DCC AC Yes, but equal positive and negative transitions just like sine wave AC so a full wave bridge rectifier treats the “AC Square wave” the same as a sine wave AC signal and converts it to unfiltered DC. Be advised there are low frequency pulses in commercial AC transmission lines that are used by the power companies. We just do not see them in the AC we used in the home. Also, the DCC decoders do not send pure DC to the motor. They send PWM pulses that vary in width for motor speed. A DC volt meter will see DC but a 'Scope will see positive or negative going pulses. Rich
There's 60 Hz sinusoidal wave alternating current, such as what most people have in their houses in North America, but there is also such a thing as square wave alternating current, such as that used by DCC.
Been there Been there, done that, have the T shirt. I retired as an industrial machine mechanic five years ago but was involved in AC and DC computer controlled machine drives that use 480 three phase, DC digital and AC digital drives. I was fortunate to be involved with motor drives an they evolved. Mostly paper winding machines. You might say, Large scale DCC with the systems that run large DC motors. Rich
I’m sorry but I’m just not buying it. Once you run AC through a full wave bridge you have DC not an “AC Square wave”. I forgot what its called when you make a AC Square wave, but it’s not a full wave bridge. A DC square wave does not change polarity it only pulses from 0 to a voltage above 0 or it can also be a negative voltage but not both. If it pulses between Negative and Positive it is AC. DC square waves are used to send a signal by varying the pulse magnitude or length of pulse. You can reverse the polarity as in DCC trains to prevent shorts, but when you do this you still have a square wave. I don’t know if AC is actually being used in DCC, but when I first studied up on it a few years back, I was under the impression it was a DC square wave.
The problem stems from the terminology and the word association. The DCC amp meter was designed to read current levels on a DC voltage that alternates. DC does not typically operate in the manner it does in the DCC world. AC power that we all know is Alternating Current its counter part is DC or Direct current. The measuring of current is something else but pertains to this thread. Measuring DCC current which is Direct current that alternates in its polarity or bipolar DC is what this thread was referring to. Inobu modified sine wave
Ok, I’ll buy that. I’m done, I don’t want get away from the topic, sorry. I’ll ask this question about AC and DCC in a thread of its own after I bone up on it a little.:tb-biggrin:
I agree, there is good information here. I posted a simplified DCC explanation that may clear things up to better see what the OP is referring to here. Inobu
Ye gods. Let's get this straight. DC "that alternates in its polarity" is NOT DC, it is AC. That is the definition of AC - it goes above and below 0, where 0 is the local reference, usually called ground. (Whole other can of worms there, so moving on ... ) DC that is not smooth, such as mains power passed through a rectifier with no capacitor, has an AC component because it goes up and down, but it is still DC because it only varies on one side of the local 0 reference. DCC power to the rails IS AC. No argument about it - it goes above and below 0. If it didn't address 0 wouldn't be able to control a non-decoder locomotive. The reason is that the net effect of balanced AC (equal + and - cycles) on a DC motor is nothing, because it gets equal pushes in both directions. The DCC system can effectively adjust the AC output so that it is offset from 0 and the + and - cycles are not balanced. This introduces a DC component into the AC signal. The DC component causes a DC motor to start turning.
Here we go again. You know what you need to do? Go to NMRA and tell them to re write their spec sheets. it says and I quote "The DCC signal is an alternating DC waveform, which contains the digital information, This coded signal controls a specific decoder placed in a specific locomotive causing it to use as much of the track voltage as it needs to move forward or backward, turn its headlight on or off or even dim it for meets with other trains on another track. " I have worked in the communication industry and know that this is a form transmission used in T1's and it is DC in nature. Put it on an O scope and you can see it for your self. It will be a square wave and not a modify sine wave which is a by product of AC. Once again it is terminology. There is a difference between Alternating Current and current that alternates. DCC has current that alternates that happens to be DC. It is not Alternating Current. Inobu
Folks, get your 'Scopes out and compare DCC waveforms to AC. Do some measurements. Also, you are entitled to your version of Reality. Don't forget, there are many people who do not believe that NASA sent anyone to the moon. I worked as a NASA contractor at a long range radar tracking site for over fourteen years and I saw the real data but to each their own. Rich
It's funny how people can sound so convincing and I'm one to always check myself leaving a possibility of being wrong. So, what do I do? double check myself. Here is what is did. I get a DIY booster and pulled the schematic for building a DCC booster. I traced the input leads from the track and found that it is connected to a LMD18200 National Semiconductor chip. It leads connects to ports 2 and 10. I checked the data sheet to verify what the outputs for ports 2 and 20 were. The outputs are DC. The data sheet description stated This chipset is ideal for driving DC and stepper motors. No where does it states that it has AC output capabilities. If DCC has AC on its tracks then it needs to have a component that delivers AC. Which it does not. Inobu Last entry for me.
This is way over my head. I am going to purchase one of the circuits from RPaisley. My question is what type of mutimeter should I purcahse?
Very good. Go to the head of the class. Though I suspect you are just looking for an argument. I have been a technician for many years. This can be very difficult to explain to those who do not understand what is happening. I prefer to say type of AC. Ranters will want to run on with that term. Rivet counters will never understand. A full wave bridge rectifier will treat the DCC as AC and produce a pulsating DC voltage to be smoothed by capacitors. It does not concern itself with terminology. I have used my Function Generator that puts out AC sine wave, square wave and triangular wave signals into a bridge rectifier. I adjusted the controls for equal positive and negative transitions. The bridge rectifier treated all of them the same and produced DC. Rich
Get a cheap digital meter. XXXXX XXXXX has them for sometimes less than $10.00. There are many on ebay for that price or less. I will not mention sources to keep from upsetting the powers to be here. Naysayers will try to convince you to buy a expensive meter BUT, if you make a mistake using the meter, it will only cost you a few dollars. Do a search for inexpensive multimeter. Some are in a yellow, orange or grey plastic case. Probably all made at the same factory in China. I have three of these meters. One in the car, one in the garage. One in my tool box. Others in the club I belong to have them also. They compare very well to my expensive meter which I used at work. Rich
Good deal Great shopper. One thing to watch out for with digital meters, the amps scales are protected by a fuse. You might have to look around for the fuse if one blows. Some meters have two or three fuses for protection. Rich
Some of the cheapo ones fall into the 'no user serviceable parts inside' category. The meter IS the fuse and when you pop it, you buy a new one
Fuses All my cheap ones I have one fuse. My two more expensive meters have two fuses. I very seldom use those two meters anymore. This not rocket science. Rich
I now have the circuit and meter. What is the proper way to connect the meter to the circuit. I don't want this be a permanet installation.
Meter Ok, which circuit are you using? I want to be sure. One uses the voltmeter like my circuit and the newest circuit uses the current portion of the digital meter. Rich
