R8247 driving a relay

[zeroOneman]

As mentioned in another thread, I am currently looking at using BM1 braking modules on my layout. In some sections of my layout I have colour light signals, driven by R8247 accessory decoders. I would like to put a relay across the 'green output' of the decoder, so that when the signal is green the BM1 is bypassed. It all sounds wonderful, but other than knowing what a relay does, I'm in the dark - do I need a particular type of relay? How much current will the relay draw from the decoder? I guess there is a limit to how much current the decoder can handle as well there being a limit to what my power supply can handler (I'm still using the 1A power supply)

Thanks in advance for your help

Andy

[96RAF]

I use R8247 to pulse into the coil of a realy that in turn fires a CDU through the relay main contacts to operate solenoid motors.

 

In your case you need to fire into the coil of a latching relay which will hold the selection closed. The other side of the R8247 port then latches the relay onto the other contacts to hold the selection open.

 

Search on the forum for R8247 latching relay or it may even be in the acc decoder instruction sheet. There have been several diagrams posted for the set up.

Rob

[Flashbang]

Hi

As your decoder is producing a continious output to power the signals aspects, then no need for any special relay!  For example if in the UK Maplin N87ED 12volt relay is fine http://www.maplin.co.uk/p/12v-dc-2a-dpdt-relay-n87ed

Use a relay with a 12 volt rated coil. Connect relay coils to decoders C and whichever terminal is feeding the green aspect  + or -. 

I would also add a 1N4001 diode across the relays coils conected so as the banded (Cathode) end is to the 'C' wire. The diode removes any bemf generated as the coil volts colapse.

Via the relays contact(s) switch other circuits.

 

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[zeroOneman]

Thank you both for the incredibly fast replies - I now have 5 DPDT relays on order, I'll post back once I have some results.

[Chrissaf]

01man,

Just for completeness of information the datasheet for Flashbang's suggested Maplin relay shows two versions are available from the manufacturer a standard sensitivity relay and a high sensitivity relay. These relays are quoted in the datasheet as having an operating current of 43mA and 17mA respectively on a 12 volt operating voltage (the Maplin product page does not state which of the two versions it sells). Assuming worse case scenario, your decoder port needs to supply 43mA for each relay. The R8247 has a total current capability for ALL four ports in continuous use of 240mA as quoted by Hornby Customer care in this previous post.

.

So in conclusion, as long as everything you connect to a single R8247 unit does not consume in total, more than 240mA then you should be OK.

.

EDIT: The customer 'question & answer' section of the Maplin product page infers that the Maplin relay is the 'high sensitivity' version with the 17mA coil operating current.

[zeroOneman]

Thanks for the heads up Chris. The ones I have ordered from evilbay are quoted as having coil power of 150mW, and a coil resistance of 960 Ohms. Which, by my calculations, is 12mA. The signals are Z04 signals - also from evilbay, they use LEDs (with resistor) and I have rewired them as they had common negative.

Andy

[Chrissaf]

12mA......correct

[zeroOneman]

Thanks to everyone's help I now have three working BM1 units. One controlling the bay platforms of my branchline is constantly active, the other two are controlled by the relevant signals. My only issue is that the gap in the track for one of them is constanly getting shorted by the carriages & so the loco overruns the signal, sometimes by one carriage length & ocassionally by more. I've already filled the gap with filler, this evening I have also coated the gap & the inside of the rails with clear varnish - I'll wait till tomorrow before testing it.

Here's a youtube link to the first 'automated' test -