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8-pin mini power relays and point control - Electrics - DC - Getting You Started. - Your Model Railway Club
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 Posted: Sun Nov 17th, 2019 01:51 pm
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Barry Miltenburg
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Hi all you DC users out there.

In pusuit of a multi-functional point motor I have been investigating the traditional PECO offering, the SEEP alternative and the new PECO twist-lock device with the various switches that are either built-in or attachable.

The SEEP PM-1 comes with a single switch built in allowing me to change the point frogs on my Code 75 live frogs. 

The PECO motor (along with the Gaugemaster copy) PL-10 doesn't come with a switch but the PL-13 single switch is an easy addition.  I have been using these for years and find them very reliable although they are not the cheapest of things and require careful fixing if the motors are mounted directly under the points (my preference).  I used evo-stick until they all started falling off so now use a small blob of hot glue.

The PL-15 twin microswitch is a real faff to put together and get working but it does give you the ability to change the frog polarity AND then run either a signal or LEDs on a mimic board.  The drawback is the price - at £8-10 EACH they can be expensive when you need 50 or so as I do on the new layout.

Sol suggested relays but as I am a total ludite when it comes to electronics (I am an electrician but please do not confuse the two) I have always fought shy of such devices.  With time on my hands today, I started to investigate what a relay was, what it did, how I could use one and how much they cost.  The results are stunning.

A relay is, essentially an electromagnet in a box.  If you pass a (usually low voltage) current through it, the electromagnet works and an internal switch turns on.  This switch is NOT connected to the same circuit as the one you feed in.  In industry, this means that you can use a low voltage circuit and a button to fire up/connect a circuit carrying much higher voltages without exposing the user to those higher voltages - the on/off switch ONLY controls the low voltage circuit.

Typical low voltage for a mini power relay is 12 volts DC - handy!!  The voltages that can be handled by the secondary circuit can be up to 240 volts but we are very unlikely to use that.

Relays normally come "NO" or "normally off" meaning that the activation of the primary circuit turns the internal switch on.  They can also be (or have pins providing) "NC" or "normally connected" which means that the activation of the primary circuit turns the internal switch off.

Now I know what a relay is and what it does.  So what.

Relays come with defined number of inputs or "pins".  A 4-pin relay gives you the primary feed and return and then a secondary feed and return.  If you turn the primary current on, the electromagnet closes the internal switch and the secondary circuit goes live.  Thus a 12 volt primary circuit could turn a 5 volt lighting circuit on or off.

A 5-pin relay has 2 pins for the primary feed and return and then 3 pins for the secondary circuit - a feed and two outputs for (for example) a red light and a green light on a mimic panel.

An 8-pin mini power relay has a primary feed and return and then TWO SEPARATE intenal switches that can control TWO SEPARATE other circuits using 3 pins each.

When this 8-pin device is applied to the model railway, it can be seen that the switch turning the power on or off could be the switch built into a SEEP PM-1.  The relay is normally in an inert, stable state - particularly when the point is set for its NORMAL position (i.e. straight).  When you throw the point (via a momentary on-off-on switch and CDU for example) the relay becomes active because the switch in the SEEP point motor turns it on, the electromagnet is energised, the internal switches throw and thus (a) the point frog polarity can change and (b) LEDs can indicate the position of the point on a mimic panel.

In this case, the 12 volt power supply for the point motors can also be the feed current for the relays (without a CDU of course), the frog polarity circuit is inert until a controller is turned and the LED circuit is 9 volt running bi-colour LEDs.  The three circuit are totally independent and so this mix of voltages can happily co-exist.

If you start to get really excited about this, you can get 11-pin relays and get 3 separate circuits to use - frog polarity, mimic board LEDs and signal control.  Then there's 14-pin..................................

Cost?  Our friends in China can supply 12 volt 8-pin mini power relays that can handle the sort of ampages we use for about 50 pence each if you buy in bulk (£1.50 if you want one) post free.  How do they do that?????

Thats it folks - job done.  When the layout starts to appear, I will be installing 8-pin 12 volt mini power relays to each point with the SEEP PM-1's internal switch as the on/off switch for the primary circuit.  When I get a bit more timeI will post a wiring diagram sketch.

In the meantime I'm learning Mandarin - why not, they are very useful chappies.  Ha-so!!!!
Barry



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 Posted: Sun Nov 17th, 2019 04:25 pm
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Headmaster
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Now I don't understand electronics at all, but even I followed that Barry.  Great stuff.  Circuit diagrams would be great - even though I'm DCC!
Michael



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 Posted: Sun Nov 17th, 2019 04:46 pm
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Sol
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If you Google    12 volt dpdt relay wiring
click on Images & you will find many types & diagrams - latching and standard non-latching

and with some hunting in E-bay / AliExpress , find 4 pole double throw relays




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 Posted: Sun Nov 17th, 2019 05:05 pm
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RFS
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An interesting topic and a few observations from me

Have you considered using slow-motion point motors such as Tortoise or Cobalt? I use Tortoises which have two built-in switches for frog polarity etc.  They're more reliable and are much kinder on the point blades etc.

The polarity switch on the Seeps is notoriously unreliable. 

Have you thought about using latching relays? You can get a ready-made one from Gaugemaster (GM500D) that is a DPDT change-over switch and it's wired together with the point motor. Costs about £5 and is a much better option than the PL-15. Before I switched to Tortoises I used some latching DPDT relays (HFD2) which I mounted on some circuit board and used them to switch polarity for Peco PL-10s. Cost about £1.50 each I seem to remember. 




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 Posted: Sun Nov 17th, 2019 06:50 pm
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Barry Miltenburg
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Hi Robert

I have looked at Cobalt or Tortoise but have been put off by the price and the size.  Call me old-fashioned but I like the snap of the Peco/Seep motors and have never had any reliability issues with either damaging Code 75 pointwork over the last 25 years or so that I have been using the Code 75+solenoid motor combinaton.

I have been using SEEPs for about 5 years and whilst I would admit that they are tricky to fit and get lined up properly, the switches have always worked for me.  There was a thread on here somewhere where someone complained that the centre pins worked loose but I have not come across that - perhaps I have just been fortunate and I have that pain to come!

I'll have a look at the Gaugemaster offering - thanks for the tip

Barry



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 Posted: Mon Nov 18th, 2019 08:19 am
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Barry Miltenburg
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I had a look at the Gaugemaster latching relay today as suggested.

Latching relays are slightly different in that they require a trigger to activate the internal switches and then another trigger to de-activate them.  Normal relays either pass a current or they dont and they are inert when they dont - latching relays are inert in either position and require a current to change.

Given this requirement, latching relays will require that the switch on the point motor diverts current either through one pin or the other and thus they have 3 primary pins rather than the normal 2.  Normal relays are either on or off.  Latching relays are on or on hence the need for a feed pin and TWO return pins for the two options.  There is a wiring diagram on the Gaugemaster website.

This unit offers 2 secondary circuits that are independent from each other so point frogs and signals can be worked.

The picture of the unit on the Gaugemaster site suggests a diode or two to ensure no "feedback" of current flow where it is not required so this is a little board with a relay and other bits rather than just a relay in a box.  For all that its a neat little unit and probably perfectly adequate for DC operation.  The price is higher if this is a factor for you.  Not sure where they are made - probably China!!!

I will post a wiring diagram for my normal 8-pin relays later when the meetings with banks and solicitors are over today  :pedal

Barry



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 Posted: Mon Nov 18th, 2019 09:47 am
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RFS
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It's just a straightforward unit that you wire up using the same 3 wires that you use to operate the point motor. The diodes on the board are necessary to allow for the feed being either AC or DC.

There are two versions - one for DC (GM500) and one "DCC Friendly" version (GM500D). 



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 Posted: Mon Nov 18th, 2019 12:16 pm
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RFS wrote: An interesting topic and a few observations from me

The polarity switch on the Seeps is notoriously unreliable. 




[My underlining]

Counter-intuitively, the SEEP switch will connect very reliably if the solenoid baseplate is NOT screwed tightly to the underside of the baseboard.

The small amount of 'slop' afforded by using 2mm screws in the 3mm baseplate holes and leaving them SLACKED OFF enough to allow the baseplate to skip sideways on activation will

a. Be kinder to your trackwork
b. Allow the wiper on the switch contact to fully cover and connect with the feed supply.

There is more than enough inertia in the weight of the solenoid and the stiffness of the connecting cables to operate a Peco Code 75 turnout. Additionally, on a double slip, where the blade travel is almost half thatr of a standard turnout, it will allow reliable frog polarity switching.

Hope this helps, I'd be interested in hearing of anyones  experience of just slacking back the mounting screws in the case of a turnout/slip where frog polarity switch is/has become problematic.

Douglas



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 Posted: Thu Nov 21st, 2019 02:50 am
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I'm delighted you struggled with electronics Barry - I'm in the same camp although you do have the advatage of being an electrician so have some understanding of this wierd invisible force .............................

Somewhat irrelevant in this thread but I haven't experienced any problems with SEEPs either - I did take Doug's advice and leave the mounting screws slacked off slightly and have a wonderful gadget designed to help position the motor below the baseboard.  I now however, use Tortoise by preference.

Thanks to your explanation, I now also have a vague understanding of what relays are, how they work and what they can be used for on model railways.  It is indeed a very dark art to me and the problem is, by tomorrow, relays will once again be a race where a baton is passed to the next team member ..............................  By that I mean that for me, it has to be a case of hard learning with very little "natural" understanding, therefore very quickly forgotten.

Maybe I ought to take a screenshot and print it off for reference ..............



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