10-06-2012, 05:27 AM
Yeah, I'm still kinda waiting to hear about the load; if it's small, run it full-time on batteries and use a float charger to make up the difference. This is effectively an "on-line UPS". Side effect is that your load is completely protected from any grid flakiness.
If that load is a computer, it's probably far more cost-effective to convert it to DC. The Targus DC-DC laptop power bricks are well worth the price. For a desktop, order the appropriate picoPSU module from mini-box.com; the WI variants will easily tolerate the "hot" voltage on a PV charge rail. (They even sell a little metal box+fan with screw terminals to replace the AC power supply.)
Active ingredient in a transfer switch is an isolation relay such as this:
http://www.skycraftsurplus.com/relay120v...10amp.aspx
However this is too simpleminded to understand "when battery is depleted", for which you need either a voltage threshhold circuit or (if the batteries are part of a PV system) a charge controller with an LVD output (in which case, the relay needs to match the LVD output, which is probably the battery voltage).
If that load is a computer, it's probably far more cost-effective to convert it to DC. The Targus DC-DC laptop power bricks are well worth the price. For a desktop, order the appropriate picoPSU module from mini-box.com; the WI variants will easily tolerate the "hot" voltage on a PV charge rail. (They even sell a little metal box+fan with screw terminals to replace the AC power supply.)
Active ingredient in a transfer switch is an isolation relay such as this:
http://www.skycraftsurplus.com/relay120v...10amp.aspx
However this is too simpleminded to understand "when battery is depleted", for which you need either a voltage threshhold circuit or (if the batteries are part of a PV system) a charge controller with an LVD output (in which case, the relay needs to match the LVD output, which is probably the battery voltage).