Tell me about ac coupling

[bigrockcandymountain]

Ok, so i have read a few timea now the benefits of putting extra solar through an ac grid tied style inverter and backfeeding your off grid system.  A few details need explaining to get through my thick skull.

I would like to add about 2kw of pv to the new shop, and tie in to the existing off grid system.  I already have 240v from the inverter at a normal panel in the shop.  I also pulled wires to run dc from the future panels back to the house and in to a mppt charge controller to charge batteries with. 

You guys are suggesting i could just use a grid tie inverter and connect to the 240v ac right in the shop.  Here is what i don't understand.

When we have large ac loads and the battery inverter (magnum ms4448pae) is powering them the theoretical grid tie inverter would just help and take some strain off the battery inverter. 

When it doesn't make sense is when i want the theoretical ac inverter to backfeed and charge batteries.  My inverter can only be a charger or inverter, not both.  So as soon as it switches to charging mode, the ac output dies and the gti would shut down too.  How are you guys that do this getting around that?

[DamonHD]

I think that I don't have the system layout that you are interested in, nor is it anything like a beefy as you'd want.

But ... I have separate off-grid and grid-tied systems each with solar PV and storage.  Batteries are fed from a solar controller in the first case and AC-coupled in the second.  The (tiny) off-grid system can take over a small load from the grid when the off-grid system has plenty of energy to spare.  The grid-tied battery shaves flows to/from the grid but would not protect from a grid outage.  Schematics are available for both.

https://www.earth.org.uk/expanding-off-grid-PV-system.html
https://www.earth.org.uk/Enphase-AC-Battery-2.html

Rgds

Damon

[clockmanFRA]

Hi,

Firstly your DC to AC 120v or 240v Mini Grid Inverter must be truly BI-DIRECTIONAL.
Unfortunately most main Inverters add further complications into the controls that allows all sorts of trickery but also make things real complicated.

Okay this is my standard reply to AC Coupling concept when creating your own Mini Grid.
 And Mods, sorry about mentioning OzInverter stuff, but just trying to explain a AC Coupling system that has been fully operational from 2015.

RENEWABLE ENERGY.
‘OzInverter’ AC COUPLING, and Back charging the batteries. 


For true total domestic renewable independents, or as it is referred to OFF GRID or MINI GRID.
I have always seen AC coupling as the way forward, rather than just DC and many expensive charge controllers just feeding the batteries and powering a large Inverter that creates 240vac PSW, (pure sign wave).

Some time ago I originally bought a very expensive, so called Rolls Royce of commercial Inverters, 48vdc to 240vac, firstly it couldn't do the specified 6kW and found that it could only do 4.2kW constantly. Secondly it needed a lot of expensive propriety ancillary control equipment integrated into the system to function and back charge the batteries correctly. And thirdly It raised the 240vac HZ frequency from 50HZ to 60HZ and domestic equipment failed.   Basically it was trying to be a 'Jack of all trades and master of none'.

It went back, and the company put a gagging order on me not to talk about their crap toy Inverter.

2014-15, 'Oztules', on Flinders Island, Tasmania, stepped in, and like me he wanted a true and real Inverter that would do the AC coupling using a H bridge design, and without all the fuss.   Our Mantra .... KEEP IT SIMPLE, MAKE IT ROBUST, and importantly MAKE IT COST EFFECTIVE.
And hence we designed and created the efficient and powerfull ‘OzInverter’, that you can make your self for about 800 euros. And yes, I can supply all the necessary PCB boards and a DIY Book.     See …………. http://www.bryanhorology.com/ozinverter.php


A very cost-effective solution for handling that 19kW of power from the PV panels arrays, is to use what is called 'AC Coupling'.

Houses that you see around the World with PV on the roofs will be using GTI's, (Grid Tied Inverters) that take the PV DC output and change it to AC and feed it back at a few volts more into the Mains Utilities Grid for that Country.
These GTI's are slave machines and need to see the correct AC voltage and the correct HZ frequency, so to get their internal electronics/transformer to operate before they will feed into the Grid a few volts over the Mains Utilities supplied voltage. 

There are many Good Quality GTI's available second hand, i use fleebay etc, and i prefer GTI's with a toroid transformer,   see below photo of previously used SMA's........ .       80 Euros each. 



Now our 48vdc ‘OzInverter’ creates a very stable 240vac or 120vac at a stable 50H or 60HZ, depends on your country domestic voltage, and therefore allows 'AC Coupling'.   The GTI's back charge through the ‘OzInverter’ to the battery bank any surplus power not being used on the OFF GRID or we call our ‘OzInverter’ created MINI GRID.

Three methods of controlling the back charging from GTI's is possible for 'AC Coupling'. 

A.   Use the Internal codes/settings in the GTI's to sequential shut down when a specified ac output voltage is reached. This works reasonably well with my system as some installations GTI,s are up to 400 meters away from the ‘OzInverter’ and batteries, and the batteries do push back slightly, but this depends on the cable voltage sag.   

B.   Use dc voltage comparators circuit to shut down the GTI ac side with a relay when the DC battery voltage rises above a charging rate voltage. But you will need to run a data cable to all your installations, and again allow for voltage sag. 

C.    Use PWM dc controllers that are connected directly to the 48vdc battery bank. These Diversion controllers, (Morningstar Tristar PWM at about 200 Euros each), will regulate the charging and any excess power when the batteries are full and will dump/divert to other permanently connected sources, ie, Air Heaters 2kW each or Hot water heaters, underfloor electric heating, etc.

The above are a cost effective and very reliable system.
A. is used most, and C. is my guaranteed safety system. Where i do not have access to the GTI internals, then i use B. 

For a 19kW Array I prefer using 2off 1.7kW & 4off 2.5kW GTI's for 14kW, and i only use DC Charge controllers for the 5kW as these can gently finish charging that precious 48vdc battery bank. I also have 3off Hugh Piggott design wind turbines, DC coupled direct to the 48v battery bank

NOTE,   I have not used a HF, High Frequency GTI, because second hand old heavy toroidal types are easily obtainable and very cheap, plus you get to use the GTI internal MPPT .   'Oztules' and others have experimented with HF types and do not find any real difficulties.
NOTE.  Its best to use GTI’s at a max output of 2.5kW as above this the GTI tends to surge on a long cable connection.
 
I trust this information helps. I can go into each mentioned process far deeper if you so wish.?

So is your Mini Grid Inverter truly Bi-Directional.?

[bigrockcandymountain]

Perfect.  Thanks clockman for a great write up as always.

No, my inverter is not really bidirectional at all.  The AC input(for me generator power) is a separate set of terminals and when the inverter sees power on there, a transfer switch actuates, and the inverter becomes a charger and the generator power just flows through the inverter and out the other side to power loads.  The inverter siphons off some power to charge the batteries.  It works well, but it seems like coupling ac to the output side will not work with this inverter.

I'm still not there on the building an oz inverter but i think I'm getting closer every day.  What is the learning curve like for someone with very basic electrical knowledge, zero code writing knowledge. Etc? Also, is 120/240v split phase north american power more difficult?

The inverter i have is rated at 4400w and about 8kw surge.  It won't start a 3hp single phase induction motor though.  Getting an ozinverter ready for when it gives up would be a good idea. 

[clockmanFRA]

No, you don't need to write any code, as we use the 8010 SMD chip which according to 'FRACKERS' has about 64k of code already written in it.

 Its the soft start that with large toroid's needs to happen, because a toroid can pull huge surges.

You just add in a centre tap when you are winding the secondary on the bare toroid, so 130 turns then take a tap at 65 turns, this means that all the control board stays the same, but with the taps you get 120vac on each side of the tap and 240 on the main secondary winding of say 130 turns.

I explain and show lots of photos etc, in the book.

Sometimes its best if you have a reasonable mechanical engineering skills as this is real POWER electronics/electrics, and some just electronic guys find it a challenging doing the chunky stuff.

The 3 PCB's are all through hole components and all readily obtainable,  and the only SMD 8010 processor is fitted on a  daughter board.  The PCB tracks are wide and large and the solder points are reasonable large to avoid PCB substrate separation.   The PCB's were deliberately designed to be easily repaired and components replaced with out difficulties, ie we kept it simple and robust.

Anyways i point out the critical bits.

Trust this helps.

[Scruff]

Afaik the easiest way is with a toroidal design inverter.

New fangled "hybrid inverters" can do it too. Most old skool rugged low-frequency ones can do it intrinsically (Studer, Trace, SMA, Victron) as a neat feature of the topology although the more primitive of these require diversion control or another means of AC throttling. Although the train crash method of inverter overvoltage disconnect cascade trigger anti-islanding is an employable method.

CM...ya said it yerself...ya bought a Rolls Royce... ...
...for those not inclined to build one...buy a Toyota.

[clockmanFRA]

The words i normally use are , "supposedly the Rolls Royce of the Renewable energy world".

But you are correct Scruff, scarcely so. Damon i think Scruff has friends everywhere keeping an eye on us all. LOL.

But Yes i do like Toyota. Always had Toyota since the 1980's.

I have a Toyota Avensis that is 8 years old, its diesel, most cars in France are diesel, but this Toyotas diesel is the last one they made for this size of car, now they fit ones that are made by BMW,. This Toyota has fantastic minimal emissions, ie, each year the tester has trouble finding any emissions coming from this particular design of diesel.

[Scruff]

I bought a Bentley of the marine energy world. That was a lemon too. It died. Twice. Said the mustard was too hard or the knife too blunt or something.

You could broaden "Toyota" to Japanese. My 2 Mitsubishi's are 20 year olds. The power to weight is high by modern standards. 1.3litre, 4 bangers.

So I might have access to vast quantities of Studer Xtender 24Vs, 2.4kVAs and maybe some 3.5kVAs left....pm me if yer interested...better than half price...

[Bruce S]

And Mods, sorry about mentioning OzInverter stuff, but just trying to explain a AC Coupling system that has been fully operational from 2015.

CloackmanFRA;
No worries from me ! You proved yourself a long long time ago.

Cheers
Bruce S

[Scruff]

Attached is a document I requested from the Swiss. Interesting scalability concepts. I reckon I could implement their system topology described within.
It's of more community cooperative-based utility than Moe Solo...I could commission a mini-grid in my workshop just to have one to play with.
The inverters have all the required parameter controls built-in. Versatile dofers...I can't imagine much I can't do with one..

[clockmanFRA]

Good general coffee table document Scruff, but not much detail info, also not sure of date, nice to have known battery size etc.

Yes STUDER are a well known for their control equipment.

But, and here's my big BUT!, .......... Frequency shifting is something that STUDER, SMA etc, have been pushing in the AC coupling route for well over a decade now.

 I have tried a Frequency control system but, and another big BUT!, ....... in real situations with AC voltage sag from one building to another and adding later additional Power into the Mini Grid system causes all sorts of issues, especially if charging battery banks and having DC coupling to that battery bank. 

The solution from STUDER, SMA etc, is to have control and feedback systems for every bit of the MINI GRID system, ie, so a MIDNIGHT DC controller can be regulated and controlled by a master circuit supplied by STUDER, SMA, etc.  (I know that MIDNIGHT do this with software for the Classic controller with SMA interface).

Now this to me defeats the system of a so called simple MiNI GRID system so heavily pushed by SMA back in the early 2010's years where frequency control for AC COUPLING would be the 'Holy Grail'.

Looks good on paper, BUT, ...... In real environments of the Off Grid or creating your own MIN GRID for many independent buildings, the frequency shifting has to be precise, and sadly it is not.  Unless you have all that extra control equipment, buses, Hubs, PSU units etc etc, all off course proprietary supplied by the Manufacturer or approved by the said manufacturer. 

This of course suits the STUDER, SMA etc of this world, as you are locked into their complete never ending proprietary equipment.  What i dislike about these companies is that all this extra control gear is not mentioned in their sales or pre-purchase literature.  Yea, you get some folk saying but you should rely on an approved technician fitter to set it all up for you, yea right, seems like a open cheque book where the costs start to outweigh the benefits.!.

Okay, you and me both know that Off Grid systems, or MINI  GRID systems are never the same in real life.

When you get to running a complete house /dwelling or several buildings, you need real gear, and not 'toys' or manufacturers saying overrated energy outputs that just do not supply sufficient power,  for those normal family life expectations.

 And all folks that have or want a AC COUPLED system have some very important factors in there minds.   
1.      How does it work for me. ?
2,      How complicated will it be, so i can install it all myself, i can maintain it, and repair it myself.  ?
3.      And very importantly HOW MUCH WILL IT COST!  ?
4.      If i start small and if i keep expanding as Funds allow me, i don't need to keep upgrading everything. ?

In this day and age of ever rising energy prices, lack of energy supply, rationing of energy by utilities, i would like to think that Governments would allow easier access to a Self Energy creation systems for small groups of dwellings. And allow easier ways of forming small community cooperatives of energy suppliers, where everyone in that community has Pv on the roofs or renewable energy generation, and are AC COUPLED to that communities created MINI GRID. 

But!..... sadly Manufacturers of the present Renewable energy creations equipment just see big opportunities a head, with over inflated prices. And its their duty to try and get stuff as complicated as possible so they can sell more electronic gizmos, which of course is what the share holders want.

All this i personally found out in 2015, and with thanks to 'Sparweb' and 'Oztules', who already knew all of the above, put my mind at rest and illuminated my creative and dexterity skills in the correct direction.

'Oztules' also saw that the AC COUPLING was a distinct possibility for simple but larger installations, and hence the OzInverter was deliberately created with the H Bridge design to allow the inverter to be Bi-directional. 

However, since the design and making the SIMPLE, ROBUST, COST EFFECTIVE OzInverter, several of the renewable equipment manufacturers don't particular like me, one even having a legal threat over me, not to talk about their 'crap toys'.

Other manufacturers have said to me about all the stuff we do here, "Your stuff works, but its just far to simple, lasts far to long, and is far to cheap, so there is no profit margin in it for us."


Thanks Scruff for getting me talking, or ranting, I will sort out the above for proper condensing and publication.

Scruff, I am not quite ready to Join the 'Greta' brigade.  But,  the present commercial business model will have to change for sustainable growth and continued humans living on this planet.
 Sadly i get the impression today that most Humans don't really care, as they have enough hassle coping with every day real life.
  But, yep another but!........ I am ever the Optimist, my mothers side, so there is hope for me by showing others that also show a glimmer of interest.





 

   

[Scruff]

Comparing Studer to SMA is night and day CM.

The Xtenders work. No external hardware needed. Their effecticve frequency operating window is 48hz to 52hz. Voltage drop is irrelevant for this purpose it's signal is zero-crossings per second.

I know SMA led you up the garden path and when you started to scrutinise it they just threw BS at the issue.
Studer are more like you and I. They use their own products and stand over them.
It works....if I get really bored I'll prove it.

[clockmanFRA]

Not actually had a Studer main Inverter that push pull, runs on batteries and AC Coupling.

Go On scruff get a real working STUDER example to convince me that frequency shifting works on a minumum of 5 STUDER GTI's Inverters that are AC COUPLED on the same mini grid.   This i have to look see........

[bigrockcandymountain]

I love the direction this thread has taken.  Looks like we all might learn a few things here.  I'm off to educate myself on frequency shift so i can keep up. 

Maybe you guys will go in to specifics of the ways this can fail in the real world and the ways to overcome those failures for those of us who haven't tried it.

[Bruce S]

Having been around long enough to watch the build that ClockmanFRA and Otzules went through along with having read the entire book.
This along with the details that Scruff continues to post.
I'm with BRCM on this! I'm watching with close interest where this information will be going.

Cheers
Bruce S

[clockmanFRA]

Okay scruff, if you can get a STUDER hub unit to manage freq shift safely and stay within parameters then i may change my mind  on the concept.

AS you know the management of the frequency is flipping important. With that 'toy machine' i purchased, i lost a washing machine, microwave and other domestic appliances when the Frequency just went crazy and defaulted to 60HZ from our European 50HZ and the GTI's were never fully under control.

However i do have an open mind, especially if STUDER's hub unit can deliver, and that it is not stupid money.

OzInverter ......
I have looked at our data for the 8010 PWM chip that drives the OzInverter. Reading the specs it is possible to alter the frequency setting to a variable frequency arrangement.

8.6 Frequency Setting
EG8010 has two frequency modes: constant frequency mode and adjustable frequency mode.
In adjustable frequency mode, EG8010 only uses unipolar modulation, and pin (20)MODSEL has to
connect to low level. Pins FRQSEL1 and FRQSEL0 set the frequency mode. In constant frequency mode, “00” outputs 50Hz frequency and “01” outputs 60Hz frequency. FRQADJ has no function in
constant mode. Pin (16) is used as VFB2 voltage feedback circuit under bipolar modulation. In
adjustable frequency mode, “10” outputs frequency in range of 0-100Hz and “11” outputs frequency
in range of 0-400Hz. Pin FRQADJ adjusts the frequency as shown in figure 8.6a. Pin FRQADJ’s
voltage varies from 0-5V, which is corresponding to the fundamental wave output frequency from
0-100Hz or 0-400Hz. This function accompanies with pin VVVF can be used in the single phase
frequency transformer system.


So i would need to design and build another 2 control boards that are 50HZ frequency shift and another 60HZ frequency shift and alter the pin settings and incorporate a circuit that has a variable resistor that controls the chip voltage between 0 and +5v, , however some serious testing would be required to get a stable circuit and also set the the plus and minus frequency parameters STUDER would require. Then we need to to have a battery monitor circuit that then alters the frequency on the variable resistor voltage.

However this caught my attention regards frequency shifting .......   
8.7 VVVF (Variable Voltage and Variable Frequency Mode)
To ensure motor’s electromagnetic torque is constant while varying frequency, setting
VVVF=“1”will keep the value of V/F at a constant, Voltage is adjusted as the output frequency
changes. When VVVF=“0”, output voltage is not changed when frequency varies.



So it looks possible Scruff with the OzInverter, what does the STUDER HUB actually want?......

[clockmanFRA]

Okay Scruff, a quick search and Studer says this.

The Xtender is a true energy manager, unique and compact, that has 5 main functions. It can be an off-grid inverter, battery charger, current injector, transfer system and provide support to an AC source. With these functions, the available energy can be managed and used in an intelligent and efficient manner.

Reading the above, makes this a Main Hub Inverter unit, interesting that it can be stacked and fine tuned.

However the Steca Xtender XTH 8000-48  is here in Europe 6,806.€   thats $7,899
 Studer says, 46kgs, idle power used 30w, 5.6kW runs, 6.4kW for 30 minutes, 16.8kW for 5 secs.

HMM all that sounds familiar with another commercially manufactured Inverter unit that has about the same specs on the toroid transformer.

OzInverter when built to specs, about 50kg, idle power about 33w, runs 6kW, 10 to 15kW for about 30 minutes, Surges up to 50kW.  not tested for 5 secs though.   'Oztules' was correct, on real output power and self build cost, the commercial boys can not beat the OzInverter design.

 

[Scruff]

Terminology;
DC coupling: synchronising voltage of DC sources aka turning them on.
AC coupling: sychronising voltage, phase & frequency of AC sources aka potent electrickery.

The SMAlly Islands have no problem AC-coupling. The issues you were experiencing were with throttling implementation CM.

GTIs AC couple, they have to. Anti-islanding has so many helpful triggers to play with...voltage, frequency, source voltage presence..

My Studer-AJ (Lead-Fi) and XPC (Leadite) inverters cannot syncronise to a phase. If you synchronise a phase to them (AC couple say a GTI) they charge the battery. There is no throttling. The AJ doesn't actually officially have a charger. The battery inverter will trip over-voltage and knock out the GTI on anti-islanding..I call this the train crash method. A little more ingenuity gets you battery voltage-controlled relay bang-bang method. Or you could employ diversion control.

My Xtenders can synchronise to a phase and use that to augment output, charge a battery and/or backfeed.
They can also receive a synchronised phase and use that to charge a battery and or backfeed.
They can use frequency and clever relays and alarm trips to signal or control a power source present at it's output, in islanding mode...if that power source responds to these deviations. ....most respond to the bang-bang method. In grid-tied operation, throttling is not necessary.

I haven't dabbled with frequency control as a means of throttling AC coupled power sources or triggering opportunity loads nor load shedding..

I use the grid as my reliable dump load, anti-islanding to knock out the SB-1700 and a TS MPPT to keep her lit.
I can pilot the SB1700 on manual control in a powercut involving immersion diverter CT migration.
Attached is report on how an Xtender can frequency control an SB-1700 as a second stage PWM-esque Charger.

More modern GTIs have proportional frequency deviation throttling.

[Scruff]

Go On scruff get a real working STUDER example to convince me that frequency shifting works on a minumum of 5 STUDER GTI's Inverters that are AC COUPLED on the same mini grid.   This i have to look see........

I only have Studer Battery Inverters. My GTI is a SB-1700 in Studer Grey. Steca are re-badgers by the way.
Nobody makes a good everything. I won't be a brand whord.

I've been stirrring that Studer mini-grid in my noggin' wondering A: where's the application suitability and B: How do I do it.
For all 6 of you following along that may have read the pdf let's see if we can extrapolate a control mechanism for that unique and clever system. The answers are in the document if you know the hardware well enough. The prime purpose was to share over-production (like normal GTIs and utility networks)

Overview:




Constraints:



Potential Method*
(*theory) I've asked for clarification...it's not as forthcoming as installer permission access.

You'll need a remote.










{Edited}

Yes! Well spotted! 4 and 5 are the same! I'm not sure if using the AUX 1 relay to trigger the Remote Entry (by software) is necessary...because that would reduce the potential to optimise production in Zone 1 so I expect it's in the mini-grid parameters. {Edit: added SmartBoost (input limit)}

[Scruff]

Oops...forgot six...twas on another page..

[clockmanFRA]

Yes, i can see what Studer are trying to do.

Thanks for the tip on STECA's GTI's.


For the benefit of other Forum members reading this Thread, so sorry Scruff, I am not trying to tell you how to suck eggs.!

Okay your definition of DC Coupling is different to mine.

I am talking as a whole system with one 48v dc battery bank, and AC 240v.  ........

AC coupling is using the output from the GTI's that is now AC at say 240v, and now back feeding through the H Bridge design OzInverter and now coming out of the OzInverter as DC raw at about 60vdc. This Dc voltage and AC voltage pushing into the H Bridge is very much regulated by the Secondary windings accurate turns  count, that only see AC, this secondary can push out or receive into the H Bridge. 

Now the Primary windings, again exact turns count, are DC only output, or DC input. So the OzInverter runs from the batteries when, for instance there is no wind or no sun, (night-time) or no hydro. Then the battery bank is keeping the MINI GRID operating.
Sun comes up on the PV installations, MINI GRID starts to see the GTI's awake, the GTI's see a stable AC voltage HZ on the MINI GRID, and is within parameters and start back feeding AC into the MINI GRID.
 
If The MINI GRID has power consumption going on ie, morning electric kettle for coffee, then the voltage drop from the kettle on the MINI GRID is pushed back up by the GTI's.
 
Once the OZInverter AC control board settings are reached then the AC goes automatically through the H Bridge and becomes DC and this DC pushes back into the batteries.  Its Raw DC up to 60v.

Okay we control the DC battery charging by either of the 3 MAIN METHODS that i have already mentioned earlier in this post.
Also note that out of my 19kW of renewable energy sources, 5kW is directly to MPPT DC Controllers that can assist re-charging the batteries or just act as a trickle charge as the 2 DC controllers are also connected to the DC battery bank.

However, DC COUPLING for me is where my 3off 12 footers,3.7m diameter wind turbines are DC output at about 61vdc, and because of the nature of wind turbine need to see a constant load, no load and they go supersonic and your picking up the bits. So the DC load is the battery bank. 

SO my 3off wind turbines DC COUPLED direct to the battery bank can be wild and the voltage rise and fall quickly. I have 4off Tristars set on diversion load and these will dump from the battery bank anything over the charging regime they are managing.
And Tristars are good at that and very robust and virtually bullet proof charge controllers.

What i find is that most commercial Inverters, from a 48vdc source to a AC 240, voltage struggle to cope with the DC COUPLING from Wind Turbines and my 5kW PV also DC charging the battery bank.   It seems that the commercial Main MINI GRID Inverters want to be in charge at all times and can not cope with the the other DC COUPLED charging sources.  Great on paper but real life installations most folk want a mix of DC COUPLED sources and AC COUPLED sources on the same system.

For OzInverter's its not a problem we kept everything very simple so the OzInverter is the gate keeper between the AC sources and the DC sources, and happily automatically shuffles between them.  Again this was a deliberate simplicity well discussed by me and John, (Oztules).
 
Voltage Sag, most of you dealing with electrics/electronics just dismiss this but here voltage sag is important. Its funny watching calibrated AC meters all showing different voltages, only a couple of volts around our MINI GRID depending on location and power use at that location, this means that i can get the the GTI's to automatically sequential shut down, (when battery is charged and no other AC Power being used), depending on their location.   We have 16mm/2 main AC 240v MINI GRID power feed to all our 9, to be 10 soon, separate buildings installations, so from one end of our property to the other can be up to 1/2 mile away.

What i understand from the commercial boys is that there Main MINI GRID Inverters would be based around PV as that was the main market. And as i have been told by the commercial boys DC COUPLED devices integrated into a system are a problem.

Okay Battery charging in the winter if you must.

Generators are expensive to get a suitable one, HZ and voltage stability, to AC feed into the Ozinverter created MINI GRID. So I recommend, actually John, 'Oztules' in 2015, using a AC rubbish output generator through a modern lightweight INVETER WELDER and using the DC output direct onto the Battery bank, battery bank should be above 800ah capacity. Its RAW DC at about 60 volts so be careful when the batteries get charged and start pushing back and the TRISTARS battery charging controllers diversion loads start dump working.

As 'Noneyabuisness' has said..........  https://www.ebay.com.au/itm/Giantz-250-Amp-Inverter-Welder-DC-MMA-ARC-IGBT-Welding-Machine-Stick-Portable-/392043456772?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=705-154756-20017-0

Anyways, Scruff we are just trying to keep stuff simple, robust and cost effective. OzInverter not expensive, Tristar's controllers not expensive, second hand GTI's are not expensive, Inverter welders used as battery charger are not expensive, battery bank, hmm still working R&D on my PLANTE design batteries. 

[Scruff]

I'll try tell ya how to blow an egg CM!

Okay your definition of DC Coupling is different to mine.

Quite. I mightov made mine up. If I couple AC to AC I get AC but you get DC?

What i find is that most commercial Inverters, from a 48vdc source to a AC 240, voltage struggle to cope with the DC COUPLING from Wind Turbines and my 5kW PV also DC charging the battery bank.   It seems that the commercial Main MINI GRID Inverters want to be in charge at all times and can not cope with the the other DC COUPLED charging sources.  Great on paper but real life installations most folk want a mix of DC COUPLED sources and AC COUPLED sources on the same system.

My powerplant Xtender handles AC coupling fine and DC coupling fine. It's tripped it's own over-voltage threshold by latent backfeeding response in..you know those cold Autumn days when sunbeams are lensing cloud edges like an eyefulla arc weld and the array pummels the system with surges. Hitting two moving targets at instantaneous max output ain't easy. I could increase the Over-Voltage alarm trip. At the moment I've AC coupled one Xtender and DC coupled another.
The LFP is AC Coupled.

It can trip it's own over-voltage with SmartBoost hysteresis too if the threshold is too narrow.
I have yet to see if my 7kVA twinset fair any better managing a system built entirely of other manufacturers' supporting hardware inclusive of 4kW mixed couplings.

What i understand from the commercial boys is that there Main MINI GRID Inverters would be based around PV as that was the main market. And as i have been told by the commercial boys DC COUPLED devices integrated into a system are a problem.

I know that smell CM. You do too. All too familiar.
"Professional" installer says putting a DC charger on a DC effin' battery is a problem?

Okay Battery charging in the winter if you must.

Investment Return Pyramid;

Solar versus Utility : Solar
Small Wind versus Utility: Utility (eDiT: moved up on the grounds of positive return potential...if most of the following are true: turbine is capable, turbine didn't cost the world, neighbours didn't protest, maintenance costs are low, average site wind speed and hub height is >5m/s without turbulence...ie. site specific)
Battery versus Utility: Utility
Diesel versus Utility: Utility
Utility versus Utility (V2G): Just don't!

Solar versus Battery: Solar
Solar versus Wind: Solar both together!
Wind versus Battery: Wind
Battery versus Diesel: Battery
Diversion versus Storage: Diversion
Export versus Storage: Export

Overproduction best deal (in order of personal precedence):
Heat water - Give it away - Store for later


Nice use of voltage sag as a trigger. Simple. I woulda tried to "fix" it.

I think calling the OzInverter not expensive is overlooking a vast amount of invested time in it's development.
Didja ever invest 2000 hours in a project before?   


An obvious way to make a lot of systems more beneficial is to unify them.

Solar lamp-post? Shyte!
Solar coupled installation with a lamp-post? Doing it right!

[bigrockcandymountain]

Looking at your pictures that are, i assume, out of the studer manual makes me scratch my head.  Why on earth would you want dispersed batteries if you are forming a mini grid. It's almost like they want to sell a bunch if expensive electrinic equipment.

In my caveman brain, the reason for a mini grid would be to have one large, central battery.  Then all you would have on your house would be solar and a grid tied inverter.  The main battery inverter would be in the shed with the batteries.  You could have generator backup and even medium scale wind collectively owned and feeding the battery dc. 

I also see no problem charging a dc battery with as many different sources as necessary, all at the same time.  I have done this lots with no ill effects.

Using a frequency signal is a great way to shut down or modulate the dispersed solar gti systems though. I can see the light that far at least. 

[Scruff]

Looking at your pictures that are, i assume, out of the studer manual makes me scratch my head. 

Not the manual. I requested it.
Have a read of the attachment in this post.

Why on earth would you want dispersed batteries if you are forming a mini grid. It's almost like they want to sell a bunch if expensive electrinic equipment.

Expensive to get cables in parts of Switzerland.
I can make 3 phase with inverters cheaper than asking the network to cable me in two spares from kms away.

In my caveman brain, the reason for a mini grid would be to have one large, central battery. 

That's an inverter not a network (grid)

I also see no problem charging a dc battery with as many different sources as necessary, all at the same time.  I have done this lots with no ill effects.

One example is one charger can regulate the absorption better than two because it's reading a battery voltage at it's terminals not a battery and third-party charger.
Unless they are clones pparralleell chargers are not better than singles. However single is not always practical and if the system is under constant load then it doesn't really matter either.
Specifically, CM is saying certain products aren't becoming of the self-professed talent to orchestrate/abide it without negligent harm to the user's end loads and installation while also referring to the propriety turn of hardware integration for modern contrivances of questionable intent.

Using a frequency signal is a great way to shut down or modulate the dispersed solar gti systems though. I can see the light that far at least.

It sure saves a lottov cable. Don't say it too loud though..I think CM is still upset about the washing machine! ....what? Oh!...and the microwave...

[bigrockcandymountain]

Ah yes, now that it is in context it makes a lot more sense.  I didn't read the whole thing.  I got to the point where they said there was no metering and paying for shared power.  My mind then wandered into "how would you make this sharing work financially?"

Frequency shifting sure looks good on paper.  I hope no more microwaves are harmed before you guys get the details sorted out though.

I hear you on 3 phase and the costs of running wire.  I'm running a vfd to make 3 phase for my lathe.  My inverter can be networked with 2 others to make 3 phase too.  I think it needs a router in the mix though to make it work.  It's been awhile since i looked through the manual.

Hmm, I think we have a different idea of the definition of mini grid too.  I would define it as exactly like the main grid, only smaller.  A central power generating source and houses hooked up to it through ac lines.  I'm not saying that is right, that is just how i pictured it up to now. 

[Scruff]

Frequency shifting sure looks good on paper.  I hope no more microwaves are harmed before you guys get the details sorted out though.

You know how welding is extremely high skill & difficult...until machines started compensating for users and setups. Very $$$$ machines that make it look easy?
How 4x4 was high skill & difficult...until electric drive came along with regen braking and 100% torque at 0 RPM?
Seamless frequency shifting throttling is the hardest thing you can ask of an off-grid installation that I'm aware of. Making it look easy is an accolade to the expertise and fidelity of such a product's engineering.

I hear you on 3 phase and the costs of running wire.  I'm running a vfd to make 3 phase for my lathe.  My inverter can be networked with 2 others to make 3 phase too.  I think it needs a router in the mix though to make it work.  It's been awhile since i looked through the manual.

If I get three-phase the next thing I'll need is a forklift to move in my new appliances. 
I can use one phase to power the other two with utility via the coupled phase's battery charger.
I can also run integral mode that cuts all phases if there's an imbalance on legs.

Hmm, I think we have a different idea of the definition of mini grid too.  I would define it as exactly like the main grid, only smaller.  A central power generating source and houses hooked up to it through ac lines.  I'm not saying that is right, that is just how i pictured it up to now.

Terminology is muddled with marketing and confusion. The people making schlick marketing pdfs haven't a clue what they're pitching in a measurable context.

"Coupling" is connecting two things.
AC Coupling and charging a battery on a transformer secondary are exclusive.

An AC Coupling inverter can adapt it's voltage, current and frequency to synchronise or couple to another AC power source.
Most AC coupling inverters can then use that coupling to charge a battery...because otherwise what would be the point?

DC coupling. You connect a wind turbine to a battery they are coupled. The battery charges as a byproduct of the process.

Strictly speaking The question; Can I AC couple this and that is specifically: Can I synchronise it?
Colloquially is it expected that accompanied to this process is a battery charger and an input throttling mechanism. This actually (to my understanding) has nothing to do with AC coupling. It's like saying I have a DC transformer or an AC battery.

Way back on the introductory post you mentioned AC coupling your GTI to your inverter. You can AC couple a GTI to anything..it's designed to. What we are really asking is will the system retain all it's smoke if I do.
Hard to say.
Yes if you can use all the power the GTI is producing at all times.

Some inverters can divert it to battery charging and limit input if necessary.
Some inverters can divert it to battery charging with no input limit.
Most inverters go bang...if it doesn't say hybrid or give you a hernia to mount it then it'll probably go bang.
Or trip for a few instances before going bang.

The problem that's always been with AC coupling is how to turn a GTI into a charge regulator. Not because AC coupling is defined by battery charging but that's an obvious place to use it first...but the next part...when the battery is full, is the real kicker...
AC diversion control is the external solution. Treat your GTI like a wind turbine.





A grid to me consists of multiple connected installations interacting but independently managed. In simplest terms two or more voltage sources that can be synchronised.

Off-grid I interpret as multiple connected devices.  If you share; it's a grid. If you own it's an installation with an inverter. Maybe it is a grid...off-grid-grid..no needs a flashier title...teal?
If you share with yourself?! Bets are off.

[Scruff]

PS your inverter isn't AC coupling Big Rock your GTI is.

[clockmanFRA]

'Scruff', your comment, ........... "I think calling the OzInverter not expensive is overlooking a vast amount of invested time in it's development.
Didja ever invest 2000 hours in a project before?   "

Yes, i do invest alot of time in very strange projects over the years. This big project here,..... still at it 20 years later, another 4 years then i can put my feet up. yea doubt that.

 I can, from scratch have a OzInverter working and finished in a week.

Parts of a OzInverter are about $800, if you salvage the toroid cores then even cheaper. The 2nd edition OzInverter book and the 3 off PCB boards did take alot of time, yes. 
 But very satisfying to see OzInverters working all over the World and built by ordinary folk with reasonable skill and reasonable dexterity skills.
If you stick to the books instructions and follow the explicit guidance you cant go wrong.

As you know the PCB's are especially designed for all through hole components but also have large solder pads, large tracks and tuned tracks etc.
 As 'Oztules' said,......   

“Looking good.. now with just off the shelf components, we can finally make a real inverter.. that is easy to fix as well. utopia indeed for remote living I don't think any other unit on the market can say that.... usually you have to replace propriety boards... if you can get them." . ‘oztules.’

But, perhaps I am banging my head against a brick wall in these present times, because most of the Humans want stuff now, don't want to learn, and don't want to pay anything.
Being ever an optimist, i do find a few that want to go forward, and that is always a satisfying pleasure.

And besides there are nice folk on this forum that offer lots of encouragement.!

[Scruff]

Putting a pin in niche applications like mini-grids and frequency-shifted triggering...my preferred use of a "hybrid" or AC Coupling battery inverter that can charge from a GTI and export excess is the ability to turn anything surplus to absorption requirements to utility network power (back-feed).
That means anything I buy on eBlague that makes a 24v battery >26.6V can be grid-tied. Powering my running loads, heating water and trickling onto the mostly fossil-fueled network.

For the record my Hybrid Inverter plays nicely with third-party DC coupled hardware. Your mileage may vary.

[Bruce S]

 hmm still working R&D on my PLANTE design batteries.

Any luck on moving forward on this? Will you be going with a see thru container so you can see what's happening?

Bruce S

[clockmanFRA]

Yes Bruce, still plodding away, just got alot of over more important stuff on at this moment in time.

I have just checked and it seems that polypropylene does come as transparent and workable, so therefore can be easily injection moulded to what ever size i require.
  However its making a slightly tapering shape and having internal ridges in the insides for plate support that needs a lot of practical experimentation as this will set the case thickness.

[Bruce S]

ClockmanFRA;
I won't deviate much more on this posting.
Since I read your first posting about this I've been researching about as much as I can without building some too, especially since they can be built to your specific voltage needs.

Cheers
Bruce S

[clockmanFRA]

Okay Bruce,

I will start a post at some stage on the PLANTE battery making.

Just to reply to you Bruce.  Yes the cells can be made to whatever you want, however for standardisation i will stick with just 2v cells at, and this for me is crucial, about 50kg /110lbs, ie what a single person on there own can cope with lifting.
Also i will stick with 2v output for each battery so i can really get the Amperage up.  'Plante' Battery with the right lead plate thickness will last a real life time, but the amperage is about only a third to a half when compared to a good commercial manufactured 10 year life battery that is a lead matrix oxide paste plate system.

Phillip Hurley's book, 'The Battery Builders Guide' is interesting and mentions his attempts at a PLANTE battery build. However the work he did is minimal in his book about the cell it self, as he seems to have got bogged down with the hardware and messing about with molten lead.  But it does have a few sentences that are 'gems'.