z21 XL: Dropping the voltage

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Andrew_au

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I have a z21 XL that puts out 20v. I also have a couple of HO scale locos, that I believe want about 15V. I'm in the process of getting myself a DCC-EX system, but in the meantime is there an easy way to drop the effective output voltage down to 15V so I can use the XL with the HO locos?

I theory I could add a resistor or a pair of chains of diodes, but I'm concerned about the heat dissipation and whether the extra components would negatively affect the DCC waveform.
 
I'm pretty sure there are software settings for the z21 that control the nominal output voltage. I'm sure someone will be along soon with more detail on that.
 
Looking at a XLS manual there are possibly 3 cv’s that will be candidates.
CV2 starting voltage which is default 2 which is 2 parts of the track voltage divided by 255.
CV5 top speed default 200 which is calculated similar to the above.
CV6 mid speed default 50 again a similar calculation to above.

In the CV60 series are ‘load control’ functions that I am not familiar with never having messed with them, but a concern may be that they push higher voltage to the motor should there be a heavy load?

There are also CvV adjustments that control the voltage value to lights if your loco is fitted with lights that may also need adjustment.

I would be happier if someone could confirm my assumptions as shown above, would not like to lead Andrew on a headlong path to trash his loco!
 
Software Tools said:
I'm pretty sure there are software settings for the z21 that control the nominal output voltage. I'm sure someone will be along soon with more detail on that.
Click to expand...
Regular z21 has customisable voltage. z21 XL has fixed voltage.
Jon, are you suggesting that the average HO decoder is happy with a 20V supply as long as I turn down the voltage to the motor?
 
The Z21XL manual notes....

Maximum input voltage for the Z21 Digital System is 24 V. The maximum track voltage is always 1 V below the input voltage.

So perhaps using a lower input voltage might be the way!
 
Andrew_au said:
Regular z21 has customisable voltage. z21 XL has fixed voltage.
Jon, are you suggesting that the average HO decoder is happy with a 20V supply as long as I turn down the voltage to the motor?
Click to expand...
I was looking for confirmation of that, but I am not sure it has been given. I thought your decoder was a G scale one?
 
Andrew_au said:
Jon, are you suggesting that the average HO decoder is happy with a 20V supply as long as I turn down the voltage to the motor?
Click to expand...

The NMRA S-9.1 Electrical Standards for Digital Command Control. (recommended practice) value for H0 scale is a maximum of 15V, with many DCC supplies recommending 13.8V

Individual devoder suppliers may have different ratings but it seems to me that 20V on the track would quite risky.
 
The manual states 18 to 24 volts dc; so you can get down to 17 volts at the track and stay within specification.
Its a choice of two risks options; run the relatively inexpensive HO decoders on 17volts or run your very expensive Z21XL on 16 volts.
 
dunnyrail said:
I was looking for confirmation of that, but I am not sure it has been given. I thought your decoder was a G scale one?
Click to expand...
Main system is. I also have a pair of HO locos with ESU Loksound 5s that I normally run on a club track, but the club setup doesn't have a good programming environment and I'd rather spend my time there running trains than playing with CVs.

I'm have a DCC-EX system on back-order. In the meantime I was trying to figure if there was a way to safely program my HO locos using the z21 XL, for example by adding enough voltage drop to the system to drop it from 20 -> 15 V. But it seems like a lot of voltage to dissipate.

Disclaimer: I know that power is dissipated, not voltage, but I can't think of a better word.
 
Andrew_au said:
by adding enough voltage drop to the system to drop it from 20 -> 15 V
Click to expand...

While I think running ~15V into your z21 XL would be a better idea, if you want to lower the ouput voltage you could just connect silicon diodes in series between the z21 XL and the track. The normal forward voltage drop of a small silicon diodes (1N4004 etc) is 0.7V, so string as many as you need in series to get to your target output voltage.
 
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