Deleted
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Amps
Aug 18, 2005 17:32:48 GMT
Post by Deleted on Aug 18, 2005 17:32:48 GMT
How many AMPS are given to the train from the track?
Taa muchly,
Sam
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Amps
Aug 18, 2005 17:54:58 GMT
Post by q8 on Aug 18, 2005 17:54:58 GMT
How many AMPS are given to the train from the track?
Taa muchly,
Sam ------------------------------------------------------------------------ Do you mean DRAWN from the juice?? Modern stock or old???
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Amps
Aug 18, 2005 18:01:49 GMT
Post by Deleted on Aug 18, 2005 18:01:49 GMT
How much can the track actually give in optimum conditions? (With no other trains about and clean rails etc..) Actually, come to think about it, drawn would be more useful to me... Modern & old please q8? Sam
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Amps
Aug 18, 2005 18:13:02 GMT
Post by q8 on Aug 18, 2005 18:13:02 GMT
Well I can tell you that some of the old stock drew very high amperages indeed. A "Q" stock for example drew 3,300 amps at startup and a CP about 2,100. An "R" Stock with all motors working about 1,200.
The champions though were the very old stocks like "F" and "T" which drew near on 4'000 amps at start. All these amperages lessened as the train accelerated.
As for these modern AC motor jobs or stock after "R" I have no Idea. "A" stock may draw about 2'000 I should think
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Deleted
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Amps
Aug 18, 2005 18:30:14 GMT
Post by Deleted on Aug 18, 2005 18:30:14 GMT
Aaah righty, thanks q8...
Would the amps consumed get higher with the Weak Field flag up?
Sam
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Amps
Aug 18, 2005 18:46:59 GMT
Post by q8 on Aug 18, 2005 18:46:59 GMT
Not really. Weak field only comes into play after top notch is reached
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Deleted
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Amps
Aug 18, 2005 18:57:48 GMT
Post by Deleted on Aug 18, 2005 18:57:48 GMT
So if some trains took 4000 ( ) odd amps to start, how many were actually avaliable on average? One for Tom or aetearlscourt! Sam
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Amps
Aug 18, 2005 19:04:46 GMT
Post by q8 on Aug 18, 2005 19:04:46 GMT
No you have the wrong idea. If you look at the ammeter in a sub-station the needle is generally at zero with no train in section. Even with a train in the area amperage being drawn is on the low side until he starts to motor. It's the POTENTIAL in the current rails that does the business. I can't really explain potential but someone here will know.
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Deleted
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Amps
Aug 18, 2005 19:18:04 GMT
Post by Deleted on Aug 18, 2005 19:18:04 GMT
Aaah right, so amps are only supplied as needed then? That would explain breakers dropping with too much electricity is being put out for trains, passing the POTENTIAL for the rails etc?
Sam
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Amps
Aug 18, 2005 19:25:03 GMT
Post by q8 on Aug 18, 2005 19:25:03 GMT
No No No Mr C. It's not the PUTTING OUT it's the TAKING OF that determines these things. Electricity is like a horse. You can't PUSH it. It has to be led.
Imagine electricty like some deadly snake. It lies there doing nothing at all until someone comes along and touches it. THEN it strikes. Electricity has only one aim. To get back to earth where it came from. All humans do is utilise that and make it do some work along the way.
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Deleted
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Amps
Aug 18, 2005 19:30:36 GMT
Post by Deleted on Aug 18, 2005 19:30:36 GMT
That's what I meant really, wrong wording! So do trains complete the circuit to take the electricity, or do they 'suck' it out so to speak? Where is it earthed too? Sam
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Amps
Aug 18, 2005 19:38:19 GMT
Post by q8 on Aug 18, 2005 19:38:19 GMT
A power station literraly sucks electricity out of the earth via what is mis-named a generator for want of a better word. ("extractor" would be closer) A substation gets it's power by sucking it from the power station
A train enters section and immediately it does so current is sucked from the substation to that train via the positive conductor rail. The equipment on the train uses it for whatever purpose and whatever it does not use us sucked back to the sub via the negative conductor rail and the the Earth itself will suck it back into the ground.
That in simple terms is how the whole cycle works.
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Deleted
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Amps
Aug 18, 2005 19:40:25 GMT
Post by Deleted on Aug 18, 2005 19:40:25 GMT
Aaah right, so the circuit isn't complete before the train passes over the pos and neg rails?
Sam
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Amps
Aug 18, 2005 19:42:51 GMT
Post by q8 on Aug 18, 2005 19:42:51 GMT
Got it in one !! NO circuit is complete until something uses it.
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Deleted
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Amps
Aug 18, 2005 19:47:04 GMT
Post by Deleted on Aug 18, 2005 19:47:04 GMT
Aaaah superbo, thanks for the explanation(s) Q8... very helpful!
Taa muchly,
Sam
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Amps
Aug 18, 2005 22:36:16 GMT
Post by compsci on Aug 18, 2005 22:36:16 GMT
It might help to go back to the classic simple physics experiment of the hand operated generator attached to a light bulb.
If no bulb is attached, the generator handle is really easy to spin as there is no load on it. The more bulbs you add to the circuit, the harder it gets to keep the handle turning with sufficient speed to keep them all lit.
Now just replace the hand generator with the feed from the national grid and the bulbs with trains and you should be able to see that more energy is needed with more/faster trains, but this energy is only supplied at the rate at which it is needed.
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Deleted
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Amps
Aug 22, 2005 10:32:44 GMT
Post by Deleted on Aug 22, 2005 10:32:44 GMT
its like when we have a possesion in sidings or depots the train maintainers have to make sure the train is totally dead as the start up current for upto 6 trains or more is too much for the breakers in the substation then they have to go round turning back on the trains one by one
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Phil
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Amps
Aug 22, 2005 10:56:12 GMT
Post by Phil on Aug 22, 2005 10:56:12 GMT
Right Sam- a bit of GCSE Physics.
Imagine the posi rail as a water reservoir at a great height. The neg rail is at ground level. The difference in heights gives you the VOLTAGE (potential if you like). Nothing at the moment is happening. Now you open a tap in the downpipe (a train starts to motor). Water flows out of the tap (it is NOT sucked). The amount of water flowing corresponds to the CURRENT being taken. As long as there is water in the top reservoir the pressure (voltage) stays the same.[ If you increase the height of the reservoir the pressure (voltage) increases and when the tap is opened it can push harder if needed.] A fuse or circuit breaker trips if there is too much CURRENT, whatever the voltage. Reason is that flowing current always creates heat and too much heat is dangerous. So too many trains starting at once could create a trip, not necessarily on the train but in the supply.
Hope this helps
Phil
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Amps
Aug 22, 2005 12:23:40 GMT
Post by Deleted on Aug 22, 2005 12:23:40 GMT
rbruce - you got to that one before me - was thinking about a similar analogy to explain it.
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Phil
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Amps
Aug 22, 2005 13:01:21 GMT
Post by Phil on Aug 22, 2005 13:01:21 GMT
rbruce - you got to that one before me - was thinking about a similar analogy to explain it. I hope I did- I was a physics teacher in a former life!!
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Deleted
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Amps
Aug 22, 2005 13:11:29 GMT
Post by Deleted on Aug 22, 2005 13:11:29 GMT
thats just how my physics teacher would put it.
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Aug 22, 2005 13:11:38 GMT
Post by Deleted on Aug 22, 2005 13:11:38 GMT
Right Sam- a bit of GCSE Physics. Imagine the posi rail as a water reservoir at a great height. The neg rail is at ground level. The difference in heights gives you the VOLTAGE (potential if you like). Nothing at the moment is happening. Now you open a tap in the downpipe (a train starts to motor). Water flows out of the tap (it is NOT sucked). The amount of water flowing corresponds to the CURRENT being taken. As long as there is water in the top reservoir the pressure (voltage) stays the same.[ If you increase the height of the reservoir the pressure (voltage) increases and when the tap is opened it can push harder if needed.] A fuse or circuit breaker trips if there is too much CURRENT, whatever the voltage. Reason is that flowing current always creates heat and too much heat is dangerous. So too many trains starting at once could create a trip, not necessarily on the train but in the supply. Hope this helps Phil So the tap opening corresponds to the circuit being completed by the train starting to motor? That definately helps... Sam
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Amps
Aug 22, 2005 13:17:30 GMT
Post by Deleted on Aug 22, 2005 13:17:30 GMT
I hope I did- I was a physics teacher in a former life!! I feel totally humbled - it beats my A level. (Knowing he's beaten, goes quietly )
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Phil
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Amps
Aug 22, 2005 14:23:32 GMT
Post by Phil on Aug 22, 2005 14:23:32 GMT
So the tap opening corresponds to the circuit being completed by the train starting to motor? That definately helps... Sam Yup- series opens it a bit, as it notches up tap opens more, more again for parallel. BUT with motors the faster it goes the less current it needs so, once in full parallel, speeding up the motor gradually closes the tap. That's a bit oversimplified but I won't go further at this stage coz we'd have to get into back e.m.f. which is a real load of fun (and that's why I have deliberately avoided weak field).
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Colin
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Amps
Aug 23, 2005 2:31:57 GMT
Post by Colin on Aug 23, 2005 2:31:57 GMT
Great way to explain it! I wanna go!
So as the motor increases and needs less, it's like a toilet cistern filling up. The more it fills, the less it needs, so the flow slows until no more is needed.
Right?
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Phil
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Amps
Aug 23, 2005 10:03:50 GMT
Post by Phil on Aug 23, 2005 10:03:50 GMT
Great way to explain it! I wanna go! So as the motor increases and needs less, it's like a toilet cistern filling up. The more it fills, the less it needs, so the flow slows until no more is needed. Right? Yes-ish! At the balancing speed (the 'maximum' speed of the motor) a little current is still needed to overcome friction etc. but basically current for the motion drops to zero. Thats why you only ever burn out your electric drill/mower/strimmer at stalling speeds: it can't burn out at running speed. It's also why electric motors don't need governors- they are self governing at the balancing speed. [And basically weak field simply interferes with this balancing speed]
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Amps
Aug 23, 2005 10:38:21 GMT
Post by Deleted on Aug 23, 2005 10:38:21 GMT
That's a bit oversimplified but I won't go further at this stage coz we'd have to get into back e.m.f. which is a real load of fun (and that's why I have deliberately avoided weak field). Please explain back emf and weak field - I never did understand it. (I know this will probs be waaaaay above most people's 'level', so I'll go and get a life immediately afterwards!)
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Aug 23, 2005 10:56:55 GMT
Post by Deleted on Aug 23, 2005 10:56:55 GMT
Back E.M.F. is a flow of current produced by a motor as a direct result of the function it provides.
Basically, as the motor armature spins within the charged electromagnetic windings, it not only acts as a motor, but also as a generator - IIRC this is due to the way motor windings are designed. The current produced by this activity is called "Back E.M.F.", and it interferes with the input current making the motor go.
Someone above mentioned "balancing speed" - when the Back E.M.F. matches the energy being input into the motor, the electromagnetic windings in the motor become saturated, the balancing speed of the motor is reached and it will never go any faster.
Weak Field is a neat workaround to the problem of Back E.M.F. It works by inserting a set of resistances into the input circuit to the motor. By doing so, the Back E.M.F. is disrupted and the electromagnetic field generated by the windings weakens, allowing more energy into the motor and permitting it to go faster. Rinsing and repeating with more resistances further disrupts Back E.M.F. and allows the motor to go faster and faster.
okeydoke, where's Q8...
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Phil
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Amps
Aug 23, 2005 11:38:31 GMT
Post by Phil on Aug 23, 2005 11:38:31 GMT
Back E.M.F. is a flow of current produced by a motor as a direct result of the function it provides. Back EMF is a voltage, such that back EMF is proportional to speed: i.e. double motor speed, double back EMF. Nothing to do with design- it's fundamental physics back EMF is a voltage in the opposite direction to supply voltage (as ikea says, because spinning motor can't help but act as generator as well), and current depends on net voltage, so bigger back EMF = lower net voltage = lower current when back EMF gets big enough it (almost) equals supply voltage so by definition cannot get any bigger. Now the motor just cannot get any faster. Electromagnetic field strength has not changed at all up to this point weak field acts on the current to the electromagnets. Big field = big 'push' so lots of torque for starting (and lots of current). Once up to speed not nearly so much 'push' is needed to maintain speed. What weak field does is to reduce current to electromagnets (there is a choice of how this is done, one is by field divert) and so the strength of the field itself , so the motor acting as generator does not have to push so hard against this field. Result is it can go faster before back EMF = forward voltage. I'm dreading the questions I'm going to be asked at the next meet....
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Phil
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Amps
Aug 23, 2005 11:51:37 GMT
Post by Phil on Aug 23, 2005 11:51:37 GMT
I hope I did- I was a physics teacher in a former life!! I feel totally humbled - it beats my A level. (Knowing he's beaten, goes quietly ) you'd love to know that until 10 years ago this was all part of the basic A level Physics course!
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