Model Railway Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
2,698 Posts
Also I have a couple of Relcos in the circuits, are they a bad idea for a DCC loco ?
This is actually a very important question.

Relcos are a very bad idea for DCC layouts: DCC and Relco Units - Model Railways On-Line

They output high-frequency 50v spikes. The NMRA specification for voltage tolerance of decoders is 29v (IIRC). This means that Relcos are outputting a voltage which is double what decoders are designed to accept, therefore, the use of Relcos with DCC is highly likely to damage all of your decoders very quickly!

Having said that, more expensive decoders have overload circuitry built in which may well shut their decoders down to protect them, but I would suggest that it isn't worth trying to find out.

Having accidentally connected a Relco to a DCC track on my work bench, I can confirm that a DCC command station will actually destroy the Relco.

Also remember that Relcos are a 'continuity maintaining' device. They are not 'track cleaners' as they were advertised as. At best, they put off the evil day of track cleaning for longer. They detect a broken circuit and output a high frequency voltage spike to ionise the gap. This has the effect of restoring the circuit and enabling a loco to continue.
I used Relcos extensively in my DC days and found them to be very effective on small layouts, but less so on larger layouts as they seemed to be 'quenched' as more track length was added.

Relcos are redundant on DCC layouts anyway. DC control changes the voltage across the rails from 0 to 12v to maintain speed. In DCC, there is a constant 16vac supply across the rails and decoders drop the voltage from that to motors inside a loco in order to achieve speed control. There is no drop of track voltage in DCC to make things run slower. In my opinion, this constant track voltage is probably the single most important 'un-sung' benefit of DCC as it very significantly improves operational performance through not having low voltages. This benefit negates the need for Relcos on DCC layouts. And as a result, most people get far better performance with DCC operation than DC. So long as they don't use 14 or 28 speed steps...
 

·
Registered
Joined
·
2,698 Posts
So would it be OK to use Relcos on a DCC ready loco which hadn't actually been converted to DCC ?
The definition of 'DCC Ready' is a loco which has a DCC socket fitted, into which a blanking plug has been inserted, meaning that the owner can subsequently remove the blanking plug and plug in a decoder.

The key is the presence of a decoder, not how the loco is wired.

So long as a loco has NO decoder fitted, it can be run on a DC layout with a Relco, regardless of whether it is 'DCC Ready' or not.
 

·
Registered
Joined
·
2,698 Posts
In principle yes, as it is a 12V DC loco.

Personally I wouldn't use a device of this sort on the size of motors in N gauge product, because it cannot discriminate between loss of conduction at railhead and commutator; and I believe many small motors now use a fine metal wiper on the commutator, rather than the much more tolerant piece of copper carbon.
To be honest, I found that of all the gauges/scales, Relcos were actually most beneficial on N gauge products, in my case, 009.
 

·
Registered
Joined
·
2,698 Posts
1. The lights work at proper brightness all the time.
2. You will get inertia built in to the loco (no need for an inertia controller).
3. Less likely to stall when running slowly.
4. No need to fit a decoder when you convert to DCC.
.1. I am not sure the lights would work at full brightness all the time, with a DC controller through a decoder you are still only putting a few volts through to make it move, the same (if not less) volts than would be required on D.C. without a decoder fitted.

.2. Why? Unless the Loco has a stay alive fitted, and I am not even sure that a stay alive would work as well running on D.C.

Not wishing to be confrontational it’s just that are my impressions if running DC on a DCC fitted Loco, I cannot see how you can fool physics.

If indeed your correct it sounds to good to be true, but happy to see it work that way for sure (y)
My observations on this:

1. This depends on the decoder, some do, some don't.
2. DCC decoders have voltage controls built in to tightly control the voltage supplied to a motor. These are based on the principal of dropping the voltage from a higher voltage. You can never get more voltage out than you put in. So while a DC controller drops the track voltage, the decoder will be trying to maintain the voltage to the motor, but won't be able to due to insufficient track voltage. You are likely to get a conflict here with undesirable/uncontrollable behaviour.
3. This is not true. The DC track voltage is dropping off, so the effect will be exactly the same as it is for normal DC operation with no decoder fitted: it is more likely to stall due to continuity issues between rail/wheel with low voltages
4. That is true because the loco will already have a decoder fitted.

My suggestion is: don't bother running DCC fitted locos on DC. They will never exhibit their full functionality to its potential, therefore, running on DC is always going to result in disappointment. Move to DCC and you won't look back!
 

·
Registered
Joined
·
2,698 Posts
Sorry, my quote on note .2. should have been .3. I couldn’t see how less stalling would be possible, quite correct.

I still don’t get how the lights running on a DCC Loco supplied with a D.C. voltage would work from zero volts, or even at a few volts for example when crawling along, you still need enough volts to gets the lights to illuminate, with DCC you have 16V or so to play with (or the decoder does) so lamps are bright at standstill.

I get the LEDs only require a very small current to operate, but the decoder needs those volts to operate as wel……if it ain’t there, it ain’t there.
A DCC decoder requires a few volts to get itself running. Once that voltage has been reached, lights will operate. My observation is that it depends on the decoder as to whether the brightness is constant from then on as volts increase with DC track voltage (increased speed).
But it is true to say that once the volts to the decoder drop below a certain level (ie DC loco crawls to a stop), the lights go out.
Of course, with a DCC track supply, there is a constant 16v across the rails and speed is controlled by the decoder in a loco dropping that voltage to the motor, not by the voltage on the rails dropping.
 

·
Registered
Joined
·
2,698 Posts
Fair enough - if you are resurecting 1970's equipment, there's a high probability that it won't be suitable for DCC - that would really depend on whether the motor is isolated from the chassis.

To me it is the same as the question of would one convert a Hornby Dublo 3-rail to DCC. It wouldn't be worth it for a number of reasons. Just enjoy it for what it is.

That of course, brings us full circle to the reality that a few modern items are likely to be added and you would want to run them. If you have a DC layout, I wouldn't be putting DCC fitted locos on it - no point because you're never going to gain the benefits of DCC running them on DC control.
 
1 - 6 of 6 Posts
Top