Using latching relays in a control panel ??

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End2end
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Using latching relays in a control panel ??

Postby End2end » Sat May 02, 2020 8:16 pm

I wanted to give this subject it's own thread after seeing and discussing Memran's Control panel internals as can be seen (and read on from) here - viewtopic.php?f=22&t=55210&start=45#p679579

Looking at the 3rd picture down on the link at the circuit boards with white blocks on them. The latching relays.

I'd also like to use this idea of implementing latching relays as it seems so much tidier than the conventional wiring I was considering.

I was going to run wires all the way back to the control panel from all my SEEP PM1 point motors (using the extra switch on them) to identify the point position.
As you can imagine those extra 3 wires PER point motor just to light 2 LED's on the control panel would not only mean a lot more wires under the baseboard but also a mass of wiring in the control panel.
This way, by using the latching relays I could eliminate the need for all that wire and directly power and wire my control panel LED's off the relays.
Well that's the theory. The difficult part is how to build the circuit and also to build it for multiple point relays per board.

Before I jump to questions I wanted to share some of the information I've garnered so far.
You can use a COMMON RETURN bus for the point motors. This can then be just jumped across each relay in the control panel.
On the control panel fascia the point switching can be controlled via a Stud and probe, an (on) off (on) momentary switch as well as other types.
You can use one 1 relay on 1 switch to control 2 point motors. (crossover pair of points from one track to another).
LED's are powered through the relays using a 2nd power source. (5 or 12v).

The practicality of actually trying to build these circuits includes more than just a latching relay in the circuit so I am trying to find something already made that I can use.

After looking around I found this 12v 16 channel board-
https://www.ebay.co.uk/itm/1-2-4-8-16-C ... 0005.m1851

The information on the sale states:-
16 Channel:
1.This relay module is 12V active low, and each one needs 15-20mA driver current.
2.Uses two 8-channel ULN2803APG darlington arrays chip to control relay module.
3.It is a 16-channel relay interface board, which can be controlled directly by a wide range of microcontrollers such as Arduino, AVR, PIC, ARM, PLC, etc.
4.It is also able to control various appliances and other equipments with large current.
5.Relay output maximum contact is AC250V 10A and DC30V 10A.
6.Standard interface can be directly connected with microcontrollers.
7.The working status indicator lights are conducive to the safe use.
8.Widely used for all MCU control, industrial sector, PLC control, smart home control.

I've seen reference to "high" and "low" (Level) but I don't know what that actually means
Could this be the solution as it's pre-made?

If not, are there any multi-boards available commercially that can do what I need?

Ideally I'd need a board with 22 relays, although if a 16 way and an 8 way could be connected together somehow that would also work. I may even find a use for the spare 2 relays if the boards add up to 24.

If multi-relay boards are not available commercially for what I need I will have to try and work out how I can build it myself which will take MUCH longer. :?

Thanks
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Roger (RJ)
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Re: Using latching relays in a control panel ??

Postby Roger (RJ) » Sat May 02, 2020 8:52 pm

Consider the Block Signalling Points Position Indicator http://www.blocksignalling.co.uk/index. ... or-ppi4-dc

The problem with these units (and the latching relay idea) is that they don't indicate which way the point is set, only the way that you wanted the point to switch. If something stops the point from moving, such as loose ballast, the indicator says the point has switched but in reality it has been prevented from moving. A switch operated by the point itself will always give a true position indication.

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Re: Using latching relays in a control panel ??

Postby End2end » Sat May 02, 2020 10:07 pm

That's easy enough to overcome with layout due diligence Roger. :wink:
I'm just trying work out the different PPI boards on offer. They seem to have manuals for 10 different boards.
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Re: Using latching relays in a control panel ??

Postby Ironduke » Sat May 02, 2020 10:23 pm

Roger (RJ) wrote:Consider the Block Signalling Points Position Indicator http://www.blocksignalling.co.uk/index. ... or-ppi4-dc

Looks like those boards do everything you need.

But first thing I thought was,
End2end wrote:by using the latching relays I could eliminate the need for all that wire and directly power and wire my control panel LED's off the relays.


Why use relays if you're only lighting up LEDs? You could just use a bit of cmos type logic at a fraction of the cost.

End2end wrote:As you can imagine those extra 3 wires PER point motor just to light 2 LED's on the control panel would not only mean a lot more wires under the baseboard but also a mass of wiring in the control panel.


And the second thing was, ain't nothing wrong with wires.
Regards
Rob

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Re: Using latching relays in a control panel ??

Postby End2end » Sat May 02, 2020 11:00 pm

Thanks for your reply Ironduke
I don't now what or how to use CMOS
As for the wiring, running more wires just for the panel LED's direct off the SEEP PM1's would an an extra 100 foot (roughly) of wiring plus some of the point motors are surface mount and don't have the facility thus the idea to use latching relays all contained in the control panel as much as possible.

Just scouring ebay I found these
https://www.ebay.co.uk/itm/Points-Posit ... CrQ8MdDyCA

The BLOCKsignalling PPI4-DC looks like a good board even though You have to externally connect the LED's negative wires together and there's no dimmer component like one of their other boards as far as I can see. I wonder if they can be dimmed using another component?
I think all the manuals for the different blocksignalling boards on their website maybe for older boards they sold in the past too as they only have 3 different types on their webshop - http://www.blocksignalling.co.uk/index. ... ory/view/4

Both boards are quite expensive as I'd need 3.
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Re: Using latching relays in a control panel ??

Postby Ironduke » Sat May 02, 2020 11:45 pm

well actually 4000 or 7400 series cmos is a bit old hat these days but it is literally cheap as chips.

in the circuit below you have only 2 wires per point motor from the panel with a CDU "bus" wire running around the layout.
The control panel runs on a single 12V supply.
Each 74HC00 IC can run two point switches.
The only downside is you need DPDT switches. And a large piece of Veroboard to build the circuit on. And some brainwork.
cpwppi.png


Also this circuit:4 point CDU controller shows a way to use a SPDT switch but it needs more components. Actually I think it's way more complex than it needs to be because its also doubling the supply voltage for the CDU to increase the power output.
Regards
Rob

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Re: Using latching relays in a control panel ??

Postby Bufferstop » Sat May 02, 2020 11:53 pm

Just for a couple of LEDs you hardly need anything heavy, I'd see if I could divide them up in groups of four and use some lengths of cat5 twisted pair. Each cable would contains four pairs of colour coded wires neatly twisted together, you should be able to keep them looking neat and tidy beneath the panel.
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Re: Using latching relays in a control panel ??

Postby Suzie » Sun May 03, 2020 8:50 am

It is probably worth going back to looking at the original requirement and thinking through the various solutions. Latching relays certainly have their place, and I use them when appropriate, but for this situation it is a bit of overkill.

I suggest that the best solution would be to run a single wire from the common switch contact on the PM1 (F) back to the control panel to provide the indication. Run a common 5V power bus round the layout connected to the PM1 auxilliary contacts (D) and (E). This will give you a total of 24 wires in your application which I think will be manageable, and you will have 5V available to power lighting etc. too.

At the control panel end you just need to connect a pair of LEDs with 220R resistors in series to the 'F' wire of each point, one from the 'F' wire to +5V, and the other to 0V.

Given how much wiring there will be if electronics is involved (admittedly the wires will be shorter) I suggest this method is simpler and will take less time to complete. I am sure that wiring is not the biggest concern or you would have used stall motors that needed only two wires! You don't have to use 5V, you can use any suitable DC supply, just adjust the value of the resistors accordingly.

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Re: Using latching relays in a control panel ??

Postby Suzie » Sun May 03, 2020 9:10 am

If you do want to produce something similar to the PCBs shown in the linked picture:-
Image
you could just buy the relays and fit them to stripboard. Suitable relays are available from Rapid:-

https://www.rapidonline.com/panasonic-t ... le-60-1314

or RS:-

https://uk.rs-online.com/web/p/latching-relays/6996304/

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Re: Using latching relays in a control panel ??

Postby Bufferstop » Sun May 03, 2020 10:46 am

Surely the latching relay has to be only a poor substitute for the switch and wires! Some devious soul could put the whole thing out of step by manually throwing the odd point or two. Now why is everybody looking at me?
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Re: Using latching relays in a control panel ??

Postby Bufferstop » Sun May 03, 2020 11:22 am

Another system has just risen to the top of my mental swamp, I can't say I've seen it used much, but it has the dubious advantage of being self correcting after a point is manually thrown. Dubious because if you throw them all whilst the power is off they will all try to change at once when it is restored (oow narsty). It utilises the switch on the point motor to set the return path and the switch on the panel to select the coil to feed. The panel switch can be an ordinary change over. I'll try to describe what happens, starting from power on.
At power on the switch on the panel is set to the last coil to be energised, the built in switch at the point motor is set to the opposite coil. If it isn't both switches are set to one coil and it fires, changing the switch at the point to the opposite coil. When the panel switch is thrown the coil fires because it's return is via the local switch. The opposite coil is now ready to fire as its return path is selected and it's just waiting for the panel switch to change. The panel switch can also feed a pair of indicator lamps as the switch is always connected to the last coil to fire. Think about how the light switch on the stairs works, it's the same principal.
If you search through many old H&M point motors you will find some which have a built-in switch with contacts connected to a set of terminals, and a second switch between the coils and the return terminal. It was introduced to avoid the possibility of coil being permanently energised and burning out, but also made it possible to use an ordinary changeover switch.

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End2end
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Re: Using latching relays in a control panel ??

Postby End2end » Sun May 03, 2020 11:44 am

Just a quick rushed reply as I'm going out today.

I don't want to rely on the SEEP's switch mechanism for panel lights.
I want to eliminate as much wiring as possible around the layout. It's a mess under there as it is. :lol:
I want to make as easy as possible for me to implement it. (Thus the idea of using the multiple latching relay or Blocksignalling boards).
There will still be a physical switch on the fascia of the control panel to switch the points. These switches are already wired.
The layout lighting already has it's own DEDICATED 12v bus.
I wouldn't know how to solder the latching relays or what each leg connects to. (This would have been researched if I was going to make the boards myself but If I buy commercially available boards I don't need to learn that) :D
The circuit would not just include a latching relay. There needs to be diodes and other components.
And in general it's a much tidier and dare I say elegant solution.

Why are latching relays overkill If, as mentioned in a previous conversation, I could possibly control something else with them as well? :idea:
Not sure yet what though.

@Bufferstop. Are you the phantom point switcher?! :shock: :lol:

Like I say, it's just a quick rushed reply so if I missed any questions or left anything out do let me know.
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Re: Using latching relays in a control panel ??

Postby Bufferstop » Sun May 03, 2020 3:52 pm

Curses I've been spotted again! I've given and been to, far too many demonstrations not to spot the presenter who's learned the script but hasn't a clue how it works. When that happens my fingers sort of gravitate to the little glitch that causes chaos.
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Re: Using latching relays in a control panel ??

Postby End2end » Sun May 03, 2020 9:45 pm

After pricing up the 22 relays I would need they come close to buying 3 Blocksignalling PPI4's.
With the other components I'd need to hand make them (even though I have the LED's and switches already), the boards seem good value.

I'm still trying to work out which boards I would need as there is 3 manuals for the PPI-4.
I sent Blocksignalling an email asking if there is a dimmer component on the board to turn down the brightness of LED's and if multiple boards can be connected together to run more than 8 SEEP point motors and the answer was yes to both but don't interconnect the output LED's between the boards.

I need to send another email asking what the difference is between the 3 boards they have manuals listed for then I should have a better picture.
The search continues.
Thanks
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Re: Using latching relays in a control panel ??

Postby Ironduke » Sun May 03, 2020 11:31 pm

End2end wrote:I'm still trying to work out which boards I would need as there is 3 manuals for the PPI-4.


There are three "PPI" models and two versions of manual for the "PPI4"; "J" and "L". I think these are just different hardware versions of the same thing.

I think you need the PPI4-DC
and this is the manual

The PPI5-DCC is for DCC. Most DCC Accessory decoders have a common +ve DC/CDU output and sink each point motor coil to ground, whereas on DC layouts, usually the -ve/ground is common and the coil is switched to the supply.

The PPI-4K is for Kato point motors which only have two wires and are switched by reversing the polarity of the pulse.
Regards
Rob


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