Automatic control of SW4024 [RE-wrenches]

[Sharkey]

	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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