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
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
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
Only the electronic loads require conversion to DC-generally at a lower
what about refridgerator, stove and heaters/air conditioners? These take
Power is in watts and is the rate of change of energy (1 watt=1
Energy is in Joules or watt-hours (1 watt-hour 600 Joules)
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
(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
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
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
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
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
increase Amps also ?
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
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
(unless you are a South American genius who just downloads the extra power
from the ionosphere) ...<grin>
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.
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.
Thats better and it explains how the number of electrons are
counted.. the coulomb is chemically accountable...so many
atoms of silver or whatever oxidized...and we know how many
atoms per unit of weight.
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.
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.
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.
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
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 ;-)
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 next...so
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
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.
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.
> > Having said that, I' sure some snake oil salesman will sell
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.
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.
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
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
Same net power (wattage) though on each side.... minus a few
percentage points for loss in the transformer (usually over
Watts = volts x amps
I =E/r were I=amperage, E= voltage and R = resistance
thats Ohms law..you 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
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 delayed...so 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 changes...at the same time
qualified electricians are dying young of budweiser
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.
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
when you could do the math in say 2 joules...for micro flows
Watts is just that volts x amps....no 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 bulbs...run 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
You owe to your mentors to do some study on your own now
before asking more questions.
create Amps ?
I applogize :( A battery produces Voltage, due to the chemical energy
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
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
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
No need to appologize- you asked a reasonable question because you want to
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
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.
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
Now. that I understand Power in = Power out (+/-) I can see A will
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
thus is a chemical reaction eg Ni-Cd will produce 9 Volts (a common box
then how can I produce addtional Watts? Extra electrodes or and different
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
So will the result increase P ?
> P = V * I.
Also: P=V^2/R (V squared / R)
Increase V or I increases P
Decreasing R increases P
Don't confuse yourself with the transformer case, a transformer can only
increas EITHER V or I , not both.
The file you are downloading, look in the Foundation course first, technical
basics. Then look at the technical stuff in the intermediate.
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