Using a Growatt MIN series inverter with LG Prime battery

[lapsmith]

Hopefully this post will help anyone else considering this combination.

First, if you want to use this combination for partial home backup, make sure you get a Growatt V2 inverter. The V3 inverter which is all most sellers have will only do whole home backup and you must use their pricey SYN transformer. With the V2, you can do partial home back and use a much less expensive autotransformer.

The biggest problem I found comes when the grid is down (I don't use my LG battery for night time backup, only power outages). What happens is that if the grid is down and it is night time, and if a large load trips off the inverter (in my case it was a water well that would run fine during the day), there is no way to restart the inverter. You will have to wait till daytime. The reason is that the battery does not energize the output terminals until it receives comm from the inverter. And you can't get comm from the inverter until it is powered up. Catch 22.

I have a possible workaround, but not recommended for those uncomfortable working with high voltages. I haven't tested it yet so use at your own risk! If you apply about 80 volts DC to the PV input from a small battery, it will start the inverter. I tested it with two 40V power tool batteries in series and it worked. So it should start the inverter long enough to get the LG battery back on line. Then you would disconnect the portable battery and you are back in business.

One thing I'm not sure of and am hesitant to test on my system is whether the solar panels can handle being back driven by 80 volts. It depends on the diodes and my data sheet doesn't list a reverse voltage. Does anyone have any thoughts on this? Worst case is that you disconnect the PV inputs at the inverter and then apply the 80 volts.

 

[1201]

Wow that's what I would call a major design flaw.

 

[DIYrich]

One thing I'm not sure of and am hesitant to test on my system is whether the solar panels can handle being back driven by 80 volts. It depends on the diodes and my data sheet doesn't list a reverse voltage. Does anyone have any thoughts on this? Worst case is that you disconnect the PV inputs at the inverter and then apply the 80 volts.

When you put strings in parallel, they see the voltage of the other strings.

 

[lapsmith]

When you put strings in parallel, they see the voltage of the other strings.

So are you saying that it won't be a problem? I thought about panels in parallel with the following logic... which may very well be flawed...

When in parallel, they are both generating power. If one is in shade, it will be at a lower voltage, but still has some voltage to reduce the reverse voltage the diode sees. If strings were equal, as they should be when paralleled, I wouldn't think that voltage difference would be on the order of 80 volts. Please correct my thinking. Or just tell me I'm worried about nothing.

 

[DIYrich]

If one is in shade, it will be at a lower voltage, but still has some voltage to reduce the reverse voltage the diode sees.

On a 500v string, the difference in voltage of 2 panels dropping out due to shading is 80v. 3 panels, and you easily exceed the 80v you are concerned about.

 

[MajicDiver]

What happens is that if the grid is down and it is night time, and if a large load trips off the inverter (in my case it was a water well that would run fine during the day), there is no way to restart the inverter.

Hey @lapsmith , you have generator connection right? Make sure the PV switch is turned off (so if PV does start you won’t reverse power generator later), start generator with connection to the inverter gridtied output with breaker shut, inverter will power on. Then the LG battery will wake up or can be woke up I assume. Then disconnect generator and let inverter power backup loads from battery.

The ARO batteries have a forced start button that starts the battery- I’m virtually positive that the battery output picks up long enough to kick the inverter on and communication starts - going to have to test to make sure it works later today - I think I did last year if I’m not dreaming……you’ve got me worried enough to make sure now!

 

[lapsmith]

Hey @lapsmith , you have generator connection right? Make sure the PV switch is turned off (so if PV does start you won’t reverse power generator later), start generator with connection to the inverter gridtied output with breaker shut, inverter will power on. Then the LG battery will wake up or can be woke up I assume. Then disconnect generator and let inverter power backup loads from battery.

Good idea and yes, I have a generator connection. However, the way my system is wired, the inverter is connected upstream of the main breaker panel that is back fed by the generator. So with the generator interlock flipped, the main breaker can't be turned on so the inverter can't be powered that way. Besides, I would have to take out the generator, hook up the propane tank, etc. so it is more trouble than just connecting a small battery.

The ARO batteries have a forced start button that starts the battery- I’m virtually positive that the battery output picks up long enough to kick the inverter on and communication starts - going to have to test to make sure it works later today - I think I did last year if I’m not dreaming……you’ve got me worried enough to make sure now!

Nice feature (if it really exists) I notice some versions on the MIN inverter have a small button on the back and I seem to remember in one of their manuals that it is used to manually start up the inverter. I've even seen a picture of one with the cover off on Ebay and it goes to the top right connector on the comm board, which my inverter, and most likely yours, has. But it can't do anything that I can think of since the inverter is off. Not sure I want to test it with my system.

 

[MajicDiver]

Nice feature (if it really exists) I

Just tested it, the black start button on the battery wakes up the battery and applies power to the battery input of the inverter and the inverter powers up.

Additionally, my inverters do not have the black start button on the back for some reason (will contact Growatt about that at some point) but if I short the two prongs on the com board the button would be connected to the batteries wake up and system starts.

 

[lapsmith]

Just tested it, the black start button on the battery wakes up the battery and applies power to the battery input of the inverter and the inverter powers up

Nice that your battery start button works.

Additionally, my inverters do not have the black start button on the back for some reason (will contact Growatt about that at some point)

Maybe they figured it wasn't needed if the start button is on the battery.

if I short the two prongs on the com board the button would be connected to the batteries wake up and system starts.

Interesting. So are there two wires going from the battery to the inverter for that purpose? If so, where do they connect on the inverter?

 

[MajicDiver]

Interesting. So are there two wires going from the battery to the inverter for that purpose? If so, where do they connect on the inverter?

There is a battery on the card, I assume a wake-up pulse is sent over the communication cable to the battery, see table from manual below. If a person knew the voltage it could probably be done many ways.
Now I’m wondering if perhaps the reason there is no button like the one on eBay has, perhaps it’s to prevent draining the battery on the card…….

 

[lapsmith]

There is a battery on the card, I assume a wake-up pulse is sent over the communication cable to the battery, see table from manual below. If a person knew the voltage it could probably be done many ways.
Now I’m wondering if perhaps the reason there is no button like the one on eBay has, perhaps it’s to prevent draining the battery on the card…….

I think you nailed it! The voltage on the enable pins on my LG battery is 10.4 while connected to the inverter. I just tested the inverter sitting on my bench and shorting the pins on the connector going to where the push button would be gives 4.6 volts on the orange/orange-white pins on the comm cable. It is interesting that they probably put a boost converter on that 3V battery to get the 4.6 volts. Kind of surprised that would be enough to start up the battery since it is currently seeing 10 volts. I'll try to test it tonight with the connected system.

I don't think the card battery could be drained since it is very likely only connected when the push button is pressed. I would also expect to see a diode on the card battery to prevent 10 volts hitting the 3V battery if the button was accidentally pressed while the inverter was on.

 

[MajicDiver]

I think you nailed it! The voltage on the enable pins on my LG battery is 10.4 while connected to the inverter. I just tested the inverter sitting on my bench and shorting the pins on the connector going to where the push button would be gives 4.6 volts on the orange/orange-white pins on the comm cable. It is interesting that they probably put a boost converter on that 3V battery to get the 4.6 volts. Kind of surprised that would be enough to start up the battery since it is currently seeing 10 volts. I'll try to test it tonight with the connected system.

I don't think the card battery could be drained since it is very likely only connected when the push button is pressed. I would also expect to see a diode on the card battery to prevent 10 volts hitting the 3V battery if the button was accidentally pressed while the inverter was on.

We learn by collaborating - each of us takes turns climbing up on the other’s shoulders and we all get taller each time.

I’d really like to have some pictures of the sealed “shell” of the V3 inverter you took the circuit boards out of

 

[lapsmith]

We learn by collaborating - each of us takes turns climbing up on the other’s shoulders and we all get taller each time.

I’d really like to have some pictures of the sealed “shell” of the V3 inverter you took the circuit boards out of

Sure thing. Do you mean the inside of the plastic case that covers the main circuit board?

 

[MajicDiver]

Sure thing. Do you mean the inside of the plastic case that covers the main circuit board?

Yes

 

[lapsmith]

Yes

Here you go. What makes it more work to disassemble is those openings for the wires. If they were slotted, it would be simple to remove the cover. Thats what I'm going to do with the inverter meant for parts

 

[MajicDiver]

Here you go. What makes it more work to disassemble is those openings for the wires. If they were slotted, it would be simple to remove the cover. Thats what I'm going to do with the inverter meant for parts View attachment 217632View attachment 217633View attachment 217638View attachment 217639

I’d say they did it intentionally.

 

[lapsmith]

Back to the missing pushbutton. I traced the circuit and it is not the 3v coin cell that gives the start pulse, but a 1F 5.5V super capacitor. It is protected by a diode. Waiting till dark to test it.

 

[MajicDiver]

Here you go. What makes it more work to disassemble is those openings for the wires. If they were slotted, it would be simple to remove the cover. Thats what I'm going to do with the inverter meant for parts

@lapsmith So, the main circuit board must be mounted to the heat sink?

 

[lapsmith]

Yes. There is a 3/8" gap between the back of the pcb and the heat sink. There is room for a whole bunch of smd components, resistors, caps, diodes and some transistors, but no IC's. The high power components (IGBT's, diodes, and h-bridges) are sandwiched between the main board and heat sink with their heat conducting surfaces in direct contact.. A pretty efficient design, imo. The power inductors are embedded inside a cavity in the center part of the heat sink.

 

[MajicDiver]

Yes. There is a 3/8" gap between the back of the pcb and the heat sink. There is room for a whole bunch of smd components, resistors, caps, diodes and some transistors, but no IC's. The high power components (IGBT's, diodes, and h-bridges) are sandwiched between the main board and heat sink with their heat conducting surfaces in direct contact.. A pretty efficient design, imo. The power inductors are embedded inside a cavity in the center part of the heat sink.

Thanks! I have another 2 picture requests:
1. I searched your posts and have found where you uploaded closeup photos of parts of the main control board, but not one that shows the whole thing in one picture, could you up load a picture of each side of the board?

2. Can you upload a picture of the heat sink surface which the board is mounted to?

Looking forward to hearing how your test with the "push button" goes,

 

[lapsmith]

Back to the missing pushbutton. I traced the circuit and it is not the 3v coin cell that gives the start pulse, but a 1F 5.5V super capacitor. It is protected by a diode. Waiting till dark to test it.

Happy to report that it works as you predicted. Inverter started up in a few seconds. So glad I don't have to mess with jumper batteries, etc. Thank you, sir.

I wonder why they eliminated it, especially when they are promoting their relationship with LG.

 

[lapsmith]

Thanks! I have another 2 picture requests:
1. I searched your posts and have found where you uploaded closeup photos of parts of the main control board, but not one that shows the whole thing in one picture, could you up load a picture of each side of the board?

2. Can you upload a picture of the heat sink surface which the board is mounted to?

Looking forward to hearing how your test with the "push button" goes,

Here you go. I just buttoned it up so glad I had taken these earlier. The first one is of the switching power supplies which mounts above the main board.

 

[MajicDiver]

Here you go. I just buttoned it up so glad I had taken these earlier. The first one is of the switching power supplies which mounts above the main board.View attachment 217684

What is the 3rd picture? And what are the wires going to thru the slot?

 

[lapsmith]

What is the 3rd picture? And what are the wires going to thru the slot?

Thats the heat sink. The 2 exposed aluminum and 4 rectangular pads are where the power components are thermally connected. The wires go to the coils (inductors) embedded/potted inside the heat sink.

 

[MajicDiver]

Thats the heat sink. The 2 exposed aluminum and 4 rectangular pads are where the power components are thermally connected. The wires go to the coils (inductors) embedded/potted inside the heat sink.

Do you know the purpose of the coils in the heat sink? What do they do?