Living on mostly 12v and reducing power

[DavidH]

Hello!

I have been slowly driving everything I use to natural gas, 12v, and now 5v, but I still have some big ticket items at 120v and 240v on a split phase system that I can not get rid of.

Devising a split phase 240v solution, but not to go 100% off-grid for 24x7x365… only for a few days at a time.

Thanks, DavidH

[Sid Genetry Solar]

3 hours ago, DavidH said:

Hello!

I have been slowly driving everything I use to natural gas, 12v, and now 5v, but I still have some big ticket items at 120v and 240v on a split phase system that I can not get rid of.

Devising a split phase 240v solution, but not to go 100% off-grid for 24x7x365… only for a few days at a time.

Thanks, DavidH

Could you elaborate a touch?  Personally, I've converted as many items to DC power as possible, and it really does lighten the inverter load.  I have the following items 100% powered by DC:

• 48v: all LED lighting
• 48v->24v: water pumps
• 48v->12v: laptops, (hacked) computer monitor, speakers, clock, phone chargers
• 48v->12v: tankless propane hot water heater (not an easy project!)

Larger appliances tend to require a lot more power than can feasibly be run at lower voltage DC setups--or to convert them becomes unfeasible/extra costly.  But I've still hacked several...

• GE Profile Advantium 120 convection microwave...ALL logic runs on 12vDC (boy was that a challenge!), 120vAC is only used for the heater coils / magnetron / circulation fan.
• Kenmore Elite French-door fridge: internal lighting and logic already ran on 12v, though from an AC power supply.  Was very easy to disable that and directly wire it to 12v.  Only uses AC for the compressor and defrost heaters (note that I'm not using the icemaker...that'd be another whole story!)
• simple chest freezer: added a 12v thermostat to control the compressor (which runs on 120vAC).

Other appliances such as a washing machine have such a short use cycle that it's easier to just unplug 'em when not in use.

Still have yet to hack that induction cooktop to run off 12vDC when in standby...

[DavidH]

Hi Sid,

Anything that requires a transformer / wall wort, those devices were replaced with similar devices that used 12v supplies, then I skip the wall worts.

Low voltage variable color & brightness LED lighting strings I use are 12v powered. The strings are extendable, use a wireless control, so eliminating the wall wart transformer is a big savings.

Multi-cell battery chargers are 12v run.

Anything that heats I moved to gas, to avoid electricity.  

Since I have this 12v infrastructure, if I wanted to use a GS inverter, is there a way to boost my 12v battery system to 24v so I can run my 240v A/C compressor? (I will not need to run other 240v appliances.)

Could I somehow charge a 48v battery bank for a GS inverter from my existing 12v system?

Could I use my non-sine wave 120v inverter from my 12v system to charge/feed the 48v  battery bank?

Thanks!

[Sid Genetry Solar]

Will try to get back with you later...

[Sid Genetry Solar]

17 hours ago, DavidH said:

Since I have this 12v infrastructure, if I wanted to use a GS inverter, is there a way to boost my 12v battery system to 24v so I can run my 240v A/C compressor? (I will not need to run other 240v appliances.)

Technically the GS 6k inverter can be configured for 12v, BUT the maximum current (and definitely the surge current) will be considerably limited due to the high amperage.  If the A/C is a mini-split with a variable-speed compressor, it'd probably be alright...but if it's an old-style single-speed compressor, maybe not so much.

 

18 hours ago, DavidH said:

Could I somehow charge a 48v battery bank for a GS inverter from my existing 12v system?

What about...converting the battery bank to 24 or 48v (doubling or quadrupling the maximum wattage of your exiting MPPT units, assuming they support the higher voltage)...and using 15-20A step-down converters for 12v appliances?  If you're working with a small RV, a 12v system would probably work fine...but if a larger house, you'd have considerably less voltage drop with 24 or 48v "bus" lines, and point-of-service step-down converters to 12v.

I personally use the "60v->12v" 10/15A step-down converters that can be found on eBay/Amazon/Aliexpress...their no-load current seems to be around 15mA, and I haven't had any issues at all with them.  Pretty amazingly powerful, too.

[DavidH]

Pragmatically, I have multiple small 12v UPS’s wired in parallel, able to drive my WAN, LAN, lights, and security system for over 24 hours with no power. When I lose batteries, I have redundancy to wait for batteries to arrive in the mail. It works well.

There was a 66 hour power outage that drove me over the edge, I added a quiet 12v generator with 3000W inverter system in a pinch, to save 2 refrigerators of food and get the heat back on - that met my budget. (One outlet supplied 1500W, with 3000W peak, two outlets would do 3000W continuous with 6000W peak.) When I bought the unit, there was a sign that said “pure sine wave”, but ”sine wave” turned out to only apply to the low end unit. It ran the heat & refrigerators, but very disappointed that it would not recharge my UPS’s when they were running out of capacity. (I knew it could not run my A/C due to split-phase need.)

I have several 24v UPS’s to handle larger compute loads, off-the-shelf external  battery pack on my pure sine wave unit supply my compute needs for ~24 hours during an outage. I originally considered getting a second identical sine wave unit, do a mod to split-phase with another off-the-shelf battery pack, but this would only get me ~2400W running compute equipment for 24 hours. The external battery pack vented & literally melted down (just sitting around charging, no power outage) - a huge disappointment since I was depending on off-the-shelf equipment to give me a degree of reliability & safety. (Even this path would not get my A/C running… although I contemplates mods to add 2x more and sync up the split-phase to eventually get there… leaving the gap of charging the 24v batteries when we had no power for long periods of time.)

A 240v split phase generators are so noisy and noise was a factor for my approach. (Everyone hears a neighbor’s 240v generator, no one hears my 12v DC generator.)

I go through this explanation to illustrate that reconfiguring this 12v system is less feasible, I am not married to extending my 24v system after the melt-down (with it’s gaps), but there are 12v components that are helpful & proven reliable.

I am thinking about effectively replacing my 12v 3000W inverter and reducing big battery dependency on 24v UPS’s with a GS (more off-the-shelf, more capacity.)

Over time, I plan to add solar panels, but that is not a priority.

I understand the input current limitations if a GS is configured for 12v. I have massive cables on my [non sine wave, non split phase] 3000 Watt inverter.

That being said, adding a battery system to the GS, backed with capacity from my 12v system seems possible. I was thinking a dozen of these (ignore the W, the limiting factor is 40A 12v input or 480W each):

https://www.ebay.com/itm/1800W-40A-DC-DC-Converter-Step-Up-Buck-Boost-Power-Adjustable-Constant-Current-/383901055938

Since this is only needed during long power outages (~2x a year), I am considering temporarily paralleling some off the shelf EGO 56v batteries (used weekly in my yard, kept charged all the time.) I may commission a friend to build higher capacity packs using old 56v EGO BMS’s (14s of SPIM08HP batteries) while adding a 3D print an extended top case. I figure if the smaller batteries can power my chain saw, a half dozen bigger batteries can handle surge capacity of the house. (I do not expect the GS to charge the batteries in this configuration, but the batteries to supply the load spike when cranking up the A/C compressor.)

This offers some wonderful dual use capabilities, easy modular replacement, and fast replacement with a trip to Lowe’s during a crisis.

I never want to have to deal with ripping apart a melted down battery pack again… I resorted to a hammer & crow bar to open up the case, to get access to the batteries, so they could be appropriately recycled. Destroyed my external UPS battery case, what a shame.

This being said, since you brought it up, I am also wondering how much loss there would be on the top end of the GS 6K split phase pure sine wave inverter if configured to 12v. If still supported, my compressor is rated at 19.5 RLA and fan rated at 1.3 FLA. See photo. Do you think it would work? It is a new unit, just 1.5 years old.

[Sid Genetry Solar]

On 6/25/2021 at 3:04 PM, DavidH said:

This being said, since you brought it up, I am also wondering how much loss there would be on the top end of the GS 6K split phase pure sine wave inverter if configured to 12v. If still supported, my compressor is rated at 19.5 RLA and fan rated at 1.3 FLA. See photo. Do you think it would work? It is a new unit, just 1.5 years old.

Well, if you've seen the latest YT videos Sean's posted...for comparison, the A/C unit that's giving us such grief with the 12kw GS prototype unit...is rated at 114 LRA (the important number, this indicates the maximum possible surge current).  Sean's A/C is also fairly new: it was brand new when he moved into his current house 2 years ago.

LRA = locked rotor amps.  The nameplate of your A/C is 130A, which is 16A more than the current A/C we can't seem to get started.  A GS 6kw @ 48v can't start it (doesn't blow up, it just can't start the compressor)...but technically, the 6kw GS is rated for 50A surge...with 130A being nearly 3x the GS 6's surge rating.  (It manages to start Sean's 77LRA smaller A/C unit without too much difficulty, which was rather surprising.)

On 6/25/2021 at 3:04 PM, DavidH said:

I figure if the smaller batteries can power my chain saw, a half dozen bigger batteries can handle surge capacity of the house. (I do not expect the GS to charge the batteries in this configuration, but the batteries to supply the load spike when cranking up the A/C compressor.)

Keep in mind: we're talking an order of many times' difference in the power requirements of a cordless chainsaw vs trying to start a 130LRA A/C unit.  A chainsaw might run 400-600W tops.  To start that A/C unit?  31,200W...or roughly 50 times the estimated power requirements of the chainsaw.

[DavidH]

Hi Sid,

My question was just before the gs12 test. I was hoping for a good result on the gs12.

The 56v batteries I am targeting come in 14s and 1p, 2p, and 3p configurations… each parallel bank capable of 20Ah sustained discharge rate (individual cell rating my mfg), BMS for charging only, no BMS on output terminals, so much higher peak current is possible.

I think I can get enough straight chemical capacity to handle the LRA. I figured to get a soft-start module, anyway.

I was thinking about your control board and telemetry. Dropped a note on YouTube.
 

 

[Sid Genetry Solar]

8 hours ago, DavidH said:

I was thinking about your control board and telemetry. Dropped a note on YouTube.

I didn't quite understand what you were getting at on the YT comment.  Could you elaborate further?

 

8 hours ago, DavidH said:

My question was just before the gs12 test. I was hoping for a good result on the gs12.

I'm not quitting on the 12kw.  Have 3 things to try...should be able to get it working one way or another!  For one, FET crosstalk/drive issues are the bulk of it...need to figure out how to get the best drive signals on the gate without punching the gates out with overvoltage...AND limit the maximum throttle.  I recall that @Ben managed to explosively blow out a set of FETs with no load on the inverter...by connecting the AC output wires up wrong.  That tells me that these high-wattage transformers won't accept a square wave input...they'll basically dead-short the battery and blow the FETs out.  So I need to determine what a safe maximum throttle is...and go 20% less than that.

Then that big A/C should roar to life with nary a whimper...

[InPhase]

It seems like with all the money spent with boost converters and cordless tool batteries and blow ups and melt downs that you could have just bought some batteries to make a  36 or 48 volt system. A golf cart place near me has a special offer for six Crown 205 Ah 6 V batteries for $655, which would get you 36 V. Or six Crown 165 Ah 8 V batteries for $815, which would be 48 V.

Don't get me wrong. I'm all about cobbling things together, but I don't have any critical needs. If I did, I'd bite the bullet and get a good set of batteries and a charge controller as the foundation of my system, and then cobble on top of that.

[dickson]

It seems like with all the money spent with boost converters and cordless tool batteries and blow ups and melt downs that you could have just bought some batteries to make a  36 or 48 volt system

 

I  started  with  12v system  3 years ago  because 12v  battery  are  easy to buy  .  I  try  boost converters from China   to go to  48v   from 12v battery .   5  boost  converters caught   fire  before  I  finally  get   4 to  work at  48v .  Now I use ebike chargers with  regulator .   

[dickson]

I'm not quitting on the 12kw.  Have 3 things to try...should be able to get it working one way or another!  For one, FET crosstalk/drive issues are the bulk of it...need to figure out how to get the best drive signals on the gate without punching the gates out with overvoltage   Then that big A/C should roar to life with nary a whimper

 

I  know  your 12kw GS  inverter will run Sean  4 ton AC  with no problem  .     My   15kw  PS  inverter  run my  4ton heat pump  with no problem  but it  is using more power  than I first   think .  My battery  run down  in  2 hours .  I   have  picture  of  LRA  117   which is 4 times  more than I   thought  the  surge of  28000 watts  should be  .   That is why  the ASL9  transformer  get so hot  and  the  mosfet  135 F degree .   L1 and L2 is balanced and    is directly wire  with  breaker  to  heatpump .    Heat  pump may not start if  L1  N  L2  to transfer switch and not be balanced  .   

[Sid Genetry Solar]

1 hour ago, dickson said:

My   15kw  PS  inverter  run my  4ton heat pump  with no problem  but it  is using more power  than I first   think .

Nice, very good to know.  That means we have zero excuse here on GS inverters 😉

1 hour ago, dickson said:

That is why  the ASL9  transformer  get so hot  and  the  mosfet  135 F degree .

Can you provide a photo of the transformer model tag?  I seriously doubt it is an ASL9; for a 15KW PJ, it will likely be an ASL6.5, one step larger than the core used in the GS 6.

[Sid Genetry Solar]

1 hour ago, dickson said:

My battery  run down  in  2 hours .

Should be somewhere over 120A on your batteries.

[dickson]

Should be somewhere over 120A on your batteries

Yes  120a  to 180a   I  start  at 60 v  and  run down to 50 v because of square wave  or  when transformer  temp go to  165 degree F .    One third  of battery on  charger  and one third on standby and one third  being use .   I let the  transformer  cool  for 2 hours  and then use the standby battery  and  recharge  the first  group .   

[dickson]

Can you provide a photo of the transformer model tag?  I seriously doubt it is an ASL9; for a 15KW PJ

 

I bought  on ebay  auction  and is probably rebuilt  and is shipped  in 5 days  from walnut  california   warehouse  by UPS  with no damage .  

[Sid Genetry Solar]

Well, surprise then...it is an ASL9 core.  Funny that it can't sustain an 7.2kw load...they normally use it in their "20kw" inverter...

[dickson]

.it is an ASL9 core.  Funny that it can't sustain an 7.2kw load...they normally use it in their "20kw" inverter.

 

I  am sure it can  sustain  8000kw load at  75 degree F .       Nobody  in this  forum  know  what  118 degree F  in the patio  do to the transformer temperature  after one hour  running  a heat pump starting  surge 28000 watts  with the battery voltage  going down  every  5 minutes  and the sine wave  going to a square wave .   Even  RV  have AC  inside to cool the  inverter .     It will be a test I will do with your GS  12kw inverter next summer  and  I do not know if you  will  warranty  a inverter at that outside temperature  before I try .   Thank you  and  nice talking to you .   

[DavidH]

On 7/1/2021 at 8:50 AM, InPhase said:

It seems like with all the money spent with boost converters and cordless tool batteries and blow ups and melt downs that you could have just bought some batteries to make a  36 or 48 volt system.

My use case is for 2 or 3 times a year, short spells, crank up the quiet 12v generator when the outage extends past a 15 minutes.

if I use lead acid starting battery 48v system, float it, never discharge below 50%, I’ll likely replace  batteries every 2-3 years, for virtually no use, due to self discharge.

I may be able to use AGM 48v system, never discharge below 50%, replace every 5-6 years, due to self discharge.

Move to LiFePo4 or Li-Ion, maybe eek out a longer life expectancy out of the batteries, if they are never charge past 90%, never discharge past 20%, I will likely change batteries every 5-6 years, due to self discharge. I will never be able to charge Li-Ion to 4.2v, since leaving it there & not using it destroys the battery.

Since I use high quality 56v tools on the weekends, I will likely need to replace batteries every 5-6 years. A smart BMS in a tool discharges the battery after 30 days of non-use, extending the life of the tool battery. Tool BMS’s typically don’t limit output, allowing for 4-5C output, to handle spikes.

In the end, I hate replacing my 12v batteries all the time, typically after a few outages. I don’t want to spend a lot more money for just convenience for what I have today for the privilege of re-buying more expensive batteries. I would rather invest in a system where my investment is 1 time on the inverter hardware and multiple times on tool batteries (that I actually use & run down the street to replace) with my 12v quiet generator.

[InPhase]

So why not just use the generator instead of the batteries? If the use is for short periods, why bother with batteries at all?

[DavidH]

On 8/21/2021 at 7:52 AM, InPhase said:

So why not just use the generator instead of the batteries? If the use is for short periods, why bother with batteries at all?

My 12v generator will run for days with an AGM for peaks, without filling up the tank, it is great! One 1.5K leg of my 12v Bluetooth 3K inverter powers 1/2 the house runs with my heating & ventilation with 2 refrigerators. The other half of the house requires less than 1500 watts, but my Bluetooth inverter is not split phase, therefore the other half remains dark. The A/C load requires 130LRA or 31.2K peak watts, since it cools the space for 2 families, and this is not accommodated.

The GS 12k unit would handle the peak load, while day to day temporary operation would be severely overkill.

Honestly, I was getting ready to modify 2x APC 1500 units to run as master/slave, but it would not give me my A/C and it is a dual bank 24v solution. In the end, I would have to boost 12v to keep those banks supplied with no A/C.

When I saw the Genetry systems, it does the split phase and the 12K gets me closer to getting my A/C working. If I could run it at 12v, it would be perfect!

if I have to buy another generator, I would have to keep it 6 feet from the house, it would be a lot more noisy (the big issue), I would have to keep the fuel constantly topped off. Overall, I don’t want the bother.

I could get a whole house natural gas generator, but it is still noisy & needs to be 6feet from the house. (My 12v generator is so quiet, you can’t hear it run.)

I have been looking at other solutions, including running a motor at 12v from my generator to generate 240 split phase, and just deal with the loss of efficiency. I could do this, enclosed in a garage, or behind a locked walled area. This would still be preferable.

I could also get a wrecked hybrid, and mess with the inverter. I could also get  soft start circuit & talk to my HVAC man to install it, and maybe go with a GS 6K, especially if they would support 12v for me.

Maybe they would have putty on my soul, I don’t know, and ship what my use case needs, instead of me having to hack all kinds of crap together.

[Sid Genetry Solar]

7 hours ago, DavidH said:

If I could run it at 12v, it would be perfect!

Ugh, LOTS of amps.

Am working with a commercial customer that is trying to make 12kw 12v inverter--maybe you'll be able to buy an inverter off of them!  However, that's crazy amps--you're talking past 1,500A @ 12v.  Best case inverter efficiency is going to be under 70% simply due to the molecular electrical losses.

That 31.2kw surge?  Let's add 40% simply due to molecular electrical losses, and that's 31.2 * 1.4 = 43.6kw / 12v = a cool 3,640 amps.  This jumps the gap between "stupendously difficult" and "electrically impossible."  Why?  At 12v, if the ENTIRE inverter resistance--battery cables, chassis wiring, MOSFETs, transformer, etc. is MORE THAN 0.0032 ohms (3.2 milliohms), it will be impossible to get 3,640A to flow @ 12v.  Notice that I didn't say that any work was being done with this 3,640A.  The inverter resistance will have to be far less than 3.2 milliohms in order to get any power to flow on the output side...otherwise the entire 40kw gets burned up in wire losses in the inverter, and no significant power is produced.

Let's not mention that the FETs used in the 6k and 12kw GS inverters are rated at 3.5 milliohms on resistance.  And they're very good FETs.

At 48v, add only 20% for losses (probably way overcompensating), and that's only 780A.  Far more manageable!

 

7 hours ago, DavidH said:

and maybe go with a GS 6K, especially if they would support 12v for me.

Technically CAN support 12v on a 6kw from a hardware standpoint.  But we definitely cannot recommend it--at least not with the current design.  Full 6kw is 600A! 

Have heard that we have 1 GS customer with an inverter wired for 12v, and he's had it up to 5kw with no issues.

[dickson]

it will be impossible to get 3,640A to flow @ 12v.  Notice that I didn't say that any work was being done with this 3,640A.  The inverter resistance will have to be far less than 3.2 milliohms in order to get any power to flow on the output side...otherwise the entire 40kw gets burned up in wire losses in the inverter, and no significant power is produced.

Too  dangerous for fire  and  cost of  wires will probably  be  more than  a  12kw  GS inverter .  I  see on youtube one  FET  is  900 dollars and need  many FETs for an inverter that  one person try  and fail  and gave up after losing  thousands of dollars .    I  am running  60v on a PJ inverter just to  run a heat pump  129 LRA  for little over an hour  no  matter  how  many time I try to run longer  but never longer than  90 minutes .   The transformer just  overheat  and shut down .   

[DavidH]

On 10/3/2021 at 8:28 AM, Sid Genetry Solar said:

Ugh, LOTS of amps.

…trying to make 12kw 12v inverter--maybe you'll be able to buy an inverter off of them!  …

That 31.2kw surge?  Let's add 40% simply due to molecular electrical losses, and that's 31.2 * 1.4 = 43.6kw / 12v = a cool 3,640 amps.  …

At 48v, add only 20% for losses (probably way overcompensating), and that's only 780A.  Far more manageable!

I was hoping to over-provision with a GS 12K with 12v in order to keep everything “stock” in my setup.

I figured @ 12v, I could use 4x super capacitor banks in parallel, to provide transient peak current requirements. (48v is much harder to provide the same current surge capacity with Super Capacitors... I could provide vastly more peak current with 4x super capacity banks in parallel @12v rather than 4x super capacitor banks in series @ 48v.)

Well, it sounds like I am going to have to start hacking things up, then.

I will start to work on a “soft start” for my HVAC Compressor, this will reduce my largest load @130 LRA to 130/5.5= 23.6 Amps (This would bring me well within range of GS 6K.)

That leaves me with some questions…

1. Is a GS 6K @ 36v, in ATS mode supportable, if I keep my peak load below 50A @240v

2. Could a GS 6K @ 36v, take solar input from panels & keep my battery bank charged, if my mains are powered (on ATS mode)? (Trying to find an alternative to my quiet 12v generator.)

3. Could a GS 6K @ 36v, take solar input from panels & keep my battery bank charged, if my mains are off (power outage, on ATS mode)? (Trying to find an alternative to my quiet 12v generator.)

4. Is 2 or 3 viable with grid tie inverters, on the output lines of a GS 6K @ 36v?

5. Will an auto-transformer be needed in a supportable solution, for simultaneous 120v split phase & 240v on a GS 6K, to tie the neutral of a split-phase? (I am still trying to be sure on this point... some other vendor solutions require this.)

(I am trying to find the least amount of hacking, at this point, for my whole-house UPS objective… yes, I have read the GS 6K document 2x, it was very good, but before making a big spend, I am trying to get my proverbial ducks in a row.)

[Sid Genetry Solar]

3 hours ago, DavidH said:

I was hoping to over-provision with a GS 12K with 12v in order to keep everything “stock” in my setup.

I figured @ 12v, I could use 4x super capacitor banks in parallel, to provide transient peak current requirements. (48v is much harder to provide the same current surge capacity with Super Capacitors... I could provide vastly more peak current with 4x super capacity banks in parallel @12v rather than 4x super capacitor banks in series @ 48v.)

Surge current isn't the consideration at hand.  See, if you had a 12-24kwh battery bank @ 12v, you'd have considerable amperage available.  The issue becomes getting the amperage through the entire inverter and actually being able to accomplish the intended goal without losing the entire power usage in system losses.

Remember, amperage is the enemy of efficiency.  That's why long-distance power transfer is inevitably at as high of a voltage as feasibly and safely possible.  The lower the amperage, the lower the losses.  Simple Ohm's Law.

 

3 hours ago, DavidH said:

I will start to work on a “soft start” for my HVAC Compressor, this will reduce my largest load @130 LRA to 130/5.5= 23.6 Amps (This would bring me well within range of GS 6K.)

95% load anyway.  6000W / 240v = 25A.  Remember that the LRA rating is <1sec, so it won't have any bearing on system capacity (i.e. heat limits), but rather entirely an absolute power limit.  No matter what kind of "soft start" you come up with, you will not be able to reduce the startup surge to the FLA rating...that's just how synchronous AC motors work.

 

3 hours ago, DavidH said:

1. Is a GS 6K @ 36v, in ATS mode supportable, if I keep my peak load below 50A @240v

Well, 240v * 50A = 12,000W, so not exactly. 

ATS function isn't dependent on battery voltage though; if it works at 48v, it'll work when configured at 12, 24, or 36v as well.

 

3 hours ago, DavidH said:

2. Could a GS 6K @ 36v, take solar input from panels & keep my battery bank charged, if my mains are powered (on ATS mode)? (Trying to find an alternative to my quiet 12v generator.)

3. Could a GS 6K @ 36v, take solar input from panels & keep my battery bank charged, if my mains are off (power outage, on ATS mode)? (Trying to find an alternative to my quiet 12v generator.)

GS inverters as of yet do not have a solar charge controller built in.  However, they can charge from AC input--though the AC input will have to be able to power the entire load in addition to the battery charge power requirements, in order to charge the batteries.

 

3 hours ago, DavidH said:

4. Is 2 or 3 viable with grid tie inverters, on the output lines of a GS 6K @ 36v?

Yes.  It'll help considerably to have a Rev. C control board in the GS inverter (which I FINALLY just ordered last night).  Once we receive them, all GS inverters will ship with a Rev. C control board.

Bonus points if your grid-tie inverters support frequency shift throttling (most cheaper/readily available grid-ties don't)...if so, the GS inverter will be able to gently regulate the grid-tie output as needed for battery charging + loads, etc.

If the grid-ties do not support frequency shift throttling (i.e. on/off), the system will be far cruder...but should still work quite well.  (If there's a power excess, the inverter will start shifting the output frequency from 60Hz up past 62Hz--or at least until the grid-ties trip off.  Expect a slow oscillation here, as most grid-ties will then run a 5-10 minute timeout before they try to power back up again.  If the power needs / battery charge is still less than the grid tie inverters' total output power, the GS inverter will trip the grid-ties off again.)

Curious then if you have grid-tie inverters already picked out...if so, what are they?

3 hours ago, DavidH said:

5. Will an auto-transformer be needed in a supportable solution, for simultaneous 120v split phase & 240v on a GS 6K, to tie the neutral of a split-phase? (I am still trying to be sure on this point... some other vendor solutions require this.)

No.  GS inverters provide true split-phase output, no hacked-up solutions needed.