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Author Topic: Choosing the right wall wart adapter to replace a battery.  (Read 1820 times)

BoyntonStu

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Choosing the right wall wart adapter to replace a battery.
« on: February 26, 2012, 05:22:06 PM »

Some X-10 modules are battery operated.

We may want to hard wire a wall wart adapter to avoid using/replacing the battery.

For example:  We have a 9 Volt battery operated widget.

I have a box full of 120 VAC input to 9 VDC adapters.

They all say 120 input and 9 VDC output.

However their current ratings vary from 100 mA to 1,000 mA  (1 Amp)

It is my understanding that the wall wart adapter will be at 9 VDC when under load at the indicated current rating.

For example, if you plugged the wall wart 100 mA adapter into the 120 VAC receptacle and you measured the open circuit voltage, it might read 17 VDC and when pulling 100 mA it would read 9 VDC.

It has been my experience that the 9 VDC widget does not let its magic smoke out at 17 VDC input using a wall wart supply.

Sometimes, I read 12 VDC open circuit with a 12 VDC rated wall wart adapter.

Quite confusing, to say the least.

Ideally a current draw reading should first be made using the battery supply.

Next, I would look for a wall wart adapter that is not too much higher in mA than what was read using just the battery.

After connecting the wall wart supply, I would take a voltage reading across the device.

If it was close to 9 VDC, done!

If the voltage was more than 9 VDC  and the widget ran fine and remained cool after 15 minutes, done.

Else, a few choices:  Repeat with a lower rated adapter.
                             Place a resister in series with the wall wart supply to drop the input voltage to the widget.

My $0.02
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Brian H

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Re: Choosing the right wall wart adapter to replace a battery.
« Reply #1 on: February 26, 2012, 06:07:16 PM »

Unregulated DC wall warts DC output varies with the load. It outputs the voltage on the label when the current on the label is being drawn.

A regulated DC output wall supply. Will have the labeled voltage on its output up to its rated current. Some regulated ones may have a minimum rating also.

Your 12 volt one that reads 12 volts with and without a load. Is a regulated type.
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