Using latching relays in a control panel ??

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

Postby End2end » Sun May 03, 2020 11:48 pm

Thanks Ironduke.
I actually received a rapid reply from them and yes it is indeed the PPI4-DC.
Now I need to raise the money for 3 of them.
Thanks
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Suzie
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Re: Using latching relays in a control panel ??

Postby Suzie » Mon May 04, 2020 1:29 am

If using latching relays on stripboard you don't need any diodes if you are using a CDU - they are DC devices. They have two coils just like the PM1 and you wire the two coils in parallel with the PM1 terminals A, B, and C. All quite easy really. Think of the PM1 as a latching relay (for that is what it is) and you can't go far wrong.

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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 12:16 pm

I've read back through the thread and your right Suzie. I cannot remember for the life of me where, how and why I found I needed diodes? :?

Leaving out those components for now, the 22 relays alone are roughly only £10 cheaper than the 3 x PPI4-DC boards althogether. Hardly anything in it at all cost wise.
Just for sheer convenience I think the £10 price difference is a no-brainer now I have a deeper understanding of the PPI4-DC boards..

I found their video of how to set up the board - https://www.youtube.com/watch?v=gXXORgfXEt0 The board is introduced into the circuit just before the 10 minute mark.
There is a programmable chip on the board which can turn down the brightness of the LED's which is very useful. :)
These seem the way to go for me.
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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 5:20 pm

I've just found that Micro Minitures also make an 8 way points position indicator board.
https://www.microminiatures.co.uk/produ ... with-leds/
Comparable price to the Blocksignalling version.
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Re: Using latching relays in a control panel ??

Postby Flashbang » Mon May 04, 2020 6:54 pm

The major problem with PPI (Point Position Indicators) and Latching relays while they both work well they do not actually indicate that the point motor has actually moved! All they indicate is that the operation switch or lever has moved which is by far not the correct indication. :o

To reduce wiring layout to panel by using a one wire indication method from the actual point motor back to the panel is cheaper and provides a 99.9% true indication the motor has actually moved over and by that it is also highly likely the point blades have also moved over too.

Of course by using the PM1 or PM4 point motors built-in change over switch for indications that contact can no longer be used for electrofrog polarity switching on a DC layout

Diodes in a latching relay coils feed path are there just ensure that when using AC as the supply to the motor the relay operates correctly. But so long as you are using a CDU and you know that the operating switch or lever etc is in the CDUs Positive output feed, then they can be omitted. However, if used, and they cost serious money at around £0.07 each!, they will not cause any issues. :D

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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 7:29 pm

Nope. I still don't get it.
Can someone please SHOW me how it is wired.
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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 7:35 pm

Thanks Flashbang. :)
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Re: Using latching relays in a control panel ??

Postby Suzie » Mon May 04, 2020 7:38 pm

End2end wrote:...Just for sheer convenience I think the £10 price difference is a no-brainer now I have a deeper understanding of the PPI4-DC boards...End2end


Quite agree!

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Re: Using latching relays in a control panel ??

Postby Suzie » Mon May 04, 2020 7:43 pm

Flashbang wrote:The major problem with PPI (Point Position Indicators) and Latching relays while they both work well they do not actually indicate that the point motor has actually moved! All they indicate is that the operation switch or lever has moved which is by far not the correct indication. :o

To reduce wiring layout to panel by using a one wire indication method from the actual point motor back to the panel is cheaper and provides a 99.9% true indication the motor has actually moved over and by that it is also highly likely the point blades have also moved over too.

Of course by using the PM1 or PM4 point motors built-in change over switch for indications that contact can no longer be used for electrofrog polarity switching on a DC layout

Diodes in a latching relay coils feed path are there just ensure that when using AC as the supply to the motor the relay operates correctly. But so long as you are using a CDU and you know that the operating switch or lever etc is in the CDUs Positive output feed, then they can be omitted. However, if used, and they cost serious money at around £0.07 each!, they will not cause any issues. :D

Example PMx indication LED wiring.. Note LED colours shown are purely for the example..
LED indications wire wire - Seep PM .jpg


You will need separate resistors for each of the LEDs - not just one for each pair (the LEDs will light very brightly very briefly!), but apart from that this is the solution I have used in this situation and it works really well. As a bonus you get a third indication with both LEDs on if the point gets stuck in a mid way position.

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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 7:59 pm

Ahh now I think I understand the lighting of the LED's. As they are connected together in opposite only one 1 lights at a time.

So...
3 short wires coming off the PM1 solder points -
C - common return for point throw connected to the Common Return Bus
E and D - For indication connected to their own dedicated 12v bus run around underneath the layout

3 Long wires coming of the PM1 solder points -
A and B - connected to a switch on the panel for the actual point switching
F - Connected to the LED's in the panel

Is that correct?

Also where would the 2 x 1KOHm resistors need to be in the circuit?
I thought it doesn't matter which leg of an LED a resistor needs to be attached to and thus only having to use 1 resistor per pair of LED's in Flashbang's diagram sort of makes sense to me.
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Re: Using latching relays in a control panel ??

Postby fourtytwo » Mon May 04, 2020 8:08 pm

Unfortunately apart from the flaw pointed out by Suzie that would cause a dead short across the power rails through the LEDs resulting in there destruction, the reverse voltage rating of LED's is typically a mere 5V meaning in this application the survival of the unlit LED is a matter of chance rather than certainty!

It is a good idea but needs some more components to make it work reliably such as an inverse IN4148 or similar low current diode connected across each LED in addition to Suzie's resistor per LED to prevent PSU shorts.

Who wants to update the diagram.........Flashbang ?

Thinking about it the original circuit would work with incandescent lamps, but not LEDs
Last edited by fourtytwo on Mon May 04, 2020 8:19 pm, edited 1 time in total.
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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 8:15 pm

I've seen something else in the diagram that I am not sure about.
From the 12v PSU bus shouldn't the red + wire go to point D and the black - wire go to point E on the PM1?
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Re: Using latching relays in a control panel ??

Postby End2end » Mon May 04, 2020 8:20 pm

Is there also a way to dim all the LED's?
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Re: Using latching relays in a control panel ??

Postby fourtytwo » Mon May 04, 2020 8:25 pm

End2end wrote:I've seen something else in the diagram that I am not sure about.
From the 12v PSU bus shouldn't the red + wire go to point D and the black - wire go to point E on the PM1?
Thanks
End2end

Having only been briefly acquainted with such motors on club layouts would that not just reverse the indication, so its a matter of preference ?
F presumably being the common or pole of the switch ?
Please excuse my ignorance if I am talking rubbish :(
Does the pain of N gauge steam ever end!

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Re: Using latching relays in a control panel ??

Postby fourtytwo » Mon May 04, 2020 8:27 pm

End2end wrote:Is there also a way to dim all the LED's?
Thanks
End2end

YES use larger resistor values to reduce current, best to experiment with one LED on the bench first!!
You could also keep the same resistors and reduce the supply voltage.
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