Dual Coil Latching Relays

[Joseph Sroka-10.2.8]

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.

2. 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?

3. 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.


*****************

Thanks.

--- Joe

 

[Ken Taylor]

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.

2. 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/ > Voltage column?

3. 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).

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.

Cheers.

Ken

 

[John Fields]

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.

---
In a dual-coil latching relay, 'pickup' and 'dropout' translate to
'set' and 'reset', and since the set and resert voltages are the
same, I think the dashes imply that. In any case, a pulse will be
sufficient to set anmd reset them.
---

2. 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?

---
I wouldn't think so. The relays show polarized coils, the implication
being that there are bias magnets in the relay to assist in switching.
If that's true, then placing AC on the coil would have the effect of
making and breaking the contacts at the line frequency, so where the
contacts wound up would be unpredictable.
---

3. 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?

---
I have a few SPST AC latching relays, so I think DPDT are available,
but they would be huge and expensive. Besides, if all you want to do
is switch between two LEDs you don't need DPDT, you need SPDT. Or,
maybe, just a couple of transistors.
---

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

---
Well, there _are_ a few more things that need to be worked out, like
you need DC for the LEDs, you need some way to sync up the LEDs to
correspond to the track switch position, and you need some way to
convert the single signal from the momentary pushbutton switch into
the two signals needed to run the relay coils or whatever's switching
the lamps.

I'll be happy to help you out, but I'm just wondering, aren't there a
set of electrical contacts in the track switches which could be used
to do what you want?

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

---
In a dual-coil latching relay, 'pickup' and 'dropout' translate to
'set' and 'reset', and since the set and resert voltages are the
same, I think the dashes imply that. In any case, a pulse will be
sufficient to set anmd reset them.
---


---
I wouldn't think so. The relays show polarized coils, the implication
being that there are bias magnets in the relay to assist in switching.
If that's true, then placing AC on the coil would have the effect of
making and breaking the contacts at the line frequency, so where the
contacts wound up would be unpredictable.
---


---
I have a few SPST AC latching relays, so I think DPDT are available,
but they would be huge and expensive. Besides, if all you want to do
is switch between two LEDs you don't need DPDT, you need SPDT. Or,
maybe, just a couple of transistors.
---


---
Well, there _are_ a few more things that need to be worked out, like
you need DC for the LEDs, you need some way to sync up the LEDs to
correspond to the track switch position, and you need some way to
convert the single signal from the momentary pushbutton switch into
the two signals needed to run the relay coils or whatever's switching
the lamps.

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.

I'll be happy to help you out, but I'm just wondering, aren't there a
set of electrical contacts in the track switches which could be used
to do what you want?

[1] If palm readers are clairvoyant, why do they have to ask you for
your credit card number?

 

[Dave]

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

 

[John Nagle]

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.

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.

http://www.cglonline.com/products/industrial/rail_p3.htm#4

John Nagle

 

[[email protected]]

2. 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?

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.

3. 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?

bistable relay

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

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


NT