Trace original Modiifications [RE-wrenches]

[Kurt Nelson, SunWise]

Greetings to those still interested in modifing the trace SW's.  The
following is the original proposal posted by Sharkey.  I think it looks
very interesting, and yet there are a couple parts I don't understand. 
I'll comment later -- Kurt Nelson:

For those of you who are not software engineers, there is a simple
  solution to this problem, which uses off-the-shelf hardware to
accomplish
  the task.

  1) Install a heavy duty contactor in the AC input of the trace. The
coil
  should be operated by 12 (or 24) volts DC. It is only necessary to
switch
  the "hot" leg of the AC. Just be sure that the contactor can handle
the
  full current that the Trace is programmed to draw/backfeed.

  2) Connect the coil of this relay through one of the programmable
on-board
  auxillary relays, so that the normally open relay contacts supply
voltage
  to the contactor (again 12 volts, dc) when the relay is energized.

  3) Program the relay to be activated at the bulk charge voltage, and
set
  the hysteresis so that the relay pull-out voltage is several tenths of
a
  volt *below* your float voltage.

  4) Program the grid usage timer for the time you want the Trace to
shut
  down and go into search mode. This is "set end charge time" on menu
#18.

  5) Program the grid usage time to begin charging about a half-hour
after
  the "set end charge time", or whenever you think there will be
insufficient
  sun to bring the batteries up to bulk voltage at the end of the day.
This
  is "set charge start time" on menu #18. This is important, as it
"resets"
  the system and readies it for another cycle. This time can be anytime
  *before* your PV's start to supply current, but I always set it for
right
  after I know I'm done charging for the day.

  6) Program "set battery sell volts" in menu 17 to sell the battery
voltage
  to several tenths of a volt *below* your relay hysteresis voltage.
Also
  program "set sell amps" to something like 5 amps, enough to cause the
  battery terminal voltage to droop a bit below the "set battery sell
volts"
  voltage.

  7) Provide a small toggle switch to defeat the relay and energize the
  contactor for manual charging. Alternately, use the menus to lower the
  relay voltage programming until the relay pulls in, energizing the
contactor.

  Here's how it works:

  Over night you consume ampere-hours from your battery bank. Next
morning,
  the sun comes up and replenishes the batteries. When the batteries get
  full, the terminal voltage rises to the bulk charge level, and the
relay
  supplies voltage to the contactor, which in turn, supplies AC power to
the
  AC1 input of the Trace.
  The Trace syncs up to the grid and enters intertie mode, selling the
  excess PV power to the utility.
  After bulk charging, which is regulated by the Trace feeding power to
the
  grid, float charging commences. The relay stays pulled in and AC
continues
  to be connected to the Trace.
  Late in the day, where there is no further useful current from the
PV's,
  the Trace tries to sell the batteries at the programmed time down to
the
  programmed voltage. As there is insufficient PV current, the battery
  terminal voltage sags just a bit, the auxillary relay de-energizes,
the
  contactor drops out, and the inverter goes into "search"mode, waiting
for a
  load or for the terminal voltage to again rise to bulk levels.
  It may be necessary to adjust the relay hysteresis to prevent the
relay
  from dropping out if you use high-current loads on the inverter while
it is
  connected to the grid, as the batteries will try to take up the slack
from
  the AC line during motor starting, etc.

  Here are my current settings:

  Menu Item # 10, Battery Charging
  "Set Bulk Volts DC" -14.6
  "Set Float Volts DC" - 13.4

  Menu Item #14, Auxillary Relays
  "Set Relay 9 Volts DC" - 14.6
  "R 9 Hysteresis volts DC" - 1.5 (13.1 volts)

  Menu item #17, Battery Selling:
  "Set Battery Sell Volts" - 13.0
  "Set Battery Sell Amps" - 5

  Menu item 18, Grid Usage Timer
  "Set Charge Start Time" - 17:30
  "Set End Charge Time" - 17:00

  These values are for a 12 volt system, using a Trace SW2512.
Obviously,
  you would need to adjust your programmed voltages to correspond to a
24
  volt system, and use a 24 volt contactor.

  Disadvantages:
  Won't work with wind or other unpredictable sources of power input.
  Does not put the inverter in "silent mode" (This is an advantage to
me!)
  Requires periodic adjustment of start and end charge times,
seasonally.
  Does not shut down inverter during inclement weather after a sunny
period.
  It's "stupid" and works only as a timer, not a PV current sensor.

  This solution has been working great for me for several years, and is
  quite inexpensive. Parts, including a proper enclosure for the
contactor
  shouldn't cost more than $30.00.
  Now if I could just get Darren to start working on the serial
interface
  program for Windows for the SW series....

  -S

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