Sieg lathe motor conversion

[SmithDoor]

The internal fan normally blew the carbon dust away from commutator onto the insulating mount of the brush holders, thus shorting the surface ... Check inside yours. Also some of the clearances between brush holder metal and earthed body metal were less than 0.020inch, 0.5mm. And there was evidence of arcing.
The attached are an old photos of the original brush holder that had suffered a lot of carbon dust pollution and arcing.
View attachment 158157Plus a view of the replacement brush holder installed

View attachment 158156

Arcing had occurred between the Philips assembly screws (earth to body metal) and the aluminium of the brush holder.
Also on the under-side, directly from aluminium rivet heads for the brush holder to casting metal (earth) on the body. Photos are after the whole assembly had been cleaned of l the carbon dust that covered everything.
The arcing had caused the thyristors to blow. = expensive repair.

Diagram showing fault paths that short the Thyristor in the AC to DC bridge.
View attachment 158178
Explanation: The Live to + to motor to - to Neutral is switched ON and OFF by the thyristors, according to their trigger voltage. The wave capping of the AC input by the thyristors varies according to the feedback of the control trying to maintain a constant speed of the lathe, as the load varies. At very low speeds, the DC voltage is very low, thus current low, and speed low. At high speeds, the wave capping by the thyristors is reduced, so the DC voltage presented to the motor is high, current high and speed high. At a fixed speed, if the load is seen to vary, by a speed change, such as a cutting load, then the voltage is instantly increased by the thyristors to increase Voltage as a consequence until equilibrium of the speed is achieved. – This is almost instant and undetectable in normal use.

But if arcing occurs inside the motor, or the motor connection is interrupted by worn brushes failing to make contact properly, the motor slows, and the control turns-up the voltage using the thyristors. Rapid switching of the motor on and off when brushes are worn, or when arcing occurs (short to earth at a brush) will cause a voltage spike from the back EMF from the armature – which may cause major arcing, serious damage to anything else on the mains circuit, or cause sudden current spikes that blow the mains fuse. I have seen evidence of these damaging voltage spikes and over-current on mains devices on the same circuit. The original input mains filter had blown a copper track. The power board for the speed meter low voltage supply had a shorted track between the mains input soldered points. And a Mains fuse and holder had exploded with excessive over-current ( >30A estimated as a 30A over-current device had triggered => safe.).

If the armature winding fail to earth (as mine have) from overheating OR overvoltage from damaging voltage spikes, then the diode bridge is shorted and the mains will blow fuses. And earth leakage devices. And likely thryristors, etc.
I suggest you check and clean yours, if the same type of motor.

I hope some of this makes sense?

Dave, I use low speed setting. BUT that is a belt change, not an electrical matter.

Low speed belt setting the motor is running faster.

What I am think the carbon from brushes is getting into electrical and forming a carbon resistor making the motor hotter. It something that is easily overlooked or may not even be seen.

If fan running to slow to move carbon out is where problem is.

The motor top speed is 6,000 rpm when spindle is turning 1,000 rpm .
So if turning at 100 rpm then motor is turning at 600rpm.
Fan was not designed for that Low speed to move carbon out.

You put all fans you want on outside of motor it will not move carbon from inside the motor.

Dave

 

[Steamchick]

Hi Dave, yes, I understand that, which is why my replacement system is a brushless servo motor. The unknown factors are:

• Can the servo design handle the long running at load when I am doing a considerable amount of machining?
• Does the torque a lower speed settings give me a better machine? - Or worse?
• How do I monitor the temperature - or increase cooling - when running at low speeds? - perhaps the controller has some built-in safe-guard controls = TBA!
• Will I have adequate torque at the higher speeds for the machining I do?
• Will the output bearings withstand the belt loading from the lathe cutting reaction? - It may not be designed for a high belt load (pre-tension) of my Vee-belt design, especially if only designed for Toothed (Timing) belt drives from the motor. (These have much lower pre-tension loads).

When I get the motor and controller, (in a month?) I can fit them and see how it performs.
K2

 

[Steamchick]

Hi Dave,
Just one (Academic) point you raised: "the carbon from brushes is getting into electrical and forming a carbon resistor making the motor hotter..? " The carbon from brushes was almost all being blown away from windings and brushes onto the insulator an causing it to flash-over. As in the evidence of the photos and examination of the aluminium surfaces where arcing had occurred. I am not sue how a large resistor value (low current) from the carbon dust acting as a resistor could have overheated the motor. It does not affect the continuity resistance of the commutation (Brush contact). But my electrical experience for jobs over 30 years ago tells me that carbon dust reduces the insulation resistance to the point where flash-over (tracking) will occur. This can be across insulation between segments of the commutator as well as the brush holder insulation. A hundred years or so ago, some DC machines did have "commutator fires" from carbon dust being ignited by arcing, until better design prevailed. But I have not seen evidence of commutator arcing on my motor.
I probably overheated when I was doing some work with prolonged running at a slow speed and high torque. To monitor that without contacting the core of the armature is very difficult, but "exit air" temperature from the motor may give some indication. - When the motor (fan) is slow, or load is high, the temperature will rise...
I just don't know how to monitor this?
K2

 

[SmithDoor]

Hi Dave, yes, I understand that, which is why my replacement system is a brushless servo motor. The unknown factors are:

• Can the servo design handle the long running at load when I am doing a considerable amount of machining?
• Does the torque a lower speed settings give me a better machine? - Or worse?
• How do I monitor the temperature - or increase cooling - when running at low speeds? - perhaps the controller has some built-in safe-guard controls = TBA!
• Will I have adequate torque at the higher speeds for the machining I do?
• Will the output bearings withstand the belt loading from the lathe cutting reaction? - It may not be designed for a high belt load (pre-tension) of my Vee-belt design, especially if only designed for Toothed (Timing) belt drives from the motor. (These have much lower pre-tension loads).

When I get the motor and controller, (in a month?) I can fit them and see how it performs.
K2

If took servo power feed on BP the brushes are bottom and part you see the carbon cover plate.

Dave

 

[SmithDoor]

Hi Dave,
Just one (Academic) point you raised: "the carbon from brushes is getting into electrical and forming a carbon resistor making the motor hotter..? " The carbon from brushes was almost all being blown away from windings and brushes onto the insulator an causing it to flash-over. As in the evidence of the photos and examination of the aluminium surfaces where arcing had occurred. I am not sue how a large resistor value (low current) from the carbon dust acting as a resistor could have overheated the motor. It does not affect the continuity resistance of the commutation (Brush contact). But my electrical experience for jobs over 30 years ago tells me that carbon dust reduces the insulation resistance to the point where flash-over (tracking) will occur. This can be across insulation between segments of the commutator as well as the brush holder insulation. A hundred years or so ago, some DC machines did have "commutator fires" from carbon dust being ignited by arcing, until better design prevailed. But I have not seen evidence of commutator arcing on my motor.
I probably overheated when I was doing some work with prolonged running at a slow speed and high torque. To monitor that without contacting the core of the armature is very difficult, but "exit air" temperature from the motor may give some indication. - When the motor (fan) is slow, or load is high, the temperature will rise...
I just don't know how to monitor this?
K2

I think could hard to tell because the motor used at different horse power.

But could work if run with no load in beginning . Then if temperature goes up years later at no load

Dave

 

[awake]

Interesting. Based on a very limited sample size - one Grizzly 7x14 mini-lathe - I would have thought that the typical import controller was a PWM circuit driving a DC permanent magnet motor. This is also what every treadmill motor / controller I've ever acquired has been (maybe 8-10 examples). Admittedly, one of the low-end treadmill controllers was nothing more than a primitive SCR circuit, so very similar to what you are describing above, but most have been based on AC-rectified-to-DC driven as PWM through MOSFETs or in one case, an IGBT. The Grizzly control was MOSFET based.

OTOH, the variable speed routers that I have disassembled / repaired - only a couple of samples - have been more like the typical thyristor circuit, clipping the AC circuit.

 

[SmithDoor]

Interesting. Based on a very limited sample size - one Grizzly 7x14 mini-lathe - I would have thought that the typical import controller was a PWM circuit driving a DC permanent magnet motor. This is also what every treadmill motor / controller I've ever acquired has been (maybe 8-10 examples). Admittedly, one of the low-end treadmill controllers was nothing more than a primitive SCR circuit, so very similar to what you are describing above, but most have been based on AC-rectified-to-DC driven as PWM through MOSFETs or in one case, an IGBT. The Grizzly control was MOSFET based.

OTOH, the variable speed routers that I have disassembled / repaired - only a couple of samples - have been more like the typical thyristor circuit, clipping the AC circuit.

The control board use has more the rotor.

1. Acceleration control.
2. Break
3. Consented speed control as torquegoes up.
4. high speed limit
5. Low speed limit
6. Very high current

The drill motors and rotors do not need all this is your finger will do job and a lot lower current and Los cost too.

Dave

 

[NapierDeltic]

Hi Dave, yes, I understand that, which is why my replacement system is a brushless servo motor. The unknown factors are:

• Can the servo design handle the long running at load when I am doing a considerable amount of machining?
• Does the torque a lower speed settings give me a better machine? - Or worse?
• How do I monitor the temperature - or increase cooling - when running at low speeds? - perhaps the controller has some built-in safe-guard controls = TBA!
• Will I have adequate torque at the higher speeds for the machining I do?
• Will the output bearings withstand the belt loading from the lathe cutting reaction? - It may not be designed for a high belt load (pre-tension) of my Vee-belt design, especially if only designed for Toothed (Timing) belt drives from the motor. (These have much lower pre-tension loads).

When I get the motor and controller, (in a month?) I can fit them and see how it performs.
K2

Hi Steamchick.
I am very interested in the result of your replacement.
If what I have seen on Ali is the same you have ordered, my guess is it will pass. I have an Einhell lathe which is a Sieg under cover, that recently started loosing power. I have thought to a 500W brushless spindle but looking on available sources I have seen the servo brushless motor also. From its shaft diameter and larger rotor, I would say it gives a better torque and endurance.
There is a potential problem with brushless motors (and with brushed alike) and that is the life of electronic components, especially in very hot workshops. I had an issue with what I consider the constant speed circuit of the board (on my mill) that translated in spikes that blown the fuse several times.

 

[Steamchick]

The controller. A pretty standard board, used on many machines I think? 5 Thyristors. 4 make an AC to DC bridge, controlled by a voltage from a potentiometer. - And other stuff I don't understand or even know about!
I'm explaining my problems, to help others avoid similar failures, from a lack of cleaning carbon from the brush zone (My first failure), OR when brushes get worn less than 13mm long! (My recent failure).
The FIRST TIME you hear a "phut", or "pop" or other small noise from the machine, or the speed starts to wander at NO LOAD, STOP the machine, and examine the brush holder and brushes (means dismantling the motor - mark alignment before disassembly). Use an 8A fast blow fuse in the main fuse on the machine, and hope you do not get the large BANGS! that I have experienced. - Those are expensive.
K2

 

[Steamchick]

Posty delivered a new fan today. 90 mm diameter, 12V, 0.25A. Computer brushless thing. I plan to glue it to the end of the new motor so it supports the draught from the internal fan, and gives draught when the motor is running slowly and the internal fan gets lazy.
You can never have too much Draught! Or was that a quote from a Real Beer swigging friend?
K2

 

[SmithDoor]

Posty delivered a new fan today. 90 mm diameter, 12V, 0.25A. Computer brushless thing. I plan to glue it to the end of the new motor so it supports the draught from the internal fan, and gives draught when the motor is running slowly and the internal fan gets lazy.
You can never have too much Draught! Or was that a quote from a Real Beer swigging friend?
K2

I was thinking of fan ducking air to input air on motor with real good filter for both air and oil.
Or just carbon build up like everyone else's does and buy new motor after the motor dies.

It is possible to clean motor every few years too.

Anyone can put sencer inside motor burshes for carbon builded up too. When the LED lights up time to clean .

In life most will use a tape over the LED and clean some day (never)

Dave

 

[Steamchick]

Dave, the simple problem is simple. Carbon dust is created from wearing the brushes. It is very fine, electrically charged and like smoke, blowing from brushes to an insulating board - of the opposite electric charge. So some carbon collects on the surface of the insulating board - until the surface continuity is suitable for a voltage peak to flash-over the surface... and burn-off the carbon and damage the insulator. Or carbon in the air passing a couple of sharp corners, that are assembled very close to each other, assists the air to break-down and flash-over when a high voltage spike ionises some air at a point or sharp edge. Cleaning helps prevent flashover. I used Silicon sealer where I had seen signs of flashover across air gaps, and similar places where flashover had not yet happened. It has 3 times the dielectric strength of air. But the surface of the silicon needs cleaning from Carbon dust.
Removing sharp edges and points also helps.
You won't stop some carbon from polluting the brush holder, on a motor of the same design as mine.
Good maintenance prolongs use, and saves money. Ignore it and replace when it fails.
K2

 

[Steamchick]

Andy, Post #46 - You have repaired a couple of these boards... That says it all. I bet they failed because of the MOTOR problems, because otherwise there is no reason for them to fail - if less than 25 years old (modern electronic component life before the guarantee expires, and smoke escapes!). Electronic components almost always fail either from simple overheating, (Early life failures or poor cooling of the boards in the housing) or because the related devices have drawn more current than "designed" and that has overheated the component. Voltage spikes and flash-over draw more current through the components... and they fail.
The evidence is that they are all good when new, just fail after "some use"...
I am advocating Cleaning - annually - and replacing brushes before they get to 12mm when they stop working properly, as a maintenance schedule to help keep the motors turning... and not blowing-up the electronics..
K2

 

[SmithDoor]

Andy, Post #46 - You have repaired a couple of these boards... That says it all. I bet they failed because of the MOTOR problems, because otherwise there is no reason for them to fail - if less than 25 years old (modern electronic component life before the guarantee expires, and smoke escapes!). Electronic components almost always fail either from simple overheating, (Early life failures or poor cooling of the boards in the housing) or because the related devices have drawn more current than "designed" and that has overheated the component. Voltage spikes and flash-over draw more current through the components... and they fail.
The evidence is that they are all good when new, just fail after "some use"...
I am advocating Cleaning - annually - and replacing brushes before they get to 12mm when they stop working properly, as a maintenance schedule to help keep the motors turning... and not blowing-up the electronics..
K2

It comes down to longevity, torque under power and cost.
I read ads on the brushless motors they try say a good things but do not have twist the truth . I do have few thing that brushless best part is longevity

The size motor right you probably not see any different.
It low speed you watch out for on brushless to brush on mini lathes or other tools.

Dave

FYI I think I will start a thread good for most to understand the differences.

 

[NapierDeltic]

Hi Steamchick. Can you please write down dimensions of new brushes of original lathe motor; all 3.

L.E. Do you think adding some copper spacers in the back of brushes could be a wise method to extend their life?

 

[Steamchick]

Original brushes 7mm x 17mm section x 17mm long. At 12mm long they cannot be pressed any further by the spring arrangement onto the commutator. I would have to be desperate to use a spacer under the spring as you suggest - maybe just for a necessary job while awaiting delivery of new brushes. Curiously, one brush was only worn 2~3 mm less, so because I had used my second set of brushes, I still had 2 of the old brushes at 14mm, I.E. an extra 2mm to use... while awaiting delivery of my 3rd set of brushes. But that was when I found it had blown-up the variable speed control! So please change your brushes BEFORE they get too short. And remove and examine the brush holder for any signs of arcing (black dots on aluminium, or black marks on the insulator material). Fill the gaps with silicon sealer, or other insulation with high dielectric strength. Replace an arc-damaged brush holder insulator.
New brushes from 3&@y :
Carbon Brush Blaukraft Sander Bws 230-20 -7 X 17 x 20mm
but the 7mm measure 6.9mm with a micrometer and were slack in the brush holder. Not a failure mode, but may have some effect?
K2

 

[NapierDeltic]

Thank you very much, Steamchick!
I am pretty happy with my motor level of power so I'll follow your advice.
I am still interested in the results of your motor upgrade.
A more powerful motor (in reasonable limits) cuts-off worktime, which shouldn't be ignored:

https://www.mini-lathe.com/mini_lathe/reviews/sieg_sc2/sc2.htm#google_vignette

 

[NapierDeltic]

Looks promising - at least with this controller:

 

[Steamchick]

Thanks Napier.
Looks pretty straightforward, though my installation is totally different!
I need to strip-out all the "Old" stuff first.
But a point I picked-up from the video - the fan is centrifugal, so works the same airflow both ways - IN at the end face and OUT around the sides of the body. So I shall stick my computer fan onto the end so it blows IN the end face - and ensures a good continuous cooling airflow when the motor is continuously running at slower than the factory 3000rpm setting. (say at 300rpm when the motor's fan will hardly do anything over a whisper!).
I reckon I'll spend more time on "tin-work" and fitting the controller, etc. than on the 4 holes I need to drill to mount the motor onto my existing motor bracket....
Biggest problem will be mounting the controller box, as it is configured for Sewing machines, not where I want the wires etc. on my lathe.
I'll let you know how I get on...
K2