Can a tiny latching relay serve the same purpose as an Atlas Snap Relay?

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In trying to operate a small LED to show which way a turnout is set, my options are limited by the small space of my control panel.  Atlas Snap Relays wired in parallel with the switch motor do the job of turning a LED on/off, but require two or three extra wires from each relay to the control panel.  In order to keep the relays and wires at the control panel, I tried connecting little PC board-mounted DPDT latching relays to the wires that power the switch machine, and the LEDs lighted OK but the switch machine would not throw.  Can any of you electronics experts clue me on why a big Atlas relay operates but a little PC mechanical relay (not solid state) will not operate jointly with a double coil switch machine?  And any advice on what little relay and wiring diagram would do the job would make this old man happy.  At my control panel, instead of toggle switches, I use a tethered positive-polarity probe touched to metal button contacts to power Atlas switch machines, because the method made a reasonably compact control panel for a large layout.  A bunch of toggle switches for a yard ladder would not fit.  Help!    bauie

[retsignalmtr]

are you using the ac terminals of your power pack to power the switchmachines? those little relays may require dc current to operate properly. you could get a circuitron snapper to power the switches they supply more power to the switch machine as they are a capacitor discharge unit and they convert the ac from your power pack to dc.

[MisterBeasley]

I'm surprised that the switch machine and relays aren't throwing over together, but I would generally agree with retsignalmtr's suggestion that you use a capacitive discharge circuit to power both the switch machines and the relays.  This is particularly true if you're using Peco switch machines, which are more power-hungry.

When I first wired my layout, I found that the Peco machines would work most of the time, and they always worked on the bench, but I couldn't count on them.  I built my own CD circuit (a few dollars worth of parts - just a bridge rectifier, 2 capacitors and 2 resistors) and drove it off the same AC terminals I had been using.  (The rectifier changes the AC to full-wave DC.)  Once I did that, I had no problem.  A CD circuit will also protect your switch machines in case a toggle switch fails or hangs in the closed position.  With your probe system, of course, this isn't going to be a problem, but it's a good thing to note this about CD circuits in general.

The latching relays I use are DC-only.  Moreover, the coils are polarity-sensitive, unlike the switch machines.

I use 3-lead bipolar red/green LEDs for my panels, incidentally.  That saves space on a small, tight panel.

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Hi, retsignalmtr,    I'm using 24 volt DC from an old toy power pack, because the combo of Atlas switch machine/Snap relays that I installed at some turnouts years ago just did not work reliably with the AC or lower voltage packs.  Now I have DCC and the separate DC for turnouts is even more important.  When I started building my layout 30 years ago I couldn't find enough cash for new wire and I used old telephone wire, which still is OK but just barely.  Once I did try a cap-discharge power for turnouts.  It did work,  too good.  The points would bounce halfway back.  So the 24 volt DC came next and does the job, except on the little relays experiment.  The 24 volts jolt does not burn the little relays, and I'm still stumped for a reason they don't cooperate with an Atlas switch machine.   Anyway thanks for your ideas!      bauie

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Mister Beasley, your words of advice and caution are greatly appreciated.  Even with the probe/contact system, a grandson of mine managed to smoke a switch machine.  When I built a capacitor-discharge unit some years ago I tried going too high on the capacity and the turnout points bounced.  Instead of lowering the cap I changed to 24 VDC which still works OK but not with a small relay/Atlas switch machine together.  I wonder if there is some electronic flaw in connecting the 2 different sizes of coils in the devices, because the 24 VDC jolt does operate one or the other.  This baffles me.  So I am going to build another cap-discharge circuit and keep hoping.        And your suggestion of 2-color LEDs to save space is great.  Thanks!    

bauie

[larak]

If each operates independently, then you appear to have a large impedance mismatch between the parallel coils or some sort of resonant circuit. Either of these can throw most of the energy to one device leaving not enough for the other. It's tough to diagnose theoretically without a lot more technical information. As a test I would go with the CD suggestion. See if applying a bit more energy to the coils works. It's a quick and easy test.

Karl 

[[e-mail]]

If each operates independently, then you appear to have a large impedance mismatch between the parallel coils or some sort of resonant circuit. Either of these can throw most of the energy to one device leaving not enough for the other. It's tough to diagnose theoretically without a lot more technical information. As a test I would go with the CD suggestion. See if applying a bit more energy to the coils works. It's a quick and easy test.

Karl 

Measurement shows Atlas switch machine coils resistance is about 10 ohms and the PCB latching relay coil is about 600 ohms.  By George, Karl, that must be the problem.  Thanks for that advice!       bauie