand the issues related to hazards with AC current and particularly larger systems as the power grid in the US undergoes changes...risky the same time qualified electricians are dying young of budweiser poisoning....
Those paying attention to that article will save a lot of lives.. and maybe their own.
If it loses current, then how can one create or induce
x Amps) in the
You induce current flow with a circuit between a line and ground or neutral...or two lines etc.. the amount of current flow is entirely dependent on the resistance to electrical flow in the ciruit...and the voltage (pressure) available from the power company (fixed).
supply due to
thats not correct...most appliances are AC... only a few or DC...some elecronics for instance.
Can one
DC, and yet still
sure...using a rectifier... or inverter... easily available..but there is no advantage, even though some dingbats with no clue what so ever postulate that DC uses the 'wasted half' of the AC cycle. a notion founded in ignorance beyond human comprehension.
monitor and printer?
Look those up in coversion tables.... they are different means of measurement, and stated appropriately according the means... each means has its value.. joules is for very very small flows.. The math gets messy if you try to .0000000000000000000002 watts.. when you could do the math in say 2 joules...for micro flows of current.
Watts is just that volts x time designation attached. When you say watt hours you are saying so much current (volts x amps) for one hour... a thousand watts is roughly 9 amps at 110 volts .... 10 light those for an hour you use a killowatt hour, or 1000 watts for an hour... (kilo means thousand) cost 5 to 20 cents depending on your location. Usually about 13 cents and rizing. 5 cents where there is established and contracted hydro electric generation.
You owe to your mentors to do some study on your own now before asking more questions.
Phil Scott
Reply to
Phil Scott
"Barry Fawthrop" wrote in message news:W5h7d.40092$
questions It really
be used to create
Watts out
same ratio.
keep the same
of course not.... you need to understand that there is no free energy created by math tricks or whatever. Look up the second law of thermo dynamics...regardless the hord of dingbats who think they can devise a carburettor to get 50,000 horse power hours from oxidizing 4 cents worth of petro chemicals or whatever.
You need to understand these actualities... in any system there is only so much potential energy. Although you can change systems, and arrange for the petrochemicals in this example to react at a nuclear level, that is fission or whatever, and get a million times more energy.
the dingbat contingent tries to mix the two out of thier viable contexts to get magical results... There is no substitute for understanding basic physics. You can learn this in a physics for dummies book or high school physics book without too much trouble.
Lacking that you will never ever get answers to your questions on more than a very shallow level.
Phil Scott
Reply to
Phil Scott
in message
questions It really
amp of current
(i wonder who
I dont know who did that, it is very easy to do chemically though.. you now how many free electrons are involved per lb of material to complete a chemical reaction...I didnt know it was a billion electrons per second...I thought it was some other similarly large number.
pushes them
through a one ohm
A great example of ohms law... and useful in the thinking process regarding these issues.
You gave the man some good explanations.
Phil Scott
Watts out
same ratio.
battery charger
full load. the
using 100 volts
real transformer
yet keep the same
what goes into
the extra power
handle more current
Reply to
Phil Scott
questions It
1 amp of
(i wonder who
1 Coulomb /
of charge.
Thats better and it explains how the number of electrons are counted.. the coulomb is chemically many atoms of silver or whatever oxidized...and we know how many atoms per unit of weight.
Phil Scott
Reply to
Phil Scott
"Brian Reay" wrote in message news:
in message
questions It really
be used to
correct name)
waiting to be
conductor (eg a wire or
reactions can
cell that
the +ve end where
to "release
a secondary (or
misconceptions in the
to -ve.
Not bad...but the early days were DC where there was actually uni directional flow and the + - designation was fully approprate, as it remains to day with batteries and rectified AC to DC voltage to a large extent.
Now we have AC primarily for our power generation and distribution and there is no + or -, or more correctly said there is, but it reverses 60 times a second (in the US). so we dont lable our wiring plus or minus but in phases. from the transformer... each phase out of sycn with the current flows on the phase differential between the phases...or from the wave ocilations in a single line to a neutral or a ground...but none of this marked positive or negative... You have the power LINES..and the grounds or neutrals only with AC (as you know, this rant for was for the OP)
Watts out
same ratio.
yet keep the same
you one ;-)
The US high school grads rank 38th behind Shri Lankan Hut dwellers in math and science, Ive seen registered professional mechanical engineers in the US think they can use a 100 dollar 14 volt impact screw driver to remove 2" stud bolts from a locomotive engine block just because it said 'high torque' on the box.... then fly 4 morons to california to try and prove it.
The mind simply shorts out.
Phil Scott
Reply to
Phil Scott
Eh? What do you think 'flows' from +ve to -ve? OK, in semiconductors the 'holes' seem to move that way but only because of a 'pass the parcel' game with the electrons.
Even worse, they will do it more than once ;-)
Reply to
Brian Reay
i guess i miss remembered my collage physics on the number of electrons.
maybe we could round off the number to 1 billion and call it a metric coulomb? :) i guess not
i was trying hard to avoid saying "coulomb".
i often have to try to explain technical issues to a GM/VP. usually the eyes start to glaze over after i past the point of saying the thingie was broken and i fixed it and it only cost $2,000.
Reply to
----------- Conventional current flow- hey -when it was defined it wasn't known that the major charge carriers were electrons. One can use electron flow but then there is the question of which equations should change sign- so why bother as it really doesn't add to circuit analysis etc. Also with AC - the electrons just wobble and don't go anywhere but the circuit concept of "current" exists.
Reply to
Don Kelly
See my comments earlier in the thread.
Helps with understanding- charge on a capacitor, semiconductors, valves. Little things like that.
-- Brian Reay
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Reply to
Brian Reay
Thank you all so much
OK I was wrong saying
I applogize :( A battery produces Voltage, due to the chemical energy stored within.
I still not sure how one can create or produce Amps?
Let me put it this was using for example a 9V box battery It supplies 9 Volts and I'll "guess for this example" 1 Amp, thus giving 9 Watts
Now I could put two batteries in series and get 18 (9+9) Volts, this would increase Volts, So how could I do something similar and increase Amps
seeing a 9V box battery is Ni-Cd I would again "assume" this chemical reaction produces the 9V and 1 Amp. What reaction would produce 9V and 3 Amps for example?
Or could I create a battery with 3 anodes and 3 cathodes and would this produce 9V and 3 Amps? (9V and 1 Amp on each pair) in parrallel?
I realize that you can't simple increase Amps and Volts, as that would create extra Watts which is related to Energy, and Energy can neither be created or destroyed.
Thanks in advance Barry
Reply to
Barry Fawthrop
No need to appologize- you asked a reasonable question because you want to learn.
I think we are hung up on terminology. I'm trying to be precise so as not to mislead. If you said "How can I make a larger current flow?" it would be a better question. The answer is then, increase the voltage or decrease the resistance. See below.
The Voltage, Current, and Resistance in a circuit are all related by Ohms law:
So in the examples you give, doubling V will double I and the power dissipated also increases.
BUT that wasn't where this bit of the thread started- you were talking about transformers at that point. With transformers the power available at the secondary is "the same" (actually slighly less) than the power at the primary. Not the same as your above example,
If you look at the links below you will find some basic training material covering this. It is intended for those starting our in amateur radio but includes the above. Please download and use if it help.
Reply to
Brian Reay
Amps is not a thing, it is an expression. It describes the rate of flow of an electrical current.
The use of an analogy to water may help.
Say you have a tank filled with water, with a spigot at the bottom connectd to a hose. The water exerts pressure on the tank, the spigot, the hose - whatever it touches. That water pressure is analogous to voltage in an electrical setting. Say you open the spigot - water flows through the hose. We measure the rate of water flow in gallons per hour. In an electrical circuit, a switch is analogous to a water spigot. We operate the switch to allow current to flow, just as we operate the spigot to allow water to flow. In the electrical circuit, the rate of flow of the current is not gallons per hour, it is amperes. You don't "create" amperes - but you can control the rate of flow of current, thus changing the number of amperes.
In the water tank example there are two ways to increase the rate of flow. 1) You can increase the water pressure. That will make the water flow faster. 2) You can use a larger diameter hose. That will allow the water to flow faster.
In an electrical circuit, you can increase the rate of current flow (amperes is the expression of that rate of flow) by increasing the pressure (voltage) or by decreasing the resistance. Decreasing the resistance is analogous to using a bigger diameter hose.
In both cases the size of the supply is a limiting factor. You won't be able to get much rate of flow under normal circumstances if you have ony 1 ounce of water. But with a 100 foot deep 3 square mile resivoir of water, you can easily get a huge flow. Same is true of electricity. If you have a small AAA size battery, you can't get the same rate of flow from it as you can from its big brother automobile battery.
Reply to
Thanks Brian
I checked the links out and could not find anything I'm busy d/ling a .zip file +/- 7hrs so I'l wait
I understand the ohms Law relationship, and even though I'm on batteries DC I still want to get to AC.
You put it better how can I create a greater current flow ?
I started with transformers (I was wrong. to start with) I knew transformers increased or decreased V but had no idea what it did to A Now. that I understand Power in = Power out (+/-) I can see A will decrease as you increase V. Thus being wrong with transformers I moved back a step to a battery as a source or "power" supply. How does one increase power (Watts)
P = V * I. V can be increased using a transformer, but this will lower I thus no change in P (+/-)
So my question how can I increase A.
I know chemical reactions will produce V, based on Joules vs Watts or Volts relationship. thus is a chemical reaction eg Ni-Cd will produce 9 Volts (a common box battery), then how can I produce addtional Watts? Extra electrodes or and different reaction?
What factors will generate greater Watts.
+/- is a Battery 9V
------- + step up transformer -------------| | ---- - (increase V)------ ---------| |----- + (a) +/- | | | | --->---- + step down transformer ---->------| ----- - (increase A) |
|-------------- - (a)
Will V and A at (a) be greater than the V and A of the +/- battery ? Since the step up leg will increase V, while the step down leg will increase A. So will the result increase P ?
Reply to
Barry Fawthrop

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