In article ,
"Arfa Daily" wrote:
"Smitty Two" wrote in message
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In article ,
"Arfa Daily" wrote:
"Smitty Two" wrote in message
news
Please tell me whether this is an inverter or a bridge rectifier, if
you
recognize it out of circuit context.
http://members.cox.net/prestwich/51.jpg
Selenium stack bridge, by the looks of it. Equipment it's in ?
Arfa
Ancient European slide projector with rotary carousel. Trying to help a
friend get the thing going again, via email since he lives in another
city.
Problem with it is that this motor:
http://members.cox.net/prestwich/52.jpg
turns very slowly.
It didn't make sense to me that a rectifier would be fed by a motor
winding, but there you go. So now it seems the motor is 240, but there's
a secondary winding in there putting out about 17, and he's getting
about 12 VDC out of the bridge, so that part seems OK now.
Is there anything on that type (shaded pole?) of motor to fix, or is it
an R & R job? (remove and replace)
This used to be very common practice back in the day. Record players often
used a motor constructed in that way. FWIW, I can't remember ever having one
of those motors, which were used in all sorts of things from tape recorders
to fan heaters, that had any kind of electrical problem. It used to be very
common for the oilite type bearings to completely dry out leaving a gummy
residue, which then made the motor run slowly. Usually, when the motor runs,
the rotor moves forward a couple of mm in its bearings. If it is not able to
do this, that can cause it to drag on the 'brake' pad that's sometimes
fitted in there. They don't have a lot of power even when working correctly.
Also, the bearings are usually 'self-centering' as in they are fixed in a
sort of ball mount. If the motor has been knocked or jarred, the bearing
balls can be knocked out of line, and don't re-centre if it has gone gummy
in there. The motor in the picture looks as though it may have simple fixed
bearings, though.
Usually, these motors are very easy to service, being held together by two
long screws which pass through one bearing plate, through the stator core,
and into the other bearing plate, where the holes are threaded. In the case
of this one, the rivets that they have used would have to be drilled out
first, and then long screws with nuts substituted to hold it back together.
Servicing usually involves cleaning the shaft and bearings with a solvent
such as IPA, and soaking the bearings in a light machine oil for a while,
before poking the rotor shaft through each in turn, and giving it a 'swing
around' - a bit like working a joystick if you will - to make sure that the
ball mounts are free to move. They should be tight enough to stay put
wherever you leave them, but free enough to move fairly easily. The rotor
and bearings are then assembled back onto the stator core, 'working' the
ball mounts on the bearings as needed, until the rotor runs totally smoothly
with the bearing plates refixed to the core by the screws. You should be
able to easily spin the rotor with your fingers, and it should spin on for
quite a while - several seconds at least.
When it's all back together, it doesn't hurt to add a little more machine
oil to the bearings, particularly if there are felt 'resevoir' pads in them
or by them. On some motors of this type that I have seen, there is actually
a little oil hole in the bearing housing. Good luck to your friend. Hope he
succeeds in rescuing it !
Arfa
Thanks for your usual comprehensive treatise! I forwarded your comments
to my friend. I'm off for a weekend of work and play at "her" house in
another city, so he's on his own for a bit now, and maybe by the time I
get back he'll have it sorted out. The machine is critical to his
business, not just a hobby, so he's anxious to have it operational.