Power notches on modern emu

darwins

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6 Jan 2018
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York
Looking at power handles on electric multiple units, I notice in cab pictures that almost all modern electric units (even Pendolinos!) have 5 notches 0, 1, 2, 3, 4 (with Siemens Desiro units having an extra notch). This seems to be true both for separate power handles and combined power and brake controllers.

At first sight this looks like the old control system for dc motors using pneumatic cams for automatic acceleration - OFF / Shunt / FULL SERIES / FULL PARALLEL / WEAK FIELD.

However, I am pretty sure that nothing built after 1990 used such a system. Mostly AC motors now and solid state control. So why the notches? Are they equivalent?

I would expect Notch 1 would give minimal power for shunting, but beyond that how does it work?
Do all the notches offer automatic acceleration? (Simply corresponding to different maximum power outputs or speeds). Or do you have to "notch up"? Do different notches provide different rates of acceleration? (For different conditions of adhesion).
 
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hexagon789

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Looking at power handles on electric multiple units, I notice in cab pictures that almost all modern electric units (even Pendolinos!) have 5 notches 0, 1, 2, 3, 4 (with Siemens Desiro units having an extra notch). This seems to be true both for separate power handles and combined power and brake controllers.

At first sight this looks like the old control system for dc motors using pneumatic cams for automatic acceleration - OFF / Shunt / FULL SERIES / FULL PARALLEL / WEAK FIELD.

However, I am pretty sure that nothing built after 1990 used such a system. Mostly AC motors now and solid state control. So why the notches? Are they equivalent?

I would expect Notch 1 would give minimal power for shunting, but beyond that how does it work?
Do all the notches offer automatic acceleration? (Simply corresponding to different maximum power outputs or speeds). Or do you have to "notch up"? Do different notches provide different rates of acceleration? (For different conditions of adhesion).
Not sure how Pendolinos/Electrostars are set up, but the late-1980s Mk3 units such as the 321s are set up:

OFF
Notch 1 - minimal power, used for shunting/low speed movement
Notch 2 - half power
Notch 3 - full power, generally enough to maintain 100mph on the level
Notch 4 - weak field, opens the weak field contact at about 40mph.

A very similar arrangement to old camshaft control, except you can reduce/increase power to your heart's content rather than having to shut-off and apply a lower notch to reduce power.
 

Llama

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29 Apr 2014
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I understand, and might be wrong on this, that the lowest notch being 'shunt', while having one meaning on the railway, was named that because it effectively created an electrical shunt between the field and armature coils of DC motors which were prevalent until recent times.

On a 319 field weakening happens at about 25mph and only in power notch 4 (but if power is then reduced to lower notches the field weakening stays active in those notches).
 

Fincra5

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6 Jun 2009
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1,920
Looking at power handles on electric multiple units, I notice in cab pictures that almost all modern electric units (even Pendolinos!) have 5 notches 0, 1, 2, 3, 4 (with Siemens Desiro units having an extra notch). This seems to be true both for separate power handles and combined power and brake controllers.

At first sight this looks like the old control system for dc motors using pneumatic cams for automatic acceleration - OFF / Shunt / FULL SERIES / FULL PARALLEL / WEAK FIELD.

However, I am pretty sure that nothing built after 1990 used such a system. Mostly AC motors now and solid state control. So why the notches? Are they equivalent?

I would expect Notch 1 would give minimal power for shunting, but beyond that how does it work?
Do all the notches offer automatic acceleration? (Simply corresponding to different maximum power outputs or speeds). Or do you have to "notch up"? Do different notches provide different rates of acceleration? (For different conditions of adhesion).
On an Electrostar there's nothing stopping you getting to 100mph (90mph DC) in Notch 1 (of 4). It will take you a long time however! :D It's just how much power is put down; basically 25%, 50%, 75% and 100%.

Its useful for keeping the train to the White Line when gradients come into play.
 

St. Paddy

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11 Sep 2019
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Hitchin
Not sure about 717s but on a 700 the 'notches' are on the HMI display at 20% intervals.
There’s a power percentage gauge on both units but although there are marks representing every 20%, they’re not strictly notches as you can vary infinitely in between.
 

ComUtoR

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they’re not strictly notches as you can vary infinitely in between.
Drivers are weird creatures at times. They have been adding hand drawn 'notches' since day 1. When I swing the handle down, due to muscle memory, I can put it in almost the exact same spot each time. That spot is marked in pen by other Drivers. Same with the brake. Hand drawn 'notch' marks that I can brake at without thinking.

I'd be interested to know if in other units without traditional notches, they get drawn in.
 

St. Paddy

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Drivers are weird creatures at times. They have been adding hand drawn 'notches' since day 1. When I swing the handle down, due to muscle memory, I can put it in almost the exact same spot each time. That spot is marked in pen by other Drivers. Same with the brake. Hand drawn 'notch' marks that I can brake at without thinking.

I'd be interested to know if in other units without traditional notches, they get drawn in.
Most 717s have a mark where someone thinks it’s a good holding position for the brake whilst stationary.
 

37057

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3 Jul 2009
Messages
343
Sounds like vandalism!

Cl.350 power wise.... the Power-Brake Controller (PBC) essentially closes micro-switches to operate relays which then provide each Tration Control Unit (TCU) with three 110V signals (Traction A, B and C). The circuit is fitted with interlocking relays so that power can only be obtained in the correct condition (DRA off etc). The PBC is also fitted with a position encoder which transmits to the TCUs via MVB / TMS for variable power demand. Cl.185 actually works the same way except the signals are sent to the Voith "Power Unit Interface" modules. The brake system on both EMU and DMU work the same way except there are only two service brake 110V input signals (A and B) and are sent to the Brake Control Unit (BCU), with the TMS overlay working in the same manner.
 

apinnard

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2 Aug 2017
Messages
110
Not sure how Pendolinos/Electrostars are set up, but the late-1980s Mk3 units such as the 321s are set up:

OFF
Notch 1 - minimal power, used for shunting/low speed movement
Notch 2 - half power
Notch 3 - full power, generally enough to maintain 100mph on the level
Notch 4 - weak field, opens the weak field contact at about 40mph.

A very similar arrangement to old camshaft control, except you can reduce/increase power to your heart's content rather than having to shut-off and apply a lower notch to reduce power.
Notch 4 for the infamous Brentwood Bank?
 

380101

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18 Feb 2015
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783
Drivers are weird creatures at times. They have been adding hand drawn 'notches' since day 1. When I swing the handle down, due to muscle memory, I can put it in almost the exact same spot each time. That spot is marked in pen by other Drivers. Same with the brake. Hand drawn 'notch' marks that I can brake at without thinking.

I'd be interested to know if in other units without traditional notches, they get drawn in.
It's the same in the 380 which has the same controller and HMI as the 700s. Hand drawn or scratched notches for power, additional speeds marked round the outside of the speedo etc - how some can't work out that 90 is the next big line after 80 on the speedo I do not know!
 

rebmcr

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additional speeds marked round the outside of the speedo etc - how some can't work out that 90 is the next big line after 80 on the speedo I do not know!
Not a driver, but I find it easier when I can see things 'at a glance' rather than taking the time and effort to 'work it out'. Even if it's a fraction of a second, it breaks the flow and takes attention away from the main task.
 

westcoaster

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DTOS A or B
Drivers are weird creatures at times. They have been adding hand drawn 'notches' since day 1. When I swing the handle down, due to muscle memory, I can put it in almost the exact same spot each time. That spot is marked in pen by other Drivers. Same with the brake. Hand drawn 'notch' marks that I can brake at without thinking.

I'd be interested to know if in other units without traditional notches, they get drawn in.
Exactly this, every time with out fail or looking 60% power or 60% brake. 700's do not need anymore than this.
The drawn line always come upto 40% ( less than the old notch 2 / single yellow operating instruction).
 

TRAX

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Paris, EU
At first sight this looks like the old control system for dc motors using pneumatic cams for automatic acceleration - OFF / Shunt / FULL SERIES / FULL PARALLEL / WEAK FIELD.

However, I am pretty sure that nothing built after 1990 used such a system.
Indeed. Camshaft traction control has been replaced quite a while ago, first with GTO (Gate Turn-Off) systems, and now with IGBT (Insulated Gate Bipolar Transistor) systems.
 
Last edited:

Nick Ashwell

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20 Dec 2018
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182
Even on the smooth controls without notches are they actually smooth dials inside or are they notched so much that it feels smooth (I forget the technical names for the types of electrical switch)
 

Llama

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The ones on the CAF units seem to be both, you can take whatever %age traction power you like from 1% to 100%, but there are a couple of discrete clicks as you go through the range.
 

driver9000

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The ones on the CAF units seem to be both, you can take whatever %age traction power you like from 1% to 100%, but there are a couple of discrete clicks as you go through the range.
They're the relay positions when running in degraded mode without the CCU. Handy to listen out for though.
 

Panupreset

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8 May 2015
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Notch 4 for the infamous Brentwood Bank?
Yes! And even then you will struggle to maintain linespeed (90mph). It’s up hill gradient for long stretches after Stratford on the down. Line speed is 80mph through Shenfield so if your not stopping there loosing speed up the bank isn’t all that much of a problem. If I am stopping at shenfield then usually I will shut off just past Brentwood and the gradient and curvature will wash off some of speed which is handy as it’s a low adhesion area.
On the up I leave Shenfield and accelerate up to 80 and shut off which will be around Seven Arches bridge and the downhill gradient will bring the sped up to about 90mph by around soon after the M25.
 

37057

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3 Jul 2009
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They're the relay positions when running in degraded mode without the CCU. Handy to listen out for though.
I always consider the three step brake to be the "normal" brake, with the variable CCU braking as secondary even though it's reliable. They're the signals the OTMR reads after all!
 

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