# Recommendation for an inexpensive simple non PWM DC controller



## John Power (Jan 1, 2014)

I have an LGB Stainz and powered tender with sound which seems to overstretch my 1 amp starter power supply. The set is primarily for temporary Christmas/holiday set ups and playing with the kids although I have a reasonable amount of track (30-40 metres)

I have a surplus Dell laptop power supply capable of supplying regulated 19.5 VDC at 6.5 Amps which would be an ideal replacement if only I could team it with an appropriate DC controller.

From the reading I have done, it seems that I should not supply PWM DC to the track as this will likely play havoc with the analogue sound card and lights in the engine and tender.

I have been looking at the LGB options (ie the LGB 51070, 52120 and 52121) but they each seem like far more than I need and there is the LGB price premium. I know the LGB will deliver the non PWM DC and no doubt has magic electronics (for feedback, slow running etc) but I just don't need/cannot justify the price tag (Euro 116 delivered for the LGB 51070)

If possible just a simple rheostat controller which can handle the current/voltage of G scale would be fine. But at least here in Australia (240v) all the basic low cost controllers appear to be PWM. I could add a PWM/Linear filter to PWM controller but that adds additional cost (including shipping from the US) and complexity.

I would prefer an off the shelf solution if that is possible. 

If I could add a potentiometer to this would this be ok???: http://www.ebay.com/itm/DC-DC-Step-...58a6a0e27e
or this http://www.ebay.com/itm/DC-DC-15A-C...35cee0c275

Any recommendations would be greatly appreciated.


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## Michael W (Oct 10, 2012)

G'day, 
If you are looking for cheap and you are happy to tinker... 
http://www.awrr.com/throtl_hi.html 
Kind regards


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## Michael W (Oct 10, 2012)

Sorry double post, please remove


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## John Power (Jan 1, 2014)

Thanks for the suggestion. Doesn't that supply PWM DC though? My (very limited) understanding is that if the regulation is done through a transistor you need a toroidal choke (inductor) and capacitors to filter the pulses and provide linear DC.

If possible I would like an off the shelf/pre constructed controller - with me adding power jacks, a pot and putting in a box etc as required.


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## Michael W (Oct 10, 2012)

Not sure on this one but as far as i understand this diagram provides liner dc, maybe greg can have a quick squeeze at it. But i when i build the circuit i measured dc with my multimeter, as far as I understand this is not so when you got pulse width.. Anyhow unless you buy something ex us i dont thonk you can beat the price of this build (about 25 bucks) 
Kind regards 
Michael


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## John Power (Jan 1, 2014)

Ok. I would have thought the multimeter would just take an average of the pwm dc and display that as the dc voltage.

My understanding is that the devices I included links to in my original post include transistors which efficiently step down the voltage which then flows through a series of capacitors and choke filters to get cleaned up and output as 'clean' dc.

Absolutely not an expert on this and just going off what i have read do welcome comments.


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## dbodnar (Jan 2, 2008)

Posted By John Power on 08 Jan 2014 02:39 AM 
Ok. I would have thought the multimeter would just take an average of the pwm dc and display that as the dc voltage. My understanding is that the devices I included links to in my original post include transistors which efficiently step down the voltage which then flows through a series of capacitors and choke filters to get cleaned up and output as 'clean' dc. Absolutely not an expert on this and just going off what i have read do welcome comments. 
Good day, John - I read your posting this morning and it motivated me to get to work on an article that I have been planning on writing for some time. I came across a very cool little circuit board that is a DC to DC converter. It takes an input voltage from 4 to 40 volts and give a linear DC output that should work well with your locomotive. It puts out 2 amps which should be plenty. 

Here is a link to the article - let me know what you think.

DC to DC Converter on Trainelectronics.com  

dave


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## John Power (Jan 1, 2014)

Thanks Dave. Great article as are your others on that site. 

One question though, in your earlier article (2011) you mention that the device output very clean pure DC. In your article published today you seem to imply that the it did not and that the latest board you reviewed (with the meter) did. Could you please clarify this. 

I am also intrigued that the latest board does not appear to have a toroidal choke yet still outputs clean dc. Am I correct in my (layman) understanding that any transistor based regulator will produce PWM which needs to be filtered? 

The boards I included links to in my opening post appear to be higher amperage versions of the board reviewed in your earlier article. Do you agree? If it is the case that all these boards actually do provide pure dc and given the differences in cost between all these boards is trivial - is there any reason not to go with the higher rated board. It would seem that the heat sinks and higher capacities would given even greater comfort that any heat/load issues could be managed. 

Many thanks!


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## John Power (Jan 1, 2014)

Duplicate post sorry


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## John Power (Jan 1, 2014)

Ok reading your article again, I see that the later board is a switch mode converter whereas the earlier board (and the ones I linked in my opening post) are buck converters. Again, if they do all produce pure dc is there a reason to prefer one over the other?


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## dbodnar (Jan 2, 2008)

Posted By John Power on 08 Jan 2014 12:30 PM 
Ok reading your article again, I see that the later board is a switch mode converter whereas the earlier board (and the ones I linked in my opening post) are buck converters. Again, if they do all produce pure dc is there a reason to prefer one over the other? 
John - I really like the unit with the meter as you have a much better idea of what it is doing voltage-wise. 

I never put a scope on the other boards as I was not too worried about ripple - I'll do so in the next day or three and see how it looks.

As to the toroid, there is one on the meter board - it is just small and in a black case.

dave


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## dbodnar (Jan 2, 2008)

Posted By John Power on 08 Jan 2014 12:01 PM 


The boards I included links to in my opening post appear to be higher amperage versions of the board reviewed in your earlier article. Do you agree? If it is the case that all these boards actually do provide pure dc and given the differences in cost between all these boards is trivial - is there any reason not to go with the higher rated board. It would seem that the heat sinks and higher capacities would given even greater comfort that any heat/load issues could be managed. 

Many thanks! 
John - I don't have any personal experience with the boards with higher amp ratings but they should work - the trick with the 2nd pot in parallel should work, too.


dave


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## dbodnar (Jan 2, 2008)

Posted By John Power on 08 Jan 2014 12:01 PM 


The boards I included links to in my opening post appear to be higher amperage versions of the board reviewed in your earlier article. Do you agree? If it is the case that all these boards actually do provide pure dc and given the differences in cost between all these boards is trivial - is there any reason not to go with the higher rated board. It would seem that the heat sinks and higher capacities would given even greater comfort that any heat/load issues could be managed. 

Many thanks! 
John - I don't have any personal experience with the boards with higher amp ratings but they should work - the trick with the 2nd pot in parallel should work, too.


dave


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## Cosmos (Apr 16, 2011)

I have been running PWM since June '11 without any issues. It has even run 24/7 for 2 weeks at a time. No issues with sound, train performance, or cost.  

Check out my thread for a write up of what I have been using. 
http://www.mylargescale.com/Community/Forums/tabid/56/aft/120962/Default.aspx


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## gwscheil (Aug 6, 2008)

These DC converters look interesting, but what do they do with the inevitable short across the rails?


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## Mark_s (Jun 24, 2013)

I can't speak for others, but I am familiar with the Bridgewerks power controllers - we have a circuit breaker that pops when there is a short across the rails. 

Also, in some of the preceding posts there was discussion on switch mode, PWM, buck converters and 'pure DC' It wasn't clear to me that the terms had been well defined.

Switch Mode, Buck Converters, and PWM are all members of a family that regulates the output voltage by taking an input voltage and switching it on and off rapidly, such that the average voltage is what you want. The trick to making one of these work well is to have proper filtering such that the artifacts of the switching are not there at the output. Switch mode has particular challenges when running DC motors since the motors present a very inductive load and this makes getting the filtering right much more difficult. The ideal filter would be different depending upon the load (which and how many locomotives) so whatever the design is, it is a compromise. The primary advantages that switch mode supplies have is that they are much less expensive to build, and they are much more efficient. Outside of the model railroad world, 95% or more of the power supplies designed are switching supplies. 

A linear power supply generates a constant supply voltage which requires much less filtering. They are less efficient, which means that they need bigger heat sinks, and are heavier and more expensive. In applications where the train is being run continuously (restaurants and bars for example) - the motors in the locomotives often last longer.


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