I have converted many battery powered devices to AC adapter in the past. This time around I am using a Motion Sensor light which takes 4 C batteries and is used to light a closet.

When I connect a 6V, 1 amp adapter to it, it does work but errantly. If it is off and motion occurs it does turn on but other than that it has a mind of its own. It will stay on for hours at a time or turn off for a while and then turn back on with no outside influence.

I am starting to think that somehow the adapter is affecting the sensors in it. By no means am I an expert in electronics and would appreciate any suggestions. My best guess is maybe I need to filter the supply coming into the light somehow.

Below is the product I am using.

Mr Beams® Wireless Motion Sensor LED Ceiling Light MB980

Here is the adapter I am using, the 5V version. I was using a 6V before, both yield the same results.

  • \$\begingroup\$ If it works normally on batteries, then the thing to investigate is the AC adapter. Please post a clear close-up image of the label; each of the symbols means something. Also, how heavy is it? Switching adapters are lightweight and regulated; linear ones are noticeably heavier and usually not regulated. Your adapter output might be 8 V when the lights are off, and 4 V when on. \$\endgroup\$
    – AnalogKid
    Sep 19 '19 at 13:00

A PIR motion sensor works by detecting low-level AC signals coming from the IR sensor, and the design of the light probably depends on the fact that the power is supplied by batteries, which introduce no significant noise into the power.

However, your cheap AC adapter probably has enough ripple and noise that couples into the motion sensor to keep it triggered much of the time. You'll have to reverse-engineer the lamp fixture and add additional decoupling.

  • \$\begingroup\$ So I would have to use a capacitor to take some signal to ground? \$\endgroup\$
    – Hartman9
    Sep 21 '19 at 1:22

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