Stevio778 Posted February 19 Share Posted February 19 (edited) Hello, I have a black Z21 command station which is powering a small railway test layout TT120. When I use a voltmeter on the tracks I am getting a reading of just around 8.28 AC which seems rather low? Can anyone throw some light on this for me. I am running a TT120 William Whitelaw and Mallard loco on it OK but want to run a TT120 08 shunter with a Zimo MS490N 6 Pin Mini Sound Decoder in it. Only I don't want to damage this decoder in any way. best, Steve this is my test layout Edited February 19 by Stevio778 Link to post Share on other sites More sharing options...
WIMorrison Posted February 19 Share Posted February 19 What voltage does the Z21 Maintenance App, or the Z21 App say that is being output? That is where you will get the true voltage. Almost all multimeters (especially low end of the market) are designed for 50/60Hz low frequency sine waves and they cannot accurately measure a DCC signal. 1 Link to post Share on other sites More sharing options...
jpendle Posted February 19 Share Posted February 19 Hi, You're multimeter reading is incorrect. Because of the nature of the DCC signal cheap multimeters can't measure the voltage accurately. From memory the Z21 track bus is set to 18V by default. As Iain says use the Z21 App on your phone to check the track voltage (Settings/ Z21 Settings). FWIW I just increased the track voltage on mine to 20V as some of my Zimo equipped locos weren't running fast enough (I'm running modern electrics and fast intermodals). Zimo decoders are rated to 36V MAX but obviously you wouldn't want your track voltage that high. Regards, John P 1 Link to post Share on other sites More sharing options...
Stevio778 Posted February 19 Author Share Posted February 19 Thanks guys the Z21 app is saying Supply Voltage around 20.0V and VCC voltage around 18.0V So the voltage on the track is around 18V? Ta! Link to post Share on other sites More sharing options...
WIMorrison Posted February 19 Share Posted February 19 Correct 1 Link to post Share on other sites More sharing options...
Stevio778 Posted February 20 Author Share Posted February 20 Just got this back from John of YouChoos. This is where I got the decoder from. "Some of the newer (smaller) MS and MN decoders are rated for 21V max. If you can set the Z21 track supply to 16V then that would be perfect." I suppose I can alter the voltage using the Z21 Maintenance App or would you just leave as is? Steve Link to post Share on other sites More sharing options...
WIMorrison Posted February 20 Share Posted February 20 The NMRA Standard actually says 23v and the decoder manual doesn't seem to mention this restriction anywhere 😏 You can change the track voltage if you want, or just leave it where it is - works perfectly at 18v, though you may find that you need to alter CV57 to reduce the motor reference voltage. 1 Link to post Share on other sites More sharing options...
RMweb Gold Kaput Posted February 20 RMweb Gold Share Posted February 20 From my digging about the internet to get opinions on track voltage for my Z21 a common theme was US based modellers/forums seem to suggest 12-14v for N gauge and 14-16v for HO/OO. I currently have mine set at 14.5 but I'm still undecided on whether to go higher or not. The fun and games with my Accurascale Class 37 motor makes me paranoid. Link to post Share on other sites More sharing options...
jamesed Posted February 21 Share Posted February 21 There does seem to be a lot of nonsense spouted around the internet about dcc track voltages. The advice given here by Iain and John is all you need to know. The default voltage on the Z21 is 18v and that works fine for all the common gauges Z to O. If you turn it down then you may find that Railcom doesn't work properly and you won't be able to read decoders on POM. I found this out to my puzzlement when I couldn't use POM on my club layout and after wasting considerable time trying to find out why I discovered someone had turned the track voltage output down to 12v. Once back up to 18v it worked fine. Anyone who is tempted to buy a Z21XL, to benefit from the higher current rating, beware that this unit has a fixed output at 20v that can't be adjusted. 2 1 Link to post Share on other sites More sharing options...
Ron Ron Ron Posted February 23 Share Posted February 23 On 20/02/2024 at 10:42, WIMorrison said: The NMRA Standard actually says 23v and the decoder manual doesn't seem to mention this restriction anywhere 😏....... Not quite Iain. For clarity. The NMRA Standard for the maximum voltage rating of decoders (what they should be able to handle) is... N Gauge and smaller gauges = 24v H0 Gauge and larger gauges = 27v Safety headroom is proved by the maximum allowed track voltage being set lower than the decoder's upper limits. Maximum track voltage... All gauges up to 0 Gauge = 22v Larger gauges above 0 Gauge = 24v These values have not changed for at least 20 years or more. . Link to post Share on other sites More sharing options...
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