1000ma AC - # of snap relays (etc.)

[Anonymous]

Hi all,

I've searched and searched, to no avail - Comments on the following much appreciated:

1. The track section is a simple double crossover, where I want to throw all four turnouts from one standard Atlas #56 control box. (This scenario is part of Atlas layout #HO-10021 btw.)

2. General opinion is that these (4) turnouts work best connected to the a.c. terminals on my 'power pack'....

3. Would also be nice to drive (2) Atlas 200 snap relays (lights etc.)

Given this need to throw 6 pieces of iron thru' their coils at once I went wiith a dedicated, 18v, 1A Radio Shack supply (273-1890).....

.....And failed miserably :-(

Testing suggests 2 devices can be reliably driven, 3 possible, from this 1000ma supply....

Wow...

and the feed wires to these switch machines are, maybe, 24ga.... Hmmm... I must be missing something..... At least I hope I am....

Help please! - I'm figuring some kind of capacitive delay may be the answer, but am struggling with the circuit and device type to use.

Great forum - Been lurking for a while and am now hoping for an answer - Thanks,

Best regards,
Ian

[rrinker]

What you need is something called a Capacitor Discharge Power Supply. A couple of Model RR companies offer them, but if you can lay your hands ont he old Kalmbach book "Practical Electronic Project for Model Railroaders" there is one in there. It is one of the easiest electronic circuits to build and great for a first time electronic project. What it does is basically store energy in a large capcitor and then send a big blast to the switch solenoid(s) when you press the button. But since it discharges rapidly, and current it limited until you release the button, you won't burn out your coils if you hold the button too long, or the buttons get stuck. I built the 'rapid recharge' version from the above mentioned book (I think it's the second of the capacitor discharge circuits) many years ago when i was in N scale, it's almost a MUST at least back then, as the coils int he N scale Atlas turnuts tended to be VERY delicate. After installing this circuit and powering it with an old train set power pack, I never burned out another switch machine, AND they always SNAPPED right over.

--Randy

Edit: Here is the same circuit on this page:
http://home.cogeco.ca/~rpaisley4/CDPSU.html. Scroll about 1/3 of the way down to the "Current Blocking Switch Machine Power Supply". The simple top one is the same as the one I built years ago, or close.

[Anonymous]

Hmmmm..... Thanks for the link - I guess the circuit will work, but it immediately raised another question:

- I'm being told that a.c. is the best way to power the snap relays (positive 'snap' etc). But, the first thing the circuit mentioned above does is feed the a.c. into a bridge rectifier to output D.C, which is then used to charge the capacitor etc......

Why not just use a 'spare' dc output in the first place and eliminate the rectifier?

Thanks again for any insights,
Ian

[cwclark]

MY experience with Atlas snap turnouts and relays is that they will only operate two pieces of equipment at a time...either two turnouts or 1 turnout and a snap relay...i tried to do what you are doing many years ago and found that I had to either install an Atlas slide / push button momentary switch for only two turnouts at a time or one for one turnout and one snap relay...and yes..you must use A/C for the atlas coil type equipment...I don't think a discharge unit will do you any good here because the amp draw from 4 simultanous coils at one time is a bit too much for a 12 or 18 volt system....Chuck

[rrinker]

A strong enough capacitor discharge system should throw 4 or so at once without a problem. Either way, it's not a waste, a CD power supply is superior to driving twin coil switch machines than running them right off the AC source.
As for AC vs. DC, the main reason for saying this is so people don't try to run them off the track output of the power pack. Another reason to not use DC is arcing around the switch contacts. As for the bridge input to that circuit - if I recall the circuit I built, it did not have this bridge. I don't remember it having the dioide on the output side, either. Not saying there's anything wrong with Rob's circuit, it will work as is just fine. There just are simpler alternatives as well.

--Randy

[Anonymous]

QUOTE: Originally posted by rrinker
[...snip...]

There just are simpler alternatives as well.

--Randy

Where?!......... I can't find 'em.... [Circuitron does appear to have the device (http://www.internettrains.com/800-5303.html)] but, this seems like overkill to a problem that it seems *lots* of people must have whenever they want to power more than 2 relays at once.....

[Note that neither Loys Toys or Tonys trains lists this part btw.... I'm amazed!]

Thanks for feedback thus far - I'm off to Radio Shack to purchase a few capacitors, to be fed from a *DC* supply (eliminate the rectifier) to 'experiment' further......

Cheers,
Ian

[rrinker]

Yeah, that's a good commercial one right there.

Be careful with those capacitors, don't mess the polarity up, or there will be a large BOOM. You can build a very simple circuit with a large capacitor and resistor, but the donwside is the larger you make the capacitor, for more enegy to fire the coils, the longer it takes to recharge - to the point where you might not be able to throw all the turnouts you need to keep the train from derailing. The transistor in those other circuits provides a 'shortcut' to quickly recharge the capacitor while still limiting the continuous current that flows to the coils.

--Randy