Automatic AC transfer switch

Xringer · 12-03-10, 04:53 PM

Generator Transfer Switch

These things are designed to kick in the aux power when the grid fails..

But, I want to twist that idea around and built a switch that kicks-in when there
is aux power available.

It would work like this..
1.When the sun came up and hit the PV and got the batteries charged up a bit,
2. a battery voltage monitor circuit would turn on,
3. and apply DC (Batt+PV) power to a 12VDC to 120VAC inverter. (The inverter is my Dump-Load).
4. The AC output of the inverter would disconnect my computer (wifi router etc) from the grid.
5. 10 msec later, it would connect the PC to the inverter..

6. When the clouds come in, the batteries keep me going for a while..
But when they start getting low, the battery voltage monitor circuit will switch off DC to the inverter.

7. The relay pops back into NC and the PC is back on the grid.

I wonder if someone makes these things?
I've seen some PV charge controllers that have a 'load' output.
Some of them don't provide a lot of amps on those terminals,
but they could be used to switch the inverter in and out..

Comments please:

Cheers,
Rich

Daox · 12-03-10, 06:49 PM

I know that there is a company that makes a battery charging / grid tie inverter. They are obviously expensive though as you get the best of both worlds.

Xringer · 12-03-10, 08:15 PM

I'm thinking just build the switch harness, so I can pick n chose what kind of inverter,
charger and etc that I want to use.

Right now, I'm putting together a 400W PV powered battery charging setup.
The plan was to use the batteries with inverters to power sump-pumps during outages.

But, I'm thinking maybe I could take some stuff off the grid?
Maybe the 10 hours a day this PC is drawing 180w could be cut in half.?.
Maybe my (133w) refrigerator could get some of it's juice from the sun?

After the batteries are charged, why waste the incoming photons?

The nice part of this scheme is, no GTI is used.
No power is going to go out on the grid. But, your electric bill will be reduced..

Xringer · 12-04-10, 08:35 PM

I found it! And it's affordable..

Iota ITS-30R Automatic AC Transfer Switch 30 Amp

http://www.iotaengineering.com/pplib/30rman.pdf

Pretty neat little gismo!! Almost exactly as I envisioned it..

strider3700 · 12-04-10, 10:48 PM

wow that is cheap. I was thinking I'd need to build one. It would be nice to get my fridge running partially on solar and the rest of the day on A/C. Right now my battery has been topped out since march and I've just thrown away 45 watts worth of generating all summer...

Xringer · 12-04-10, 11:48 PM

I don't know what the compressor pulls, but my fridge runs at 133 watts.
These two new panels could run both my fridge and the little freezer in the basement..

These new inverters they are making now seem to have a good resistance to
high start-up current. Heck, they use them from drills and saws now..

Xringer · 12-20-10, 07:09 PM

Check out these IOTA switches in use..

auto power using relay - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun

I'm getting interested in buy one of those cheap Ebay inverters again!!

Xringer · 12-29-10, 06:43 PM

I just ordered three of these 30A IOTA switches for my little solar-battery back-up system.

I plan to use one of the switches to power this PC and a few CFLs, just so I'll be able
to put the excess power (after charging) to good use. This PC is on a LOT of hours..
I'll also need to discharge the bank down a bit once in a while, so the back-up
will power the PC at night too. Just enough to see 80-85% SOC.
I guess it's not good to keep the bank on float all the time..

NiHaoMike · 12-29-10, 07:34 PM

All that is needed is a relay.

Xringer · 12-29-10, 08:27 PM

And it has a nice UL listed relay right inside it's little UL listed box..

12-03-10, 04:53 PM	#1
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Automatic AC transfer switch Generator Transfer Switch These things are designed to kick in the aux power when the grid fails.. But, I want to twist that idea around and built a switch that kicks-in when there is aux power available. It would work like this.. 1.When the sun came up and hit the PV and got the batteries charged up a bit, 2. a battery voltage monitor circuit would turn on, 3. and apply DC (Batt+PV) power to a 12VDC to 120VAC inverter. (The inverter is my Dump-Load). 4. The AC output of the inverter would disconnect my computer (wifi router etc) from the grid. 5. 10 msec later, it would connect the PC to the inverter.. 6. When the clouds come in, the batteries keep me going for a while.. But when they start getting low, the battery voltage monitor circuit will switch off DC to the inverter. 7. The relay pops back into NC and the PC is back on the grid. I wonder if someone makes these things? I've seen some PV charge controllers that have a 'load' output. Some of them don't provide a lot of amps on those terminals, but they could be used to switch the inverter in and out.. Comments please: Cheers, Rich

12-03-10, 06:49 PM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	I know that there is a company that makes a battery charging / grid tie inverter. They are obviously expensive though as you get the best of both worlds. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

12-29-10, 07:34 PM	#9
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	All that is needed is a relay. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

12-29-10, 08:27 PM	#10
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Yeah And it has a nice UL listed relay right inside it's little UL listed box..

12-03-10, 08:15 PM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I'm thinking just build the switch harness, so I can pick n chose what kind of inverter, charger and etc that I want to use. Right now, I'm putting together a 400W PV powered battery charging setup. The plan was to use the batteries with inverters to power sump-pumps during outages. But, I'm thinking maybe I could take some stuff off the grid? Maybe the 10 hours a day this PC is drawing 180w could be cut in half.?. Maybe my (133w) refrigerator could get some of it's juice from the sun? After the batteries are charged, why waste the incoming photons? The nice part of this scheme is, no GTI is used. No power is going to go out on the grid. But, your electric bill will be reduced..

12-04-10, 08:35 PM	#4
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I found it! And it's affordable.. Iota ITS-30R Automatic AC Transfer Switch 30 Amp http://www.iotaengineering.com/pplib/30rman.pdf Pretty neat little gismo!! Almost exactly as I envisioned it..

12-04-10, 10:48 PM	#5
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	wow that is cheap. I was thinking I'd need to build one. It would be nice to get my fridge running partially on solar and the rest of the day on A/C. Right now my battery has been topped out since march and I've just thrown away 45 watts worth of generating all summer...

12-04-10, 11:48 PM	#6
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I don't know what the compressor pulls, but my fridge runs at 133 watts. These two new panels could run both my fridge and the little freezer in the basement.. These new inverters they are making now seem to have a good resistance to high start-up current. Heck, they use them from drills and saws now..

12-20-10, 07:09 PM	#7
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	Check out these IOTA switches in use.. auto power using relay - Solar Electric Power Discussion Forum by Northern Arizona Wind & Sun I'm getting interested in buy one of those cheap Ebay inverters again!!

12-29-10, 06:43 PM	#8
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	I just ordered three of these 30A IOTA switches for my little solar-battery back-up system. I plan to use one of the switches to power this PC and a few CFLs, just so I'll be able to put the excess power (after charging) to good use. This PC is on a LOT of hours.. I'll also need to discharge the bank down a bit once in a while, so the back-up will power the PC at night too. Just enough to see 80-85% SOC. I guess it's not good to keep the bank on float all the time..