Model Railway Forum banner
21 - 27 of 27 Posts

·
In depth idiot
Joined
·
8,427 Posts
A DC loco should have a capacitor across the motor terminals, and this will shunt the high frequency from the Relco preventing it from damaging the motor. ...
Side note, unrelated to OP's question.

I note your 'should'. Are the capacitors in current RTR product effective? Sourced as cheaply as possible, I suspect their primary purpose is to be a visibly present component for compliance.

I give all new locos a couple of hours test on DC before a decoder is installed, and this last dozen years have seen a high proportion of capacitors fail in that time. (This is with RTR OO, but the UK N product is all coming out of the same manufacturing system.)

What I haven't done is systematically put the DMM on the capacitor(s) before DC test running, and also checked that it is actually in circuit, because for a DCC operation it's a redundant component. Considering the incidence of flaky connections found in RTR model circuits, it's a fair bet that some capacitors are 'incapacitated' through lack of connection...
 

·
Registered
Joined
·
156 Posts
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!
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.
 

·
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
·
30 Posts
Discussion Starter · #24 ·
Move to DCC and you won't look back!
I can quite believe DCC is far more flexible and more reliable but I don't really want to swap to it. This is partly because I am refurbishing my 1970s N gauge layout for my lad mainly and want to retain more of the 1970s feel (but with better locos than Lima....), and without spending a fortune. And partly because it's a different attitude.. I want to get a DC system working as well as possible, it's like steam v diesel. The latter will always outperform the former, but steam has an interest all of its own !
 

·
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.
 
21 - 27 of 27 Posts
Top