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Mark Pelham
Joined: 05 Sep 2008
Posts: 5
Location: Crawley, UK
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 Posted: Mon Nov 03, 2008 7:14 pm Post subject: Class 103 additional feature! |
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Hi All,
This is my first post on any forum but thought you may be interested in what I found today.
Whilst running in my latest 103 series unit today, at some stage one of the pickup springs in a powered unit decided to become a bar heater and melt a hole in the side of the plastic body!javascript:emoticon(' ')
It may have occurred during a derailment, I was using a conventional controller to run two trains (on different tracks)simultaneously!javascript:emoticon(' ')
Never mind, more reason to rebuild the bodies!javascript:emoticon(' ')
Mark |
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David K Smith
Chief Cook and Bottle Washer
Joined: 03 Sep 2008
Posts: 435
Location: New Jersey, USA
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| Posted: Mon Nov 03, 2008 8:31 pm Post subject: |
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Mark, welcome to the forum!
Running T on a conventional throttle? Erm... their rated maximum is 4.5 VDC, so it's no wonder you invented a new form of space heater...
_________________
—David
http://www.t-gauge.net/
http://1-450.blogspot.com/ |
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Claude_Dreyfus
Joined: 21 Sep 2008
Posts: 12
Location: West Sussex - UK
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| Posted: Mon Nov 03, 2008 8:45 pm Post subject: |
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Ouch! 
As David said, these are such dinky motors that anything stronger than a AA battery-powered controller would fry the little blighter! Still, as you say, at least you have the basis for something interesting to convert them to.
Also interesting to see another T Gauger only a couple of miles up the road from me  |
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Mark Pelham
Joined: 05 Sep 2008
Posts: 5
Location: Crawley, UK
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| Posted: Mon Nov 03, 2008 9:06 pm Post subject: |
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I realise the voltage is lower so I only used a fraction of the controllers output. I also thought that the extra two motorised cars would help by the increased current draw. I suppose the current capacity of the controller is far greater than the Eishindo controller such that the overload didn't trip!
Oh well, at least it can be put down to part of the T scale learning curve!
I shall post photos of my layout plan and the actual thing once I start construction. I have all the track, I just need some foamboard to start building the base.
Cheers,
Mark |
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David K Smith
Chief Cook and Bottle Washer
Joined: 03 Sep 2008
Posts: 435
Location: New Jersey, USA
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| Posted: Mon Nov 03, 2008 9:11 pm Post subject: |
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| Mark Pelham wrote: | I realise the voltage is lower so I only used a fraction of the controllers output. I also thought that the extra two motorised cars would help by the increased current draw. I suppose the current capacity of the controller is far greater than the Eishindo controller such that the overload didn't trip!
Oh well, at least it can be put down to part of the T scale learning curve! |
If the power supply had any sort of pulse (even just ripple from lack of filtering), the motor may receive considerably more voltage than you think it's getting. The only guaranteed safe way to operate them is with the supplied throttle. The only alternative to this I could recommend is a custom PWM circult that ensures nothing past 4.5 V is delivered to the rails.
_________________
—David
http://www.t-gauge.net/
http://1-450.blogspot.com/ |
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Chris333
Joined: 25 Sep 2008
Posts: 74
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David K Smith
Chief Cook and Bottle Washer
Joined: 03 Sep 2008
Posts: 435
Location: New Jersey, USA
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Chris333
Joined: 25 Sep 2008
Posts: 74
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| Posted: Mon Nov 03, 2008 9:40 pm Post subject: |
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Yeah I ordered all the components to try it myself  |
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JohnDMJ
Joined: 21 Sep 2008
Posts: 34
Location: Hampshire - UK
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| Posted: Sat Nov 08, 2008 1:58 am Post subject: |
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long time since I played with a 555. Can't remember its operating voltage, but anything that operates on pulse width modulation has to be better for motor control than adjusting a continuous voltage level - let's face it, even railways at 12":1foot (1000mm:1m for the metricated amongst us!) use a form of pwm in the inverter controllers so much in use today. (If an electric train appears to change gear [from the high pitched whine that is clearly audible] then it's running an inverter-based, hence pwm, system!)
I was trying to find a controller circuit from an English magazine called 'Everyday Electronics' from the mid 1970's; it used a CA3046 chip (very high tech then:wink:) to generate a PWM controller that was not voltage dependent, IIRC.
(Techie aside for the uninitiated: pwm (pulse width modulation): in a given (fixed) timespan, blast the motor with full voltage for a controllably adjustable length of time such that the sum of time blasted + time not blasted always equals the fixed timespan. The shorter the blast, the slower the speed of the train.) |
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David K Smith
Chief Cook and Bottle Washer
Joined: 03 Sep 2008
Posts: 435
Location: New Jersey, USA
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| Posted: Sat Nov 08, 2008 2:06 am Post subject: |
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| JohnDMJ wrote: | long time since I played with a 555. Can't remember its operating voltage, but anything that operates on pulse width modulation has to be better for motor control than adjusting a continuous voltage level - let's face it, even railways at 12":1foot (1000mm:1m for the metricated amongst us!) use a form of pwm in the inverter controllers so much in use today. (If an electric train appears to change gear [from the high pitched whine that is clearly audible] then it's running an inverter-based, hence pwm, system!)
I was trying to find a controller circuit from an English magazine called 'Everyday Electronics' from the mid 1970's; it used a CA3046 chip (very high tech then:wink:) to generate a PWM controller that was not voltage dependent, IIRC.
(Techie aside for the uninitiated: pwm (pulse width modulation): in a given (fixed) timespan, blast the motor with full voltage for a controllably adjustable length of time such that the sum of time blasted + time not blasted always equals the fixed timespan. The shorter the blast, the slower the speed of the train.) |
Just to reassure folks, and to make a distinction, the "blasting" taking place here is never more than the maximum voltage of the power source. This must be contrasted with more traditional "pulse power," which helps motors along at lower speeds by feeding them very short spikes of voltage in excess of the maximum, as much as 50% or more.
_________________
—David
http://www.t-gauge.net/
http://1-450.blogspot.com/ |
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JohnDMJ
Joined: 21 Sep 2008
Posts: 34
Location: Hampshire - UK
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| Posted: Sat Nov 08, 2008 2:09 am Post subject: |
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| Chris333 wrote: | | I wonder if this circuit would work? |
At a quick glance, don't see why not as long as there is enough to get the 555 awake (see other post). Bang a BD131 (or BC127[? - it's been a while ]-BD131 Darlington pair) on the output and there's no reason for it not to IMHO. [That will save the 555 having to provide the current for the motor, for which it is not designed.)
I'm off to buy some bits to breadboard this up and will feed results back here.
(My normal controllers tend to use BD131 or 2N3055 for the output stages; 2N3055 is perhaps overkill for this stage based on power consumption!! )
Last edited by JohnDMJ on Sat Nov 08, 2008 2:29 am; edited 1 time in total |
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JohnDMJ
Joined: 21 Sep 2008
Posts: 34
Location: Hampshire - UK
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| Posted: Sat Nov 08, 2008 2:20 am Post subject: |
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| David K Smith wrote: | | Just to reassure folks, and to make a distinction, the "blasting" taking place here is never more than the maximum voltage of the power source. This must be contrasted with more traditional "pulse power," which helps motors along at lower speeds by feeding them very short spikes of voltage in excess of the maximum, as much as 50% or more. |
Thanks for making that point; "blast" was probably the wrong word, but, yes, pwm = bursts of full supply voltage to the motor for varying lengths of time.
In my work, I've seen motors 'designed' for much larger voltages go up in flames!
Just one point, though, but pwm relies on the inertia of the moving item to carry it through the slacks (non-blasts) of full power so there may be a trade-off given the light weight and magnetic adhesion of these trains. Only experimentation will tell!
J |
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David K Smith
Chief Cook and Bottle Washer
Joined: 03 Sep 2008
Posts: 435
Location: New Jersey, USA
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| Posted: Sat Nov 08, 2008 2:35 am Post subject: |
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| JohnDMJ wrote: |
Just one point, though, but pwm relies on the inertia of the moving item to carry it through the slacks (non-blasts) of full power so there may be a trade-off given the light weight and magnetic adhesion of these trains. Only experimentation will tell! |
That's where it's good to be able to vary the frequency. High-end PWM throttles allow you to adjust both the pulse width and the pulse rate in order to find the motor's "sweet spot" of operation.
_________________
—David
http://www.t-gauge.net/
http://1-450.blogspot.com/ |
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JohnDMJ
Joined: 21 Sep 2008
Posts: 34
Location: Hampshire - UK
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| Posted: Sat Nov 08, 2008 2:39 am Post subject: |
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| Good point - but you're going to need an NE556 or two NE555s to achieve this! |
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Chris333
Joined: 25 Sep 2008
Posts: 74
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