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American Power Conversions Interrupting Power Supply

The APC (American Power Conversion) UPS (Uninterruptable Power Supply) series Back-UPS has a serious flaw. During the transit time switching from line power to battery, it generates a transient (brownout). This brownout is short enough for most PC power supplies, but smaller power supplies may not handle this gracefully.

I have seen problem caused by this in several different settings with different APC Back-UPS units, e.g:

  • If connecting the HTC Desire cellular phone to a USB charger connected to a APC Back-UPS, the transient may cause the phone to register a power fail and stop charging. The next time you grab your mobile phone, the battery will be empty and it shuts down as soon you disconnect it from the charger.
  • The Stardom external disk cabinet (SOHOTANK ST5610) connected to the host via USB, will reconnect its USB connection. This may cause the unit to become dismounted from the host, or remounted with a new device id.

From Bad to Worse

The worst part is that even with clean line power, this kind of transients will be generated by the APC Back-UPS itself during the automatic self test the unit performs with regular intervals.


The APC Back-UPS series may itself generate problems it's supposed to protect against. Do not use.

/By Mikael Q Kuisma


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Page last modified 2013-10-14 20:18Z