Switching Solenoid Points with Relay's ???

[Northome]

Hi All,

I have been giving lots of thought to a complete re-wire of my layout, Firstly I need to make a new Mimic board for several track alterations I have completed and also to incorporate Frog switching for the electrofrog points in the new sidings area, most of the other points on the layout are Hornby insulfrog.

 

This got me thinking of how I could incorporate LED switches for "track direction" and Frog switching etc. and also being able to utilise both manual and dcc switching.

So this is what I have come up with and would like your thoughts as to 1, Whether it would work.??  2, Is there something already out there that I could purchase to do the same job ??, (at a reasanble cost) bearing in mind ADS 8 SX have not been available for nearly 2 years. and 3. Is it worth the effort and cost of components ??.

attatched are a couple of pictures of the relay board I am thinking of making but not being an electronics engineer I am not sure if it will work or not and would apreciate another set of eyes on it ??

/media/tinymce_upload/26ee8482c2e38d4f56a683e67f8d98df.png

The layout is on temperary breadboard but would be a PCB on production.

Hopefully it is viewable as I have had to convert it to a picture rather than pdf.

 

The relay board will be worked from both a manual switch and also switchable via DCC accessory decoder (not sure which yet).

 

your input would be greatly appreciated and allow me to carry out any mods required before production.

 

I have just noticed that under conversion the traces for the switch inputs have moved / distorted so will upload a second picture of the PCB. (sorry)

/media/tinymce_upload/a0b503eb16d266e15386239d7c8e4bad.png

many thanks in advance

Rob.

[Terry_Vincent]

Just to let you know that as of today "2ktechnologies" have some stock of

Part:DCD-ADS-8sx

[96RAF]

Do you have a circuit schematic for the proposal Rob as I am better at working those out than tracing PCBs. Apologies if that causes you more work, but I know some of these circuit design software packages can generate all sorts of diagrams.

 

The essential bit of the design is to isolate the analogue and digital elements via the relays. You have seen my schematic which uses rotary and push button switches for the manual side, and relays to use the DCC side, but in my new layout I would also like to incorporate signal lamps to indicate points direction so I will be following this topic with interest. Thankfully I have no electrofrog points, so no additional switching required for those.

[Northome]

Not sure how this will turn out converted to picture but will try my best, Its a pity we can't unload a PDF which would be better quality, however, here goes.  

It has taken me all day to draw out a schematic (specially for you Rob LOL)  so I hope it explains the workings a bit easier ?? (fingers crossed).  I am aware that the DCC and manual Switch need to be isolated from each other hence the reason for 4 individual relays.  

The input (switching side) are totally separate and cannot crossover, The Output (solenoid side) are linked 2 + 2 and then also linked to the Latching relay coils, so as such will only allow this relay to change when there is output to the solenoid (if that makes sence). The latching relay also has "power off memory" so should never be out of sinc with the solenoid ???.

I have included both a Schematic diagram and also the same with the PCB layout below. just in case of any difficulties following the wiring path.

Hope this helps./media/tinymce_upload/a297de8c406003545ca3f9c7e795f1b6.png

[Northome]

Hi Rob,

I have posted up (hopfully) a schematic drawing for you to have a look but will probably be another week before it appears again as it has to be varified picture, all being well it should explain it a bit easier ?

 

As explained in on the Picture post both DCC and switch are completely insolated from each other so should be no issues I hope hence the reason for 4 relays instead of the normal  2.

I just thought, I will email a pdf copy over to your Robs Rails site, you may be able to see it sooner.

Thanks for your help on this looking forward to the future discussions and I am sure Chris and Flashbang may have some good ideas to throw in the ring, you never know between us all we may be able to get something working (or not as the case may be)lol

Cheers

Rob 

[Northome]

Hi Terry,

Yes I have noticed they are starting to show in many places, It seems there may have been a delivery to the UK, I have had one on Back Order from Hattons for the past 18 months or so, and I am sure I will here from them in due course, but thanks for the info anyway.

[96RAF]

Rob has posted his schematic awaiting approval by Admin, but I have taken the liberty of short cutting the system by posting it for him via an email copy.

/media/tinymce_upload/e1ddfea70b13d32b03015a982f798725.JPG

 

As I see it the relay side logic is much the same as my method except you are using additional relays for your momentary switches to release the CDU charge into the solenoids. My method was to direct the CDU charge through my push button switch contacts - brutal and probably not doing them much good either.

 

I cannot comment reliably on the yellow box bit controlling the frog switching and associated indicators as I have shied away from electrofrogs for whatever illogical reason.

[Northome]

Regarding the the "Yellow Boxes" metioned,  I currently have approx 20/25 of these fitted to my layout and can honestly say they have never been a problem (so far) (and now I have said that !!!!!), 

 

These are a standard 12v DPDT (HFD2/012) Latching Relay of which I use for a variaty of functions including LED switches, Frog Switches, Reverse loop Switches (coupled to the solenoid), Static lighting switches, and Signal switching.

There is one thought that may be of an issue "having them trigger off the CDU", I currently throw all my relay's from my 12v aux power supply, If we now trigger the relay from the CDU power and that CDU is of a very high output variety, (mine will throw 6 sets of points at once with no problem) then there may be an issue of overloading the 12v relay coils, to this end it may be a thought to utilise a 24v version (HFD2/024) of the same relay, and I think as these have a wide trigger voltage range, I believe the 24v would have no issues if only 12v was used as the trigger. ??? 

[96RAF]

I had been using the 12v pulsed (from internal CDU) output of a Hornby PAD R8247 into the relay coils without problems for years. My relays were simple 12v 1960s tech standard car headlight relays (Hella, Bosch, etc) and they have never failed despite not having protective diodes to guard against collapsing field spikes.

 

The pulse is very short duration and in my case only pulled the relay in for an instant, but still long enough for the extermal circuit CDU to dash through the main contacts.

 

Are you saying you want to trigger yours from the main CDU as well?

 

Modern PCB relays may be less robust but I am discussing their use in another post with intent to use the same PAD outputs and the matter is ongoing subject to bench test as my relays are 5V.

 

We currently have several discussion going at once on loosely related topics and each can learn something from the others, which is good.

[Northome]

Well yes of a fashion but only the latching relay would be triggered from the CDU.  if you look at the schematic the DCC Acc. decoder would trigger 2 std. relays and the manual switches would trigger the other 2 std. relays that would then operate the CDU on the other side of the relays (the output) to the solenoid. 

 

The trigger (coils) of the Latching relay are connected to the output (solenoid side) of the std. relays so therefore would recieve the power from the CDU. I too am not sure how reliable a 12v coil would be receiving the quick (boost) power from the CDU, I just thought that if we went to a 24v coil there would be no issue of overload and still think it would also trigger if no CDU was being used and the voltage was only 12/15v from an aux power supply.

 

Also I too have several 5v relays on my layout and they seem to have no problems being triggered by the 12/15v aux power supply. 

 

To be honest I would not foresee any problems using 12v latching relays powered by the CDU, I was just airing on the side of cation, overkill if you like, but I tend to use a theory "What will do a lot will do a little, but doing a lot with a little is inviting tears"

[Northome]

The CDU I use is a "Mega CDU" with 4 x 20,000uf capacitors, my problem is, as I have not tested the output voltage and amperage of the CDU pulse, I have no clue as to if 12v is enough to cope over the long term.

The last thing you would want is for the relay attached to a PCB to fail through overload with prolonged use.

Better men than me could probably give us the answer ?

[Rog RJ]

I think you will find the mega CDU has 4 off 4700uF capacitors making a total of "nearly" 20,000uf (according to their specifications)

[Chrissaf]

Relays will only draw as much current as they need for any given supply voltage. Let's say for example the relay coil on 12 volts will only draw 30 mA. That is all it will draw even if a 12 volt CDU capacitor is capable of supplying 10 Amps. Thus the capacitors will keep the bulk of their charge on tap for when it is genuinely needed.

.

As an Analogy think of a car battery. When you start the engine, the starter motor might draw 150 Amps from the battery, but that same battery can provide 50mA to operate the dashboard clock. It's all basic mathematical Ohms Law. Low resistance means drawing high current, High resistance means drawing low current. A solenoid motor coil can be as low as 4 ohms resistance, whereas a 12 volt relay coil might be nearer 100-300 ohms. Solenoid and Relay coils have resistance therefore they are respectively self regulating with regarding how much current they draw.

.

However external CDUs tend in the main to be supplied with voltages higher than 12 volts. Typically about 19 volts. What is really the factor to consider is voltage not current, increase the voltage across the relay coil, that will force more current through the coil and Current times Voltage = power = heat [more Ohms Law].

.

This 19 volt CDU voltage caveat however doesn't normally apply to the outputs of DCC Accessory Decoders. These tend to be nearer 12 volts at 14 volts. It is usually only the DC Analogue CDU wiring solutions that generate the higher voltage pulses.

.

But the other factor to consider is time. It takes time for the current in a relay coil to generate heat. It is the heat that damages the coil. But when a relay coil is being operated by the pulse for operating a point motor solenoid, that pulse is very brief only 100 milliseconds (if using Hornby Accessory Decoders).

.

Regarding the 12 vs 24 volt relay coil comment. If the CDU input power is around 19 volts as in a DC Analogue point control system, then yes I would say a 24 volt coil might be prudent to adopt. If the latching relay operating pulse is coming from a DCC Accessory Decoder ... then I feel that 12 volt coils will suffice.

.

So all in all, I think perhaps you are unduly worrying pessimistically. Unlike Rob I haven't as yet done a full assessment of your proposed circuit, so take your primary guidance from him, my comments are secondary.

.

[96RAF]

Carry on Chris - my assessment was more of a comparison with what I had previously used and trusted and with what I am scheming up in the other posts in the DCC area on here.

 

I am still trying to get my head round the exact flow path when either a DC or DCC switch action takes place. Each post from each contributor is adding bit by bit to that understanding..

[Northome]

Hi Guys,

I have tried to simplify the Relay Schematic for ease of following Flow path.

 

The Board actually requires NO permanent feed to operate, Switches and relay output could by powered from external power source if preferred.

 

The only reason the permanent "Track or Aux DC" input on the board is to give power for the LED and/or to provide a power source to the momentary switch (if desired). both of which are controlled by Jumper settings (J1, J2, J3) Hope that makes sense ?/media/tinymce_upload/a3e4ef0754f1777b68b3857df9129f0c.png

[Northome]

Hi Rog, I stand corrected, and it is indeed 20,000uf, thank you!

[Jacov]

Have you looked at the Train-Tech PC2 quad point decoder. The decoder is similar to the Hornby accessory controller and is compatible with the Hornby DCC, except it can only be used for point control or other momentary signal devices as its output is only pulsed and it cannot give a permanent output (e.g. to power signal lights). Its main advantage is that each of the 4 channels have an additional 3-pin connection on the decoder box that can be connected to a passing connection switch (i.e. the analogue/DC switch used to control points on the old analogue layout - such as the switches in the Fleischman mimic setup) which overrides the DCC setting but still moves the points via the controller, hence eliminating the need for a separate DC power source and the relay interface. This allows you to use both DCC and analogue control of the points (e.g. making it easier for my grandsons to control the many points on their layout). The connection can also be wired up to light up LEDs in the analogue switch (e.g. some point control switches, such as Fleischman, have LEDs to indicate which way the points have been set). If you go to the Train-tech site you can download the manual for the PC2 decoder and see what it does exactly. Gaugemaster sell a similar product (I believe it is the Train-tech unit badged up for Gaugemaster)

[STG]

I prefer using a raspberry pi with relays to control points and signals. I find it much easier than designing a PCB because when the layout is changed it doesn't take much rewiring, and not a massive hardware change. This gives me an executeable app on the main control device which connects to the raspberry pi, the app communicating and displaying a virtual mimic board.

I find DCC equipment expensive, and since I could program it seemed a good project.