Power jack inverter as charger from GTI inverter

[Pete]

I am in the process of installing new panels on my system. I have a 12 volt system with a 5000 powerjack.
I am loathe to spend more money on MPPT regulators, I am going to add 1000 watts of panels so would need at least 2 x 50 amp regulators. The cost is astronomical.
I have read a few articles here about using GTI inverters to feed the system .
I need to know just how to hook the GTI up?
The powerjack has an input socket for 240 volts, if I could just plug the GTI in there it would then use the Powerjack as a charger and that would be fantastic.
But how would this work with the anti islanding part  of the GTI .
Hope that some of you more knowlegable folk can do me an easy outline or mud map to follow.
Pete

[frackers]

The Powerjack inverter is what is known as 'stiff'. What this means that its output is quite well voltage regulated and so is the frequency and it has a very low impedance (i.e. variations of load have little effect on voltage)

The GTI will use various techniques to determine whether it is still connected to the grid - a favourite is to try shifting the frequency of the mains - if it moves then no grid!!

The main thing to be wary of is that the GTI knows nothing of the state of the batteries. If the Powerjack output voltage rises with battery volt then the GTI 'may' drop out if the mains goes too high. Some are adjustable for this.

If that is not the case then a relay between the GTI and the PJ operated by battery volts would provide some protection if not actual regulation.

Oztules has a circuit that monitors the battery volts and PWMs the DC panel voltage going into the GTI to simulate a cloud going over! Something I'll be tackling in the near future when I have up to 8kw of solar potentially available to hook into the battery system

[Pete]

Thanks Frackers, I was planning to plug the GTI into the input end of the Powerjack. My idea is to use the battery charger function of the Powerjack to charge the batteries via the GTI. I currently plug the generator into the powerjack to use the battery charger function. It has an 80 amp charger built into the inverter.
What I thought would happen is that the powerjack would then control the charging rate via its inbuilt charger, and shunt any excess power via the internal relays to the house wiring.
I am not sure if there is power at the input socket when the inverter is on though. My take is that it would need to have 240 volts at that socket for the Powerjack to appear as the grid.
I have looked at Oz's circuit but without a diagram it is difficult for me to actually see what he is doing with it.
It seems that as he says GTI's are really cheap, MPPT's are really expensive.
So the GTI appears to be the way to go. I just need to get one to work.
Pete

[noneyabussiness]

You need a CLEAN 240v at the gti input... if you hook directly to the output of the powerjack it will sync and back charge the batteries if the load is not sufficiently high.. the charge regulator that oztules has brilliantly designed is on the INPUT of the gti to regulate the current going into it so as to regulate the charge voltage on the batteries. .

The charge circuit on the powerjack is not used, oztules has repeatedly said its pretty useless, and in my personal experience i have to totally agree. ..

Over at backshed forum " madness " has pcb's you can purchase very cheaply that have all the charger stuff (for gti input) and more and code etc. To suit...

[Pete]

Thanks for the explanation Noneya. 
I will look further into it and figure out which way to go.
Thanks again
Pete

[sunnypower46]

I'd like to have a look at the circuit mentioned above that Oz is using to PWM the DC input to a GTI.  Not having any luck with my search parameters.  Could someone help me with a link?

My current method to prevent battery overcharge utilizes a quad voltage comparator IC to turn on/off the gate of a IRF4110 in the negative leg of the panel output on its way to the microinverter (GTI).  A Morningstar dump load controller and resistor bank handles the first 1500 watt overage back-feeding through my PJ8000-24 and serves as an instantaneous power reservoir of sorts if a load comes on or a cloud interferes.  Beyond 1500 watts overage, the voltage comparator monitoring the dump load power (voltage) output commands the IRF4110 to "open" causing lack of panel input current and subsequent shut down of one or more (as desired) microinverters.

This works well, but the penalty is the five minute delayed startup of the standard single input microinverter when it's needed again.  FWIW, the relatively new twin input microinverters (APS and NEP, plus others) allow shutdown and immediate restart of one input, if the other input is continued to be fed.

If anyone wants more info on this method, I'll open a new thread.  For now, I just like to look at what Oz has tried.

[oztules]

If you replace the quad comparator, or modify your circuit to use some of the comparators to be a triangle generator, and then feed that into another one of the comparators, you will have made a pwm controlled driver for the GTI. I do this all the time for my solar controllers for the electric fencers.

However, I did this initially for the HV GTI, and it worked, but in the end decided to use a nano, as that gives us a easier regime to change parameters.

So if you replace your quad with the nano, the rest of the circuit must essentially remain the same from what you describe.

I assume you have isolation to the gate source interface of the 4110, if not, I use  3210 opto driver, and use a plug pack.... actually, that statement relies on what voltage your running the panels at.... microinverters may be low voltage.... and yep 4110 is low, so isolation is not critical. I have noticed it is useful though to isolate the noise from the nano ( I'm running 350vdc into IGBT's), and the best solution was the isolated power supply route.

I found an old circuit board so this will give you a idea.
If you look at the 339 you will see that it is a voltage controlled pwm using the quad comparators.



The G and S are the gate and source of your 4110


...........oztules

[sunnypower46]

Oz>:  (With apologies to Pete).  Thankfully, I'm working with 72 cell panels and voltages under 60vdc. 

A problem with the newer microinverters is their DC input circuits are now closely monitored for faults via integral DC ground fault detection.  If our homebrew control circuit creates a fault, you'll be needing to contact your "professional certified solar installer", who is the only one authorized to clear it via remote monitoring software.  No hardware push to clear button for the DYI community.  Therefore, in reality, we've got an expensive paperweight.

So, as you point out, it's imperative to DC isolate the signal controlling the 4110 gate.  At present, my 4110 gate control voltage (12vdc) comes from a 12-15vdc source about 75ft distant feeding a LM317 linear regulator and a MornSun 81212S-1W isolated DC-DC converter module (1W) at the solar panel.  The LM317 provides some line filtering and keeps the output impedance to DC-DC module low.  This, of course, wouldn't work at PWM switching speeds.

The opto driver provides the speed and control isolation, but the voltage needed to switch the gate would have to come from the panel itself to maintain isolation, I presume.

Let me toss this idea out as a simple way to reduce panel output and thus control the battery overcharging concern.  In theory, couldn't one use a 4110 to short an appropriate 100W/200W power resistor across the panel output and just waste the power (<10 amps?) outdoors that way?  Probably makes more sense to do it indoors on the AC side at the inverter input with a load bank that is relay or SCR controlled, though. Yes-No-Maybe?

[oztules]

The use of micro inverters complicates an otherwise simple system.... as you need to relay the battery voltage out to your panels so as to make a decision..... so you are probably just as well to use the dump load method on the AC side.... this leaves the 75 feet transmission as a simple ac line, and nothing else.

I am not a fan of shorting panels. In theory, it makes no problems, in practice, you will need to have reliable built panels with no slightly weaker cells in them... else all the power in the panel will end up across that cell, and the glass may crack from localised over heating.... been there done that too....

Otherwise, a simple voltage divider from panel + to the 3120 will drive the fet perfectly well. The 3120 can take 30v on Vcc... but like I said, it just complicates what was essentially a simple system.


.....oztules

[sunnypower46]

"The use of microinverters complicates an otherwise simple system . . ."

The way I control battery overcharge in my setup; yes it surely does.  But, I don't think you meant to suggest that a microinverter system design was any less preferable to a central GTI setup.  California solar installers are quickly moving from central to microinverter installs.

I swapped an existing microinverter for one of the latest Enphase IQ7+ units to check it out.  They are now transformerless, use a 2-conductor only 240vac harness with no additional ground wire required, 290W AC continuous output and can efficiently utilize panels 350W to 440W.  So far, I'm impressed.  If you dig deep into documents on their website, they even discuss using them in offgrid setups using PowerJack type inverters as the local grid and mention the subject of backfeeding and overcharging batteries.  It's interesting that they never say "don't use our inverters this way".

If you check the direction Enphase is headed with their upcoming IQ8 modules (supposedly due end of year), they're talking about continued daytime power output for the user despite a utility grid shutdown.  So, somehow they plan to internally produce the AC voltage, sync with the other microinverters and modulate each microinverter's output in a way that always matches the power needs of your changing loads.  And, they state no battery is required by the user, unless desired.  Quite the game changer if they can do it at an affordable cost.  I have my doubts as to how well they will handle compressor startups, etc.  The current crop of HF inverters do that poorly; and the newer microinverters have no internal transformers.  Where's the "grunt" going to come from?

Anyhow, I think you've got me changing course on how to handle battery overcharge in my setup.  I'll look deeper into dumping excess energy beyond what the Morningstar dump controller can handle, via control of additional loads on the AC side.  The dump controller provides a nice linear DC voltage output to work with once its target battery charge voltage is being exceeded.  Maybe I'll look at switching in/out a 20gal electric water heater to preheat water going to my main natural gas water heater.  It would be nice to use the excess energy rather than waste it.

[oztules]

I can readily understand why installers would go the micro inverter route. No solar cables, HVDC switches, fusing, HV DC wiring, HV safety, 400vdc on roofs for the fire dept to deal with.... etc etc.

But for off grid, it has no merit, only draw backs.

On grid needs no control, off grid requires  control. On one of the outer islands here we have 40 panels in one area, and 20 panels  hundreds of meters distant. The 40 panels run at low voltage via a 7kw 48v controller costs maybe 50 dollars to build, and is local to the battery storage.

The other 20 panels are AC coupled via a big GTI back up to the house, and helps run the shearing shed and Reverse Osmosis water plant... no control required, as it runs in deficit to the RO and shed use. Micro inverters would just add huge expense, and no gains, whereas second hand 5kw GTI's are cheap, and if you want, you can configure them to accept generator HVDC and still charge the batteries hundreds of meters distant.

So every installation has it's own foibles, and micro inverters just do not fit in any off grid circumstance I can think of. Offer no advantages, only problems once you leave the on grid environment, as they offer very little if any benefit, only challenges as you have found.

Anyway, thats not the issue here. You have micro's installed, thats what we have to deal with.

We can do things once we centralize the power, by then we find control too hard to do at the panel end sensibly, so we are left with AC dumping, cheap, simple, easy to do..... so we might as well do it.

I would just build a nano controller, with 3 stage charge control, and couple that to a water pre heater, and perhaps an array of oven elements in case the water gets out of hand.

That way your field wiring is simple AC to the panels micro's... thats it. Your control wiring is all local..your back in control.

My conditions are very remote, and I could never use gear that required outside help/interference... does not compute.

Starting heavy loads is really not related to the transformer, but to the low impedance storage you have available. If they sprung for some serious capacitance in the HF units, they could start stuff up just as well as the transformer designs. Mine can easy do 20kw surges for 5hp induction motors, as we have the battery as the storage at 48v, but we could just as easily have a 350v battery of only a few AH instead of the HV caps, in the HF unit, and see the same result. The transformer is only an impedance matching device after all.


..........oztules

[sunnypower46]

I don't take exception with anything in your last post.  I think we've covered the overcharge issue from all points of view.  How we best solve the problem is obviously system dependent.

I started my installation without considering use of the Morningstar TS-60 diversion controller.  It seemed a good idea at the time to just automatically flip on/off panels at the micro input via a battery voltage comparator and FET switch at the panel.  I actually have made this work quite well.  But, using the TS-60 with its 3-stage charging profile is a much better solution for the batteries and my PJ8000 (which has been running 24/7 for 18 months now).  Were it not for the fact that I'm limited to 1500-1800W diversion, it alone would have solved the issue.  The TS-60 PWMs up to 24vdc into six 300w resistors in my setup.  I don't know whether syncing a pair of TS-60s is feasible.  Tough to consider without a schematic.  Technically, it should be possible.  My max solar output is about 3200W, for reference.

So, I'll just let the existing TS-60 work its magic on the first 1500-1800W and switch in extra AC loads as needed.  Your suggestion of oven heating elements was welcome as that method was not on my radar.

You're right about the transformers, or lack thereof re: "grunt".  I didn't think that through very well.  That said, no manufacturer really wants to put electrolytics, let alone extra ones, in roof mounted, essentially HF micro modules with 25-year warranties.  It will be interesting to see how well the proposed new Enphase units do in the real world when not grid tied.  Perhaps a "Caution - Operating high surge devices when off grid will cause temporary system shutdown . . . ." will be necessary.

Oz, thanks for the back and forth.  Your perspective is always enlightening. 

[DanyaOray]

Hello....as per my knowledge the Powerjack inverter is what is known as stiff. What this means that its output is quite well voltage regulated and so is the frequency and it has a very low impedance. The GTI will use various techniques to determine whether it is still connected to the grid.

[sunnypower46]

My experience with microinverters feeding PJ8000(24v)s suggests the PJs are not as "stiff" as you might expect.  I've tried APS, NEP and Enphase micros.  They all marry up with the PJs just fine.  But, if you want to switch on/off other than resistive loads attached to a micro fed PJ; be prepared for frequent micro shutdowns/restarts.  The PJ is not so "stiff" with reactive (motor) loads.  The current generation of micros appear to be quite sensitive to instantaneous voltage drop-offs, which the PJs can't respond to fast enough.  I had to switch to inverter type pool pump and mini-split AC to get consistent power out of the micros.  You better have an inverter type refrigerator, also. 

Just to be clear, my PJs power all my loads just fine.  Descent voltage and frequency control.  Good sinewave output, no issue with "buzz" in sensitive audio equipment.  But, the micros are designed to expect the "mass" associated with the utility grid.  The PJs just can't compete.

So, I use two PJs in my setup.  One creates the local grid for the micros and serves to charge the battery bank; and also powers those loads that cause no micro trip-off issues.  The other PJ is fed only via the charged battery bank and handles the "problem" loads.  Having two PJs also provides a degree of redundancy with a little load re-wiring, if needed.

[lighthunter]

My experience with microinverters feeding PJ8000(24v)s suggests the PJs are not as "stiff" as you might expect. 

Just to be clear, my PJs power all my loads just fine.  Descent voltage and frequency control.  Good sinewave output, no issue with "buzz" in sensitive audio equipment.  But, the micros are designed to expect the "mass" associated with the utility grid.  The PJs just can't compete.

Hi Sunny, I really appreciate the information you have shared about your setup. Ive always been interested in what micros have to offer but they didnt have the capacity or cost effectiveness when i was making decisions.
So, for that and other reasons Oztules mentioned i went the large GTI route and experienced some of the same issues you mention with the grid ties going off line for whatever reason (many nuisance offlines). I improved the problem by correcting things like exact balancing the 120/240 and setting regulation voltage at exactly 243v AC a sweet spot but it never eliminated the problem. At the time I was using a 24v pj with massive transformer (200lbs) and small LFP bank
26V 40AH. LFPs are very stiff, 50 amp charge to 80A discharge barely made 1 volt fluctuation. Though i tested it to 4KW, I never used more than 2.2kw from this setup using transfer sequencing.  Eventually i modified the pj to 48v (with 50lb dual core torroid) and connected it to a 510AH traction bat (FLA)
The battery voltage fluctuates more now under load with the 48v than it did with the 24 yet now the grid ties never notice. I can go from battery charging at 54v to discharging at 47v supplying over 7KW, (2KW general loads and a 5.5KW dryer that just switched on) and the grid ties keep right on as though nothing changed.

Something Oztules pointed out was the inverters ability is directly related with the reserve and while the battery AH is a huge factor, the 48v vs 24v is also a huge factor. I think there is a practical ratio between maximum incoming to bank size, bank voltage and outgoing. What works for you is the best for your setup just sharing what ive seen  to be true. All the best to you and your project