Model Boat Mayhem - Forum

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: AC-DC MOTORS  (Read 2041 times)

portside II

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,519
  • tugs at rest
  • Location: Howden.East Riding of Yorkshire.England Near the banks of the river Ouse
    • goole model boat club indi site
AC-DC MOTORS
« on: January 11, 2008, 09:56:39 PM »

Whilst rummaging around the bins (skip inspecting) the other day i came across one of those fibre optic Xmas tree's ,the tree was a bit mangled but the base was intact.
So with a quick application of the pliers the motor that turns the coloured disc was out and the wire removed with the power supply (transformer plug) which is 12v.
Me thinking radar motor  {-) , then i looked at the transformer closer and after the 12v was AC  :( .
Not tried it yet on a battery but it works on the transformer  ,is it worth keeping ? will it work on 12v DC ? if not can it be converted easily ? .
daz
Logged
I like to build my boats to play with, not to just look pretty,so they dont !

gingyer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,523
  • Location: Glasgow
Re: AC-DC MOTORS
« Reply #1 on: January 11, 2008, 11:56:00 PM »

It should be ok as AC and DC motors operate the same.
what you need to do is find out how may cables are
coming out of it (2 i reckon) then connect it to battery
the thing that may change with the changed from AC to DC
is the speed of the motor.
Colin
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,564
  • Location: Blackpool, Lancs, UK
Re: AC-DC MOTORS
« Reply #2 on: January 12, 2008, 01:16:22 PM »

If the motor has a permanent magnet and just two wires, it will be a DC motor, and will be reversible.  There will probably be a rectifier somewhere between the transformer and the motor. 
Just connect the motor to a battery, if it spins, problem solved, if not either its broken or intended for AC only.
Motors work by generating a magnetic field in the rotating part which pushes against the field generated by the permanent magnet in the fixed frame.  In a conventional motor, the commutator and brushes keep the field shoving the same way.  If AC is applied to one of these, it will just buzz a bit and get hot, as it is trying to turn one way then the other in sympathy with the supply.  Some motors have a field coil which replaces the permanant magnet.  These work on AC and DC, but only turn one way.  Some motirsa have the magnet rotating, and the coils fixed and a cunning arrangement of electronicery to arrange the forces to make it all work.
Yours is probably the ordinary permanent magnet brushed motor, as they are the cheapest to make
Logged
"With the right tool, you can break anything" - Garfield

sweeper

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 199
  • When all else fails, read the instructions
  • Location: On the edge of reason, in the state of Confusion
Re: AC-DC MOTORS
« Reply #3 on: January 13, 2008, 12:56:42 PM »

Re: the 12v motor.
For an application such as rotating a disc, very little output power will be required. It is quite possible that the motor is of the shaded pole variety (also used in mains powered clocks and some electric razors).
These motors will start in either direction at random. In clocks, it is normal for them to fitted with a recoil spring to throw the armature into the correct rotation (to prevent the clock running backwards).

Cheap to make, low tech and reliable.
Logged

portside II

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,519
  • tugs at rest
  • Location: Howden.East Riding of Yorkshire.England Near the banks of the river Ouse
    • goole model boat club indi site
Re: AC-DC MOTORS
« Reply #4 on: January 15, 2008, 11:32:37 PM »

finaly got into the shed today and tried the motor ,
on the power supply that came with it ,no probs a nice smooth turn .
put it on a 12v battery and nothing  >:( "xxxxx" all so its into the bin with the motor and the power supply and the wire in the drawer for spares.
daz
Logged
I like to build my boats to play with, not to just look pretty,so they dont !

Seaspray

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • Model Boat Mayhem is the best model boat site
  • Location: East Ayrshire Scotland
Re: AC-DC MOTORS
« Reply #5 on: January 16, 2008, 07:39:35 AM »

Was on the www.modelfireboats.com site and they done a good write up about AC/DC motors.

I will be considering a AC motor next time but have to look into the special ESC that you need for these motors


Martin
Logged

Model Boats Website

  • www.model-boats.com
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 39
  • Model Boats Website
    • Model Boats Website
Re: AC-DC MOTORS
« Reply #6 on: January 16, 2008, 05:01:27 PM »

Quote
It should be ok as AC and DC motors operate the same.
what you need to do is find out how may cables are
coming out of it (2 i reckon) then connect it to battery
the thing that may change with the changed from AC to DC
is the speed of the motor.
Colin

ehh?? No, no, no, AC and DC motors don't operate the same! There designed differently, and won't work on both AC & DC!

DC MOTOR

A DC motor has a split ring commutator, which (as it rotates) swaps the current going through one coil to go through the opposite coil. When the current switches sides the shaft then turns to the opposite side attracted by the magnetism. The split ring then swaps the current again causing the magnetism to change again therefore making the shaft turn again. This process just keeps going.


AC MOTOR

An AC motor has two separate rings for each commutator to touch*, this means that the motor itself will not swap the currents around automatically and relies on the input voltage type. An AC current is like a sine wave and is constantly switching the from positive to negative, this is what makes the motor turn.

*This isn't always the case, if the coil is placed around the outside (with the magnets on the centre shaft) there would be no need for commutators at all.

If a DC current is applied to an AC motor the motor will seize (or become harder to turn by hand) since it is constantly attracted to the energised coils only.


Just to add to what Seaspray says, there is also a difference between "AC motors" and "Brushless motors", brushless motors have three wires that are connected in a star formation with the coils within, like three phase motors, however AC motors will only have the two wires which rely on the alternating current.

So in answer to what portside II was originally asking "is it worth keeping". - No, although possible, it wont be easy generating an AC current from DC, and even more difficult to modify the motor to accept DC.

Hope this helps,
Fireboat :)


Bee

  • Guest
Re: AC-DC MOTORS
« Reply #7 on: January 16, 2008, 10:52:58 PM »

Rather than waste a possibly good motor offer the combination to a model railway or other land based modeller who might be able to use it for eg a windmill. They may have some more suitable motor in exchange.
I remember a windmill model i had years ago that was AC powered. The electromagnet made a small disc on the axle vibrate axially. This pulled it onto a piece of cloth a bit like fake grass with a distinct but sloping knap which edged it round.
Logged

portside II

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,519
  • tugs at rest
  • Location: Howden.East Riding of Yorkshire.England Near the banks of the river Ouse
    • goole model boat club indi site
Re: AC-DC MOTORS
« Reply #8 on: January 17, 2008, 10:45:21 AM »

ok
Free to good home 1 small 12v ac geared motor with transformer and lead
ex fibre optic xmas tree .
wanter pays postage or can be collected from goole pond on a saturday
daz
Logged
I like to build my boats to play with, not to just look pretty,so they dont !

sweeper

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 199
  • When all else fails, read the instructions
  • Location: On the edge of reason, in the state of Confusion
Re: AC-DC MOTORS
« Reply #9 on: January 17, 2008, 12:36:08 PM »



A DC machine is fitted with a commutator, this can be described as a rotating switch.The supply is fed to it through brushes. It's function is to ensure that whichever armature coil is under a given magnetic pole is always connected to the same pole of the supply. The force on the conductor in the armature (by Farraday) is to REPEL that conductor i.e. the shaft will rotate. The action of the motor can be seen as a continous repition of this action.
Although you can get AC machines fitted with commutators, by far the most common arrangement is to have two SLIP RINGS. The supply is fed to these by means of BRUSHES.
Sorry if this appears to be pedantic in reading, it is purely intended to clarify the use of certain terms and concepts.
Logged

Seaspray

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,316
  • Model Boat Mayhem is the best model boat site
  • Location: East Ayrshire Scotland
Re: AC-DC MOTORS
« Reply #10 on: January 17, 2008, 02:09:57 PM »

A little read on the site I mentioned. Will tell you the difference between  these two types of motor




Martin
Logged
Pages: [1]   Go Up