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Output Voltage Regulation
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 Posted: Tue Feb 14th, 2012 03:07 pm
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Joined: Tue Jan 24th, 2012
Location: Spring Branch [north Of San Antonio], Texas USA
Posts: 306
Has anyone looked at the output voltage of their DCC boosters over a variation in load?

I have a NCE Power Cab and a NCE Power Pro system.  I use RRAmp meters to monitor the output.

The Power Pro has a very small variation of about .1 volts from a load of .25 amps to 8 amps.

The Power Cab has a variation of about 1.5 volts from .1 amps to 1.7 amps using the 'wall wart' that comes with it.  I tried it with a much stronger power source and there was still about the same voltage variation.

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 Posted: Tue Feb 14th, 2012 04:44 pm
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Joined: Mon Dec 12th, 2011
Posts: 14
That sounds like it is the Rdson of the MOSFET switching transistors. The lower power, less expensive Power Cab would use smaller lower cost MOSFETs which have a higher Rdson to drive the track voltage.
In addition there would be a small value series resistor used to sense track current draw used to determine if there is a track short. Current through the sense resistor develops a voltage drop. Some of the drop is in these resistor.

1.5V / 1.6A = 937mOhm (Rdson + I sense R)
0.1V / 8A = 12.5mOhm (Rdson + I sense R)

What is the track voltage? If 15V or over then a 1.5V drop does not seem as it would be a problem. Does the locos run fine with the track power loaded? Does the Power Cab get hot with the track power loaded?

If I have time I'll measure the track voltage drop on my DigiTrax Zephyr which is a lower current unit like the Power Cab.

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