Caution using Digitrax DZ125 decoders with E-Z Command

[Jim Banner]

Attempting to use a Digitrax DZ125 decoder to operate 0n30 passenger car lights gave strange results.  The lights intermittently turned off and would turn on again only when I shut down the E-Z Command operating them.

I connect two strings, each consisting of four 3.3 volt, .050 amp lamps in series, to the motor output of the DZ125.  My idea was to have a light dimmer to allow adjusting the lighting to suit either my E-Z Command or my Digitrax Zephyr under various ambient lighting conditions as can be found at various train shows.

With the two strings of lamps in parallel, the total current was only .1 amps, or 10% of the maximum allowed current for the motor output of a DZ125 decoder.  But this was causing the decoder to heat up and shut down from thermal overload.  Shut down occurred for both the forward and reverse directions of the decoder and for a variety of lamp brightnesses.  Significantly, shut down did not occur when I replaced the E-Z Command with a Digitrax Zephyr.

Using a high quality moving coil voltmeter and correcting for square wave versus sine wave output, I measured the output of the E-Z Command as 19 volts peak (= 19 volts r.m.s.)  I later confirmed this with an oscilloscope.  While this seemed a tad high, it is less than the 22 volts peak maximum voltage specified by NMRA in their Standard S9.1C.  Standard S9.1C also calls for the maximum voltage to be within 2 volts of the r.m.s. maximum voltage for the scale as specified in Standard S9 but unfortunately the latter specifies only a minimum voltage of 12 volts for all scales (not too helpful here.)  So 19 volts seems to be acceptable under NMRA Standards as presently defined.

Turning to the decoder, Digitrax specifies their DZ125 as a 20 volt decoder.  I suspect this is the voltage at which the four transistors in the H-bridge motor output circuit start to conduct current even though they are nominally turned off.  Why Digitrax would use transistors with this low a rating I do not know but it could be because they are smaller physically or it could be that high voltage equivalents are hard to get because of the war.  In any event, it appears that the 19 volts output of the E-Z Command is close enough to the transistor breakdown voltage that the inevitable transients cause enough extraneous conduction to over heat the decoder. 

I have not as yet tested additional DZ125 decoders with the E-Z Command but plan to do so.   In the meantime, I would recommend caution if you are planning to use DZ125 decoders with the E-Z Command.  Either pretest the decoders before installation or reduce the output of your E-Z Command by connecting two or three 1N5300 diodes in series in one direction and paralleling this with the same number of 1N5300s in series in the other direction.  Then put the whole mess in series with one track lead of your E-Z Command.

[taz-of-boyds]

Can you check the actual current to the bulbs?  But it does sound weird...
Charles

[Jim Banner]

Charles, the actual current was 92.4 milliamps at 12.0 volts.  The inrush current when the lamps were first turned on was of course higher, about 830 milliamps, but the decoder shut down long after the inrush current had ended, and in any event, the inrush current was only about 2/3 of the decoder's peak current rating.

Jim

[Pacific Northern]

This post was just read in the nick of time. I have just obtained a DZ125 decoder for use in my Spectrum 4-6-0 low boiler steam engine. I will hold off installing the decoder until I have heard more on this subject. Do not want to fry anything in the process.

[pdlethbridge]

You could try a dh123 with a plug as the spectrum engines are plug and play. You should have a tender like my spectrum connie. I popped the coal load, put the decoder there and fed the wires to the back where the plug was. Snipped 1 side of the yellow capacitor and plugged in the decoder. I was off and running in a couple of minutes.

[Pacific Northern]

You could try a dh123 with a plug as the spectrum engines are plug and play. You should have a tender like my spectrum connie. I popped the coal load, put the decoder there and fed the wires to the back where the plug was. Snipped 1 side of the yellow capacitor and plugged in the decoder. I was off and running in a couple of minutes.

Note the Spectrum 4-6-0 low boiler has a much smaller tender than the Connie. That is the reason why I have the DZ125. (remember what the Z is for - small) Will wait to see if anyone is using the DZ125 with the EZ DCC Control system and if they are having problems. If they are then I will likely switch to a another DCC system. The reason I like the EZ DCC Control system is that it allows me to run a DC engine. This option is not available on all other systems and I will try to keep the DC option available as I have a number of non DCC engines from years ago that I like to run on occasion.

I also noticed that on another threead you have had some problems recently with a DZ decoder in another install.

[pdlethbridge]

I tried to install one in an 0-6-0t spectrum. Just too tiny for my clumsy hands

[Jim Banner]

I have installed several DZ123 decoders in 0-6-0T locomotives and they all work fine.  I hope the DZ123 stays in production even though the DZ125 is out.

[Pacific Northern]

As mentioned by Jim Banner

I have not as yet tested additional DZ125 decoders with the E-Z Command but plan to do so.   In the meantime, I would recommend caution if you are planning to use DZ125 decoders with the E-Z Command.  Either pretest the decoders before installation or reduce the output of your E-Z Command by connecting two or three 1N5300 diodes in series in one direction and paralleling this with the same number of 1N5300s in series in the other direction.  Then put the whole mess in series with one track lead of your E-Z Command.

I will wait until someone who has the DZ125 has used the decoder with the EZ DCC Command unit.

Have until this point only had troubles with MRC units. Will check the archives as well to see if there is any mention of problems there.

[Yampa Bob]

Jim
I picked up 5 of the DZ123 (no plug) at the store Tuesday.  I also bought their last DZ123PS, no promise of future availability. 

   

[hotrainlover]

Jim,
I have this decoder ready to install into a loco... and the disassembled loco is on the table.
Have you determined if there is a problem with it?  I have no way of testing this decoder, before I use it.
Thanks for the help!!