Thinking about DCC.

S

Sarah Winfield

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After all the assistance in helping me understand how my first reverse loop works today I have been investigating how I wire up my second.

However, several questions arose while I was thinking about it.

I understand the digital signal is part of the AC voltage. Is this signal measurable?

When a locomotive hesitates or stops is it the voltage or digital signal which is interrupted?

Is there a way of measuring what the track is reading as a locomotive traverses the layout?

Thanks,

Sarah Winfield
 
As I understand it, Sarah (and I am NO kind of expert!), I don't think you would be able to measure or read the digital control signal unless you used something like an oscilloscope.... The digital command signal is, I think, created by stretching and compressing the width of the pulses of the very fast AC frequency (much faster than "mains" AC frequency, I think) that is being fed to the track. Others who have a better handle on it all may be able to explain it more clearly.....

I am pretty sure that hesitation in loco running is down to power pickup issues rather than a loss of the digital control signal.

Jon.
 
Wot Jon says..
(Well, 'good enough for television' as we would say in a previous existence) :nerd:
 
Sarah asked:

I understand the digital signal is part of the AC voltage. Is this signal measurable?
DCC is an AC square wave. The frequency varies (is modulated) to be the "data"..... it is digital data, but the AC square wave is ALWAYS there.

dcc_signal.png


The digital data is 1's and 0's like all other digital data.

When a locomotive hesitates or stops is it the voltage or digital signal which is interrupted?
The AC square wave is ALWAYS there, and nothing can interrupt it except a short circuit or failure of the command station.

Is there a way of measuring what the track is reading as a locomotive traverses the layout?
You could measure the voltage, which is only helpful if you have a voltage loss problem.
Seeing the "integrity" of the data takes an analyzer, usually a computer program running with some hardware.

DCCT-Both.JPG


Google is your friend:

https://dccwiki.com/

Greg
 
The reason I asked is I wondered if it was possible to put a meter on a wagon and to find out where problems might be on the track.

SW
 
The only problem you can 'see' is if there is a dodgy joint (hence a drop in the track voltage)..
BUT, you really need to have a load across the track in order to detect this.

You could have a suitably rated resistor to do this, and also measure the track voltage. - Though your load resistor would become uncomfortably hot, and measuring the voltage is slightly challenging.
Pulling a suitable amount of current through the wheels/pickups might be detrimental as well??
 
Sarah Winfield said:
The reason I asked is I wondered if it was possible to put a meter on a wagon and to find out where problems might be on the track.

SW
Click to expand...
The easiest way to do that is to start out running your loco on the piece of track where the power feed is located, not too fast, and follow it round the track until you see a noticeable slow-down or stop. This is most likely to be just after a track join, so immediately you know that one or both of the fishplates just passed need attention. Carry a pair of pliers with you and be prepared to give the fishplates a squeeze! Simply using the metal pliers to bridge the joint can help to narrow down which fishplate is the problem.

Also bear in mind that if running on a loop with no isolating breaks then theoretically the power can feed round both ways, which is usually helpful in alleviating voltage drops. Work round your loop in both directions checking for iffy fishplates.
 
I was just wondering if it was possible to check my layout for suspect joints before even putting a locomotive on the track?

I find if I use pliers to squeeze the fish-plates the inherent springiness of the metal because it only moves very slightly; if at all; isn't sometimes enough to correct the fault. It really needs pliers with a "nipple" to indent the fish-plate.

Believe me Gentlemen when I say I'm having fun with this G scale size railway. I doubt what I am doing is to many peoples taste but rule 8 applies!

Thank you Greg for the lead to dccwiki.

SW
 
Hi Sarah, If your track is not yet permanent, disassemble the suspect joint then squeeze the joiners (fishplates) closed a bit before rejoining. This will get around your problem with spring-back.

Phil S.
 
Sarah Winfield said:
I was just wondering if it was possible to check my layout for suspect joints before even putting a locomotive on the track?
SW
Click to expand...
My method is very similar to that advised by others except I use two 12V car headlamp bulbs in series for the load. 55W bulbs take around 4 amps, use less powerful bulbs on lower power controllers. I clip the bulbs to the track as far as possible from the track feed wires and then measure voltage at the controller output, the point where the feed wires connect to the track and then various places round the circuit. This works for both AC and DC power. If the voltmeter reading seems strange but the bulbs are nice and bright check the the meter is set correctly, e.g. not for DC volts when measuring AC (don't ask how I know this!)
 
Sarah Winfield said:
I was just wondering if it was possible to check my layout for suspect joints before even putting a locomotive on the track?

I find if I use pliers to squeeze the fish-plates the inherent springiness of the metal because it only moves very slightly; if at all; isn't sometimes enough to correct the fault. It really needs pliers with a "nipple" to indent the fish-plate.

Believe me Gentlemen when I say I'm having fun with this G scale size railway. I doubt what I am doing is to many peoples taste but rule 8 applies!

Thank you Greg for the lead to dccwiki.

SW
Click to expand...
Sarah some time back I did mention use if a small Speaker, thinking about it a Buzzer or even 12v light will do so long as tey are not in constant contact.
 
No72 said:
I thought about DCC..... Then decided RC was a whole lot easier.
Click to expand...

Steady! - Horses for courses....
You'll set Greg off! ;):giggle::giggle:

Sarah has gone DCC, but will probably end-up with a single battery RC loco, as a 'run anytime', 'go anywhere' loco.. - Well, that is how I read it? :think:
 
PhilP said:
Steady! - Horses for courses....
You'll set Greg off! ;):giggle::giggle:

Sarah has gone DCC, but will probably end-up with a single battery RC loco, as a 'run anytime', 'go anywhere' loco.. - Well, that is how I read it? :think:
Click to expand...
With a small Railway one good working loco is probably enough!
 
dunnyrail said:
With a small Railway one good working loco is probably enough!
Click to expand...
So with a small tramway I should have only 1 tram??? Seriously I don't know about the UK but DCC is very expensive and I can control up to 99 trams with less than au$200 worth of kit and I dont need to run around with a multi meter and oscilloscope testing for faults. This horse is in the right paddock ..
 
No72 said:
So with a small tramway I should have only 1 tram??? Seriously I don't know about the UK but DCC is very expensive and I can control up to 99 trams with less than au$200 worth of kit and I dont need to run around with a multi meter and oscilloscope testing for faults. This horse is in the right paddock ..
Click to expand...
$200, for the whole control system and 99 chips, that is cheap, or are the trams already chipped !!
 
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