Dual Coil Latching Relays

In another posting I asked for ideas on how to add red and green LEDs to the switch tracks of an N Gauge model electric train. See below for my earlier post.

It seems like the way to go would be with DPDT Dual Coil Latching Relays.

I would like to obtain a few (< 10) DPDT Dual Coil Latching Relays that will work with both AC and DC impulses to the coils.

Digikey, current catalog page 1229, has

24VDC 3,200 7.5 2 2 16.8/16.8/48 255-1068-ND

a DPDT dual coil latching relay.

A couple of questions:

  1. The 16.8/16.8/48 is in the Pickup/Dropout/Max. Voltage column of the catalog page. Why isn't the middle entry a "-" as it is for some of the other dual coil latching relays? Does this mean that the coil must have a continuously applied voltage of at least 16.8 volts? This doesn't seem to make it a *latching* relay.

  1. All of the relays on page 1229 state that the coil voltage is DC. Could some of these also be used with AC, if the AC is just a momentary pulse, say for a relay with a 16.8/?/48 entry in the Pickup/Dropout/Max. Voltage column?

  2. Does anyone know where I might obtain an AC/DC DPDT relay that holds the setting with no voltage other than a pulse to the coil?

A self-latching relay seems like the simplest solution, except for the questions that I have (above).

My previous post:

*********************** I have an N-gauge train with some remote-controlled switch tracks, "snap-switch" type.

This is an older style train, not the DCC type.

I would like to add red and green LEDs to the switch tracks. The switch tracks are operated from the "accessories" terminals of a small power supply which are nominally 17 V AC, (I measured it open-circuit at 17.7 V AC).

The switch tracks are operated by pressing momentarily on a momentary SPDT switch.

I'd like a simple way to hook up the LEDs either at the remote location or at the SPDT switch. Since power to the switch track is applied only momentarily, I suppose that some sort of latching mechanism is needed.

The 17 V AC is part of the complication, it seems.

For reference, the switch tracks are Atlas #'s 2580 and 2581; the power supply is Model Rectifier Corp. Railine 370N.

The switch tracks are apparently solenoid powered.

The power for the tracks only is 15 V DC. I wouldn't want to power the LEDs from that terminal pair because it turns off when the train is stopped, and includes the speed control.

Anybody here ever do this stuff with this type of remote turnout?

My guesses are some sort of relay or solid state relay, but I have no idea what the specific part number or circuit would be.



--- Joe

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Reply to
Joseph Sroka-10.2.8
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I seriously doubt you'll find an AC/DC relay. Use a DC one and feed it from the AC supply via a bridge rectifier and a capacitor.



Reply to
Ken Taylor

In a dual-coil latching relay, 'pickup' and 'dropout' translate to
'set' and 'reset',  and since the set and resert voltages are the
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Reply to
John Fields

LEDs to



that will








Just a WAG (I'm not clairvoyant[1]), but it seems he wants to use one set of contacts on the relay to do the higher current AC switching for the rails, and the other set of contacts for the LEDs. But all that's needed is a diode and I limit resistor in series with each LED and it can then be put in parallel with the rail.

[1] If palm readers are clairvoyant, why do they have to ask you for your credit card number? :-)
Reply to
Watson A.Name - "Watt Sun, th

Hi Joe, I used some latching relay's on my layout and found that they required more current than the Model RR power source was capable of supplying. To overcome this problem I found it necessary to use a capacitor discharge circuit. This circuit is also used on some RR's to drive the switch solenoid, run AC into bridge rectifier through a resistor to a suitable capacitor. The voltage across the capacitor is then used to pulse the latching relay and the resistor will limit the current from lowering the RR power supply voltage. Dave

Reply to

Yes. The prototype solution is a Compton and Greaves QL1 DC Magnetically Latched Relay. These Q-series relays are much smaller than the classic vital relay designs from General Railway Signal and Union Switch and Signal. They're widely used in India today and are still in use in Great Britain.

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John Nagle

Reply to
John Nagle



Put your ac thru a diode and you have chopped dc. This should work, but you'll need to apply a higher v than rated, maybe 2x.

Larger relays are as happy on ac as dc, though they need 2x the v at ac. Small relays however are too fast responding to ignore the 50Hz, but can be run on chopped ac if latching.


bistable relay


I doubt it, logic is usually much easier implemented electronically than electromechanically.


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