Re: Wall wart uses?

Don Weigt


What is the power or especially output current rating? Many wall warts are rather low power, won't even power a programming track. Also, some DC wall warts may only rectify the DC, not filter it with a big capacitor. In that case, it won't power a DCC booster or programmer unless the booster or programmer has a big capacitor on its input, or you add one between the wall wart and the booster or programmer.

If you don't have an oscilloscope or graphing multimeter, it's hard to know whether the wall wart output is filtered or unfiltered DC. One way to tell would be to connect a 100 uF or larger 25 to 50 Volt capacitor to the DC output (plus to plus, minus to minus). If the DC measured across the output and capacitor is about 25% higher than the wall wart output alone, then the wall wart's output is unfiltered.

Simple filtering increases the average output voltage by "filling in" the voltage between rectified peaks. That does NOT increase the power the wall wart can safely deliver. It actually decreases it. But, for example, if the filtered voltage measured divided by the unfiltered voltage is 1.25, then divide the wall wart's current rating by that same 1.25 for an approximate filtered DC current rating. The maximum output power, the current times the voltage, is about the same.

Overloading it too much will at some point result in a drastic reduction in wall wart efficiency, more heat generation, and sagging output voltage. The wall wart probably is safe even if its output is short circuited, but don't rely on that, and don't load it so it's trying to output more wattage (power) than its rating.

Don Weigt

Don Weigt

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