DCC power question relating to relays

[Tim Brien]

My current railroad is set up with numerous 30 amp car horn relays to switch power, etc. To date, many years, they have performed impecably. With the coming introduction of DCC, will the relays behave nicely with DCC power? I intend keeping my railroad as both analogue and digital power (not at the same time, though), so hopefully need to keep the relays active.

Are the relays going to be 'troublesome' on digital power?

 

[minimans]

Tim as long as the control side of the relay stays DC I can't see why not, the contacts don't care as long as the current stays within the rating for the circuit and as you use horn relays which have a high current rating I think you should be OK

 

[Tim Brien]

Paul,
the problem is that the relays use track power for control. Now with the introduction of DCC, then the 'track power' input will be DCC power. As far as amperage then my max current draw is only around 1 amp.

 

[stockers]

As far as I know, solenoids in the relays will not work on AC. The DCC supply is more or less an AC supply so I think the relays will not operate.

 

[Philbahn]

You could always put a diode across the cable feeding the coil causing an artificial dc

 

[stockers]

That would give a sort of half DC. Might work, but you might need a full rectifier.

 

[Philbahn]

Works on my GE4411 ,I use it to control the pantographs.
I am concerned about the mixture of DC & DCC

 

[Tim Brien]

I connected a relay to the track output of my deceased Piko central station. I know that the station works for DCC sound input so figured that there must be some signal to the rails. Not having the correct RMS meter to measure the DCC signal, I tried a DC meter and recorded 11.75 volts (nothing recorded on AC selection). At least there was a signal at the rails. The chosen relay sat there like a lump of plastic with no response to indicate it even knew the DCC signal was present.

Looks like all my relays will need to be bridged for digital operation, effectively taking them out of the circuit.

 

[don9GLC]

I connected a relay to the track output of my deceased Piko central station. I know that the station works for DCC sound input so figured that there must be some signal to the rails. Not having the correct RMS meter to measure the DCC signal, I tried a DC meter and recorded 11.75 volts (nothing recorded on AC selection). At least there was a signal at the rails. The chosen relay sat there like a lump of plastic with no response to indicate it even knew the DCC signal was present.

Looks like all my relays will need to be bridged for digital operation, effectively taking them out of the circuit.

Tim,
You might just have inspired me enough to carry out some basic physical measurements on DCC signals. Once I have done this I will repost to confirm the following (under item 1) that I believe to be theoretically true :-

1. You can't use a true RMS meter to measure DCC Voltage. You can get an approximation by using the ac range. You need an oscilloscope or similar to measure the peak value (not RMS). If you can measure a DC component then there is either a fault or you have set the Central Station to drive an analog loco.

2. Most relays will operate only with DC power to the coils. Larger devices that switch power circuits using AC coils are called contactors. However I am intrigued by how you have connected the existing relays. Since they are track powered, I don't understand how they respond to reduced voltage unless you have selected a very low operating voltage coil and operate them at over voltage. How are they switched, and what do they do?

3. Importantly why are they track powered? If you are using DCC as track power then the cost of track power per Ampere goes up dramatically, apart form possible conflicts with new technology such as RailCom. Its generally preferable to use a separate supply for continuous loads.

4. Why do you think rectifying the supply to the relay coils takes them 'out of circuit'?

5. Its my observation that combining DCC and DC is a far from simple matter, especially when using 'off the shelf' components that were never designed for dual supplies. Its not impossible, after all men were on the moon before DCC! But it does need a bit of engineering pre-planning. Its not a simple case of disconnecting an analog power supply and replacing with a DCC supply. And you have some technically challenging track configurations.

I appreciate that this does not help you, but you have not given enough detail to allow helpful comment. There is usually a trade off between what you would like and what you are prepared to spend. There are those who like to retreat into their 'comfort zone' of old technology and that is probably a blessing for the rest of us who like to explore what is possible. If I may be so bold, you are certainly pushing the boundaries of what is possible in combining DC and DCC. I just wonder if it is worth the effort? Since some people are more relaxed with DC that they think they understand, I'm not going to suggest they are wrong. But once you experience the advantages of DCC, you may confine DC to test tracks, as I do.


Don

 

[Tim Brien]

Don,
I have simplified matters and removed all relays. I had to work out my logic from many years ago when I wired the railroad. Basically, I had isolated track sections, about one metre in length, at several 'block' sections. This was to isolate tracks when using multiple Aristo Train Engineers. The isolated sections prevented cross/reverse polarity damage to the receivers if someone bridged a joining section. Effectively, the isolated sections were longer than my longest locomotive so if an errant operator exceeded his section then the loco would stop on the isolated section, thus preventing electrical damage to an adjoining receiver if both receivers had opposing polarity. The relays were powered by EPL microswitches to power the bridging section only when that route was selected by the switch/points.

I also used relays that 'sensed' track polarity, so that if an errant operator applied power to a section that was already powered, the relays would actuate. Thus removing the existing power supply which was powered through the 'relaxed' contact on the relay.

 

[Gizzy]

I think what you will need to do for DCC control of your relays, would be to use a decoder to change your relays.

The LGB point decoder might be suitable for this if you are using a latching type relay.

DCC uses pulses for the commands which may cause a relay to 'chatter'. I think of DCC as a kind of 'Frequency Modulation' (FM) and DC as 'Amplitude Modulation' (AM), so devices such as diodes and relays which work on DC will not work the same way as on DCC....

 

[muns]

I use 24v DC coil relays powered by fully rectified DCC track power. The full rectifier (4 diodes) converts the Square wave DCC signal into almost pure DC and thus the relays do not have any issue.

As the DCC signal is not an AC wave form (sine wave) the changes in polarity do not cause the output of the rectifier to drop its output as the switch of polarity is allmost instant unlike the AC wave form where the voltage reduces and increases over its cycle time.

 

[Tim Brien]

I considered the rectifier method for each relay, however went with removing all relays as I am no longer using the multiple Aristo Train Engineer receivers and so the need to isolate block sections is not required.

The diode situation will be dealt with by an on/off switch for each. The switch would be 'off' for analogue ops and 'on' for digital. This will give the digital signal a path, bypassing the diode.

Now my only issue is my two reverse loops. One will remain purely analogue usage. The other, due its very short length, may prove a problem with 'sensing' modules such as the Massoth, plus, I always use metal wheels so bridging the 'sensing' sections could be a problem.