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CDU
 Moderated by: Si. Page:  First Page Previous Page  1  2  3   
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 Posted: Fri Nov 25th, 2016 11:04 pm
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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



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 Posted: Fri Nov 25th, 2016 11:21 pm
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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.



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 Posted: Sat Nov 26th, 2016 11:37 am
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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 03:29 pm by Helmut



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 Posted: Sun Nov 27th, 2016 10:40 am
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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 10:42 am by Helmut



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