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Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578

Posted: 11:43am 14 Nov 2021

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This sounds like one of these Simple and Brilliant Tony ideas which a dummy like me is not quite understanding.

Do you put The AC power on one leg of the 3 phase rectifier and the solar on another leg then run the single phase output to the inverter?
Done that with 3 legs from an induction generator before to get a single phase output which the inverter ran on quite happily.

I can see that being Ok ( if the legs of the 3 phase rectifier isolate) where either the solar or the AC or both output to the inverter for a single phase output to drive it, but then How does that tie back to the 3 phase load?
If I hooked the inverter output back to that leg of the 3 phase I don't want to back feed, it still can.... Unless this is where the second Diode you mentioned comes in.

I still don't see how that would work because I'd need the phase rotation and I can't see how that would happen even it it was tied to that leg as It would be through the Diode to isolate the backfeed?? and outputting essentially DC with a Ripple would it not?

I am Sure I have this arse up so could you please spell it out for the intellectually Challenged how this would go together?

What I did before was use a small GTI on that pgase that roughly matched the Current draw of the only load on it which was my AC.
When the compressor kicked in ( the fans on the evaporator and the outdoor coils are powered by the other 2 phases) this pulled in the powered side of A DPDT relay. The resting side went to another phase so when the AC was not running, the power was not wasted. The switching between sides of the relay was enough to make the inverter reset so there wasn't a problem with switching from one phase to another although the when I first put the system together I put in some low amp breakers just in case it tried to output out of sequence. The trip out on the inverters I have used ( couple now) seems very rapid and then after they go through their startup checks which take 30 sec to a Minute, they hook in again and supply that phase and the meter slows down. The inverter powered up and supplied the majority of the power.

Due to the size of the house and the somewhat underpowered AC ( when it falls over Finally I'll put in the biggest Single phase they make which is about double this ones output) the compressor does not trip in and out much during the day and I cool the whole house so it Cool sinks. I have found though getting in early before the place heats up is as valuable as Roger and I have been discussing with the Heat sinking by keeping heating running all the time in winter.

Bit hard to get this right with the inverter power as if I over supply the meter charges me and If I under supply I am pulling from the grid which the meter charges me for and is frustrating given I have more than enough power to feed the thing 10X over on a hot day. Inverters don't output precise amounts however so it's a bit hit and miss to match the supply to the load for that phase.

I was lucky in that I was able to rotate all the phase connections so the one that only drives the compressor has the lowest draw on the phase I can't back feed. That' said, that one phase can still pull a TON of power and still make the thing expensive to run even at a 3rd of the price. The thing did not care which phase went where as long as they were in order. Surprised me but My mate said it should work and it did.

In my younger years I might have been inclined to just bypass the stinking meter but I'm older and more responsible now and don't have the balls ( stupidity) I once did at least in things like that. I -heard- of a guy years ago that put a jumper wire on the old meter so it always registered but also bypassed a lot of power. Things people do when they are poor "eh?

This dinky setup does however allow me to over panel with a constant feed so I have more in reserve for cloudy or winter weather.

I spoke to my mate couple of weeks ago about running a Single to 3 Phase VFD but he was apprehensive. He said he knows the unit I have is really fussy with the phase rotation and frequency and thought there was a good chance that the thing might spit the dummy when the compressor kicked in and didn't advise the experiment. While he installs VFD's all the time, he doesn't stock or use anything I could try and one the size I would need would not be cheap.

If you could elaborate your idea Tony for the perpetually ignorant, I'd be most appreciative.

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 07:50pm 14 Nov 2021

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Its simpler than that ...

Inverter always draws power from the highest voltage source. It will run off 100% solar until the inverter pulls the solar down to the same voltage as the rectifier.
Ideally the rectifier voltage should be set just below the maximum power solar voltage for highest overall efficiency, but its not critical.
Solar still contributes all the available solar current it possibly can, and any shortfall comes from the grid.

Three phase rectifier provides smoother dc output and excellent voltage regulation. Inverter draws a load that pulses at 100 Hz.

If you use just a single phase rectifier, that can produce a lot of 100Hz ripple current that also pulses.
As the grid and your inverter will not remain in exact phase synchronization, there can be wild low frequency voltage swings on the rectifier output, unless the rectifier is voltage regulated.

With a three phase rectifier the outputs from each phase overlap and this voltage swing problem no longer occurs.

Another possible way around this voltage swing problem with a single phase rectifier would be to phase lock the inverter frequency to the grid. I believe Peter has that problem solved with some of his magic software. I never pursued that myself, because I already have three phases here, and its a simpler solution to the problem.

My system is 100v nominally, but this would all work just as well at 48v.

In practical terms it works pretty much like a grid tie system, except absolutely nothing can ever go back out onto the grid. Its the simplest and cheapest way to reduce power bills without the supply authority being aware, or having to buy (and maintain) a very expensive battery.

In a grid down situation it will still work in a fashion, if there is plenty of sun and the load is not excessive.

Its also good because on gloomy days, solar might be quite sufficient to run your refrigeration, but probably will not have enough grunt to initially start up the compressor.
The start up surge is supplied from the grid, and as it only lasts about a second, the grid power required hardly registers.
Even in mid winter where only a few hundred watts of solar may be available, it will significantly lower your power bills.
Edited 2021-11-15 06:54 by Warpspeed

Cheers, �Tony.

Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578

Posted: 10:57pm 14 Nov 2021

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Thanks Tony. I knew it would be brilliant. It's similar to your battery Charger/ Solar idea you put me onto years ago I still use. Solar makes higher voltage through the day and powers the load and as it falls off the charger takes over rill the sun comes up again.

Unfortunately clear, easy to understand Diagrams aren't going to spare you the ongoing questions....

I was of the idea that rectifying AC gives a HIGHER DC voltage than the AC Voltage. About 1/3rd Higher if bad memory and error serves.
Your Diagram shows 120V Output from the rectifier. Is that just your example Voltage and a 230V input would give around 306V or does Rectifying 3 phase bring it down because of only passing half the wave form??
I seem to remember the voltage going up when I Rectified the 3 phase from my induction generators but then I did use 3 single phase rectifiers and tied them together on the output.

I have some Big 3 phase 100A I think they are rectifiers sitting in the drawer but the 3 singles I mounted on a heat sink which never got warm worked so I kept using them.
300V is no problem with the panels anyway. I usually run my arrays around 320V loaded anyhow.

Other question is will this work if I just run 2 Phases into the rectifier instead of 3? There will be increased ripple I surmise but I guess if the Inverter is happy, no Problems. Would putting a Cap on the output help with the ripple?

Thanks again for the explanation. Much appreciated.

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 12:01am 15 Nov 2021

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Should have made it a bit clearer.
Its not JUST a rectifier, but a whole dc power supply containing a suitable step down transformer, rectifier, and ripple filter.
Perhaps a large three phase fork lift battery charger for instance.

Operation on only one or two phases wold not be a good idea unless you can lock the inverter frequency to the grid frequency.

If you are patient, a battered old charger might be had for scrap value.
The really old ones are unloved even if they work perfectly. Often someone that spends several thousand on a new battery will replace the charger as well, it might even be insisted upon by the battery seller for warranty reasons.

Check out scrap metal and used machinery dealers for a bargain.

Cheers, �Tony.

Davo99
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Joined: 03/06/2019
Location: Australia
Posts: 1578

Posted: 12:14am 15 Nov 2021

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Warpspeed said Should have made it a bit clearer.

HA!
See, the smart people are always beaten but the stupid people on the bottom side of the zero crossing Point!

I did wonder where your mention of a battery charger came into it but I thought that may have been the more refined option. I was also thinking I'd have to Build in a bit of margin on the voltage of the solar panels as I know how much the grid voltage fluctuates here.

The principal of this is still something I am sure I can use in other applications.

Quote
If you are patient, a battered old charger might be had for scrap value.

In looking for Cheap Batteries I have seen a few of these for sale.
I'll Keep a more interested eye out in future.

I'm thinking I should just offer the local scrappy my free labour for a week just so I am on hand to "Rescue" any unappreciated " Treasure" that comes along.

I could see that going like my brother in law that ran a waste transfer station. Nothing like the hoarder I am but even he got to the Point where the Mrs said Leave the job or I'm leaving you Due to the stuff he brought home which in reality was far from Junk. Furnished their house very nicely all with brand new still packaged discontinued lines from different places as well as the shed Treasure.

I sure do miss him working there. I did well out of it too.

Thanks again for the heads up. I learn a great deal from you and other people here and feel much smarter for it.

Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 1021

Posted: 03:51am 15 Nov 2021

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I like that idea Tony, It would also filter out some of the trash that comes in from the grid, sort of protects your own gear from some of it, would that be right?

Cheers Aaron
Off The Grid

Revlac

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Joined: 31/12/2016
Location: Australia
Posts: 1021

Posted: 03:53am 15 Nov 2021

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I had a another look at the Make blue inverter and this time the manual was available for download, seems to be a rewritten version of an old 4Kw manual, going though it there is many changes from the original, perhaps the have rewritten part of the firmware, not sure.

A screen shot from the manual.

part 06. All these settings should be available, and you would want to change them to want you require, but they have in RED Prohibited User Configuration, what that means I'm not sure, but sure would not like to be locked out of those settings.
The AC charging capability should have be much higher than is listed, 20Amps is nothing, should be adjustable.
There are other settings in the manual that are locked out and some that wouldn't be changeable and shouldn't even be listed.
Its fairly cheap if it works the way its advertised, I think its clone and sort of modified, to resemble something similar to 5048MGX or something.

Looked at others from a genuine seller , there was one that had zero transfer time between off grid and grid, read somewhere it was said to be double conversion, whatever that was, will have a look later.
Back to work now.

Cheers Aaron
Off The Grid

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