Comeng Tread v's Disc v's Chopper

 
  2025 Station Master

I know the difference between the disc brake and the tread brake Comengs but I would like to know how the Chopper works.

My understanding from these pages is that the motors are used to slow the train by generating electricity back into the system but the substations in Melbourne cannot handle this.

Also I notice tht most Chopper Comeng units run with their motors turned off. How did they run for all those years when marshalled together without the Tread brake units.

Also, what type of brake is viable on the wheels? Is it Disc or tread?

Sponsored advertisement

  comeng301M Chief Commissioner

Location: Melbourne, VIC
Tread Brake Comeng Number range from
M Cars 301M - 468M, 471M - 554M
T Cars 1001T - 1084T, 1086T - 1127T

Disc Brake Comeng Numbers
M Cars 561M - 680M
T Cars 1131T - 1190T

Chopper Sets
M Cars 691M - 698M
T Cars 1196T - 1199T

for futher info visit http://www.vicsig.net/index.php?page=suburban&traintype=Comeng

hope this helps
  2025 Station Master

Thanks Comeng301m, but thats not the question I am asking. I want to know what a chopper does? Do the chopper have the same stype of brakes like the Treads?

They are also used on our trams in Melboune too.

I know what train numbers are Tread brake and Disc etc as I have seen it before on Vic Sig.
  ninthnotch Dr Beeching

Location: Not here. Try another castle.
It relates to the actual way that the motors etc are managed, not the braking system.  Someone else can explain the intracacies.
  Hitachi_Man Chief Commissioner

Location: Melbourne.
Chopper and cam shaft are different ways of making the train go basically, cam shaft is a long shaft that has many notches in it. I am not sure how chopper works but it is the more modern out of the two, and yes Melbourne trams use it.

Tread brakes and disc brakes are just the two different types of brakes and are not related to whether the train is cam shaft or chopper. Tread brakes have a block the presses against the tread on the wheels, disc brakes are a disc that is attached to a wheel and has a caliper with pads that press against the disc to stop the train.

There is also Regenerative brakes which are designed to stop the train by converting motion energy into electrical energy and feeding it back into the overhead but Melbourne's old sub-stations cant handle it so trains that have this feature just have it turned off (A waste really) rheostatic brakes work in the same way but instead of the energy going into the overhead it is just run through resistor banks to dissapate it.
  Badger Chief Commissioner

Location: Melbourne
Chopper control DOES also relate to the braking system, seeing as Melbournes tie stations can't support reflux feeding, the secondary system on the train comes into play, which is all aspects - is a rheostatic brake.

Chopper control is basically a magnetic phase shifter, it uses a quick series of 'on' 'off' to smooth out the current going into the motors.  They are quite prone to faults on a system that isn't designed for them in mind.  From memory 692M has spent more time off the road than on the road in its whole life to date.

A train has 4 different brakes - Rheo, E.P. and Auto Air and a park brake, all serve a different functions vita to stopping the train, and acting as a fail-safe device.

Rheo, any speed from 115km/h to anywhere between 15km/h to 5km/h will be used to slow the train down.  Involves using the speed of the train, to create a magnetic field oposite to the phase of the traction motors.  Causeing a repelling force and hence slowing the train down.

E.P., or Electro - Pneumatic.  Is used as the secondary brake, or primary brake if the driver chooses so.  Involves the brake handle  switching relays, which then lets a certain amount of pressure into the brake cylinders causing the brakes to retard the forward motion of the train.

Auto Air, is the last of the brake systems used to stop the train from a moving speed.  Not like the other systems, this system does NOT require power to operate.  You technically have 3 'bites of the cherry' befre you run out of air (if there is no power to run the compressor).  If all other systems fail, this one takes over.  Involves the balancing or air pressures via the brake handle, aux resivoir and the triple valve.

Park brake is just to hold the train still.  A spring will hold the brake in the 'on' possition until there is enough air pressure for the spring to be held back by air pressure in the cylinder, and therefor enough pressure to operate the brakes normally.

Hope this helps.
  Badger Chief Commissioner

Location: Melbourne
Btw, all the Chopper trains have standard westcode tread brakes.  Its not the brake rigging thats different, its the control boxes under the train.  If you look closely at a normal tread brake and a chopper train, you'll notice the difference.

If you can understand all this, it explains it quite well:

A chopper control system for controlling the amount of power supplied from a DC power source to a load having inductance. The chopper control system comprises a chopper circuit for accomplishing the on-off control of main current flowing from a DC power source to a load having inductance, and a duty cycle control circuit for controlling the duty cycle of the chopper circuit. A flywheel circuit including a series-connected circuit of a flywheel diode and a reactor is connected in inverse parallel with the load. The counter electromotive force induced in the flywheel circuit is detected by a detecting circuit and the output of the detecting circuit is applied to the duty cycle control circuit to prevent the main current from exceeding a predetermined value.
  EvanC Chief Plonker

Location: Bayswater, Victoria
run through transistor banks to dissapate it.
"Hitachi_Man"
Resistor banks. Smile
  Hitachi_Man Chief Commissioner

Location: Melbourne.
run through transistor banks to dissapate it.
"Hitachi_Man"
Resistor banks. Smile
"EvanC"
Yeah I knew that but the key board made me say the wrong thing.
  Rocket Deputy Commissioner

.

Auto Air, is the last of the brake systems used to stop the train from a moving speed.  Not like the other systems, this system does NOT require power to operate.  You technically have 3 'bites of the cherry' befre you run out of air (if there is no power to run the compressor).  If all other systems fail, this one takes over.  Involves the balancing or air pressures via the brake handle, aux resivoir and the triple valve.

Park brake is just to hold the train still.  A spring will hold the brake in the 'on' possition until there is enough air pressure for the spring to be held back by air pressure in the cylinder, and therefor enough pressure to operate the brakes normally.

Hope this helps.
"Badger"


The balancing of air pressures is initiated at the brake handle, controlled by the triple valve and is a balancing act between the brake pipe, the auxilliary reservoir and the brake cylinder.
And " three bites at the cherry "......you lost me on that one. If the power goes off you'd make the first application the last one. During daylight it would be best to try to roll in to the next scheduled stop. At night and with no headlights you'd be real smart to stop straight away. And lets not forget; no power means doors released on Comeng and Hitachis. Probably a good idea to pull up before some fool launches themself into space.
And of interest. 413M to 416M were fitted with tread brakes and Knorr equipment. They were an absolute smeg to run on the air and nobody could work out why. Have been converted to Westcode with no further problems. All other Knorr equipped trains were discs and there was never an issue with running them on the air.
I miss the sparks like a toothache !
Oh, and that park brake used to hold the train. Since it was trainlined it can be used ( against the rules ) to stop a train. A breeze on the Alamein shuttle to go down and back without touching the brake handle........I just had to try it.
  ninthnotch Dr Beeching

Location: Not here. Try another castle.
Didn't 413M-1057T-414M received at least some wheelsets etc from Hitachi 104M-1939T-169M to rectify this?
  Rocket Deputy Commissioner

Didn't 413M-1057T-414M received at least some wheelsets etc from Hitachi 104M-1939T-169M to rectify this?
"ninthnotch"


Somehow I don't think they would match up too well on the motors given the different types of drive arrangement.
However I do recall that the brake units were taken off Hitachis and that may be what you are thinking of.
Changing the wheels would not have fixed the problem that these sets were having. It was more to do with the recharge time of the auxilliary reservoirs and the lack of effectiveness of automatic brake applications subsequent to a release after the first.
  Badger Chief Commissioner

Location: Melbourne
When talking about 3 bites, I meant that in normal practise, if you were using the air (and had power to run the compressor) you have about 3 tries to stop the train including pre-releases.  Before your brake pipe doesn't have enough air to apply the brakes.  If you do run out of air, you would have to wait until the brake pipe is charged.  Which I think is 12 seconds for 3 cars, and 20 seconds for a 6 car train.

It's kinda hard to put it into words, but atleast I know what i'm talking about - and Rocket, being an ex spark driver, would understand what im on about now maybe?
  Nexas The Ghost of George Stephenson

E.P., or Electro - Pneumatic. Is used as the secondary brake, or primary brake if the driver chooses so. Involves the brake handle switching relays, which then lets a certain amount of pressure into the brake cylinders causing the brakes to smeghead the forward motion of the train.
"Badger"


Ummmm... what? Razz
  Badger Chief Commissioner

Location: Melbourne
E.P., or Electro - Pneumatic. Is used as the secondary brake, or primary brake if the driver chooses so. Involves the brake handle switching relays, which then lets a certain amount of pressure into the brake cylinders causing the brakes to smeghead the forward motion of the train.
"Badger"


Ummmm... what? Razz
"Nexas"
Ah bugger.  It's mean to say r.e.t.a.r.d.  you know, stop of hinder the forward motion of the train.  Stupid word censor!
  2025 Station Master

Thanks Badger, you have described the Chopper unit well. There hasn't been much of a forum on this topic before.

Why don't train brakes work the same as a truck which don't need air to stop, only to release the brakes. Usually a truck will not be able to move unless it has it's compressor charge and then it will be able to release the brakes. On a train i notice it needs air to operate the brake cylinders.

On the comengs, I notice from the pictures of them they only have 4 notches or numbers on the accelerator handle. Is this true?

How does the Siemens and X'trap work these days. Are they Chopper controlled?
  comeng301M Chief Commissioner

Location: Melbourne, VIC
Thanks Badger, you have described the Chopper unit well. There hasn't been much of a forum on this topic before.

Why don't train brakes work the same as a truck which don't need air to stop, only to release the brakes. Usually a truck will not be able to move unless it has it's compressor charge and then it will be able to release the brakes. On a train i notice it needs air to operate the brake cylinders.

On the comengs, I notice from the pictures of them they only have 4 notches or numbers on the accelerator handle. Is this true?

How does the Siemens and X'trap work these days. Are they Chopper controlled?
"2025"


Yes that is correct Comeng Trains have 4 notches on the acclerator handle
Siemens and X'traps do not have Chopper control equitment in them
  Badger Chief Commissioner

Location: Melbourne
There are circumstances where a train can loose brake pressure, but normally - the system is fail safe.  So if for some reason the brakes fail, they fail in the applied state.  Air needs to be discharged from the brake pipe in order for air to be put into the brake cylinders.  So if there is a loss of pressure for some reason, the brakes will apply.  Same with the park brake, once the pressure in the Main Resivoir gets below a certain amount (300kpa?) it will automatically apply due to there not being enough pressure to hold the park brake in the off position.

Notches on a Comeng/Hitachi are:

0 - Off
1 - Shunt
2 - Series
3 - Series Parallel
4 - Weak Fields

I could go into a huge explanation on what they all do, but that wasn't the question.

Siemens/X'Trapolis's use in theory, a large variable resistor.  Since they both use AC traction equipment, there is no need to smooth the current, as it's already cycling at 50Hz.  Simply, all its doing is allowing more current to pass through to the motors.
  Hitachi_Man Chief Commissioner

Location: Melbourne.
Notches on a Comeng/Hitachi are:

0 - Off
1 - Shunt
2 - Series
3 - Series Parallel
4 - Weak Fields

I could go into a huge explanation on what they all do, but that wasn't the question.
"Badger"
Pretty easy to work out IMO.
  mjja Sir Nigel Gresley

Location: Mount Waverley, Melbourne
IIRC Siemens and Xtrap use AC traction, which is quite different.

AC motors require the power to cycle at the same frequency as the rpms of the motor. That makes it very difficult to use in a transport environment, but nowadays it's possible with computers. Basically, the computer says "I want you to accelerate to this speed in the next millisecond. To do that I need to give you this much energy, and give it to you at this frequency. OK, here it is." Clever stuff indeed.
  N466 Train Controller

Location: Melbourne (East Subs)
The basic operation of Camshaft control trains is that put simply the 1500V DC is applied to traction motors through a series of resistor grids, which limit the voltage initially to the motors.

As the camshaft turns the cams operate contactors which change the resistor configurations and hence allow more voltage to the traction motors and the train speeds up, this is done in many steps, usually about 2-5 seconds apart.

These steps of acceleration can be felt by pax if sitting in a motor carriage and paying close attention as the train moves off from stopped.

This is old technology electro-mechanical motor control but by its simplicity it is very reliable.

The chopper system uses a controller (can be electronic or mechanical) to chop the DC power applied to the motors at varying rates and thus control speed, it provides a much smoother acceleration than switched resistance.

Only problem is that the chopper equipment on 692M etc is of very poor design and totally unreliable.

The Siemens and Xtrapolis trains use a combiation of varying phase and amplitude control of the AC power applied to the AC traction motors. this is all manage by on board computers in the traction control units (TCU's).

AC motors are much lighter and produce more power than the DC motors of the older trains hence along with lighter weight bodies the new trains can accelerate much faster.

N466
  2025 Station Master

How come you cannot feel the train in all instances going through the different posistions on the camshaft? I have felt it in the past and just thought the driver was using the control very roughly.

Getting back to the controller, the Comeng has only 4 notches so how does it know how to accelerate fast or slow? Does the Hitachi have a different camshaft set up as I have seen a pic of one that was open.

Are the AC controlled motors the same as stepping motors?
  Hitachi_Man Chief Commissioner

Location: Melbourne.
How come you cannot feel the train in all instances going through the different posistions on the camshaft?
"2025"
You can.
Does the Hitachi have a different camshaft set up as I have seen a pic of one that was open.
"2025"
Yes it does and is known to run for longer and require less matenance than a comeng cam shaft.

Somebody else can fill in the rest.
  Badger Chief Commissioner

Location: Melbourne
A cam on a Comeng is fan forced to keep it cool, on a Hitachi, its air cooled.  There is alot more circuitry sorounding a Comeng cam.  Whilst a Hitachi cam is quite simple compared.  IIRC, a Comeng cam has 19 steps while a Hitachi has 17.

If you pay attention when the train moves off - you can feel the train cycling up through the steps.
  2025 Station Master

So the steps are not the driver moving the control on the notches? If the driver puts the controller in position 2, the camshaft will go through each of it's steps and he train will get faster and faster.

Does this mean all Comengs will accelerate at the same speed?

Unlike the Z and the A/B's which have a pedal which the driver can floor to take off faster than if you only gently hit the pedal.

Sponsored advertisement

Display from:   

Quick Reply

We've disabled Quick Reply for this thread as it was last updated more than six months ago.