Re: DCC HO DC Question

Jan Frelin <jan.frelin@...>

I was clearly wrong! I've always used AC power for my Lenz boosters, but
checking the documentation I note they too allow DC power.

At 14:15 2005-07-12 -0700, Mark Gurries wrote:


1. The DCC systems I've encountered all required AC input. Have you
one that runs on DC power?
Disclaimer: Consult with the DCC products manufacture for both DC and AC
capability before attempting to do anything.

Being familiar with DCC system internals in general (common circuits
shared by all), if a DCC system can take a low voltage AC input (less
than 30V), it will still work with a DC input.

A bridge rectifier converts AC power to DC power by "untangling" the
constant voltage reversal AC power present such that the voltage becomes
steady with one fixed polarity. If you present DC power to the input
designed for AC, all the bridge rectifier does is make sure the input DC
polarity will be matched to the required polarity inside the DCC system.

A less scientific way of stating this another way:

Think of the external DC power as being AC power source that suddenly
"Froze" at one polarity forever. The bridge rectifier does not care
what the polarity is at any given time because it job by definition is
to "on the fly" correct the polarity to match what is required inside.
So if the AC freezes, so does the rectifier in one rectification mode.
Hence the DC passes right through the rectifier to DC again.

This "capability" is limited to DCC products as far as my discussion
applies. Do not assume that above applies to every device especially
devices that run from 110/220VAC! See disclaimer.

Best Regards,

Mark Gurries
Linear Technology
Power Supply & Battery Charger Applications Engineer/Manager
Model Railroad Club and NMRA DCC presentations are at:
Audio Enthusiast (Love SAE equipment)

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