What kind of motor is this?

[Lucien Nunes]

Interesting old machine still in use. I've talked about similar motors before but not this type AFAIK. To the trained eye, the shape of this one is a giveaway, from which you can identify its maker and the technology it uses, and probably say something about the available electrical supply. In any case the shape should tell you something. Note that the bare aluminium covers are non standard, these would normally be steel mesh vent grilles.

 

[Lucien Nunes]

Is it Stepper motor, I'm guessing because of the handle.

I meant I thought Tel's van had a starting handle!!

Is it rotor resistance controlled.

No, and all the rotor-resistance controlled motors I've ever seen have had sliprings so would have been a positive result for your previous question about that.

Split-phase (180 degree) on a farm?

As far as motors are concerned, a split-phase supply is generally used as a single-phase supply of the higher voltage. So a 230-0-230 installation would have 460V single-phase motors of otherwise ordinary construction. As it happens, this motor could optionally be used on 460V so there is a slight clue here, although not in any way to do with farming.

Historically there were special 2-phase motors for 2-phase supplies (note this is different to using two phases from a 3-phase supply as they were usually 90° apart) but again not relevant here.

Yes it's old, but we have plenty of older plant in use so not exceptional at least in my sphere.

Keep on with suggestions but I've got a meeting soon so might not reply for a while.

 

[marconi]

As a teenager I once worked on the repair of an ac repulsion motor which had a wound rotor with commutator and brushes whose axis was displaced by a few degrees from the field axis, the field coil being supplied directly by mains ac supply. The brushes were shorted I seem to remember. And I vaguely remember the displacement of the brushes could be changed by a handle for speed control.
It powered a butcher's screw meat mincer. Is the image of a similar motor? And made by BTH?

 

[telectrix]

end of the day, it's skip fodder.

 

[PEG]

.....philistine....

 

[PEG]

....is it converting anything?

 

[HappyHippyDad]

Being a domestic installer I can safely say I don't even know which part of the photo we are looking at. Interesting reading all the responses though .

 

[Lucien Nunes]

Well Marconi is close enough that I have to give it to him. Yes, made by BTH, yes brushes are shorted together and run on a comm to create rotor repulsion, yes power is applied to stator only. However, repulsion is only used for starting - it's a Repulsion-Start, Induction-Run (RSIR or R/I) machine.

There are two ways to do this. Century and others in the USA, used a centrifugal mechanism like the starting switch of a split-phase induction, but instead of operating a switch, as the motor approaches full speed it does two things. It triggers a spring-loaded actuator that lifts the brushes off the comm (to save wear) and puts a shorting ring around all the commutator segments to convert the armature into the equivalent of a squirrel cage.

This BT-H (then part of AEI) avoids the centrifugal mechanism by having two windings on the rotor. The repulsion winding brought out to the commutator, and a separate squirrel cage. At a standstill, the high slip frequency puts the cage current out of phase due to its inductance (which is why inductions typically have poor starting torque.) But the repulsion winding takes over and accelerates the motor, at a speed and direction controlled as Marconi mentions, by the setting of the brush rocker. As the speed increases and the slip frequency reduces, the cage torque dominates and the relative placing of the windings in the slots causes the magnetic flux to bypass the repulsion winding, so the motor runs as an induction. Unlike the Century there is still brush wear, but it is low because the brushes are passing minimal current.

Why go to all this complication to start an induction motor? Simply because repulsion motors have excellent starting characteristics. Smooth and torquey, without the excessive line current required by other starting methods, despite being single-phase (which were always inferior to 3-phase at starting). RSIRs handle high inertia loads and starting against full torque, but once running they are not as efficient as inductions and lack the near-constant speed. Hence, to deal with difficult loads with only single-phase power available, start as induction for best torque and lowest overcurrent, then run as induction for best efficiency and stability.

I've no idea why Tel sees it heading to the skip. It's worked fine for 80 years and will probably be good for another 80. I'm sure skips will have been banned by then.

I don't even know which part of the photo we are looking at

The round thing bottom centre

 

[marconi]

LN is a master at framing his image. Why for example:

1. Is there a box with vents? (Which looks newer vintage to the motor.)
2. are there 3 lengths of vertical conduit?
3. are there 2 lengths of flexi conduit going under the box with vents?
4. do the connections to the motor (middle conduit) not directly connect to the vented box?
5. Where do the 3 vertical conduits end up?
6. Is the bottle a clue?

 

[Lucien Nunes]

I think our posts crossed! If you know organ blowers, there are indeed lots of clues.

1. Transformer-rectifier for the 18V DC electric action. Yes it's newer.
2. To keep it off the floor, it's run across the ceiling.
3. No specific reason.
4. No, quite separate.
5. Motor supply from DOL starter, rectifier supply from contactor, rectifier output to DC busbars
6. Incidental. There are often old bottles of oil in organ blower rooms.

Organ clues include the Watkins & Watson shaft coupling, tantalising glimpse of flexible coupling top right, a similar hint of wind trunking, ancient masonry and age of plant. Organ blowers have a very high moment of inertia and have to start against heavier load that is usual for a fan or pump (because they are rated to work against backpressure and can overload the motor when filling the reservoirs). Hence the preference for an RSIR where there is no 3-phase supply.

 

[HappyHippyDad]

LN is a master at framing his image. Why for example:

1. Is there a box with vents? (Which looks newer vintage to the motor.)
2. are there 3 lengths of vertical conduit?
3. are there 2 lengths of flexi conduit going under the box with vents?
4. do the connections to the motor (middle conduit) not directly connect to the vented box?
5. Where do the 3 vertical conduits end up?
6. Is the bottle a clue?

I think our posts crossed! If you know organ blowers, there are indeed lots of clues.

1. Transformer-rectifier for the 18V DC electric action. Yes it's newer.
2. To keep it off the floor, it's run across the ceiling.
3. No specific reason.
4. No, quite separate.
5. Motor supply from DOL starter, rectifier supply from contactor, rectifier output to DC busbars
6. Incidental. There are often old bottles of oil in organ blower rooms.

Organ clues include the Watkins & Watson shaft coupling, tantalising glimpse of flexible coupling top right, a similar hint of wind trunking, ancient masonry and age of plant. Organ blowers have a very high moment of inertia and have to start against heavier load that is usual for a fan or pump (because they are rated to work against backpressure and can overload the motor when filling the reservoirs). Hence the preference for an RSIR where there is no 3-phase supply.

It's great watching the two masters spar! It's like Bobby Fisher (Marconi) and Kasparov (LN)!

 

[HappyHippyDad]

ps.. My apologies LN but I did not remove the CU containing the 45A mem fuse holder so I cannot send it to you.

 

[GBDamo]

Well Marconi is close enough that I have to give it to him. Yes, made by BTH, yes brushes are shorted together and run on a comm to create rotor repulsion, yes power is applied to stator only. However, repulsion is only used for starting - it's a Repulsion-Start, Induction-Run (RSIR or R/I) machine.

There are two ways to do this. Century and others in the USA, used a centrifugal mechanism like the starting switch of a split-phase induction, but instead of operating a switch, as the motor approaches full speed it does two things. It triggers a spring-loaded actuator that lifts the brushes off the comm (to save wear) and puts a shorting ring around all the commutator segments to convert the armature into the equivalent of a squirrel cage.

This BT-H (then part of AEI) avoids the centrifugal mechanism by having two windings on the rotor. The repulsion winding brought out to the commutator, and a separate squirrel cage. At a standstill, the high slip frequency puts the cage current out of phase due to its inductance (which is why inductions typically have poor starting torque.) But the repulsion winding takes over and accelerates the motor, at a speed and direction controlled as Marconi mentions, by the setting of the brush rocker. As the speed increases and the slip frequency reduces, the cage torque dominates and the relative placing of the windings in the slots causes the magnetic flux to bypass the repulsion winding, so the motor runs as an induction. Unlike the Century there is still brush wear, but it is low because the brushes are passing minimal current.

Why go to all this complication to start an induction motor? Simply because repulsion motors have excellent starting characteristics. Smooth and torquey, without the excessive line current required by other starting methods, despite being single-phase (which were always inferior to 3-phase at starting). RSIRs handle high inertia loads and starting against full torque, but once running they are not as efficient as inductions and lack the near-constant speed. Hence, to deal with difficult loads with only single-phase power available, start as induction for best torque and lowest overcurrent, then run as induction for best efficiency and stability.

I've no idea why Tel sees it heading to the skip. It's worked fine for 80 years and will probably be good for another 80. I'm sure skips will have been banned by then.



The round thing bottom centre

Clearer now Happyhippydad..?

 

[Lucien Nunes]

I did not remove the CU containing the 45A mem fuse holder

No worries, people keep your eyes peeled for good examples of Wylex CUs with a 45A rewireable in. Especially the type with the separate 45A way the opposite side of the main switch. Also the E7 one with normal and off-peak in the same box.

Anyway, here's a pic of a 3hp BTH RSIR of my own and its plate. Not sure why I can't delete the duplicate pics, but I have a beer to drink so it will have to do.

View attachment 49710

View attachment 49711

 

[davesparks]

Lucien, I stumbled across some cast iron control gear for vetilation equipment recently, it's going spare for anyone who can liberate it from a rooftop in charing Cross Road, are you interested?

 

[LeeH]

She’s a beauty!