Relays

[ejstubbs]

Background: I'm using SEEP point motors on my electrofrog turnouts but I've decided to use Gaugemaster GM500 latching relays to do the frog switching, rather than rely on the rather crude switch built in to the SEEP motor.  Since the GM500 can switch two circuits at once, I only need one per crossover so the incremental cost isn't too bad.

 

I've now run in to a complication relating to my insulfrog single slip.  I've decided that the slip is going to be fully isolated, with the power feed to the slip switched from adjacent power sections according to the setting of one of the turnouts that leads to the slip.  I'd like to automate that switching.  I'm not using common return wiring so switching power feeds requires a DPDT switch.  Add in the SPDT switch for the frog switching on the turnout and that means that I'd need a three pole switch rather than just two.

 

The solution I am considering is to use one of the switches on the GM500 to energise a normal (ie non-latching) DPDT relay such as this one to switch the power feed for the slip.  I would use the uncontrolled 12v DC accessory output from my controller to energise the relay.  The relay would be energised only when the turnout is reversed.  The other switch on the GM500 would switch the frog polarity for the turnout as usual (there's no frog switching required on the slip as it's insulfrog).

 

I realise that there are other ways to achieve the same result, some of which may be "better" according to certain criteria which might or might not be relevant to my use case.  However, is there actually anything fundamentally wrong with the solution I'm considering?

Edited June 30, 2017 by ejstubbs

[ejstubbs]

No, not in principle.

 

Thanks for confirming that.

 

But these relays from GM are fairly expensive, for not a lot more you can have 5 of these: link.

 

Thanks again.  However (i) I've already bought the GM relays (from Hattons, in the three packs, which works out at £4.60 per PCB mounted relay), and (ii) I've given up buying stuff direct from China.  For a start, it usually takes ages for the goods to arrive.  If they turn out to be faulty, or just the wrong thing, then: if you're lucky you get your money back no questions asked; if you're less lucky you get sent a replacement which takes a further age to arrive; and if you're really unlucky they want you to send to faulty/wrong item back.  This goes for Chinese vendors on UK eBay and Amazon, as well as those who use AliExpress.  This is not a criticism of the Chinese vendors, by the way - they are where they are, and I am where I am - but it is a vote in favour of using a UK distributor who keeps the goods in stock, can get them to me in a sensible time, and who is bound by the Consumer Contracts Regulations.

 

But maybe that's just me.

Edited July 8, 2017 by ejstubbs

[martin_wynne]

Or from the UK. £1.39+vat. Next day free delivery: http://uk.rs-online.com/web/p/latching-relays/0515571/

 

These are double-coil relays for easy circuit design, but might need some additional quench diodes to work reliably as in the Gaugemaster diagram.

 

Martin.

Edited June 30, 2017 by martin_wynne

[BG John]

I'm finding that the post from China seems to be pretty fast at the moment. Most things are arriving on or before eBay's earliest estimated date, and the things I buy through AliExpress seem a bit quicker than eBay. Of course, it may not last!

[cliff park]

With reference to Martin Wynne's comment about a diode quencher ( a diode in reverse across the coil):- the real purpose of this is to protect whatever is switching the relay. Particularly if this is a solid state device. The back emf (voltage) generated by the the collapsing magnetic field when the supply is switched off can be several hundred volts, it is often the basis of electric fence machines. It does , however , have very little power, despite the voltage, and a small rectifier diode will easily cope. If the switching device is another switch it will help to minimise arcing and prolong the life of the switch.

[Ron Solly]

Another option is to use these in conjunction with solenoid coils.

 

http://www.heathcote-electronics.co.uk/point-indicator.html#POINT-INDICATOR-RELAY

[Junctionmad]

At this stage I've received over 50 deliveries from aliexpress, over a period of 2 years. Not one went missing

Edited September 28, 2017 by Junctionmad