Using solar micro inverters with batteries instead of panels

[jimbob232]

Curious as to your results testing a PWM module. You can probably just add a parallel resistance of the appropriate size to precharge the output.

By design, a PWM module is not going to be able to deliver a stable current to a Microinverter so I’m interested in what level of current stability you get and whether you add additional capacitance to the output to reduce voltage ripple.

The concern that has been expressed is that current ripple beyond that delivered by solar panels can result in Microinverter input capacitors heating up and aging prematurely.

I guess we need someone to put a scope on both a solar panel feeding a Microinverter as well as one of these PWM modules feeding a Microinverter t understand what order of magnitude we are talking about and whether there is any real reason to be concerned…

Is duty cycle controlled by voltage or by resistance?

According to the spec sheet and label on the board it is voltage controlled...a big reason I want to try this one.

I like the idea of a parallel resistance to precharge the output...I have planned on capacitors to smooth the output, doing a very quick calc using 24v, 10a and 1/15000s I get 0.02j per cycle, so I've picked electrolytic caps that store 10x that energy: 1000uf, and I've ordered 5 of them...I'm hoping that 5percent ripple is ok for the inverter but I'll find out one way or another...


I've not got a scope although I can probably borrow one if I can't get it working very easily.

 

[jimbob232]

Do you have any way to measure the stability of the current output from your PSU once it has stabilized?

I’m curious whether a PSU feeding a Microinverter provides a relatively ‘safe’ / stable way to deliver a programmable amount if export from a Microinverter.

The claim is that the low-cost programmable DCDC boosters do not deliver a stable current but I’m hoping they are as stable as an AC-powered PSU…

I've only got the current reading on the PSU for now.
I think providing you jam enough capacitance to smooth the output it should be ok... providing the extra capacitance doesn't resonate at any point! I'm hoping it'll be fine as all the control circuitry is designed to switch at high frequency and the big capacitors I'm using should be way below that.

 

[kundip]

I assume you have a grid connection in order to enable the micro inverter to work. It needs 240 volt AC from the grid in order work. I don't understand what the buck converter is for?

I hear you. Other posts on this & other forums said connecting the microinverters directly to the battery would fry them.
So I was trying to control the current. All my inverters are connected directly to a 24v battery & are perfectly fine.
I have had one working with a buck converter for nearly 2 years now.
All the work I did in that area was great fun but somewhat misguided.
Yes I only do grid connect.
I would never, ever do off grid unless I absolutely had to.

I assume your goal is to harvest solar and produce AC or DC to power either a 24 volt DC device from the battery battery or some 120 or 240 volt AC device. That use case will determine which components you will need.
If you read this thread from the beginning, you will see several variations on this concept and no working examples.

I have been producing ~12KW of battery power per night for over a year now very cheaply.
I have ~18KW of batteries working faultlessly.
My abilities in this area were limited when I first started. I read this and other threads to start with and had much advice from many sources so at times I was fairly confused.

 

[zanydroid]

I've been analyzing this off and on too, don't have all the hardware necessary to experiment yet.

Seems that adding switching to the DC side would really end up requiring a current limiter of some sort to avoid blasting the microinverter capacitors during precharge. The available current for precharge will be many orders of magnitude higher for a battery than for a solar panel, even if solar panel were switched with full illumination. And typically a solar panel will start up slowly in the morning.

How harmful is switching the AC side?

 

[kundip]

I've been analyzing this off and on too, don't have all the hardware necessary to experiment yet.

Seems that adding switching to the DC side would really end up requiring a current limiter of some sort to avoid blasting the microinverter capacitors during precharge. The available current for precharge will be many orders of magnitude higher for a battery than for a solar panel, even if solar panel were switched with full illumination. And typically a solar panel will start up slowly in the morning.

How harmful is switching the AC side?

The Enphase M215 inverters I use.
You can connect directly to battery. No problem.
I have other posts on this.
.

 

[zanydroid]

How do you handle precharge surge? It's necessary to handle with a full size inverter so I imagine it is a higher risk on a microinverter.

When I game it out in my head, one would want to use a precharge resistor and then permanently connect the battery to the microinverter so that there is never again a large voltage imbalance.

 

[kundip]

B

How do you handle precharge surge? It's necessary to handle with a full size inverter so I imagine it is a higher risk on a microinverter.

There is no surge. The MPPT? seems to fill the microinverter slowly.
After about 5 minutes the green light comes on on the Enphase & it fires up.
Enphase uses microinverters on their battery systems. They just stack them together.

When I game it out in my head, one would want to use a precharge resistor and then permanently connect the battery to the microinverter so that there is never again a large voltage imbalance.

I have tried resistors.
They just get really hot & make no difference.
Some in this forum have made 24v batteries using AA batteries & tested that way.
I don't get your voltage imbalance question.
There is none that I have seen.
I charge the LiFePo4's up to 28.8 volts and they drop to ~24v after 14 hours.
(2x 24v 200ah)
On my posts I have already said I use one microinverter for 14 hours & the second for 7 hours. That gives me an average of 300w @ 240vac per hour for the whole night.
I have two of these setups the second inverter does the first 1/2 of the night on one. The other setup does the second half of the night.
Giving me 600w 240vac per hour all night.

 

[zanydroid]

B

There is no surge. The MPPT? seems to fill the microinverter slowly.
After about 5 minutes the green light comes on on the Enphase & it fires up.
Enphase uses microinverters on their battery systems. They just stack them together.

I have tried resistors.
They just get really hot & make no difference.
Some in this forum have made 24v batteries using AA batteries & tested that way.
I don't get your voltage imbalance question.
There is none that I have seen.
I charge the LiFePo4's up to 28.8 volts and they drop to ~24v after 14 hours.
(2x 24v 200ah)
On my posts I have already said I use one microinverter for 14 hours & the second for 7 hours. That gives me an average of 300w @ 240vac per hour for the whole night.
I have two of these setups the second inverter does the first 1/2 of the night on one. The other setup does the second half of the night.
Giving me 600w 240vac per hour all night.

The precharge resistor for string inverters is only used before the first time you plug in the battery. Will talks about it on his videos.

If one were to disconnect on DC side any input capacitors on the microinverters would eventually decay to 0V, so they would need to charge back up to battery voltage.

This is why I asked to confirm whether there is a daily DC side disconnect from batteries in your setup, since that would be a lot more stressful from a precharge angle.

 

[kundip]

The precharge resistor for string inverters is only used before the first time you plug in the battery. Will talks about it on his videos.

If one were to disconnect on DC side any input capacitors on the microinverters would eventually decay to 0V, so they would need to charge back up to battery voltage.

This is why I asked to confirm whether there is a daily DC side disconnect from batteries in your setup, since that would be a lot more stressful from a precharge angle.

Ahh. OK. I use Microinverters on my roof.
So all is 240v directly off the panels.
So I charge my batteries during the day off my 240v power.
Then I turn on the microinverters at night.
A number of times I have left the timer on all day and the microinverter has run 24 hours even with the charger being on all day.
It does not make any difference in that case to the microinverter.
It doesn't make any difference to the current the microinverter uses.
I get cheap microinverters here.
I have gotten about 70 for an average of about USD $27 each.
If you can afford to "burn" a couple have a try.
I have not been successful in doing so.
The only time I got the microinverter hot was when I had a buck (boost) converter in line & was boosting the voltage ~40v & the current.

 

[fafrd]

Ahh. OK. I use Microinverters on my roof.
So all is 240v directly off the panels.
So I charge my batteries during the day off my 240v power.
Then I turn on the microinverters at night.
A number of times I have left the timer on all day and the microinverter has run 24 hours even with the charger being on all day.
It does not make any difference in that case to the microinverter.
It doesn't make any difference to the current the microinverter uses.
I get cheap microinverters here.
I have gotten about 70 for an average of about USD $27 each.
If you can afford to "burn" a couple have a try.
I have not been successful in doing so.
The only time I got the microinverter hot was when I had a buck (boost) converter in line & was boosting the voltage ~40v & the current.

Just to be sure you and zanydroid are speaking the same language, once your battery has been depleted to the point that you want to shut down a battery-powered Microinverter, do you do so by opening a relay controlling 240VAC grid signal reaching the inverter output (AC-switching) or do you do by opening a relay controlling 24VDC battery power reaching the Microinverters MC4 DC inputs (DC-switching)?

 

[kundip]

Just to be sure you and zanydroid are speaking the same language, once your battery has been depleted to the point that you want to shut down a battery-powered Microinverter, do you do so by opening a relay controlling 240VAC grid signal reaching the inverter output (AC-switching) or do you do by opening a relay controlling 24VDC battery power reaching the Microinverters MC4 DC inputs (DC-switching)?

OK. Many Thanks for assisting fafrd.
Sorry I misunderstood your question zanydroid.
I cut the DC side.
I don't use signals to control anything.
First - the timer Switch turns the DC on & Off. (It has a relay in it as per pic below)
_The first timer runs 14 hours.
_The second timer runs roughly 7 hours.
..........I set this to turn off the second MicroInverter BEFORE the MotorMate has to.
...........So between 5 & 7 hours.
Second if that fails the MotorMate cuts the DC @ 23V
Third is the battery BMS itself.
Hopefully I have all you questions covered.

Re the Capacitors Decaying to 0volts - I really don't know.
I know when the capacitors in the MPPT fill up the MicroInverter starts producing continuously then.
Takes about 4 minutes which also tells me the MicroInverter is only taking what current it wants off the 24V battery.
After I cut the DC whether there is some residual current in the MPPT capacitors I don't know.
Whether it would drain to 0volts, if there was, I don't know.

 

[Hedges]

Re the Capacitors Decaying to 0volts - I really don't know.
I know when the capacitors in the MPPT fill up the MicroInverter starts producing continuously then.
Takes about 4 minutes which also tells me the MicroInverter is only taking what current it wants off the 24V battery.
After I cut the DC whether there is some residual current in the MPPT capacitors I don't know.
Whether it would drain to 0volts, if there was, I don't know.

The several minute delay is software complying with rules regarding waiting for grid to be stable before operating.
Of course inverter only draws power as needed to deliver AC power. Except for charging capacitors, which just happens.

PV input to microinverter either hits a decoupling capacitor first, or an inductor first. I think it is capacitor.
Battery inverters have a large electrolytic capacitor bank, and when battery is first connected several thousand amps rush in for a millisecond, causing a large spark and sometimes blowing fuses or welding relays.
PV is a limited current source so only delivers a few amps.

If battery connected PV input of an inverter, would expect inrush current. Microinverter, smaller capacitors so less inrush.
This may cause stress to transistors in your Motor Mate. Closing circuit to an inductive load, there can be low power dissipated in the switch. Closing into a capacitive load, large current and power dissipation.

Circuits intended to precharge capacitors do so gradually, because power dissipated goes as current squared, and energy as current squared divide by time. Charging in 1/10th the time causes 10x the energy dissipation. But charging must be completed before load starts drawing DC current.

If yours has cycled a number of times without failure then it seems to have some margin. When we design something like this we try to keep current within max limits of the components.

Depending on no-load consumption by microinverter, I would have considered precharging it once, then switching AC side rather than DC.

 

[fafrd]

OK. Many Thanks for assisting fafrd.
Sorry I misunderstood your question zanydroid.
I cut the DC side.
I don't use signals to control anything.
First - the timer Switch turns the DC on & Off. (It has a relay in it as per pic below)
_The first timer runs 14 hours.
_The second timer runs roughly 7 hours.
..........I set this to turn off the second MicroInverter BEFORE the MotorMate has to.
...........So between 5 & 7 hours.
Second if that fails the MotorMate cuts the DC @ 23V
Third is the battery BMS itself.
Hopefully I have all you questions covered.

Re the Capacitors Decaying to 0volts - I really don't know.
I know when the capacitors in the MPPT fill up the MicroInverter starts producing continuously then.
Takes about 4 minutes which also tells me the MicroInverter is only taking what current it wants off the 24V battery.
After I cut the DC whether there is some residual current in the MPPT capacitors I don't know.
Whether it would drain to 0volts, if there was, I don't know.


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Thanks for the detailed reply. I’d thought you were switching AC so I’m glad I asked you for a clarification.

I assume you have a multimeter so if you’d like to put on a bit off effort to address the concerns being raised about precharge, perhaps you could measure the DC voltage on the output of the relay in the morning before it turns on.

If the leakage is so low that the Microinverters input capacitors maintain DC voltage close to battery voltage over the 4-8 hours the relay is open, the capacitors only charged once when you first connected the Microinverters.

If the DC voltage has dropped close to 0V just before the relay closes in the morning, then the capacitors are charging once per day but then the next question then becomes what guage of wire and total wire length do you have between battery and Microinverter input?

You obviously have had no issue for over 2 years now, so we are just trying to understand technically why that might be.

 

[kundip]

The several minute delay is software complying with rules regarding waiting for grid to be stable before operating.
Of course inverter only draws power as needed to deliver AC power. Except for charging capacitors, which just happens.

I really appreciate You & others assiting me.

PV input to microinverter either hits a decoupling capacitor first, or an inductor first. I think it is capacitor.
Battery inverters have a large electrolytic capacitor bank, and when battery is first connected several thousand amps rush in for a millisecond, causing a large spark and sometimes blowing fuses or welding relays.
PV is a limited current source so only delivers a few amps.

OK. Thanks I get it.

If battery connected PV input of an inverter, would expect inrush current. Microinverter, smaller capacitors so less inrush.
This may cause stress to transistors in your Motor Mate. Closing circuit to an inductive load, there can be low power dissipated in the switch. Closing into a capacitive load, large current and power dissipation.

OK. This is why the Victron Smart Battery Protect did not work.
I have a separate Victron Smart Battery Protect design that has a relay.
It works really well.
My later MotorMate design was to reduce complexity.
I could do the same with the MotorMate if it is better.
Maybe the 20AMP installed fuse might offer some resistance to the inrush current
.

Circuits intended to precharge capacitors do so gradually, because power dissipated goes as current squared, and energy as current squared divide by time. Charging in 1/10th the time causes 10x the energy dissipation. But charging must be completed before load starts drawing DC current.

I did not understand this before.

If yours has cycled a number of times without failure then it seems to have some margin. When we design something like this we try to keep current within max limits of the components.

My intricate design ability =0.
Dumb luck (after many burnouts) = >0

Depending on no-load consumption by microinverter, I would have considered pre-charging it once, then switching AC side rather than DC.

I worked on the DC side to make it "easier" for people without a lot of knowledge to have their own battery.
It was so others could do this with out touching the AC side.
zanydriod & fafrd - are suggesting it would be much better to switch the AC side.
I can see now that this is most likely true - I can do this sooner if others would like me to test it out.
I now get that if the inrush current is quite seldom rather than daily it will preserve the Battery Protect & the MicroInverter.

Note:
Even one makes battery a huge difference - see pic below.
Grid dependece can drop about 20%.
.

.

Thanks Again

 

[zanydroid]

It’s possible that, when the system turns back on again as charger turns on, the current limit on the charger will limit the inrush current at that time even if the capacitors have decayed away all charge.

I don’t have a full picture of how your specific setup works but this charger-based limiting idea (if it holds up) might be something others want to pursue, in combination with only switching on the AC side.

I’m curious if M250 and other microinverters report their idle DC side consumption. I’m not sure how much these would be optimized for AC down state, that’s supposed to be free power from the sun that would otherwise not be used.

 

[kundip]

Thanks for the detailed reply. I’d thought you were switching AC so I’m glad I asked you for a clarification.

I assume you have a multimeter so if you’d like to put on a bit off effort to address the concerns being raised about precharge, perhaps you could measure the DC voltage on the output of the relay in the morning before it turns on.

I have measured 4 MicroInverters here are the voltages:
0.014
0.022
0.077
0.066

If the leakage is so low that the Microinverters input capacitors maintain DC voltage close to battery voltage over the 4-8 hours the relay is open, the capacitors only charged once when you first connected the Microinverters.

Thanks my understanding is improving - I think.

If the DC voltage has dropped close to 0V just before the relay closes in the morning, then the capacitors are charging once per day but then the next question then becomes what guage of wire and total wire length do you have between battery and Microinverter input?

I use the 4mm sq twin core solar cable to the Anderson Plug.
Then I use 20Amp general purpose wire.
None of it gets hot at all.
It, now, makes me think this might slow down some of that initial "inrush current" as well.
Originally I tried much heavier wire but I found it too cumbersome.
So I tried the above & it seems to work well.
.

You obviously have had no issue for over 2 years now, so we are just trying to understand technically why that might be.

Hopefully my answers will shed some light.
If I am standing in a room full of dynamite with a lit match please let me know.

 

[fafrd]

I will measure all 5 that I have - one is via a buck converter.

Thanks my understanding is improving - I think.

I use the 4mm sq twin core solar cable to the Anderson Plug.
Then I use 20Amp general purpose wire.
None of it gets hot at all.
It, now, makes me think this might slow down some of that initial "inrush current" as well.
Originally I tried much heavier wire but I found it too cumbersome.
So I tried the above & it seems to work well.
.
View attachment 145301
View attachment 145300

Hopefully my answers will shed some light.
If I am standing in a room full of dynamite with a lit match please let me know.

Can you estimate the length of the wires?

 

[kundip]

It’s possible that, when the system turns back on again as charger turns on, the current limit on the charger will limit the inrush current at that time even if the capacitors have decayed away all charge.

I had not realized this may be a problem.
I use dedicated Ampton LiFePo4 chargers designed by an ex Schneider technician Frick.
I also have no problem with the Victron Blue Smart Charger.
I thought maybe the 20AMp fuse & wires I use might create some resistance to the initial inrush.
I will be doing some readings for fafrd I think he wants these readings in relation to this.
.

I don’t have a full picture of how your specific setup works but this charger-based limiting idea (if it holds up) might be something others want to pursue, in combination with only switching on the AC side.

This is something I don't get.
What I am doing on these batteries, for grid connected systems, is cheap, portable, easy & quick.
It allows you to get one battery of any type & make use of it.
_ANY Battery & charger one side.
_ANY Battery protect in the middle.
_MicroInverter with timer the other side. (Micro Inverter types to be tested.)
I see all this expensive gear being discussed on this & other forums & my mind boggles.
ALSO: With rearguard to the AC side I have responded to this:
.

This simple robust system brand new (each) costs.
.

I’m curious if M250 and other microinverters report their idle DC side consumption. I’m not sure how much these would be optimized for AC down state, that’s supposed to be free power from the sun that would otherwise not be used.

Way above my understanding - I will research and learn as best I can.

Some of my working rues are:
It has to be something off the shelf that most people can afford.
Grid connected is best. IMO.
Forget efficiency - just add another panel. (easy if it is MicroInverters)
Forget optimisers if you didn't have them installed in the first pace - just add another panel.
Forget all the excess monitoring equipment use a multi-meter with a current clamp.
.

 

[kundip]

I don’t have a full picture of how your specific setup works but this charger-based limiting idea (if it holds up) might be something others want to pursue, in combination with only switching on the AC side.

A big thank you for this comment.
It makes me feel like my (albeit kind of misguided) work may have come to some good validity - after waiting a great deal of time.
You and a couple of others have shown good interest which pleases me no end.
I just hope it all stands up to scrutiny.

 

[fafrd]

A big thank you for this comment.
It makes me feel like my (albeit kind of misguided) work may have come to some good validity - after waiting a great deal of time.
You and a couple of others have shown good interest which pleases me no end.
I just hope it all stands up to scrutiny.

The fact that you’ve already had two years of success running in this manner is already standing up to any scrutiny that you need to worry about.

There are two questions everyone is interested in:

1/ are the fears of damage to typical Microinverters when powering direct from battery unfounded? We won’t know the answer to that question definitely until we get some stories of failure among the several members attempting to follow in your footsteps (including me).

In the meantime, question 2 is related to particularities of the way you’ve built your rig which might have reduced or eliminated the risks most are worried about (which again, are not validated at this stage).

Your suggestion about resistance of your relay is a good one - knowing whatever specification it has for contact resistance along with the estimated + and - wire lengths of 4mm / 6 AWG wire you are using to connect between battery and Microinverter will help figure out what maximum inrush current you might be getting.

It’s amazing what impact as little as 10mOhms can have on inrush current…

By the way, you said 4mm wire but I assume that means standard 6AWG wire, correct?

 

[zanydroid]

So with regards to protecting the battery vs the inverter/other electronics.

• The battery should be pretty fine with just regular battery fusing - that would protect against catastrophic short inside the inverter if something bad blows up.
• However, a fuse will not directly protect the inverter (though adding some series resistance might provide some protection).

An interesting comparison here would be where a GTIL would make sense, and where a microinverter would make sense. I doubt any of the GTIL are up to modern grid spec (but they're probably fine for 2011 grid spec), and they have a bit more configuration flexibility with how much power they put out. It's easy to get microinverters for any modern grid spec you want, however they are natively limited to pushing out the max power unless you get one with export limiting features, which adds a decent chunk of expense. For Hoymiles about $300 if you just want to set % of maximum output, and $900 if you want automatic export limit.

 

[kundip]

The fact that you’ve already had two years of success running in this manner is already standing up to any scrutiny that you need to worry about.

Much Appreciated.

There are two questions everyone is interested in:

1/ are the fears of damage to typical Microinverters when powering direct from battery unfounded? We won’t know the answer to that question definitely until we get some stories of failure among the several members attempting to follow in your footsteps (including me).

OK. I hope their fears are unfounded especially if they operate at the lower end of the operating range.
I am keen to see others test this.
I will try to test others also.
Maybe we should have a list of MicroInverters tested so others can see results on each type.

In the meantime, question 2 is related to particularities of the way you’ve built your rig which might have reduced or eliminated the risks most are worried about (which again, are not validated at this stage).

OK...

Your suggestion about resistance of your relay is a good one - knowing whatever specification it has for contact resistance along with the estimated + and - wire lengths of 4mm / 6 AWG wire you are using to connect between battery and Microinverter will help figure out what maximum inrush current you might be getting.

Details at the end of this reply.

It’s amazing what impact as little as 10mOhms can have on inrush current…

I am staring to get a grip on this.

By the way, you said 4mm wire but I assume that means standard 6AWG wire, correct?

That is correct.

So with regards to protecting the battery vs the inverter/other electronics.

• The battery should be pretty fine with just regular battery fusing - that would protect against catastrophic short inside the inverter if something bad blows up.

• However, a fuse will not directly protect the inverter (though adding some series resistance might provide some protection).

Working out resistor sizes is not my forte.

An interesting comparison here would be where a GTIL would make sense, and where a microinverter would make sense. I doubt any of the GTIL are up to modern grid spec (but they're probably fine for 2011 grid spec), and they have a bit more configuration flexibility with how much power they put out. It's easy to get microinverters for any modern grid spec you want, however they are natively limited to pushing out the max power unless you get one with export limiting features, which adds a decent chunk of expense. For Hoymiles about $300 if you just want to set % of maximum output, and $900 if you want automatic export limit.

I would not do the GTIL - it adds too much complexity for what you pay IMO.
There are a lot of cheap second hand MicroInverters out there - I pay on average US $27 each for them & all mine are brand new.
At this stage it is miles cheaper to replace the MicroInverter - if one blows up IMO.
Already we are talking about switching on the AC side & ostensibly the MicroInverter will be subject to very few hits of inrush current and last much longer.

In Australia there are a number of factors for cheap MicroInverters as I see it.
1. Huge solar farms seem to be swapped out at the 10 year mark some of these have 100's of MicroInverters for sale - cheap.
2. Companies seem to buy a large excess of MicroInverters and have 100's of new ones left over which they dump.
3. There have been a lot of advancements E.G. IQ8 so, older models, even if new, are dumped.
4. Users are being convinced to change to string inverters.

I am not sure how your export limit works in the US ours is 5KW per household in Australia.
So I have two fan heaters stationed outside that I can set to pull 1.2KW, 2.4KW, 3.6KW or 4.8KW and pump out hot air.
During the hot months I set the Wi-Fi timer to burn 1.2KW for 4 hours during the middle of the day.
All the rest of the burning capacity, I have, is just backup.
I never export more that 3KW on any day.
I plan to use that energy so I don't just waste it. (Gas heater to electric, electric car ETC.)
This is another one of my working rules:
Produce as much solar power as you can. (cheaply) Worry about using it later.
So I have 8 more old panels & railing bought for USD $135 to put up.
I keep adding where / whenever I can.

 

[kundip]

Do you have any way to measure the stability of the current output from your PSU once it has stabilized?

Unfortunately I don't.
On the bench top power supply it stays on the amps & volts I set.

I’m curious whether a PSU feeding a Microinverter provides a relatively ‘safe’ / stable way to deliver a programmable amount if export from a Microinverter.

Yes it does.
I use my bench-top power supply to check my inverters often.
I have run the inverters all night no problem.

The claim is that the low-cost programmable DCDC boosters do not deliver a stable current but I’m hoping they are as stable as an AC-powered PSU…

This has not been my experience.
I found the DCDC boosters flaky.
Having said that I have had one (boost converter) running for two years an it runs, just, on hot.

 

[fafrd]

Unfortunately I don't.

Yes it does.
I use my bench-top power supply to check my inverters often.
I have run the inverters all night no problem.

This has not been my experience.
I found the DCDC boosters flaky.
Having said that I have had one (boost converter) running for two years an it runs just on hot.

Flaky in terms of being difficult to set / configure using the pots, I understand.

And even ‘flaky’ in terms of the setting itself not being stable and needing to be recalibrated.

Both of those are different than the DC-DC-converter putting out much more current ripple than a standard bench top PSU…

Someone with an oscilloscope is going to have to make dons head-to-head measurements to understand what magnitude of current ripple we are talking about…

Your experience with your one DCDC converter suggests it may not be that big if a deal…

 

[kundip]

The fact that you’ve already had two years of success running in this manner is already standing up to any scrutiny that you need to worry about.

Much Appreciated.

There are two questions everyone is interested in:

1/ are the fears of damage to typical Microinverters when powering direct from battery unfounded? We won’t know the answer to that question definitely until we get some stories of failure among the several members attempting to follow in your footsteps (including me).

OK. I hope their fears are unfounded especially if they operate at the lower end of the operating range.
I can't wait until others test.
I will try to test other MicroInverters also.
Maybe we should have a list of MicroInverters tested so others can see what works & what doesn't.

In the meantime, question 2 is related to particularities of the way you’ve built your rig which might have reduced or eliminated the risks most are worried about (which again, are not validated at this stage).

OK...

Your suggestion about resistance of your relay is a good one - knowing whatever specification it has for contact resistance along with the estimated + and - wire lengths of 4mm / 6 AWG wire you are using to connect between battery and Microinverter will help figure out what maximum inrush current you might be getting.

Sorry.....I am unable to work out the inrush current - I wold need to learn that.
I will try.
The first battery setup has 5 meters of 5.6mm cable (Pic 01.)
Then 0.5 metres of 2.4mm cable (Pic 02.)
The second battery setup has 1 metre of 4mm twin core cable. (Pic 03)
Then 0.5 metres of 2.4mm cable (Pic 02.)
The second battery setup has .6 metre of 4mm twin core cable. (Pic 03)
Then 0.5 metres of 2.4mm cable (Pic 02.)
.

It’s amazing what impact as little as 10mOhms can have on inrush current…

I am staring to get a grip on this.

By the way, you said 4mm wire but I assume that means standard 6AWG wire, correct?

That is correct.

Flaky in terms of being difficult to set / configure using the pots, I understand.

And even ‘flaky’ in terms of the setting itself not being stable and needing to be recalibrated.

Both of those are different than the DC-DC-converter putting out much more current ripple than a standard bench top PSU…

Someone with an oscilloscope is going to have to make dons head-to-head measurements to understand what magnitude of current ripple we are talking about…

I don't know how to use these.
I am looking forward to seeing results.

Your experience with your one DCDC converter suggests it may not be that big if a deal…

I have tried about 5 different types of DCDC converters.
The type I found best - I bought 4 of but I was unable to replicate.
I am pretty sure, now, it was because I was adjusting the Boost Converter in-situ.
Instead of adjusting the Boost Converter on a proper constant load, separately, the MPPT / Inverter were causing me all sorts of headaches whilst I was "trying" to adjust.
Hence my "flaky" claim.
The first Boost Converter was probably dumb luck.
Learning very slowly here.