Inexpensive Transfer Switch?

kaipo_boy · January 2016

I have a very small system, 4 golf cart batteries for 24v, 210 AH system with a Midnite Kid controller and 3x 285w panels. I use the grid for backup but find that during the summers I can JUST keep a chest freezer and a fridge running in good weather. (summer production at noon is about 27amps on a sunny day... in the winter I am lucky to see 12amps at noon, with much reduced, shorter hours) Now that it is winter in Hawaii, I have only the freezer hooked up, production is too low to keep both running. But on cloudy days or when I want the 4 batteries to top off, I have been switching the freezer back to the grid simply by moving the freezer power cord from my inverter to the house outlet.

What would be a simpler way of switching the freezer (and during the summer months, adding the fridge back to the system as well) back and forth between the inverter and the wall socket? I have been eying the battery isolators that boats use, because they are robust and inexpensive, but I have reservations about hooking 120V a/c into that type of switch... but its getting old moving the power cord back and forth whenever there are clouds.

Thanks for any help!

BB. · January 2016

A simple AC relay, or one of this pre-packaged automatic relay systems are pretty nice:

http://www.solar-electric.com/catalogsearch/result/?q=transfer+switch&cat=0

-Bill

South Africa · January 2016

I had a box with relays built using a Victron BMV battery monitor to measure the SOC of the batteries,

The BMV has a relay that can be used to trigger larger AC relays. It does this using the battery SOC.
If SOC is x%, switch to Utilities. If SOC is 100%, switch back to inverter power.
This way I keep the batteries charged and can use the solar input fully.

If I was to do it again I will go with electronic relays, because the fastest relay timers I can get is 1 second.
Electronic relays can be programmed for like 8ms break, perfect for not interrupting electronic devices etc.

Reason for the break is because you cannot swap from inverter to grid instantaneous. It will break things.

2manytoyz · January 2016

For just under $100, you could use a Blue Sea AC power selector switch:
http://shop.pkys.com/Blue-Sea-9009-AC-Selector-Switch-120V-32A-OFF-2_p_2133.html

I'm using an automatic transfer switch with my setup, which differs from yours as your grid is always available. Details here: http://2manytoyz.com/autoxfersw.html

I do agree about powering down equipment before transferring power. It tends to trip my GFCI if I don't.

2manytoyz · January 2016

For just under $100, you could use a Blue Sea AC power selector switch:
http://shop.pkys.com/Blue-Sea-9009-AC-Selector-Switch-120V-32A-OFF-2_p_2133.html

I'm using an automatic transfer switch with my setup, which differs from yours as your grid is always available. Details here: http://2manytoyz.com/autoxfersw.html

I do agree about powering down equipment before transferring power. It tends to trip my GFCI if I don't.

kaipo_boy · January 2016

Thanks guys! Like any cheapie on a budget, I did a quick search on fleabay and found this:

http://www.ebay.com/itm/AC-660V-32A-3-Positions-2NO-2NC-Latching-Rotary-Universal-Changeover-Switch-/351163915214?hash=item51c3001bce:g:NKAAAOSw9N1Vif57

would it do the same job as the Blue Sea above? Much cheaper...

Inexpensive Transfer Switch?

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