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Any ideas what this is


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#1 Guest__*

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Posted 20 September 2005 - 09:49 PM

This sits on the back of the motor on of an old milling machine I have
Inside there are two sets of points that are opened and closed by a bakelite (smashed and broken) rotor arm driven indirectlectly by magnets rotating around a "dead" comutator sort of set up.
I think it's maybe some sort of device to stop you putting the motor into reverce...whilst it's running.
I dont know really.............I'm running the motor without the comutator gadget and the rotor arm.....it seams to run ok without this gadget.
the machine is three phase and also has some sort of primative resistor, consisting of two coils (really one coil split into two to make the room) wrapped around ceramic cores sitting on top of the electrical cabinet.......presumably to give the two speeds on the motor.........but there again on the motor plate is info that contridicts this by saying the motor is two speed ....so who knows........the motor is original...and is part of the machine.
first picture is the motor plate
then the next one down is the circuit diagram...the others are of the device

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all the best...mark

#2 Guest__*

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Posted 23 September 2005 - 02:39 PM

rpm encoder feeds back to operater

#3 Guest__*

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Posted 26 September 2005 - 10:47 PM

Thanks for your answer
but how would that work then, there isn't any provision for rpm readout anywhere
and the machine is about 50 years old and it does not have variable speed,
has change gears ........you take gears off reposition them to what it says on the chart on the side of the machine for a given rpm.
I still think its to stop people putting the machine in reverse, until it reaches a dead stop.
all the best...........mark

#4 oskin

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Posted 27 September 2005 - 12:52 AM

Dunno? Kinda looks like a brake to me. just a guess tho

#5 niallnz

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Posted 27 September 2005 - 01:04 AM

I think that it is a plug braking control, so that whne the stop button is pushed, contactor I drops out and contator III drops. (I'm assuming that contactor III is the pump). Contactor II can then be closed by the speed switch.

Forward, reverse and the two speeds are selected by a separate switch. the switching patern of that switch is shown on the lower half of the wiring diagram name plate.

I think that once upon a time some one wanted this to stop on a dime (so to speek).

#6 msdaif

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Posted 27 September 2005 - 11:05 AM

Picture 3:

a) The blue device on the left is a tacho-generator which is a DC generator to measure the speed of the motor in rpm.

B) As the AC motor on the right rotates, the techo is rotated and so
a voltage is developed which is linearly proportional to the motor speed.

c) Ofcourse, the AC motor can be operated without the tacho-generator.

#7 Guest__*

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Posted 27 September 2005 - 05:21 PM

It looks to me like the motor turns a constant RPM. And that the circuit diagram on the second plate suggests that the peice on the spindle is some sort of magnetic gear box that changes from low to high. Like a magnetic slip clutch.

#8 jraef

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Posted 28 September 2005 - 03:41 AM

My interpretation is that it is a 2 speed reversing motor, and the tachometer-like device is the speed selector switch assembly, but it is tied to the rotor speed as a lock-out device so that you cannot reverse it until it is at a stop. The resistor on the top of the cabinet is shown on the diagram there, next to the number 15 in the center phase. That is probably there to limit torque in reverse, since it is only in the circuit when that switch is closed, and that switch will reverse the motor direction (relative to the switch maked "I"). As a spindle drive on a milling machine, I would say that you could run it forward in 2 speeds, but if it jammed, you could back it up at reduced torque in either speed so as to not damage the attached tool, but only after it came to a stop first in order to keep from damaging the equipment.

Nowdays we would just put a VFD on it and be done.
"He's not dead, he's just pinin' for the fjords!"

#9 msdaif

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Posted 28 September 2005 - 09:35 AM

I agree with jraef. It could be what is known as "zero-speed plugging switch" which is for braking the motor by reversing two terminals.

#10 Guest__*

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Posted 29 September 2005 - 06:22 PM

Thanks guys.

Think jraef has the most convincing answer.
all the best,,,,,,,,mark

#11 jraef

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Posted 29 September 2005 - 06:32 PM

I win!

Whats the prize?
"He's not dead, he's just pinin' for the fjords!"

#12 Guest__*

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Posted 30 September 2005 - 05:21 PM

the prize is a big thankyou from me.
i was rather hoping that someone had a spare one of these gadgets hanging about that i could cannibalise for the rotor inside.
the machine works ok without though.
the machine has a phenolic resin gear inside the gearbox.........this is the machines "fuse" on the transmision........backed up also by the gadget on thew end of the motor.
think the Germans went over board to protect this machine from abuse ...by maybe students in colleges and schools maybe.
now i know of the consequences of not waiting for the machine to come to a dead stop before reversing it ...............or making sure that the machine isn't in the middle of a cut ,when starting it up...........the resistor is like you said ........a soft start gadget...maybe.
maybe one day i will find a spare..........untill then its carefully does it.
thanks guys for your help
ALL THE BEST...MARK

#13 Guest__*

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Posted 30 September 2005 - 05:21 PM

the prize is a big thankyou from me.
i was rather hoping that someone had a spare one of these gadgets hanging about that i could cannibalise for the rotor inside.
the machine works ok without though.
the machine has a phenolic resin gear inside the gearbox.........this is the machines "fuse" on the transmision........backed up also by the gadget on thew end of the motor.
think the Germans went over board to protect this machine from abuse ...by maybe students in colleges and schools maybe.
now i know of the consequences of not waiting for the machine to come to a dead stop before reversing it ...............or making sure that the machine isn't in the middle of a cut ,when starting it up...........the resistor is like you said ........a soft start gadget...maybe.
maybe one day i will find a spare..........untill then its carefully does it.
thanks guys for your help
ALL THE BEST...MARK

#14 jraef

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Posted 01 October 2005 - 12:06 AM

If the motor still works, you could easilly run it from a VFD set up to accomplish the same protections.
"He's not dead, he's just pinin' for the fjords!"

#15 Guest__*

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Posted 12 October 2005 - 04:50 PM

VFD sounds nice ..........but a 2.5 hp one, would be needed and they are in the region of 200.
I have a 5.5 hp rotary converter already, see.
Besides that, the table takes its power from the main motor thru change gears.
all the best....mark




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