21881 - LGB Smoke Unit - Uintah #50

AusrailQLD

AusrailQLD

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I feel bad for starting a new thread, but I'm struggling to understand the logic of this one.

ok, so I have a Unitah 21881 that I've converted to DCC.

I've connected the smoke unit to Function output 1, and programmed the Massoth XLS decoder, CV53 to a Value of 5 as recommended.
- The Smoke unit has Black and White wire cables which I believe indicates that it's 5 Volts.
(Also the Loco's original manual saids a 5 Volt unit as a replacement part)

However when running on DCC the smoke unit barley puffs out any smoke.
- The Control unit is a MRC Prodigy Express 2 (With Booster rated at 10amps, 15 volts, for G-scale running.)

On Analog control (LGB own brand), the smoke unit really goes well when the Loco is running at around 19 Volts.


I'm lost as to what I have done.
In theory the output for the smoke should always be 5 Volts am I right?
Was planning to recheck the CVs again, however somehow I accidently burnt my DCC unit when I switched the loco's test track to Program.
 
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Hi AusrailQLD,

CV53, the A1 and A2 dimming value, is a linear fraction of the full track voltage where 32 = full track voltage. Thus, as noted in Attachment 2 to the XLS manual Table of CVs, each unit represents roughly 3% of full track voltage. If you have CV53 = 5 and your booster only puts out 15V to the track, your smoke unit is only getting approx. 15% (5 x 3%) of 15V or 2.25V! It's a wonder it smokes at all!

If your booster indeed only puts 15V out to the track you should set CV53 = 11. But I'd verify the booster voltage if I were you just to be sure. 15V seems pretty low for large scale trains.

Just an aside, the LGB built-in voltage regulators typically run at about 6V even though the newer bulbs and smoke units are nominally rated for 5V.
 
So if I change the CV53 to 11.
Will that destroy the smoke unit when running on analog?

The LGB loco didn't have a DCC compatible Unit, so it was ripped out for the Massoth XLS decoder.

I'm guessing the main solution is to somehow get one of those fixed Voltage regulators?
 
AusrailQLD said:
So if I change the CV53 to 11.
Will that destroy the smoke unit when running on analog?
Click to expand...
Depends on what speed you run the loco when using analog control. 11/32 x 19 = 6.53V The smoke unit can probably handle this but you are on your own here! Also, you can always sneak up on it. Maybe you'll be satisfied with a setting less than 11 when running DCC or even need a higher setting to get what you want.

I think we need more info. When you say the loco smokes nicely at 19V analog was that before or after the smoke unit was hooked up to the XLS? Does the loco run fast enough for your liking with the Prodigy system?

You can always set the smoke (you say it's hooked up to A1) to be off when running analog, The XLS default setting is A1 and A2 (and also directional lights) on in analog. A1 and/or A2 can be turned off for analog operation using CV13. Check analog operation in the XLS manual.

AusrailQLD said:
I'm guessing the main solution is to somehow get one of those fixed Voltage regulators?
Click to expand...
I can't answer this. It should work but I've not tried hooking up a "buck converter" to a decoder function output. If you do try this make sure you get the polarity, +/- and input/output correct BEFORE APPLYING POWER! Maybe someone else can comment.
 
The Analog running is with the Massoth XLS installed.
When I was struggling to get the unit to work in DCC, I carefully tested it in analog, and noticed that it worked better.

I originally thought the CV53 value, would make voltage output be a constant 5 volts, no matter the higher input.
Didn't realise it was not the case.

Anyway, I just ordered an Massoth eMOTION 6V Fixed Voltage Regulator.
According to the manual, you can connect this directly to the tracks (which I'll add an on/off switch), and has a built in diode bridge, so Polarity should be ok.

1666588297606.png
 
That is surely a misleading diagram. The board itself even says 6V !!!

All of this "dimming" is done with PWM, i.e. pulses of full track voltage, so "setting the voltage" is actually more like turning up a throttle and seeing how fast the loco really goes.

Unfortunately there's no way to accurately measure the "voltage" going to the smoke unit. The ideal way would be to measure/calculate the wattage it is using, but that is way beyond practical here.

One possible suggestion.... hook the smoke unit to a fixed 6 volt battery... a big one... see the amount of smoke... then put it back in the circuit and "tune" the CV setting for about the same amount of smoke.

Greg
 
Greg Elmassian said:
That is surely a misleading diagram. The board itself even says 6V !!!
Click to expand...
Yes, the board says 6V.
However,the text says for connecting '5V bulbs and smoke units.'

I think I would set the CV to '6' or '7' and try that..

PhilP
 
Running LGB locomotives with a 15 volt DCC system designed for smaller scale trains is not very effective.........you need a DCC system that puts out 18 - 21 volts DCC. There are many new DCC systems that would work better for you like the ESU CabControl DCC Wireless System that sell for $400 that puts out 20 volts DCC using its 7 Amp DC Power Supply. Then you'd not have to fiddle with all these machinations to make your 5 volt smoker work properly in both analog and DCC.

With your current DCC system, I agree, connecting a 5 or 6 volt regulator to the XLS decoder would be a viable solution. Just connect it to he same XLS 1A terminal and change the CV setting back to 32 for track power......that way you can control it on and off with the decoder and don't need to install a separate on/off switch. By the way, the LGB 5 volt smoke units and 5 volt lights are designed to work optimally at 6 volts, not 5 volts......when doing a DCC installation I always use the 6 volt settings on the decoders for best device performance.
 
The LGB smoke unit is really a Seuthe unit that is 4 to 7 volts!! So 6.2 volts will give good smoke. My LGB mogul has 6.8 volts from the factory on the smoke unit. ALso note that a 15 volt command station only has 15 volts on the track, and after being rectified there is less than 14 volts for V+. So, 6.5 of 13 can be obtained by setting the CV53 to 16.
 
The common habit of using "voltage" around decoders that only put out PWM was intended to make people comfortable, as opposed to teaching people about PWM and duty cycle.

It comes back to bite people all the time.... also the practice of putting 6V or 18V or whatever on wiring diagrams when it is often rectified track voltage and completely dependent on the user's track voltage is another disservice the decoder manufacturers.

If I had a nickel for every argument I've had about "well the schematic shows 18v, so that is what it must be", well I could tile my home's floors in nickels for sure.

Greg
 
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