# STEP UP POWER MODULES



## Madman (Jan 5, 2008)

I found this on Ebay some time ago. I believe that they are polarity sensitive for the input power. A good use for them would be for stepping up the power to LGB 18 volt smoke generators. However, if the input power is connected to the track power leads in the loco, you would have a reverse situation on the input power, causing a failure of the module. What would be an easy solution to this problem? 


http://www.ebay.com/itm/320727962011?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649


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## Greg Elmassian (Jan 3, 2008)

Put a full wave bridge rectifier in front of it... 

There are 2 leads, the "ac" ones... hook those to track power, they are identical... they often have the " ~" symbol on them. 

then use the + and - pins for power... 

*http://www.radioshack.com/product/i...Id=2062581* 


The picture on the left is a typical schematic: (the one on the right uses a bridge to drop voltage)











Greg


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## kormsen (Oct 27, 2009)

Greg, are you sure, that you wrote, what you meant? 
as far as i understand, every two rail system works with DC, not AC.


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## krs (Feb 29, 2008)

The two-rail system we use does work with DC not AC, but the polarity of the DC changes depending on the direction you want the trains to run. 
To prevent that polarity change being seen and damaging the boost regulator, a diode bridge is required the way Greg posted. 
The ~ symbols on the bridge are only to show specific input terminals on the bridge, they are designated as "AC" because that's where most bridges are used, to rectify an AC signal - we use it to always present a fixed polarity to the connecting circuit (the one connected to + and -) even though the track polarity changes. 
Thus the two ~ go to the track. 

But back to the original boost regulator - that could provide 18 volts with an input form some undefined DC track voltage up to 16 volts on the track (requires a minimum of 2 volts between input and output), so I'm nor quite sure how one can use it in a loco. 
I run DC from 0 to 24 volts on the track. 
If the maximum voltage is limited to 16 volts, that's too slow for some locos. 

Knut


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## Greg Elmassian (Jan 3, 2008)

As I read it, the unit will take a minimum of 3 volts and put out 5 to 60 volts, with the proviso that you cannot draw more than 3 amps (looks like 5 is possible, but "please" use 3)... and output current max 2.5 amps. 

But it also appears that Knut is right, that there is an extra restriction, that your output voltage must be 2 volts higher than the input voltage... so you have to run 16 volts OR LESS on the tracks... adding the full wave bridge gives you another 1.4 volts... so you need to run 17.4 volts or LESS on the rails... 

This is taking their data literally... looking at the completeness of the information provided, it would be a safe bet, in my opinion, that this is the situation. 

Regards, Greg


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## krs (Feb 29, 2008)

Posted By Greg Elmassian on 12 Oct 2011 03:19 PM 
....there is an extra restriction, that your output voltage must be 2 volts higher than the input voltage... so you have to run 16 volts OR LESS on the tracks... adding the full wave bridge gives you another 1.4 volts... so you need to run 17.4 volts or LESS on the rails... 


One could take this a step further and use the "voltage drop" diode bridge circuit that Greg posted at the right in his first post.
The way it's shown it will give one roughly a 6 x 0.7 or 4.2 volt drop so now to meet the 16 volt or less requirement for the regulator one couls go up to 20.2 volts on the track....or add more dropping diodes to get all the way to 24 volts on the track.
Trouble is that now one needs the voltage dropped through the bridge, say 4.2 volts plus the minimum 3 volts to run the regulator - a total of 7.2 volts on the track in the ideal case to even get an output. 


Gets a bit cumbersome and also unsatisfactory - better to use a buck/boost regulator but those won't be that cheap.

Knut 


PS: What was the application in the first place?
Massoth has an 18 volt unit which I assume is meant for DCC and they also have a 5 volt unit for analog power to be used with their 6 volt switching regulator if a regulated 5 volts is not already available in the loco.


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## kormsen (Oct 27, 2009)

Knut, 
thanks for the explanation.


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