AC COUPLING, OFF GRID & MINI GRID & back charging batteries.

[clockmanFRA]

A brief information document for those who have allways wondered.

RENEWABLE ENERGY.
‘OzInverter’ Mini Grid & 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 to function and back charge the batteries correctly. And thirdly It raised the 240vac HZ frequency from 50HZ to 60HZ and domestic equipment failed.

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


'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 15 to 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........ .       150 to 300 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 ‘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 using DC Charge controllers for the 5kW as these can gently finish charging that precious 48vdc 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.

[noneyabussiness]

There is also " method D "

Pwm the dc side of the inverter, effectively having a variable " cloud " on the OGI , controlled via a arduino..

Good write-up as always though... informative ..

[clockmanFRA]

Hi noneyabussiness,

Yes a 'Method D' is a possibility, and i have seen them made and put into action.

The GTI input from the PV panels is controlled, depending of the state of charge of the battery.

However, i have not implemented the 'Method D' as i have no personal empirical evidence, and i have reservations on the 'Method D' when used with multiple GTI's. 

[Scruff]

Method C and D sound the same to me.

Method C would be my preferred

Method E: Frequency variation triggering.

Method F: "Let 'er buck" let the AC coupling inverters trip over-current/over-temp/over-voltage and self isolate taking down the GTI via anti-islanding...I don't recommend it as a method but it works...maybe not for very long if you're using cheap gear though.

[Scruff]

Method G: AC diversion with GTI isolation at a secondary threshold.
ie. Heat water...if thermostat opens isolate GTIs

[Scruff]

If yer not adverse to TRIAC control (I would be extremely anti this method on the basis of the filth it generates on the line).
Method H: DC & AC Diversion, Hugh Piggott's TriStar Follower

[clockmanFRA]

 Hi Scruff,

Your 'Method E' Frequency variation, sounds good in principle, but in real life systems with AC Coupling back charging and DC coupling on the batteries, Frequency variation goes doggy poos!, and the sending System reverts to default the US 60HZ. 

'Oztules' and i, think that Frequency shifting is just not practical.  I actually tried it and it was a nightmare and the control equipment required is way to expensive, but it seems that some Inverter manufacturers like it because of all the extra gear they can sell you.

'Method D' is actually fairly simple as 'noneyabuisness' talks about, and several in Aus have implemented it with there own PWM boards, as i said i have no actual evidence of it working with multiple GTI's.
   

[clockmanFRA]

Your 'method H' is easily adapted with those tristars. I can and do use Hughs method for heating my swimming Pool when i have alot of sun, nothing better than getting in the pool when its 33c or 86f.   

[clockmanFRA]

Scruff,   your 'method E', definitely NO,   Especially if you have 11kW AC coupled to your MINI GRID of backcharging to the batteries, the batteries will get hammered.

Nope, I am happy with 'Method A', 'Method B' and 'Method C'.   They work and are well tested,   there simple working systems and very cost effective,  and are not over complicated for normal folk.

[Scruff]

Your 'Method E' Frequency variation, sounds good in principle, but in real life systems with AC Coupling back charging and DC coupling on the batteries, Frequency variation goes doggy poos!, and the sending System reverts to default the US 60HZ. 

My Studer Xtenders can do it. Fiver says they work better than your ex-SMA jobber.

My preferred is: Method I

Hybrid Inverter, backfeed to utility power.
That's as simple as me clicking "enable" on my inverter (naff all good off-grid).

[Scruff]

Your 'method H' is easily adapted with those tristars. I can and do use Hughs method for heating my swimming Pool when i have alot of sun, nothing better than getting in the pool when its 33c or 86f.

Wanna post a scope pic of your line harmonics for the class with the follower firing at 20% > 80% duty cycle? I'd be very interested.
I've a 2kW TRIAC dimmer....horrendously nasty thing. I must get a screen capture.

[noneyabussiness]

" C " and " D " very different,  C as explained is a variable load on the low voltage DC side that increases with voltage, D PWM's the input of the GTI's directly...

I do agree the diversion load is easy to implement,  and works quite well..

On a side note, Question for clockman, i had mine temporarily on a " bang bang " cycle , dropping out when batterys hit a certain voltage, then cutting back in once dropping below set voltage.  How have your internal relays faired ?? Have you had any problems?? It got me worried, though works well , about wearing them out earlier??

[clockmanFRA]

Scruff,

These http://www.crydom.com/en/products/catalog/mcpc-series-control-relays.pdf are kept well away from all other stuff, and as they say, "use only for resistive loads."

S.. (the german company) i understand intended Hybrid with there SI Inverters, but it seems to get it knickers in a twist.
Studer, Outback, Victron, sorry not had any real experience with them, but looked inside the XW range, and i do love there very well calculated Chokes.

[clockmanFRA]

Hi NB,

Yes, never understood why folk did not like the 'Bang Bang'.   I have my 3kW on that system and as its big it is constantly on and off say 20 times a day.     If you think of the standard working environment it switches on in the morning, it goes off at night, overgrid voltage it bangs off and then on again.  So normal GTI's switch on and off all the time.

Yes i looked at the relay and tracked it down so i could always fit a quality new one, but to be honest its still going 6 years later, and now i have forgotten, (note to self, take photo and add to files next time).

I used to design relay circuits on time switches for all sorts of stuff and 15 years ago the switching cycle on good relays used to be about a million cycles life if when using the specified ratings.   However with modern crap and fake stuff goodness knows.

Next time you open up a GTI, track down that clicking relay for the final Off and the final On. 

[Scruff]

" C " and " D " very different,  C as explained is a variable load on the low voltage DC side that increases with voltage, D PWM's the input of the GTI's directly...

Practically different, principally similar.
I don't know why you'd PWM a GTI. I'd DC couple the solar.

These http://www.crydom.com/en/products/catalog/mcpc-series-control-relays.pdf are kept well away from all other stuff, and as they say, "use only for resistive loads."

I have one CM. I built the proof of concept. Tested it and then threw it into the rainy day box.
I'll get to the "for resistive loads only" in a mo.

S.. (the german company) i understand intended Hybrid with there SI Inverters, but it seems to get it knickers in a twist.

Short-sighted design. If you don't buy into their "ecosystem" it won't work. It's not compatible with other manufacturers hardware and the tech support is only supporting their own hardware. ApprenticeVolt and Macinposh are the same. It's compromised to incentivise you to buy more hardware from them to "fix it"

Studer,

Titans. I've never been able to kill one (apart from the one I force-fed 24v to the microprocessor.. ...that' one's on me). I've never met a bad one that won't do what I want. Built like tanks, exceed spec in a market where everyone else fails to meet it, or not continuously or only if you read the small print, same hardware for 20years, so good it only ever needs firmware updates. They're still untouchable. Throw hole design.

Outback,

You get what you pay for.

Victron,

Substandard hardware propped by marketing and bluetooth. Not built to last. You're paying for warranty, marketing and tech support to blow smoke up your bottom. I've had a lot of their products and I've never met one that wasn't intrinsically flawed and wouldn't have passed QC if the designer had to use it.
They solder their inverter input fuses ffs.

Yes, never understood why folk did not like the 'Bang Bang'. 

because it's very hard on gear. I try to minimise the 100A hard starts. it's shock loading inductors & transformers (vibration), aggressively charging caps, generating harmonics and transients and blowing chunks off contacts of switching elements.

Didja ever see a ferrite shoot outtov a cylinderical inductor like a rail gun? I did that to an ApprenticeVolt Crass Combi.

[Scruff]

I pulled out my 3ishkW I think dimmer for show and tell. This thing is nasty! It's a very similar design to Hugh Piggotts TriStar follower and that crydom proportional relay.



This is how it behaves.



I've hacked that scope. She's now a 100Mhz. 

This is what that output does to my utility grid supply.



Turns it into a Victron.
I've seen worse with immersion diversion products...at the neighbour's house.


I put it on Lead-Fi once and she doesn't like it. She starts growling at it and whimpering at me. It's a very expensive sounding noise.
I put the same load on my 4kVA Xtender



The added distortion is due to the inverter not being as robust as a utility network.

I wouldn't fancy that powering my appliances while the follower was following.
How about we try a 350W induction motor?...



The motor sounds like it's dying.

What's the power factor?




TRIACs are to proportional control what MSW is to inverters.

[noneyabussiness]

" C " and " D " very different,  C as explained is a variable load on the low voltage DC side that increases with voltage, D PWM's the input of the GTI's directly...

Practically different, principally similar.
I don't know why you'd PWM a GTI. I'd DC couple the solar.

  Please explain?? PWM'ing a GTI is incredibly easy, super accurate and your working with very low amperages ( admittedly higher voltages, but easy support with Mosfet/ IGBT ).. it acts as a variable cloud on the input.

Thank you for your practical input clockman, I was always worried about the relays, but we are switching reasonably low  currents and ac voltages.. I do have plenty of spares of the internal relays, just a pain to change them, but if yours are 6 years in with no issues, sounds like I don't have to worry to much...

[Scruff]

I was thinking Solar -> DC charge controller -> GTI as a way to PWM a GTI...I take it there's a less clunky way? Clouds and microprocessors aren't my thing.

[clockmanFRA]

Yes, NB, Low amps and just 240vAC thats why i like switching on the AC side, as most GTI's, my collection i have were designed for AC ON, OFF.

Scruff, All my GTI's switch on and charge their caps when the DC from the panels wakes them up with about 35watts of PV light.

After a few seconds, the GTI looks for a AC connection and switches on a relay, then it spends a few more seconds making sure its 240vAC and is stable and there is 50HZ that is stable, then it engages another relay.
Then another few seconds and the ON/OFF AC connection to the MPPT GTI Relay engages with the output from the GTI to the incoming AC240v.
After a few more seconds if that remains stable then the GTI ramps up its AC output to a few volts over the incoming 240vAC to say 244vAC or whatever the internal setting is set.  Note, the below photo shows 265vac.

As i have said I have altered all the internal settings down to just a few seconds.   
My guest is boiling a kettle 2kW, her daughter is drying a hair 2kW, so the 3kW GTI is direct feeding those appliances and drags another 1kW from the OzInverter Mini Grid.
 
Once the domestic appliances shut down and my batteries are fully charged then that 3kW GTI will try to push up the AC240v above its internal setting on the AC output, and it instantly shuts down with the internal ON/OFF relay.
The DC going into the GTI is still there, the 240AC is still there its just no longer allowing the MPPT AC output to connect and the GTI will every few seconds try to re-establish output AC connection for the MPPT AC,  but the GTI keeps checking and saying that the AC 240 voltage its connected to is over voltage.      The GTI does this a few times then goes to sleep for a couple of minutes.

Now with my lot of GTI's all these times on the internal checking relays can be altered so my lot can respond pretty quick to my guests suddenly putting on loads.     Yes the 'Ozinverter' bridges the gap while the GTI's come on stream.

If the batteries have been used for a bridging the Gap then the GTI's will backfeed through the 'OzInverter' and charge those batteries until full then they push back just a few volts on the AC240 Mini Grid, and 'Bang Bang' the GTI's AC output is knocked OFF on the AC output relay.

Now, if you want to really manage your batteries charging regime then i use those 'TRISTAR' controllers in diversion mode.



NOTE,  When in diversion Mode, No data is recorded on the LCD screen, only what is dumped.

These 'Tristars' that i have, will dump 2kW each into resistive loads , they are PWM machines and are fantastic value, they are also very HIGH QUALITY, SIMPLE and have not failed me over 14 years. I have 4off  so i can dump 8kW. Each stands alone down at the battery shed and are always connected to the battery.
 
I have 3off 3.7m diameter Hugh Piggott wind turbines that are direct DC clamped to my 48v battery, so the Tristars can also dump excess power that comes from the wind turbines.

What i like about the Tristars is that they operate instantly and have good battery charging regime's for those precious batteries.

Mine work and operate flat out, then the next steps in until its flat out, and so on.   They just carry on working even if they are overloaded.

However, the Tristars are looking after your battery, so push back on the 240AC is still there but  its a lot finer so the OverVoltage settings on the GTI's will require fine tuning at each GTI installation.





  OR install enough TRISTARS with dump loads, like this    https://uk.rs-online.com/web/p/panel-mount-fixed-resistors/7015850/    etc to cover your total amount of GTI's 240vac Output connected to your MINI GRID.      OR use DC voltage comparators looking at your battery voltage at each GTI installation to shut down using a relay on the GTI AC Input/Output.   

AC COUPLING i love it.  Many reasons why i love it.

Here is a screen shot of my old laptop with new settings of a 2.5kW GTI on my OzInverter MINI GRID.

 
 

[clockmanFRA]

Mods, would it help if i show photos of all the hardware i am talking about.?

[Scruff]

Sure gents. Bang bangin' GTI's is fine. I'd say anything below 16A is fine especially if it's AC.

Principally I try to avoid it. For 10A inverters designed around anti-islanding....yeah no worries.

I have a plan on using an ImmerSun to PWM into the hot water tank and use it's own relay to turn itself the GTI off when the t-stat opens...I haven't figured out how to turn it back on afterwards yet. I think I might end up looking for an SMA BT dongle instead.

Them ImmerSuns are nearly extinct now...hard to find a good one for the right price. They're all failing from dead FETs or incinerated input terminals.

[noneyabussiness]

Scruff, this is what I'm referring to,  im not sure on the rules on posting a link to another site here, but this is relevant ..

https://www.anotherpower.com/board/index.php?topic=1270.0

One very informative post from oztules, it has been perfected since, but explains it so well as only oz can... there is software and board gerbers if you want to search ..

How clockman does it works absolutely fine too, just another method..

[DamonHD]

Mods, would it help if i show photos of all the hardware i am talking about.?

I can't see why not?

(What trap am I falling into here?  B^> )

Rgds

Damon

[DamonHD]

I have a plan on using an ImmerSun to PWM into the hot water tank and use it's own relay to turn itself the GTI off when the t-stat opens...I haven't figured out how to turn it back on afterwards yet. I think I might end up looking for an SMA BT dongle instead.

Them ImmerSuns are nearly extinct now...hard to find a good one for the right price. They're all failing from dead FETs or incinerated input terminals.

When we all get unlocked I'm still hoping to put together a diverter based on the Eddi.  Do you have any mild and gentle views on it?  B^>

https://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html#Ahoy

Rgds

Damon

[JW]

Scruff, this is what I'm referring to,  im not sure on the rules on posting a link to another site here, but this is relevant ..

https://www.anotherpower.com/board/index.php?topic=1270.0

YES this is fine. Anotherpower were big contributors back in the day. I have no problem with them. If they say no they don't want it here that's fine. Things have change for me since I bought out the forum. They have old posts here and are welcome.

[JW]

Just a FYI since we have Flavio it is possible to transfer all there old posts and build up there forum, but we will still keep a copy of those posts.

[Scruff]

Scruff, this is what I'm referring to......
One very informative post from oztules, it has been perfected since,

Thanks NB...oh dear Oztules speaking in micro-processor tongues...I bet that's what I sound like when I whitter on about...
I'll see if I can decode it later but I really have an aversion to arduinos...

  Do you have any mild and gentle views on it?  B^>

Mild and gentle?!...heaven's to betsy I've no idea what yer insinuating there! I only do honest, impartial reviews me and any products I think are disengenuous I advise manufacturers to forcibly insert them in their posteriors and users to make an informed decision about before hopping on a bandwagon.

The Eddi is too expensive. You're talking a decade of hot water there. Will it still be alive after?
Besides the ImmerSun has two cascading PWM output channels and a relay. The Eddi has one PWM.

My budget for AC PWM diversion is a generous < €150

[clockmanFRA]

Yes NB, i remember that very infomative and inspiring post.

https://www.anotherpower.com/board/index.php?topic=1270.0

Gosh, 'Oztules' could go, honestly had difficulty keeping up with him sometimes.

What i liked about Oztules's work was his concept of keeping his circuits as simple as possible, as just a small add on to achieve what he wanted.  Emperical evedence was his way. But he was also good at holding the post on subject and not getting to distracted, which i know on some other forums he really got cheesed off with folk just not listening and armchair waffling.

Its a bt like that DC battery charger of his,  where he used a FET MMA modern lightweight cheapo small welder after looking at the Specification of the welder decided it was a safe way to charge his batteries when using a 240vac cheap generator with awful HZ frequency control that would be difficult to frequency lock. 

Just a FYI since we have Flavio it is possible to transfer all there old posts and build up there forum, but we will still keep a copy of those posts.

JW, That would be a brilliantly good idea.     Would be fantastic to have a good reference data base, especially of 'Oztules' endevours.

[Scruff]

Its a bt like that DC battery charger of his,  where he used a FET MMA modern lightweight cheapo small welder after looking at the Specification of the welder decided it was a safe way to charge his batteries when using a 240vac cheap generator with awful HZ frequency control that would be difficult to frequency lock. 

The man's a genius. I had that idea lurking in the back of my brain covered in cobwebs.

..I must stop inventing things that have already been invented.
It's funny when I "invent" something conceptually and 45mins later I order one off Alibaba! 

Would be fantastic to have a good reference data base, especially of 'Oztules' endevours.

+1 From what I've seen he's the Alpha Prime of the craft.

[clockmanFRA]

Mods, would it help if i show photos of all the hardware i am talking about.?

I can't see why not?

(What trap am I falling into here?  B^> )

Rgds

Damon

Okay, No trap young man.

Just a thought that some folk who are not so informed on matters such as some honourable forum members.    Might like some pics that explain things a bit more.   It can be wickedly difficult sometimes to get one head around concepts. And English might not be a first language.

[clockmanFRA]

.

[clockmanFRA]

HHHMMM made a mess of adding Photos, and a few more i wanted to add.

My post edit time ran out of time! 

[Bruce S]

Mods, would it help if i show photos of all the hardware i am talking about.?

I can't see why not?

(What trap am I falling into here?  B^> )

Rgds

Damon

 And English might not be a first language.

I'm American , there are those who would say English ain't our first language either  .
Kinda late to this party again, but I agree if the other forum(s) are in agreement, then posting & sharing knowledge then I'm all for it.

I will need another dram of liquid gold before I listen the Otzule talking about micros. I'm still working with Opera's postings about Uno's

Cheers

Bruce S