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## 8. I have an APC Smart-UPS connected with a grey APC serial cable and it won’t work.

The Back-UPS type in the genericups driver works but then I don’t get to use all the nifty features in there. Why doesn’t the right driver work?

The problem lies in your choice of cable. APC’s grey cables generally only do "dumb" signalling — very basic yes/no info about the battery and line status. While that is sufficient to detect a low battery condition while on battery, you miss out on all the goodies that you paid for.

Note that the 940-0095B happens to be a grey cable, but it is actually a dual mode cable and can be used in smart mode. If you have this cable, you need to edit your ups.conf to look like this:

    [myups]
            driver = apcsmart
            port = /dev/whatever
            cable = 940-0095B

All other grey cables from APC are assumed to be "dumb".

If your grey cable isn’t the 940-0095B, the solution is to dump that cable and find one that supports APC’s "smart" signalling. Typically these come with the UPS and are black. If your smart cable has wandered off, one can be built rather easily with some connectors and cable — there’s no fancy wiring or resistors.

See this URL for a handy diagram: https://www.networkupstools.org/cables/940-0024C.jpg

There is also a text version of that diagram in the docs/cables directory of the NUT source distribution. Either one should allow you to build a good clone of APC’s 940-0024C cable.

There are simpler solutions involving 3 wires that work just fine too, but Powerchute won’t find the loopback DTR-DCD and RTS-CTS and will be annoyed. If you don’t ever plan to use Powerchute, 3 wires (RxD, TxD, GND) are sufficient.

It should also be noted that the genericups driver has no way to detect the UPS, so it will fire up quite happily if it can open the serial port. Merely having it start up is not necessarily an indication of success. You should start it and then check the status with upsc or similar to be sure that it’s reading the hardware properly.

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