Just for fun can you guess what this relic does (still in use)

[Darkwood]

Just to add a few clues its part of a Lathe control which has a 22kw motor
Ive stripped the burnt out wiring but originally it is set up as 3banks one per phase but has 3 wires tapped on each bank but will hold back on more info to see if anyone recognises its use, Tony is odds on favourite i think knowing his background on here.

 

[johnboy6083]

is it a large resistor? for a primary resistance started motor?

 

[Knobhead]

Starting resistor for a slipring motor.

View attachment 14498

 

[Darkwood]

Well that didnt take long lol... yep dont often come across them that much on Lathes as they are torque limiting during start up, had issues with inching on this which uses the resistor bank (large fins) and then additional resistors (small fins) but as next photo shows it had open circuit on the additional inch resistor on 1ph this 2ph motor in inch mode.

.

 

[Knobhead]

Great fun when they fail on a crane hoist. People panic when the loads going down instead of up.

 

[johnboy6083]

so let me get this straight. The motor is started at a lower voltage (gained by using the highest resistance). the motor starter then cycles though the resistances until it is dropped out completely when the motor is at full speed/load. Is the inch resistor a very large resistance resistor, that allows the motor to inch then?

I bet these beasts get hot!

I guessed it was a resistor of some sort because it is designed like a large heat sink

 

[Darkwood]

This particular one is as mentioned before shown in 3 banks 1 per phase and on start up they are put in series with the motor till a timer shorts them out and commits supply direct to motor, but on inching an additional small resistor fin is added in series to the original bank, and yes it gets hot as ive just stripped out some burnt out wiring that was poorly specified and installed at a guess 10yrs ago.

To note which isnt obvious by pic is these blades run straight through center mount and are duplicated on other side so in effect your just seeing half here and they are physically twice the size.

 

[Knobhead]

So is it a slipring, or a primary resistance starter?

John, there's a description of both types in the "Motor's" sticky

 

[Bobster]

My guess would be a primary resistance starter. Been a while since I've worked on one of these.

 

[Geordie Spark]

I enjoy threads like this one.

Much more interesting than the all too frequent "I'm not an electrician - how do I wire my staircase light up" type of thread.

 

[Darkwood]

Primary resistance start with no wiring info but this is what i followed the old fashioned way.... wire by wire.... if i can link pdf :shout:


Its wired the old fashioned way and 60rys later still got original set-up running it---- built to last


Ive drafted a quick drawing up of the set-up although the inch is now out of the loop as it surplus to requirements as well as it had a broken resister fin on phase1
.

 

[Darkwood]

Just to gauge on the amount of heat generated we reakon that although the metal is heat fatiqued over the yrs it has melted as seen in pic 2 at the top, now the only thing i can think of that would achieve this is someone holding the inch button in for a long period rather than starting the motor up in run......(seen this done before)-- operators are like monkeys in that if you dont make the machine monkey proof then they will find a way to break it.

 

[Knobhead]

Very often you can short out sections of the resistor to get things away. I’ve done it several times on rotor resistors on cranes. Primary resistors would be just the same.

 

[Darkwood]

It was an option thought of as it was at the top end f the fins but there wasn't any benefit for an inch as it was a medium size lathe and you can turn the steel drums by hand on this machine so wasn't worth the hassle and time to keep an inch option going.

Its things like this i enjoy... old Russian lathe, no wiring diagram, no mechanical instructions, electrical equipment is 20yrs older than me and on site electricians think your a genious if you know more than how to replace a broken e-stop and all i wonder is what exactly do they get paid for?????

 

[Knobhead]

Just be caredul! I've always been a plant electrician, I make a great cup of tea!