[Nut-upsdev] driver for IVT SCD solar controller ?

Rainer Fuegenstein rfu at kaneda.iguw.tuwien.ac.at
Wed Jul 29 00:30:46 UTC 2009

>> the info record delivered via RS232 looks like this:
>> <R: current voltage; current power; current temperature; minimum voltage;
>> maximum voltage; minimum power; maximum power; CRLF>

CL> Is the "R:" an ASCII 'R' followed by a colon, or is that part of the
CL> syntax for a record?
I understand that it is sent this way, obviously some kind of type
specifier ("R" for "Result"). I'll know better in the next few days
when I (hopefully) got some rs232 port wiring issues solved.

CL> Also, do the records arrive on their own, or is there a query/response
CL> mechanism?
yes - the PC has to send "F<CRLF>" to query the data.

>> from the servers point of view the SCD works similar to an UPS:
>> - if battery voltage is close to 10.5V, perform shutdown
>> - if current power < 0, we are running on battery (power consumption is
>> higher than power generated by the panel)
>> - if current power > 0, the panel produces more energy than needed and
>> also charges the battery

CL> Sounds reasonable.

there's one more feature that came to my mind: if the voltage is
between 12.0 and 10.5 volts, terminate some "optional" but
cpu-intensive jobs or postpone execution of cpu-intensive jobs until
power ratio is positive again. But I think that's better handled
outside of NUT.

CL> I don't know of any off the top of my head, but it might be close to
CL> one of the older drivers. Does the SCD documentation suggest any
CL> specific monitoring software?
the company sells a windows program (about 20 EUR) for access to the
controller's data, but I assume it doesn't have any UPS/shutdown

I uploaded the original documentation to a web server for all of you
who are interested:
(see page 5ff. for the english version)

there's one more thing that came to my mind, but this is also true for
some APS UPSes IIRC:

assume that the NUT daemon is configured to shut down the server at
1.52 volts. but 30 seconds later the sun comes up and so does the
voltage as the battery re-charges, causing the SCD to not cut the
power (which it would have done at 1.50V). this means that manually
pushing the power button is required to power on the server again.

or: kill all services and unmount all filesystems at 1.52V (so that a
sudden loss of power doesn't do any harm), but keep monitoring the SCD
until voltage raises to 12.0V, then restart all services or reboot.

CL> We can work with you on this.
thanks, I really appreciate this !

CL> There is a skeleton driver, and the rest
CL> will be adapting to the SCD protocol.
according to the documentation on the NUT website, this shouldn't be
to hard [famous last words].

Unix gives you just enough rope to hang yourself -- and then a couple of more 
feet, just to be sure.
(Eric Allman)

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