Balancing the Loads of my Conext SW with an Autotransformer

MrM1

The Schneider SW Inverter series has a feature that is suppose to allow the user to draw from batteries until a user set threshold has been reached.  That threshold can be set to Battery voltage, which would allow the loads to be supplied by battery,  until a low battery threshold was reached,  and then the inverter would  switch over to grid power.   This can be set by a low voltage threshold, or if one has the battery monitor,  can alternately be set up on the SOC of the battery.  Schneider calls this AC Support mode.   And their load shaving "works" in a similar fashion.

Bad news,  it does not work very well.  The documentation states ...

"AC Support ensures that no current comes from the AC Input connection of the Conext SW as long as the battery’s state-of-charge (SOC) or battery voltage conditions allow it."  p 1-7

This really is not the case at all.  And Schneider has told me that this line should not even be in the documentation. 

That being said,  Apparently ... also according to Schneider, for the SW series inverters to have any success at even partial grid interactivity,  The loads must  be balanced on L1 and L2 (the SW series is a split phase 240v inverter).    The better balanced the loads,   the better the grid interactivity works so it seems (or has at least been my experience)

But as an example,  right now:
- my SOC is 88% and my battery bank voltage is 25.6v (24v system)
- I have the AC support mode set to 23v which means the system is suppose to run off batteries UNTIL my batteries reach 23v.
- Yet right now,  my loads are 1355w,   and I am pulling 18w from the batteries,  and 1337w from the grid.  
- AC Support mode is on, but obviously not working very well.  So much for the grid support for the batteries
- BUT ... my Loads are imbalanced.  I cannot change this as right now L1 is powering a 120v water heater,  and L2 is powering some LED lights and a fridge that is presently in the saving mode of its cycle.
- L1 is drawing 10.7 amps AC,  L2 is drawing .8 amps AC

While I have never seen AC support mode work as described above,  I have seen it work at about 20% grid / 80% battery when 2 conditions are met:
1. loads are fairly balanced
2. AC output is fairly hi .... upwards of 2000 watts for my 3400 watt inverter.

The higher the wattage goes up, the more the system will draw off batteries as long as there is fairly good load balance and one is inside the set threshold.    But balance is difficult to achieve all the time.  And hi watts are very impractical for all but the largest of battery banks.

So I am wondering and  thinking about Auto transformers to help overcome this.    Would something like the Outback FW-X240, which is made for 2 120v stacked Outback transformers,  work with my SW which is in a single  box,  but has 2 120v lines?

If I could use some thing like the FW-x240, or some other auto transformer possibly locally sourced,  could I not balance my loads and have much better success with Schneider's ill working AC Support mode?

How possible would this be? 

Would I need to contact Schneider for the proper size and spec of an Auto Transformer,  or would something like the OUtBack FW-x240 work out of the box,  or could I go with those specs to an AC supply house to get one like it?   Just wondering as this would sure get my SW working a whole lot closer to my original design for the whole solar system.  It was a major disappointment to learn from Schneider that their AC support mode really does not work as advertised.    And a major culprit seems to be unbalanced loads.

Any thoughts or help?  Ideas? 

Attached is a diagram from Outbacks info on how this could possibly work.  Could something like this work?   What am I missing?  Is there a less expensive way to do this and balance loads?    I realize with the Outback I am looking at 2 inverters, but they are 120v each and mine is a 240 split. 

mike95490

Yes, and autotransformer is used to balance loads.

No, I don't know the exact connection to accomplish this.   BUT, I suspect, any transformer with a CT 240V winding, of sufficient gauge/VA to handle at least 3/4 of your inverters power, would do it.   But why not wire that heater to 240V and spare a LOT of trouble? That heater is a huge imbalance and I'm surprised the inverter even tolerates it

MrM1

mike95490 said:

Yes, and autotransformer is used to balance loads.

No, I don't know the exact connection to accomplish this.   BUT, I suspect, any transformer with a CT 240V winding, of sufficient gauge/VA to handle at least 3/4 of your inverters power, would do it.   But why not wire that heater to 240V and spare a LOT of trouble? That heater is a huge imbalance and I'm surprised the inverter even tolerates it

Because I cannot find a full size element in 240v 1000-1300 watts.   I am using a 240v 4500W element at 120v which yields right at 1150 watts.  But I also want to better balance all my loads at all times for that very reason,  so my inverter will better tolerate and perform better in AC support mode. 

I discovered last night that if I just run my well pump as the load,  which after start up runs at about 800 watts .... as  240v load it is perfectly balanced, and the inverters AC Support mode performs near perfectly.  It supplies the load from the battery except for the 2% supplied by the grid to prevent back feeding of the to the grid.

mike95490

Here's how an auto transformer looks schematically   ( from https://www.electronics-tutorials.ws/transformer/auto-transformer.html )

grainger has several 240V, 750 & 1,000 w elements, and then you could use a fairly smallish (lower losses) transformer,

by shifting the big 120v loads, to 240V.  Maybe the microwave & blow dryer would need a larger transformer to support them but how many hours do they actually run, and is a $500 transformer worth $20 of electricity ?

https://www.grainger.com/category/water-heater-elements/water-heaters/plumbing/ecatalog/N-adxZ1z0o50eZ1z0nzcnZ1z0o0un

MrM1

mike95490 said:

Yes, and autotransformer is used to balance loads.

No, I don't know the exact connection to accomplish this.   BUT, I suspect, any transformer with a CT 240V winding, of sufficient gauge/VA to handle at least 3/4 of your inverters power, would do it.   But why not wire that heater to 240V and spare a LOT of trouble? That heater is a huge imbalance and I'm surprised the inverter even tolerates it

I suppose I could use a step down transformer on the water heater element and run it 240v out of the inverter thru the step down to 120v.   Would something like that work?  Then at least I would be balancing that load.

Would something like this work on the single water heater load so I could run it 240v out of the inverter but keep it at 120v at the water heater?

https://www.cesco.com/Square-D-by-Schneider-Electric-50SV1A-Schneider-Electric-50SV1A-Square-D-050KVA-TFMR/p1891141

MrM1

I've seen those elements.   they are very short.   Wouldn't that have an adverse effect on the way they heat water if they only extended into the tank 7-8" as opposed to the double loop tpye i have that go in 13"

But if I use a 240v element,  than I would not have to worry with a transformer as it would run both sides of the inverter,  but the wiring size may have to increase because of current.  Though I doubt it at 700 - 1000 watts.

mike95490

MrM1 said:    ......

But if I use a 240v element,  than I would not have to worry with a transformer as it would run both sides of the inverter,  but the wiring size may have to increase because of current.  Though I doubt it at 700 - 1000 watts.

240V loads generally, use less amps than the same load at 120V

mike95490

MrM1 said:

Would something like this work on the single water heater load so I could run it 240v out of the inverter but keep it at 120v at the water heater?

https://www.cesco.com/Square-D-by-Schneider-Electric-50SV1A-Schneider-Electric-50SV1A-Square-D-050KVA-TFMR/p1891141

That transformer is good for about 50watts and only about 5 lbs of iron.   Your 10A water heater @ 120V is 1200 watts, and that will need at least a 1.3KVA transformer around 30# or so.

jonr

>  Wouldn't that have an adverse effect on the way they heat water if they only extended into the tank 7-8"

I don't think so - water that is free to convect moves lots of heat.

MrM1

Right now I am set to try the 1000 W 240v water heater element at 6.50.  Much cheaper than a auto transformer.  Also going to call Schneider tomorrow and see what they recommend,  but I suspect that the Outback will probably be the most economical. 

Also, I had no idea it was that large.  I think 10" x 11".  That will be larger than my current switch gear box can handle and would have to me mounted in a separate box.  

Thanks for the guidance. 

Estragon

The x240 is also on the heavy side (sturdy shelf needed) and makes a slight buzzing noise, which may or may not make a difference in locating it.

MrM1

Connecting a 240v 1000w water heater element by itself to my Conext SW inverter allowed the load to be perfectly balanced,  AND the AC support mode worked flawlessly.   So it is confirmed that Schneider's AC Support mode needs a very balanced load over L1 and L2.

So I called Schneider Tech Support and asked if they recommended an Auto Transformer. They did not have one the specifically recommended.  

And then they asked why I would want an Auto Transformer ... To run L1 and L2 step down to a single 120v?    I told them, No,  I would use it to balance the load coming off L1 and L2 from their SW inverter so that the AC Support mode would actually work.  And Tech Support was pretty amazed and said,  yes that would actually work very well.  And that they had never thought of that. 

As poorly as the SW's AC support mode actually "works" ... I'm surprised it does not come preinstalled in the inverter ... or at least that the do not have a Technical Bulletin recommending it. 

MrM1

So what, besides costs, is the difference between the PSX-240 and the FW-x240.  I realized on is 6Kva and the other is 4Kva,  but is it just that the PSX comes in a housing, has a fan and a double pole breaker? 

I really do not need the 6Kva of the PSX

Would I need a fan on the FW-x240?    Could it just be mounted in a box large enough to handle it's size? 

Also, would such a transformer be suitable to mount in a craw space 3 feet above ground under a house,  not exposed to the elements,  fully enclosed so not open to animals etc, but subject to outdoor temps?    My water heater is already under there.  Plenty of room for working.  Just not sure if a transformer can be mounted in such a location.   If no I would mount it in my garage,  which really has the exact same conditions,  only diff is the concrete floor.

mike95490

They both are the same transformer, one has fan cooling to gain the extra 2 KW.  It's not likely you would need the fan.

The transformer needs some sort of protection (I've got a PSX) not sure what sort of cabinet the FW comes with, but you need to

have strain relief so the transformer wires are not strained by the hook up cables.

Estragon

I have the version in a box. I've never heard a fan run, but it just powers a pump that runs for a few minutes at a time.

I know critters get into my crawlspace , so I'd want it in some sort of chew-proof box, and it needs OCP, so I'm not sure getting the transformer alone is much of a savings. To each his own though.

MrM1

Thanks.  I'd mount it in a steel / metal vented box.  Probably lag it to floor joists and install insulated buss bars for the connections.   

MrM1

Has anyone yet tried an Autotransformer for load balancing with a 240v split phase inverter?   I am still considering it and might pull the trigger today and buy one. 

But just to make sure,  an AT like the Outback PSX-240 would work with my Schneider Conext SW 4024 inverter to balance the loads between L1 and L2 if wired Like this ... ???

Dave Angelini

Sure but I use it to balance for a clients XW who wants to run a 120vac genset into a 240 vac only AC2 input.
It should work for you but there is only so much balance it can do for a 4kw inverter. Your drawing shows a 4.5 kw load ?

I think it would be best for the economy and maybe you also if you are intent on this, to buy a 2nd inverter and stack them.

MrM1

Thanks Dave,  The drawing is just a knock of the Outback set up so the watts shown are just examples of how it would balance loads.  As you know the SW is a 3400 Watt unit (in the 4024 version) with a 4000 Watt 30 min output. 

As to stacking,  I really do not understand the concept,  except in that it would allow me to double the amount of load I am using.  But not sure how it would work to balance loads any better for the SW.  If a person only uses one Leg of Each SW - Yes the AC support mode would work better because the load imbalance issue would be solved - But then the output of the SW is limited. 

I also think I understand that there is probably only so much an AutoTransformer can do with the load to the single SW is low (Say under 400 watts) because the SW requires about 2 amps from the grid at all times (according to the manual to keep from back feeding the grid).    So I would guess a 250 watt load, not matter how balanced is going to feed 100% from the grid anyway. 

Im still debating what to do,  but in my set up, (short of getting a second SW - which is not in the cards due to other home repair responsibilities) - an AutoTransformer seems rather appealing.    I would still like to hear from someone who has tried it in this application. i know there have been a few threads about this lately for the SW,  but it seems no one has yet taken the plunge. 

MrM1

BTW,  Looking again at the specs of the SW4024,  it is rated to do that 4000-5000 watt load in the drawing above,  for  about 10-15 minutes.  

Estragon

I use a x240 in a different application. I think in this application, if either leg drew more than 25a ([email protected]) sustained, the ganged 25a breaker flips (so lights out on both legs).

Dave Angelini

MrM1 said:

BTW,  Looking again at the specs of the SW4024,  it is rated to do that 4000-5000 watt load in the drawing above,  for  about 10-15 minutes.  

Right but pushing any inverter to its limit is not going to make your specific problem easier to solve.

As for stacking, it should work but I have never tried it for grid tie and not for the issue you are having. Offgrid we stack for a machine shop or a multiple homes on the same microgrid. 

Looking at your drawing is kind of scary for an electrician who is trained to balance loads. Scotty on star trek would freak

MrM1

I know I'm right there with you on the scary. But that is actually the drawing that came from Outback and not me. I just photoshopped in a Square to represent the SW. Outbacks drawing is at the top of this thread showing 2 Outback inverters stacked one of them operating as L 1 and one of them operating as L2

MrM1

Estragon said:

I use a x240 in a different application. I think in this application, if either leg drew more than 25a ([email protected]) sustained, the ganged 25a breaker flips (so lights out on both legs).

that would really not be a bad thing because the SW 4024 is only rated for about 1800 watts continuous on each leg if I remember correctly

mike95490

You most likely will be able to get it to run, as drawn, BUT what is that 4500w load ?  How often & how long will it run ?  

You are pushing the limits of both the inverter and transformer, and sooner or later, one will give up and call it quits.

MrM1

The 4500 watt load is just in the drawing.  The drawing came from Outbacks Manual for the FW-X240 which is the same as the PSX-240  but the PSX has a metal housing and breaker included.     So the drawing has been doctored by me to show a single split phase inverter but is Outbacks "generic" drawing.

http://www.outbackpower.com/downloads/documents/integration_products/autotransformer/manual.pdf

mcgivor

What are the loads you currently have, 120V / 240V, if the 120V loads are minimal a simple stepdown transformer of appropriate size feeding a small 120V load center via a 240V breaker in the main distribution would be a simple solution, the Outback  autotransformer would probably work fine but being sized to handle 5KW would be reflected in the cost. 

MrM1

I have  both 120v loads and two 240v loads (a 1/2 HP well pump at 950 watts and a 1000 watt water heater element).   The rest of my loads are smaller.  I have never seen more that 3000 watts being used at any one time from the inverter.  A Fridge that runs 24/7 and draws 2500 Whs daily is the largest continuous load.  I use about 3500 Whs per nite from the battery, and the solar array generates enough to charge the batteries and power the loads thru the day.  The array generates 8-12 KWhs per day on average days. 

@mcgivor, if I read you correctly,  You are saying run the entire 240v L1 L2 of the inverter thru a single step down transformer and use that single 120v to power everything.   I am guessing that would cause the loads to pull from both sides (L1 and L2) evenly all the time?   I could do that with some creative rewiring.  I do have a 120v water heater element and the pump could easily be set back up to 120v rather than 240v.  

mcgivor

Personally I would use 240V wherever possible, this would limit the size of the 240/120V transformer 

mcgivor

MrM1 said , if I read you correctly,  You are saying run the entire 240v L1 L2 of the inverter thru a single step down transformer and use that single 120v to power everything.   I am guessing that would cause the loads to pull from both sides (L1 and L2) evenly all the time?   I could do that with some creative rewiring.  I do have a 120v water heater element and the pump could easily be set back up to 120v rather than 240v.   

What I meant was run the SW output to your distribution as normal , then with a 2 pole breaker in the distribution power a transformer which supports the 120V loads. This way there would be no imbalances caused because it will be seen as a 240V load. The transformer would have to be sized correctly with appropriate overcurrent protection, this would be a much less expensive option to the autotransformer. 

MrM1

What I meant was run the SW output to your distribution as normal , then with a 2 pole breaker in the distribution power a transformer which supports the 120V loads. This way there would be no imbalances caused because it will be seen as a 240V load. The transformer would have to be sized correctly with appropriate overcurrent protection, this would be a much less expensive option to the autotransformer. 

Yes I had considered that idea the other day,   run a double pole 240 circuit to my fridge and then use a single step down transformer to convert the 240v to the 120v fridge voltage.  I had a suspension that would work and a friend thought he could get me the transformer sized correctly and box that he had laying around ... but it did not work out,  he did not have a spare.

BUT,  I did find a New-in-Box old stock (2014) PSX-240 for half the price of a new ones MSRP.  I wrote Outback and they said there has been no changes in that time and that it should work for what I was thinking.  It should be here next week,  so we we'll see then.  

I might need to bounce some wiring thoughts off you kind folks before i power it up to check my wiring to be sure I have done things correctly.

Thanks

Mike