Just curious but...
me*g
How does an alternator work?
DaveK
"me*g" <me*g...@127.0.0.1> wrote in message
news:a2eqv6$i31$1...@newsg1.svr.pol.co.uk...
> Whats the difference between a dynamo and an alternator.
>
> How does an alternator work?
>
speeds.
Dynamo= direct current.Produces some useful amps at high speed.
They work by a shaft being spun around by a belt, generally driven by the
crankshaft. Faraday discovered it all-a coil with a magnet moving through it
produces electric current. (a magnet in a coil with electric current flowing
through it will start to move)
What more do you need?
Try www.howstuffworks
Will be there somewhere.
DaveK.
Roger
> Dynamo= direct current.Produces some useful amps at high speed.
And a bicycle dynamo is actually an alternator!
--
Roger
ICQ: 40038278
ICBM: 51.56N, 1.47W
"Many fall down, but few return to the sunlit lands"
J.L.E
DaveK <da...@wkinnear.freeserve.co.uk> wrote in message
news:a2etv5$ad$1...@news7.svr.pol.co.uk...
Just clear it up.... And put simply;
Dynamo produces an un-regulated DC voltage, due to use of a
comutator(sp?) and bushes), without further electronics.
Alternator produces an un-regulated AC voltage, due to the use of
Stator rings and brushes, there needs to be a rectifier (diode pack)
on the output to produce the required DC voltage.
There are other design differences also, but that were it starts
getting complex.
Dave Plowman
J.L.E <ne...@scarts.fsnet.co.unitedkingdom> wrote:
> Just clear it up.... And put simply;
> Dynamo produces an un-regulated DC voltage, due to use of a
> comutator(sp?) and bushes), without further electronics.
> Alternator produces an un-regulated AC voltage, due to the use of
> Stator rings and brushes, there needs to be a rectifier (diode pack)
> on the output to produce the required DC voltage.
> There are other design differences also, but that were it starts
> getting complex.
Just to add to this, a dynamo requires a heavy duty mechanical switch in
the form of the commutator to produce DC, which has to be capable of
handling its output. The current is produced in the rotating part, the
armature, while the 'magnet' - in fact a variable type in the form of an
electromagnet to control the output - is static.
An alternator works in the reverse way. The current is produced in the
static windings, or stator, so the slip rings needed to get current to its
electromagnet, the rotor, are much smaller since they handle little
current. This allows an alternator to have a wider speed range than a
dynamo, so can be geared to produce more output at low engine speeds.
--
* I'm pretty sure that sex is better than logic, but I can't prove it.
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Guy King
from "me*g" <me*g...@127.0.0.1> contains these words:
> Whats the difference between a dynamo and an alternator.
Dynamos have a segmented commutator which effectively switches the
output from the rotor so that you get DC out. They're not as efficient
as alternators, particularly at low speeds.
Alternators carry the current to the rotor via a pair of slip
rings...the power always flows to the rotor in the same direction. The
output comes from the stator...the fixed coil bolted to the outer shell
of the unit. Because of the shaping of the pole pieces of the rotor the
steady magnetic field from the rotor is swept round and round as it
spins, and from the output coil's point of view appears to reverse
itself frequently. This give and alternating output which is rectified
by internal diodes. The voltage control is done by varying the current
to the rotor...the more current the stronger the magnetic field, the
higher the output.
Generally the control pack is internal to the alternator, though there
are old bangers out there with external electromechanical controls.
Most cars with a dynamo can be converted quite simply to have an
alternator. They're vastly superior, but may not be "original" enough to
suit the purists. Also take great care with polarity!
--
Skipweasel...
Fools seldom defer.
me*g
>
> How does an alternator work?
>
Cheers guys, that has been bugging me all day.
Darren Jarvis
A dynamo naturally produces DC current, but only it's maximum output at high
revs. An alternator produces AC current (though this is converted to DC
internally) and can provide it's maximum output even at fairly low revs.
In car applications, dynamos haven't (to my knowledge) been fitted to cars
since the early seventies onwards.
> How does an alternator work?
Ok, you asked for it! This answer is rather longwinded and probably
patronising but I'm hoping that others will find it useful as well...
Basically a dynamo generates electricity by a coil of wire (well, lots of
coils actually) rotating in a magnetic field. The magnetic field is
provided by either strong magnets, or more usually, electro-magnets - either
way these are referred to as the "field" magnets/coils. The rotating coils
within this field are driven from the engine by a drivebelt and pulleys; the
rotating coils collectively being known as the armature - each coil connects
to two segments on the commutator (part of armature, so it rotates with it),
which is in constant contact with two carbon brushes.
As the armature rotates an electric current is induced in the coils - only
one coil will have both it's commutator segments in contact with the brushes
and through these the current flows. Because the commutator "switches" which
armature coil is connected to the output, the output current is DC since the
polarity is maintained. This is also the downside since the commutator
segments and the brushes have to carry the full output current of the
dynamo.
An alternator works as a sort of 'inside-out' dynamo. This time, the field
coils (now called "stator" coils) are connected to the output through diodes
(I'll explain the purpose of these in a moment), whilst the armature - now
called the "rotor" - is used to provide the magnetic field. The rotor is
always an electro-magnet since it needs the magnetic strength to be
variable. It is connected to a power source via carbon brushes and
slip-rings (like a commutator, but not divided into segments).
Now this is the first important part when dealing with alternators: because
the rotor is itself an electro-magnet, if it is not first powered there can
be no current induced in the stator coils. Got that? No power input, no
magnetism, no power output! In a car, the rotor coil is initially powered
from the car battery, through a resistor to limit the current (this is often
the charge warning lamp on the dashboard!). If your car battery isn't
connected, or if the warning lamp bulb has blown or been disconnected, then
the rotor coil won't be energised and the alternator won't produce any
electricity.
Assuming that the rotor coil *has* been energised by some external power
source, when the rotor is spun (using engine driven belt and pulleys, same
as a dynamo), then an electrical current will be induced in the stator
coils. In a typical alternator there are three separate stator coils which
all have one end connected together (star configuration - those who've
worked with industrial motors will know what I'm talking about). Now
because the rotor coil is effectively a powerful magnet, when it rotates the
polarity of the magnetic field it generates will alternate every half turn.
Because the magnetic field changes polarity, so does the induced electric
current in the stator coils - hence the AC current output!
The second important part of alternators is that a battery cannot be charged
from AC (and most electronics cannot run from AC) - hence the diodes I
mentioned earlier. For those that don't already know, a diode is basically
a one-way valve for electricity and it is this characteristic which filters
the AC into DC since the diodes will only allow current to pass in one
direction. Two diodes are used per stator coil to give full-wave rectified
DC current output - they also serve the useful purpose of preventing current
from the battery from energising the stator coils.
The last part of the alternator (from an electrical point of view) is the
voltage regulator unit. Now I have to admit I don't understand exactly
*how* it works and what components it uses to do it, but the reason it is
needed is thus: the current output of the alternator is largely determined
by the strength of the magnetic field within, which in turn depends on the
amount of current flowing through the rotor coil. If the current is too
much (aside from possibly burning out the windings), then the voltage will
also rise and this can damage the battery and most other devices in the car.
To prevent this a voltage regulator is fitted which monitors the output
voltage - if it starts to rise (14V is enough for charging) then the
regulator will reduce the current flowing through the rotor coil and
therefore weaken the magnetic field and reduce the alternator output.
One final thing which many people do not understand is how the charge
warning lamp works. Remember I said that this lamp was used as the resistor
in circuit with the rotor coil and battery? When the alternator is not
producing any (or enough) output, current is flowing from the battery,
through the lamp and the rotor coil. This flow of current causes the lamp
to light. Once the alternator is running fast enough it will generate
enough power to keep the rotor coil energised itself - when this happens
there is no longer a flow of current from the battery to the rotor coil, so
the lamp goes out.
I know it's probably more detailed than most people want (and I'm sure it'll
contain errors so please don't be harsh if you know better); but I've had to
acquire the knowledge to troubleshoot my own car and I kinda got carried
away with the studying...
Darren
Moray Cuthill
speed, the dynamo will produce more power (if the dynamo and alternator have
the same output).
The only reason the alternator produces more current than the dynamo, is
that it is geared to spin faster than a dynamo would (and thus start
charging quicker). This is due to the construction of the alternator, which
allows it to spin at a high speed, whereas if a dynamo was spun at such a
high speed, the armature would break up.
Also the output from a dynamo is limited due to the problems with passing
high currents through a commutator and brushes.
"me*g" <me*g...@127.0.0.1> wrote in message
news:a2eqv6$i31$1...@newsg1.svr.pol.co.uk...
snafu steve
A dynamo is longer and thinner.