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2foot6
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Hi,have been using peco point motors with AC and a probe,it works well but I have been considering a CDU to prevent coil burn outs.Does anyone have recommendations ,or what do you use? ......Peter

Si.
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Hi Peter.

I used PECO point-motors some years ago.
I operated them with a stud-panel & probe, like you seem to have.
I was powering them with 12 Volt A.C.

I did actually make a 'capacitor discharge unit' for the setup.
My feeling though, was that the rapid discharge of the capacitor...
...was really quite VIOLENT on the mechanism & blades generally !!

With the possibility of coil burn out, quite minimal IMO...
...I scrapped the capacitor discharge unit & went back to 12 Volt A.C.

A side issue is, stud or electrical-switch damage, due to massive D.C. surge.
Something that is not so much the case when using A.C.

You might be better off sticking to what you have in my opinion.
Reducing the operating Voltage of course, is another possible option.

:moose:

Si.

Helmut
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CDUs are sometimes THE solution for balky twin-coil switch machines, especially those made by Märklin. Never have seen any mechanical damage caused by this sort of actuating them, but a lot of burnt coils and meltdowns due to insufficient force ( = current! ) - mainly with AC.
If following proven principles, they give reliable, trouble-free operation. One can even adopt that to DIY motor-driven devices, in brief you charge and discharge the capacitor via the motor. I have seen on a British website that they just linked the throwbar to a cheap DC-motor's shaft and operated it as a stall-motor. You bet that if no pushbuttons are used, you'll burn out the motor sooner or later. But using a capacitor will allow for a SPDT switch as position indicator and risk-free operation.

Si.
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Hi Helmut :wave:

Those Marklin point motors, sound like some old H&Ms I used to have.

They certainly woke up the signalman, on my sleepy GWR branchline terminus. :y:

Rattled the poor ol' dudes dentures, every time a pannier tank arrived. :old dude:

My old H&Ms used to cause brownouts on the guy next doors arc-welder sometimes.
When I upgraded to the PECOs, his Saturday morning welding, became trouble free.
My Dad couldn't believe the drop in the electricity bill either. :f:

;)

I can't help thinking the designer at H&M, used to pen bank vault actuators. :shocked:

:moose:

Si.

Helmut
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The SM3 is a typical candidate for CDUs - lots of amps for just a split-second. The PECOs weren't that different either. I remember that I had some problems with powering them properly - they required sooo much more amperage than my Fleischmann's. That's where I first came across CDUs.

2foot6
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Thanks guys for your comments.After a long think and Si's
comments I will leave things as they are,but reduce the voltage to 12 volts AC providing it operates three motors at the same time.....cheers Peter.

oztrainz
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Hi Peter,
having let he magic smoke out of a Peco side-mount Peco point motor as shown below, earlier this year with straight AC and being surprised by how hot these coils can get in how short a time, I'd suggest the Peco CDU. The culprit was a single strand of wire that bridges across the switch contacts. I forgot to put my high-power spec on when soldering the wires to the switch when testing without a CDU :doh:)



Now I fire my points with Jaycar push button switches for each path like https://www.jaycar.com.au/black-miniature-pushbutton-spst-momentary-action-125v-1a-rating/p/SP0711 in tandem with a larger push button switch like
The reason for the double switch approach is that one of the clubs I was with had some of the smaller switches fail from burned contacts over prolonged use with a CDU. The work around was to close the small switch first then dump the current through it by closing the higher-rated larger switch. This defeated the problem.

I hope that this makes some sense for you,

2foot6
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Thanks John for the idea of two buttons to press,not a bad idea.Probably wouldn't suit me but will suit other members of our group.It doesn't take much to burn out the coils as I have found out in the past.I will be sticking with the probe and stud system but the CDU still sounds like the safe way to go............Peter

Si.
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" The culprit was a single strand of wire that bridges across the switch contacts.
I forgot to put my high-power spec on when soldering the wires "

Hi Peter :wave:

As John has said, the reason he trashed an A.C. operated Peco point-motor, is basically because it was wired up incorrectly.

- - - - - - -

" It doesn't take much to burn out the coils as I have found out in the past."

Peter, I would be interested to know HOW you came to burn a Peco point-motor, using the A.C. stud & probe method ?
I can't imagine for one moment that this could be an easy thing to do !
My guess is you were using cheap switches, right ?

The great thing about using A.C. with stud & probe operation, is that the coil can't possibly be energized for any significant amount of time, unless of course you purposely hold the probe on the stud for ages, which seems highly unlikely.

Even using A.C with push-button switches, providing of course they are correctly specified, is WAY less likely to burn out a coil compared to using high D.C. current, which inevitably acts like an arc-welder ! on the switch contacts.
Whether the D.C. is from a C.D.U. or from a regular P.S.U matters little.
The life-expectancy of ANY switch or stud & probe setup is far far greater using A.C, than with contact damaging D.C.

- - - - - - -

On the Jaycar switches.

I used exactly the same switch, in a DIY throttle, some years ago.
It was running really small N-scale motors in 0-6-0s on the flat, pulling 3 cars tops.
I burned out about 3 of the Jaycar push-button switches, before giving up & replacing them with something 'fit for purpose'.

I have specified & installed hundreds and hundreds of switches over the years, both professionally & for hobby use.
The Jaycar push-button switch, literally sticks in my mind, as being the worst switch I have ever used.

It isn't well designed or manufactured.
I've never seen them used in any 'decent' product.
Witnessing them in action for point-motor operation as well, they fail very very quickly.
Their main selling point is, they are cheap, real cheap !
That seller ^^^ is overcharging BTW.

I found a good use for my remaining stock of them, a few years back.
They helped fill up the giant hole in Essex, where London dumps all it's garbage !

:moose:

Si.

The only C.D.U I would ever consider, is one that is operated by an S.C.R individually installed with each turnout.
Complex though.
By the time you've paid for & done all that, or bought a proper expensive push-button switch, you could probably have afforded a slow-motion point motor.
&
That's the 'Catch-22' of it all & why 9 times out of 10, a cheap job with economy parts, leads to unreliability & ultimately failure of switches and/or coils.
Or
You could use A.C with stud & probe...
...and have CHEAP as well as RELIABLE.

I could recommend some push-button switches, if anyone is interested.
The problem is you'll never buy them, they are way way too expensive !

2foot6
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Hi Si, the motors I burnt out were years ago when I was using switches for changing the points,one of the switches arced and burnt the motor coils:bang:.One reason I went for the probe and stud system was cost,reliability,ease of installing and operation.It would be very hard to burn out motors as you pointed out and the system is almost fool proof.I will stay with the probe system using AC,but may later on, as finances allow, install a CDU...........cheers Peter.

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.

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 06:12 am by 2foot6

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.

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 12:50 pm by Helmut

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

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.

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 07:12 pm by Helmut

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.

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.

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 Sat Nov 26th, 2016 02:43 am by Helmut

2foot6
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...why do you want to change anything, if it is all OK as it is ??


Hi Si,the main reason for wanting to change to a CDU is a couple of point motors occasionally struggle to move the complete distance when operated..That is because there is three point motors on the one stud,I am running the circuit with 17 volts AC and I don't want to go any higher on a constant power supply.Therefore I think a CDU with a higher voltage and more amperage for a shorter time would be safer option for the motors rather than to reapply voltage to the motors to complete the movement. This problem occurs occasionally,but there are other operators who would be likely to risk burning out the coils(not understanding the risks)......cheers Peter

Si.
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Hi Helmut :wave:

Yeah ... Your switch is the same as the ones they burned out at Johns club, by the looks of things.

I was using the same 'vintage' design 35 years ago !
In all that time, I've NEVER seen the same push-button switch in any 'professional' product.
I wonder why ?

I mangaed to burn out quite a few, running tiny little N-gauge 0-6-0s !! with 3 car trains !!
Kept replacing the busted ones, untill one day I just got fed up with the agro !
Put a 'proper' switch in then...
...NEVER any trouble again !

Have rebuilt this throttle since, to exorcize the remaining little DEVILS ! :shocked:



As I said earlier, my remaining stock of the buggers, went to landfill a couple of years back.

Worse switch I've ever bought, installed or used.
Just consistently unreliable.
Personally I could never recomend them to any one, for 'serious' use.
They're OK for kids battery projects though, so I found.

Oh well...
...they are certainly CHEAP !
Just keep rippin' out & replacing I guess.
It's what I've seen done when people use them for turnouts as well.

Good luck with yours . . . ;)

:moose:

Si.

Helmut
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@Si
I agree that if you run across one of the cheap copies of that switch ( and there are many on sale, here in Germany, too ) they will not function as stated. But I have given these links not without reason - because these are the two brands I've used for years and I've had only two fail mechanically, and that was due to rough handling by the customer. Again, there are many cheap copies of that design on sale - but I pay 0,70€ for the SCI which is really not too expensive - the copies can be had for 0,47€ apiece.
Of course you can burn out any contact by overloading it for a considerable time, but you cannot kill these with a CDU! That's why I use them there.
Oh yes, they need a minimum amount of current to stay functional- so they are definitely NOT suited for electronic uses.
Something I forgot - the SCI and Jameco items are Underwriter's tested, listed and labeled - I bet the crap you dumped wasn't.

Last edited on Sat Nov 26th, 2016 07:29 pm by Helmut

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http://www.zeva.com.au/Projects/SpotWelderV2/
is a nice device for Si
to show that CDUs produce arcs. Of course they do, as will every other AC-transformer, too, if you make it to deliver enough amperage. The superiority of CDUs over other ways of operating solenoids is due to their inner resistnace being ~zero and ability to deliver an instantenuous current. So of course you risk to fry a contact if there is a solid short in the switch machine circuit. Toy transformers in the market have to meet certain requirements, the most important one being that in a case of a continuous short, the energy dissipated on spot must not be sufficient to cause a fire. Therefore these transformers are built in such a way that their short-circuit current is limited, e.g. a 16VAC transformer rated 32W  can only deliver ~4A @0V.
Any capacitor charged to say, 20V and being shorted by 1 Ohm, which is the common value of the sum of lead resistances, delivers 20A if shorted. As the duration of that spike depends on the capacitance, no harm is done when it is small enough. Only delicate IC structures can even be damaged then, however. When you go up to 2200µF, you can produce a short arc ( some 10msecs ) hot enough to melt the contact.
Take a transformer rated 100VA@16V intended for industry purposes -their characteristics are completely different from those for the toy market - and you'll produce very nice arc, too.
So it's all about inner resistance and short circuit duration whether there will be damage or not. No reason to for any advantage of AC over DC. Edison even fried an elephant to defend his point in the 'AC/DC war' and lost nevertheless.

Last edited on Sun Nov 27th, 2016 02:42 pm by Helmut


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