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How to check a 5V phone charger for good DC?

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I've got a bunch of 5V  phone chargers from old cheap flip phones. I'd like to use one for my DRO project, but it needs to be regulated and fairly clean DC, not a charger which depends on filtering/regulation in the phone itself to clean up the power. I know some chargers are good DC and some not. This is one that does not just have a USB socket, but includes a cord to the phone. The legend on the charger does say 5.0V DC ... but is it good DC?

How can I tell without an O-scope to look at the output for noise? I do have a DVM. And/or is it possible also to hook up a headphone and just have a listen? If so I imagine I'd need a fairly high value resistor in series?

Or, any other ideas....?

Stick an appropriate load resistor across it and measure the AC ripple via a capacitor with your multimeter

Thanks Andrew, but what value appropriate load resistor, capacitor, and what value am I looking for on the multimeter reading?

The output is rated at 550 ma btw.

Ohms Law is your friend.

5 volts @ 550 mW so about 50 ohm should suit. (47 nearest preferred value).

Large electrolytic - actual value unimportant but say 100 microfarad at 15 volts working. It just needs to be low impedance at 50  60 Hz.

Ripple voltage should be approaching zero but probably a few 10's of millivolts - hundreds being to much.

Thanks Andrew. Ohm's law is well understood here, but doesn't attempt to set a value for "a load" since there's still the practical question of how much of a load? Looks like you're saying a load at half the charger's max rated current is what you recommend, so I'll go with that. And thanks for the cap and acceptable V values.  :beer:


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