All I know is the full wave bridge rectifier produces pulsating DC voltage to be filtered by the filter capacitor. Looks just like an AC signal but flat topped and crosses thru zero with each transition which makes it an AC signal.
Good enough for me but I guess not good enough for those who count all the rivets.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
To operate a DC locomotive on a DCC system, a technique called "Zero Stretching" is used. Usually referred to as Address 0, an address isn't allowed in DCC.
I just wanted to point out that while zero strectching will work, the loco performance is pretty poor. Many systems dropped the zero strecthing feature in subsequent updates after it was generally agreed that the option wasn't really useful as more than a "parlor trick" or a way to see if your recent DC purchase will run. Its not good enough to know how well the loco will run, just to confirm that it will.
My system has the zero stretch option but I never use it because of the poor loco performance.
Guy
see stuff at: the Willoughby Line Site
One thing to consider is that if you actually don;t follow the recommendations and hookt he ground lead of the DCC system to earth ground like the ground pin of a wall socket, and you are using an AC powered oscilloscope, you are risking blowing it up.
The DCC output is an example of a floating voltage, at least in some booster designs. Neither side is tied to a ground point. This is pretty much the same way switch mode power supplies work. You really have a differential signal the correct wya to measure this is with a differential probe, the alligator clip ground pin on a standard scope probe goes right through to earth ground.
Most boosters work by outputting through an H bridge, so there will be no center reference available. The output is as close to a square wave as can be generated, but there is a finite switching time in the H bridge.
How exactly Digitrax builds theirs I don't know, but their recommended way to test track voltage is between the ground pin and rail A, and then ground and rail B, and adding the two. The ground is not really earth ground, it is a common reference point int he circuit. It is not tied to either the ail A or Rail B outputs. You'll measure say 7.5 volts between ground and either rail, when the track voltage is 15 volts. That ground is artificially generated in the middle of the waveform - I suspect via a couple of diodes. I suppose I could tear my DB150 apart and examine the circuit. Even more reason to never tie that terminal to the earth ground.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
trainnut1250 To operate a DC locomotive on a DCC system, a technique called "Zero Stretching" is used. Usually referred to as Address 0, an address isn't allowed in DCC. I just wanted to point out that while zero strectching will work, the loco performance is pretty poor. Many systems dropped the zero strecthing feature in subsequent updates after it was generally agreed that the option wasn't really useful as more than a "parlor trick" or a way to see if your recent DC purchase will run. Its not good enough to know how well the loco will run, just to confirm that it will. My system has the zero stretch option but I never use it because of the poor loco performance. Guy
Depends on the loco Athearn Ble Box locos with their loosely built motors (magnets aren't glued in, ends are held on by the top and bottom clips) buzz like crazy. Zero stretching got an old but never before run Bowser loco moving - on a DC power pack all it did was sit there until the power pack overload tripped. Use address 0 on the DCC system, which was only slightly more powerful than the DC power pack being tried, got the loco to move and allowed it to break in a bit, after which is then worked on the DC power pack. Other motors 'sing' a bit, which changes pitch as you advance the throttle. Top speed is never great, but they are locomotives and not slot cars.
Like I said - not something I would do for permanent running, but for the occasional test run, it's fine. Haven't burnt anything up yet.
Randy,
You have better luck than my friends and I do with zero stretching. My stuff always runs pretty jerky on zero stretch - Spectrum steam, Bli steam, Atlas, P2K, Athearn steam and lots of old brass....Perhaps Digitrax has a better zero stretch than CVP?
Possibly. My locos I've tried never run as fast as they would with a real DC powerpack, and some can be noisy, but they aren;t real jerky, they are fairly smooth moving once you get past the singing that even the better motors do
I don;t regular run locos like this. I'll just put soomething on for a quick test to make sure it actually runs. If I could jump the throttle between speeds, you could probably play the motor like a musical instrument
The Athearn DC BB locos I have run on my Digitrax, the zinging seems to quiet as the speed increases, but they still run smooth, with no jerking.
I don't make a habit of doing this, but I have run a few on DCC, for short periods of time. Especially before I started installing decoders. I just had to do it, to see if it works, as the Digitrax manual says it would.
The last time I did this was to see if I had individual control over a DC loco, on the track with a DCC loco, which I did.
It just sounds "wrong", with the zinging.
Mike.
My You Tube
rrinkerZero stretching got an old but never before run Bowser loco moving - on a DC power pack all it did was sit there until the power pack overload tripped. Use address 0 on the DCC system, which was only slightly more powerful than the DC power pack being tried, got the loco to move and allowed it to break in a bit, after which is then worked on the DC power pack.
while the alternating DCC voltage is not good for a DC motor long term because of unproductive heat buildup, it has a similar effect as PWM to help overcome the friction of a motor to keep it turning. (I wonder how that Bowser loco would have run with a PWM throttle)
while i've read about stiction, i was unaware of a dithering feature supported in some decoders (CVs 56 & 57).
mbinsewiThe Athearn DC BB locos I have run on my Digitrax, the zinging seems to quiet as the speed increases ...
the "zinging" is the alternating voltage of the DCC signal which occurs for a smaller percent of time as a pulse is stretched longer to increase speed.
greg - Philadelphia & Reading / Reading