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Post by zoinks007 on Feb 28, 2017 8:51:08 GMT -5
Being brand new to DCC, and after reading a lot and trying to make the best decision I could on equipment, I ended up purchasing the Digitrax Evolution duplex radio starter set. I have a single DCC-capable locomotive at present, and I'm looking forward to hooking the command station up and seeing it actually work.
Some questions for the experts, if I may...
A selling point to me of the Digitrax system was the claim it ran "all scales". However, upon reading the manual that's really indicating G - N scales, not necessarily Z. When I purchased the system, I also purchased the optional Z voltage reducer. I didn't know if I'd need it or not, but for $20 it seemed like good insurance.
So, my questions (2):
1) Is the Z voltage reducer necessary, or are today's AZL locomotives OK at running N-scale 12 V signals (everything I can find indicates N-Scale runs 12V PWM alternating current)? I can't seem to get a reading on the decoder...seems to indicate 12V would be fine.
2) My single locomotive has the TCS MZA4 decoder. I've read over the specification sheet, and aside from trying to digest the myriad of CV's, I'm not sure what address is programmed into the decoder at the factory.  I can run this thing all day long, but if I don't hit the right loco decoder address, I'm not going to see a lot of activity on the track. What's the factory decoder address setting? I'm going to assume that's in CV1? One byte...versus two bytes one could program into CV's 17 and 18... (Yes, I'll be figuring out how to reprogram that, but was hoping to just run it out of the box to make sure all worked.)
Thanks for any hints/tips...
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Post by markm on Feb 28, 2017 9:52:44 GMT -5
If you haven't done so already, take some time to read the DCC posts here. They contain a lot of useful information. 1) Basically, if the AZL loco takes a drop-in decoder it's 12V compatible. Officially, read: www.azlforum.com/thread/349/tcs-drop-dcc-decoder-azl2) I don't have a Digitrax system, rather an NCE power cab so your results may be different. When you put a locomotive on the programming track, the cab scans through the addresses and reports back the value. If you look at the MZA4 decoder worksheet, the factory default value for CVs is shaded and to the right of the CV number. It should be set to a short address of 3 (CV1). The MXA4 decoder indicates you have an MTL locomotive which is rated at 9VDC max by the manufacturer. I've seen these running on a 12V system and I know people who have burned out the motor running the loco on DCC. I believe people set the Vmax, CV5 to 162. But to be on the safe side you may want to run using the voltage reducer until you get more familiar with the system. BTW: even if you never use the voltage reducer again, it's still a hub for Loconet. Hope this helps, Mark |
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Post by zoinks007 on Feb 28, 2017 13:22:19 GMT -5
Thank you, Mark. I didn't realize the shaded value was default, but (doh) it makes sense now. I do have the MTL loco, but the vast majority of mine are AZL, so once I get some AZL decoders in I should be good to go there. Meanwhile, I'll take your advice to goof off with the MTL loco. I've been playing catch-up with all of the DCC posts but didn't recall that one mentioning track voltage until I re-read a post you made down in the mix, talking about the purple wire (third or fourth function). Gotcha...
Thank you for the help.
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Post by BAZman on Feb 28, 2017 15:36:37 GMT -5
You can 'safely' run it at the N scale setting but the Z voltage reducer is 'insurance'. It will also slow down the loco by 20% so they are less prone to the Lionel syndrome. There are easily a 1000 locos or more running on near every DCC manufacturer at 12 or even 15 volts.
The voltage rating on the motor is not like a semiconductor where if you exceed it - poof. You could likely even run it at 24 volts. It is all about power dissipation. The motor itself creates upwards of 100 volt spikes (when you look at it with an oscilloscope) and the DCC system itself has transients on it in the 50-100 volt range that get passed through to the motor. So the voltage spec is *not* from the specific value, its the heat factor
With higher voltages, you risk the issue of the motor burning up due to loading. Purely loading. This *primarily* means: Stalls. If the loco stalls (like a derail), the current goes WAY up which means Power which mean Heat. In many of our experiences, it won't happen. So I wouldn't worry about it.
The other way that Load can increase, creating heat, is long trains, grades and mechanical friction in the loco chassis/trucks. When running a loco (only), you may note that with DCC, it only takes a few Speed Steps to run it at typical speeds. Increasing the Speed Steps at some point, you will notice that you can no longer increase the loco speed. This is where the heat effect will increase, as you have essentially reached the motor's maximum torque. By programming the CV5 (Max), you can 'rescale' the Speed Steps so they better represent the Scale speed. Lets say that you reach that max speed around Speed Step 20. You could change CV5 from 255 to say 50. (CV6 Mid should be ~1/2 of Max so ~25). These values are 1/5th so now you original Speed Step 20 would now be 100. This gives you more step range for finer Speed Step control.
The CV's do *NOT* reduce the voltage to the motor !!! <--Important. They only 'limit' the Duty Cycle applied to the motor. The motor is run by 'PWM' (pulse width modulation). Speed Step 1 applies 1/128 of an 'On' time. Speed Step 64/128 or 50% On/Off and Speed Step 128 applies 128/128 or 100% on time (like a battery). Programming CV5 (Max 'voltage' in some DCC programming systems) does *NOT* change the actual voltage, only the 'effective' voltage (as read by a meter).
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Post by zoinks007 on Feb 28, 2017 15:50:54 GMT -5
Ah, and that makes sense. Once explained, it seems obvious. Clearly there is no voltage regulator (or anything of the kind) on the decoder, so the only way it could run a DC motor is modifying the PWM duty cycle. That would not decrease peak voltage, just the duration the peak was applied to the motor (fooling it into believing it is accepting less voltage). Pretty ingenious, actually.
Melted windings...been there with other motors. Spike current, and resulting heat, are your enemies, for sure.
Excellent explanation of CV5. Makes sense.
Great post...
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Post by BAZman on Feb 28, 2017 15:51:48 GMT -5
You need some sort of current protection. Our little Z scale stuff takes typically <<< o.1 Amps. The little wheel wipers and axle pick ups can't handle that 5 Amps. Poof. Or, a derail in a turnout, the wheel is wedged as the short conduit. So it overheats and you'll need to replace the axle - sometimes.
#1 rule in DCC: WATCH YOUR TRAINS ! At 12 volts and 5 Amps, that's 60 watts. HEAT.
You can make a crude circuit breaker using a o.5 Amp, 12 volt light bulb. This would be a the 'parking' lights on a car. a 1 amp bulb at worst case. The problem is if you have several locos running, the current will heat up the bulb and begin to drop enough voltage that you'll notice the speed change.
There are Electronic circuit breakers such as DCC Specialties PSX-1. This can be programmed down to 1 Amp.
The NCE EB1 can be changed from it's default by adding a o.5 ohm 5 watt resistor across their sense resistor, making it a .5 Amp (I believe my memory) breaker.
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I can run this thing all day long, but if I don't hit the right loco decoder address, I'm not going to see a lot of activity on the track. What's the factory decoder address setting? I'm going to assume that's in CV1? One byte...versus two bytes one could program into CV's 17 and 18... (Yes, I'll be figuring out how to reprogram that, but was hoping to just run it out of the box to make sure all worked.)
