Driving relays from decoder output...

[andyspencer]

So another question due to issues... Thought i'd cracked a solution to raise and lower pantographs using 2 decoder outputs. Got my relay board, voltage limiter, diodes etc all fitted and tested/working. But once connected to the decoder, it won't work.
I even tried putting the relay directly across the decoder +/grd connection. it just buzzes and won't pull in... Whats going on?

 

[Railway42]

Hi Andy
The decoder +/ ground is not DC so I think that is what the buzzing is. You don't say what relay board or circuit you are using and also what voltage the decoder output is set to. Let me know and I will try to sort it out.

Railway42

 

[andyspencer]

Hi Andy
The decoder +/ ground is not DC so I think that is what the buzzing is. You don't say what relay board or circuit you are using and also what voltage the decoder output is set to. Let me know and I will try to sort it out.

Railway42

Hi there,

So I'm using an ESU Loksound 4 XL, and trying to drive two miniature 12v DPDT relays, set up so that I'm reversing the DC polarity to the pantograph motors on the roof.
Since asking the question I've had some joy. If I leave the CV for the output at 31, so full track voltage, the relay operates correctly. Which is fine on the 12v supply of the programmer, but once on track voltage, the 22v will wreck them. The buzzing occured when I reduced the cv below 31 to try and get a lower voltage.
I then spotted a 10v output from the ESU 4XL, and connected the relay to AUX 7. This set up is now working. When I tried this 10v terminal to AUX 6 and below, when the output was off I was getting -4 volts, and +10 volts when it was on. AUX 7 is zero volts when off, and the relays seem happy to operate at 10v
What is the voltage on decoder+/ground? Is it some form of PWM?

Andy

 

[Railway42]

Hi Andy.

The voltage on the decoder is the DCC pulses. You will have no problems with a pull in voltage of 10v on a 12v relay just remember to put a diode (1n400X) across the relay coil the band end to the +v, this will stop the back EMF from the relay destroying the decoder output transistor. Glad that you sorted everything out! It's an interesting idea.

Railway42

 

[andyspencer]

I did wonder about a diode across the coil. Will do that when it comes apart again. i was copying the way it had ben done with a loco with a 12 year old V2 chip. Those relays were straight between grd and an output. So either they were 24v coils (although they had the same resistance as my 12v versions) or ESU have altered how the voltage outputs work.
I'm curious how other people have set up working panto's if they didn't have the LGB control boards??

 

[dutchelm]

I have a loco with a very old LokSound XL (2002) & use 2 of the outputs to drive relays to operate the couplers. Standard miniature relays (off an old PCB) with back emf diodes (to protect the decoder). I'm not certain what voltage they were but would guess at 24v as they are straight across the decoder. No problems & no buzzing.

Enlarged picture and relays are 24v

 

[andyspencer]

My other loco with the old Loksound was the same, with relays straight off the decoder. Maybe it was using 24v relays as well. No diodes though from memory, but did have a small capasitor across each coil.
At least I've got a solution sorted for the modern XL4's. Will be adding diodes before its run again though...