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CDU
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 Posted: Fri Nov 25th, 2016 02:03 am
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Si.
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Hi Peter :wave:

If you downgrade to a C.D.U in the future...
...allow some spare finance for a pair of industrial protection goggles & gauntlets !

The D.C. arcing & sparks flying out of your stud panel could be a serious health & safety issue.
Better safe, than sorry.

It's a good idea as well, to make sure the stud panel is screwed down really firmly.
If the probe gets welded to a stud in the panel, just pull very hard.
Wearing the gauntlets, of course.

If conditions are humid or damp, Wellington boots are a must !
You could be unlucky & get a massive electric-shock from the charged capacitor, should you accidentally touch the probe.
Last time I shorted out a reservoir capacitor, the arc took a big chunk out of my screwdriver !!

Take care.

:moose:

Si.



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 Posted: Fri Nov 25th, 2016 02:11 am
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2foot6
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Hmmmm,food for thought there Si.We don't have wellington boots in aussieland,we have gum boots(same thing).As for the electric shock from the capacitor I can't have .I have a defibrillator,pace maker and CRT unit in my chest,shocks and magnetic fields are a real no no.So what is the voltage on the output of a CDU? .....cheers Peter

Last edited on Fri Nov 25th, 2016 02:12 am by 2foot6



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 Posted: Fri Nov 25th, 2016 03:53 am
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Si.
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Hi Peter :wave:

It's not so much the Voltage, but the powerful current that could be hazardous.

The Voltage on a C.D.U could be anything you want, depending on what transformer P.S.U you use.
Perhaps anything between 9 Volts & 16 Volts.

The capacitor (depending on it's size) stores & can deliver a fairly hefty charge.
This is what all the talk about burned out switches & welded contacts is all about.

With an A.C. circuit, there is no capacitor, charge is stored within the A.C. transformer.
It simply just doesn't have the capability, to deliver such 'high rushes of energy'.

Peco point-motors & switches are so light-duty & work so smoothly, without friction, this high rush of energy simply isn't needed.
Old vintage stuff like the clunky Marklin & H&Ms I had, are hefty bits of kit, THOSE are the ones that may well NEED use of a C.D.U. to throw them.
I suspect you could easily throw a smooth Peco turnout & solenoid combo, with a simple 9 Volt battery.
Not much danger in one of those.

I'm not suggesting using a battery BTW, just saying.

Best I can explain.

:moose:

Si.



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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Fri Nov 25th, 2016 08:47 am
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Helmut
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For years, I have been helping other people to make their layouts operational. One of the critical issues always was the reliable operation of turnouts. In Germany, the ubiquituous H0 brands used are Märklin and Roco/Fleischmann. Their standard solenoid turnout motors have a tendency to become a bit sticky with age, that is >3yrs. This is also true for the actual M.  C-track system. Generally no problem, but if you try to operate some of them in parallel, e. g. in a crossover, one or both of the motors will get stuck halfway, especially after you operate them after a longer break. This is most annoying with Märklin C-track, as the motors are mounted underneath the turnout and no longer are easily accessible once the tracks have been put down and embedded in scenery.
The 16VAC simply do not suffice. I've devised two CDUs that cured these problems once and for all.
The upper sketch is normally sufficient for everything except Märklin, whereas the lower one has proven to operate up to four Märklin drives satisfactorily. It is a voltage doubler delivering some 40V, which in turn provides enough current for that split second it is needed to throw the switches over.
The lamp serves as current limiter, charge and problem indicator. As most of today's drives have a built-in cutoff at the end of travel, a lamp that stays on when one pushes the respective button twice shows that there is either a stuck turnout or a cutoff that is shorted out.

Attachment: CDU.jpg (Downloaded 17 times)

Last edited on Fri Nov 25th, 2016 08:50 am by Helmut



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 Posted: Fri Nov 25th, 2016 09:16 am
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2foot6
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Thank you Helmut for the circuit diagrams,I will make the top CDU as I have the components in my training room.The voltage doubler circuit would be to risky for me.I will post the results in a few days.........Peter



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 Posted: Fri Nov 25th, 2016 02:06 pm
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Si.
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Hi Helmut :wave:

I would expect to see a semiconductor featured in a very basic C.D.U circuit.

The circuits shown are of a 'standard' D.C. rectifier/smoothing P.S.U to me.
Except for the light bulb...
...no different than D.C. from a 'wall wart' P.S.U. really.

What decent quality push-button switch would you recommend...
...that can cope with the massive-surge, without welded-contacts/failure etc. ?

A difficult and/or expensive item to find ?

:moose:

Si.



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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Fri Nov 25th, 2016 03:08 pm
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Helmut
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@Si
A solenoid's force is determined by the current you drive through the coil's windings. If that force doesn't suffice, you can do two things:
1. Use DC instead of AC - you do not have any inductive resistance - the current increases. But there are, as you noted, sometimes detrimental side effects.
2. Increase the voltage, because that leads to increased current.

Now, if you use a capacitor-diode combo as a half-wave rectifier, the capacitor charges to ~ 1.4times the effective voltage value. 16V become ~22V to operate with. As this is DC now, the current driving the solenoid is determined just by the coil's resistance, which is in the 12..30 Ohms range ( the Märklin ones have 22 Ohms for example )
So this gives you something between 0.7 and 1.8 amps. Nothing that will kill any, even the cheapest, pushbuttons IF the duration is not long. The capacitor's discharge through the coil is a RC net whose characteristics are given by the time constant T= R*C. After a time t = 2*T, the initial current has dropped to 14% of its starting value. Now let's assume 2200µF and 22Ohm coil. The initial current is 1A, the time constant is 0.05sec, so after 0.1 sec it has dropped to 140mA. Now in the 'worst case' of time: 4700µF and 30Ohms we have 0.7A to start with and after 0.3sec it dropped to 90mA
and of current: 4700µF and 12Ohms we have 1.8A to start with and after 0.1sec it dropped to 250mA.
After 3*T, it is neglegible in all cases, and the lamp current of ~60mA prevails. ( Under normal operating conditions, you don't even see the lamp glow in most cases )
There is no way to store enough energy in the magnetic field for a voltage spike to inititate arcing by contact interrupt because it is transformed into kinetic energy to move the plunger.
All this shows there can be no resisitive overload ( heating by current leading to contact destruction ) of the PB and/or cutoff contacts. As you have noted yourself, the normal pushbutton operation, be it AC or DC, can lead to contact failure due to this effect.

Last edited on Fri Nov 25th, 2016 03:12 pm by Helmut



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 Posted: Fri Nov 25th, 2016 03:22 pm
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Si.
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Hi Helmut :wave:

Yes I know it's a half-wave rectifier P.S.U
A lot of theory there, I hope it all works out for Peter.

Do you have a push-button switch, you would recommend ?
My experience says, the ones people tend to buy, are simply not up to the job.

Nearly TWO AMPS ! will kill that 'Jaycar' push-button switch FOR SURE !
Others like it as well, I wouldn't be surprissed.

What do YOU use ??

:moose:

Si.



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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Fri Nov 25th, 2016 03:43 pm
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Si.
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" as you pointed out and the system is almost fool proof "

Hi Peter :wave:

You said you stopped using switches, cos they burnt out your coils.

You now have the 'fool proof' stud & probe system there.

& you say they whole system has & is working just fine !

My question is...
...why do you want to change anything, if it is all OK as it is ??

:moose:

Si.



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' Mysterious Moose Mountain ' - 1:35n2 - pt.II
http://www.freerails.com/view_topic.php?id=7318&forum_id=17&page=1

' M:R:W Motor Speedway !!! ' - 1:32 Slotcar Racing Layout
http://www.slotforum.com/forums/index.php?showtopic=59295&st=0&a
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 Posted: Fri Nov 25th, 2016 05:17 pm
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Helmut
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Si. wrote:
What do YOU use ??

.
This one, available from jameco
It stands up well to the short 2A pulse, too.
Consult the data sheet - this time the Chinese do not exaggerate, but mind you - the rated current is NOT for continuous duty.
When people use digital input push switches rated 50mA - that sort of foolishness didn't come to my mind, however.

Addendum
Look for SCIparts PB's. Same rating, but less expensive and come in more colors.
Try https://www.rapidonline.com/sci

The part to look for is R13-521X X=Colour e.g. B=black . 0.5A@125V is more than ample for the short 2A pulse@20...40V The resistance is 50mOhms --> metallic tongue contact, not just a flimsy wire type

Last edited on Fri Nov 25th, 2016 10:43 pm by Helmut



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