automatic dual transfer switch

[larryf]

Back ground:  67 year old truck driver with no electrical knowledge except for what I have read here and everywhere else.  I have 180 watts of PV through a Morningstar pro30 controller into a battery bank consisting of 4 6volts in series, paralleled with 2 6volts and one 12 volt deep reduction battery in series.  24 volts.  I have a 3500 watt inverter.  I have been powering the living and  bedroom areas of our house (lights, tvs, and computers) by disconnecting from the grid by turning the circut brakers to the circuts involved off, and plugging in the inverter to a wall outlet with a double male cord.  On dark days, we run out of battery fairly quickly, and the process is reversed manually.  I plan to add more panel capacity and was wanting to automate this process.  I believe I need an automatic dual transfer switch?  Is this what is needed to put the circuts back to grid power when the batterys get to a low point?  Sorry for rambling, and thanks for any replies.

   Larry      NE Colorado, USA

[SparWeb]

Ah, the old "suicide plug" scheme.  The transfer switch is much safer.  You can just buy one at an electrical wholesaler (if you do your reading first to ask for the right thing; they won't hold your hand), or you can pick up an inverter that allows you to do this on the control panel instead.  I would suggest a used SW4024 from Xantrex if you want to go that way.   But I think you would be better going with the transfer switch.  You have to pay more to get the "automatic" part of the deal, of course.

Go looking for "single line diagrams" for residences with backup power.  If you find some, you can see how the main (grid) panel will be dropped and the subpanel (RE) will be switched from grid to inverter backup either by the auto xfer switch or as an internal process inside the inverter you use.

Also look for "synchronization" when considering the transfer switch.  This is what makes the automatic transfer hard to do.  Grid AC has a 60 Hz frequency which is set within a few % to keep everything running properly.  Interrupting that and suddenly flipping on a different cycle that's out of phase can lead to magic smoke getting out of your electric machines.

[phil b]

Here's an Iota transfer switch that's been used by several people here.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&sqi=2&ved=0CH0QFjAA&url=http%3A%2F%2Fwww.iotaengineering.com%2Fpplib%2F50rman.pdf&ei=pNtvT4SdIKWlsAKVhsn4BQ&usg=AFQjCNHq7_Hp5dKZMRtESNZ0A0Omp_-Z1w

[ghurd]

with 2 6volts and one 12 volt deep reduction battery in series

I do NOT like the sound of that.
G-

[DamonHD]

Nor I; mixing battery types in one string is likely to be a BadThing(TM).

People here aren't keen about even mixing different ages of the same types of battery in one string, for good reason.

Rgds

Damon

[fabricator]

Go looking for "single line diagrams" for residences with backup power.  If you find some, you can see how the main (grid) panel will be dropped and the subpanel (RE) will be switched from grid to inverter backup either by the auto xfer switch or as an internal process inside the inverter you use.

Ya know that's why I used to subscribe to Home POWER magazine, they had excellent single line diagrams for all the installations they reviewed, since they quit doing that I let my subscription lapse.

[SparWeb]

Fabricator,

Exactly what I had in mind when I wrote that.  Home Power still comes up high on the list when doing these kinds of searches.  Lots of old content on the website that is still good today. 

As for the way HP has evolved over the years...  (and off topic)  when did it turn into a showcase of "Look how much money I spent on my fancy house"?  No don't respond to that, sorry.  Shouldn't have brought that up.

Still a good RE info resource.

Go looking for "single line diagrams" ....

Ya know that's why I used to subscribe to Home POWER magazine, they had excellent single line diagrams for all the installations they reviewed, since they quit doing that I let my subscription lapse.

[fabricator]

HP went more to a showcase of what's out there. And a lot of it is HIGH end for unlimited budgets.

[birdhouse]

there's another really inexpensive but not code approved option.  it's only a half step better than the suicide plug though...

heavy duty three way switches with the grid, inverter and breaker wires connected to it.  just note like mentioned above, you'd want to turn off electronics before flipping the switch...

maybe we should call this "the suicide switch method"

adam

[ChrisOlson]

I believe I need an automatic dual transfer switch?

I would recommend staying away from automatic transfer switches at all cost.  Automatic transfer switches swap power sources based on loss of one of the sources and this causes all sorts of problems.  Very expensive ones such as used on standby gensets in mission critical applications like hospitals (usually 500 kW - 2 MW capacity gensets) have a huge UPS on them that supplies power long enough for the genset to start and come online in the event of a power outage.  You don't even want to know what one of those costs.

The far better solution is to upgrade your inverter with a unit that has an AC input and a built-in transfer switch.  Inverters can make the switch based on battery voltage or remaining capacity, while external units are not going to do this.  And the better inverters can sync their output with the genset or utility so when it switches there is no glitch or blink in the power.
--
Chris

[fabricator]

Then you also have these things if you just want to switch over single loads.http://www.nooutage.com/TCA-1.HTM
But I'm with Chris on this one, if you can come up with the bux there aint nothing like a smart inverter.

[ChrisOlson]

Since I have both types of transfer switches here (inverter and manual) I made this video to demonstrate how seamless the switch is from backup power (either utility or genset) to battery, or vice-versa.  And why I prefer the inverter method.  There is no "automatic" transfer switch (besides an inverter) that is going to do the job properly.  I don't care if you get a like a Generac EZ-Switch, or whatever - the Generac switch, for instance, waits for 10 seconds after the loss of utility power before making the switch.

The manual switches that have dual inter-tied breakers are REALLY slow.  The Ronk switch that I demonstrate in this video is spring loaded and has a switch time of < 150 ms.  And you can still see what happens when I switch it.

Unfortunately, we do not have utility power so I have to use the genset for this demonstration.  But the concept is the same.  And none of these transfer switches that are any good are cheap.  The cheap ones are junk and will not handle repeated switching under load before you burn the contacts out of them.

A good two-pole (non-switched neutral) manual transfer switch, rated for full load switching, like I demonstrate in this video, is going to set you back at least $300.

--
Chris

[larryf]

Gentlemen:   I had a misconception about batteries in series.  I knew it was not the best policy to series different type batteries, but I thought it would be ok till I could afford better.  When GHURD and DAMON were critical of this (by the way, THANK YOU both for the wake up call) I went back to reading here and on the battery sites.  I now have a better understanding.  Now to CHRIS' video.  I was leaning toward an RV  transfer switch and then I saw your video tonight (I have been basically absent for a week).  Awwwwwwsome!!  And you went way beyond the call of duty to endure the wrath of she who must be obeyed to interrupt your service!!  That was crystal clear even to me, who mostly consider most of these discussions to be held in some  language spoken only on the moon.


But I am learning.  Larry F.  NE Colorado, USA

[ghurd]

That was crystal clear even to me, who mostly consider most of these discussions to be held in some  language spoken only on the moon.

But I am learning.

Keep reading and asking questions, especially before yoy BUY anything!
The language is learned faster that it seems.
The money saved is a tiny fraction of the frustration in buying/trying cost.
G-

[ChrisOlson]

I was leaning toward an RV  transfer switch and then I saw your video tonight (I have been basically absent for a week)

What I wanted to show you, Larry, was that if you can live with that "glitch" or blink in the power when you make the transfer, then an RV or other type of manual or automatic switch will work fine for you.  If you have sensitive electronics like computers or a HDTV that can be damaged by a "brownout" in the power when you make the switch, then a good inverter is going to be your only real option.

If you need the seamless transfer from one power source to another I think you're limited to a Xantrex inverter.  The Outback units I've seen don't sync their output with the backup power source, so they still got a little blink in the lights when they switch over.  Magnum Energy is another manufacturer of quality inverters, but I have no experience with those so I don't know how they handle their transfer of power sources.

The Ronk transfer switch I demonstrated in the video is a 200 amp two pole, with 10,000 amp RMS symmetrical surge rating, and it has "Vacu-Break" contacts in it.  It's a very expensive switch.  They make smaller, cheaper versions of it, but the cheapest one I've seen like that is about $250.

For automatic switching, there's lots of switches made for standby generators.  But they're "automatic" only to the extent that they do make an automatic switchover in the event of loss of utility power.  Beyond that they're really slow - typical time would be 10 seconds.  They wait that long to prevent nuisance starting of a genset for a short "blink" in the utility power.

RV switches and the Iota one mentioned earlier in this thread will work OK, but they are usually not rated for full load switching.  They have so many switching cycles under load and the contacts are junk in them.

So those are the different types I know about.  I'm sure there's others.  But to find a quality automatic one that will stand up to being switched a couple times a day under load, day after day, is still not going to be cheap.
--
Chris