Kit is: Axpert VM4 5600W inverter and Pylontech US3000C batteries

The scenario is that we are off-grid. We want to go away for some of the Winter but we are worried as to what the consequences will be for the inverter if the battery stops supplying current to it after a long period of grey days. Will the Axpert inverter automatically re-start when the PV voltage is high enough and restart charging the Pylontech batteries?

We don't want to switch the inverter off because we want to leave the freezer on.

I hope that this is enough detail. Thanks

54 minutes ago, zennomind said:

Kit is: Axpert VM4 5600W inverter and Pylontech US3000C batteries

The scenario is that we are off-grid. We want to go away for some of the Winter but we are worried as to what the consequences will be for the inverter if the battery stops supplying current to it after a long period of grey days. Will the Axpert inverter automatically re-start when the PV voltage is high enough and restart charging the Pylontech batteries?

We don't want to switch the inverter off because we want to leave the freezer on.

I hope that this is enough detail. Thanks

Could you provide answers to the following questions:

1. Is the inverter or battery running anything else?
2. If you have gone for 2-3 days, have you needed to run a generator to top-up your battery during this season, am assuming you're in winter presently?
3. I assume the fridge has stock, so you're not able to turn it off?
4. Do you change (lower) the temperature controls on your fridge in winter generally or not?

1. I will switch everything else off in the house. So the 14Kwh pylontech battery will only power the inverter and the freezer.

2. We're not going to be here for 21 days. During this time there could be a long period where the battery is powering the inverter and the freezer but not getting topped up. I've never let the battery get down too low that it cuts the power to the inverter.

3. Correct, it's the only thing that we don't want to switch off.

4. I don't want to raise the temperature above -18C

How many batteries? 

You can buy plug in measuring devices that will show you how much power a device uses over a period of time. You could extrapolate a figure from this and try to see how long your battery will power the freezer. 

But I think it long odds running just on battery. 

My freezer (very new, very efficient) will draw about 600Wh in a day. I have 10kWh of battery. This will shut down when remaining charge is 10%, so I have 9 useful kWh. 

So I'd get 15 days, but that excludes self consumption by the inverter. I ain't going to make 21 days. 

But how likely is it that I get no solar in 21 days? 

Eat as much of what's in that freezer as you can before you go on holiday. Hope for the best. Restock when you return 

Or arrange with a neighbour to throw an extension lead over the wall and you will make a contribution to their bill. 

11 hours ago, zennomind said:

The scenario is that we are off-grid. We want to go away for some of the Winter but we are worried as to what the consequences will be for the inverter if the battery stops supplying current to it after a long period of grey days. Will the Axpert inverter automatically re-start when the PV voltage is high enough and restart charging the Pylontech batteries?

My apologies. I didn't address your actual concern in my previous reply.

I should think the inverter will restart. Think about your inverter at install time. Something had to power it up. And it can't be designed to start  only from batteries because the state of the battery at install time can't be known in advance. 

I think the thornier problem here is will the batteries restart if they shut down, or will manual intervention be required? 

My inverter (not an axpert) has a setting allowing it to restart the battery if there is sufficient PV.

Read the manual for your inverter and see what answers you get for your questions. 

Edited December 30, 20232 yr by Bobster.

1 hour ago, Bobster. said:

 

I should think the inverter will restart. Think about your inverter at install time. Something had to power it up. And it can't be designed to start  only from batteries because the state of the battery at install time can't be known in advance. 

 

My inverter (not an axpert) has a setting allowing it to restart the battery

Just my way of thinking. 

If your battery is set to switch off at say 20% SOC. The inverter is set to switch off at 30%. This leaves power for self consumption. The next day PV will charge as charging is never disabled and will always be used to charge from grid or PV. 

As soon as the back to battery level is reached it should power the load again. There is no need to even go down the path to calculate how many days one can run only on battery power as there will be some PV every day. Without the freezer being opened you can get through a 24h or more without power. 

We can come up with a lot of what if scenarios as what we think will happen but the best is still to do the tests in advance by switch off the PV to get the battery discharged and see if all works well. 

No need to worry about the battery switching off and manual intervention is called for if the test are done a few times before hand. 

The reason for the test is we don't have to assume the outcome. Even different models of Axpert can react differently let alone different makes. 

We are dealing with an off grid inverter high voltage MPPT that can AFAIK run from PV even without a battery or grid. This cannot be done with true hybrids. This can also be checked with the battery disconnected. 

I stand to be corrected on the above. 

I think, long story-short... carry-on regardless and touch-wood, all will be well. As @Scorp007 most batteries will restart after a certain minimum voltage has been reached if they switch off and inverter too. Happy holidays & don't fret about it and enjoy yourself. Whatever will be, will be and you can't change it once you're gone, so might as well enjoy yourself.

24 minutes ago, Moffat said:

I think, long story-short... carry-on regardless and touch-wood, all will be well. As @Scorp007 most batteries will restart after a certain minimum voltage has been reached if they switch off and inverter too. Happy holidays & don't fret about it and enjoy yourself. Whatever will be, will be and you can't change it once you're gone, so might as well enjoy yourself.

We have seen batteries we need to jump start but that I think is mostly because the inverter cut of has not been set higher than the battery switch off by the BMS. 

Don't most of us try to get the most power from each cycle? And the reason is LS. 

14 hours ago, Scorp007 said:

We have seen batteries we need to jump start but that I think is mostly because the inverter cut of has not been set higher than the battery switch off by the BMS. 

Don't most of us try to get the most power from each cycle? And the reason is LS. 

That is also true, the hope and secret faith is that it's not so in this case.

21 hours ago, Scorp007 said:

Just my way of thinking. 

If your battery is set to switch off at say 20% SOC. The inverter is set to switch off at 30%. This leaves power for self consumption. The next day PV will charge as charging is never disabled and will always be used to charge from grid or PV. 

As soon as the back to battery level is reached it should power the load again. There is no need to even go down the path to calculate how many days one can run only on battery power as there will be some PV every day. Without the freezer being opened you can get through a 24h or more without power. 

We can come up with a lot of what if scenarios as what we think will happen but the best is still to do the tests in advance by switch off the PV to get the battery discharged and see if all works well. 

No need to worry about the battery switching off and manual intervention is called for if the test are done a few times before hand. 

The reason for the test is we don't have to assume the outcome. Even different models of Axpert can react differently let alone different makes. 

We are dealing with an off grid inverter high voltage MPPT that can AFAIK run from PV even without a battery or grid. This cannot be done with true hybrids. This can also be checked with the battery disconnected. 

I stand to be corrected on the above. 

A much better proposal. Simpler than all my calculations, and will give a more dependable result.

23 minutes ago, Bobster. said:

A much better proposal. Simpler than all my calculations, and will give a more dependable result.

@zennomind I think if you can set your parameters as suggested here by @Bobster. before going, should be okay, touch-wood & no manual restarting of the battery would be necessary over the course of your time away.

On 2023/12/29 at 10:25 PM, zennomind said:

1. I will switch everything else off in the house. So the 14Kwh pylontech battery will only power the inverter and the freezer.

2. We're not going to be here for 21 days. During this time there could be a long period where the battery is powering the inverter and the freezer but not getting topped up. I've never let the battery get down too low that it cuts the power to the inverter.

3. Correct, it's the only thing that we don't want to switch off.

4. I don't want to raise the temperature above -18C

We at least know what the battery size is. Without knowing in which area you stay or the size of the panels no calculation can be done. 

With this info one can do an average yield from the PV side which could give more comfort together with other recommendations so far. 

The only load of the freezer one can estimate at not more than 3 kwh per 24 hrs as a worst scenario as it will not be opened. 

If you know this value it comes to less guess work. 

I had two questions.

1. Will the inverter restart when PV comes back online after the battery has run out of power and stopped supplying the inverter. It sounds like the inverter should power back up. Thanks @Bobster.

2. Will the inverter be able to charge the battery after it has stopped supplying power because it's below the 95% discharge limit. It sounds like the BMS might need to be rebooted and so @Scorp007 idea of keeping the inverter's cut off rate above the battery's minimum cut out is a good one. The Axpert does have a Pylontech option and that automatically sets the inverter to stop drawing charge once the battery hits 46V. That could very well be sufficient as the Pylontech manual states that the BMS enters self protection mode at 44.5V.

Addressing some of your other questions and points. I own a small Permaculture farm in Western France but I spent my first 32 years in Durban and then 20 years in the UK and 2 years here. There's no house remotely close enough to run a cable from. The solar input varies dramatically in Winter according to how direct the sunlight is. My roof mounted system (3.6kwp but old panels) is around 20 degrees and works better when the light is diffuse. That is compared to my ground mounted system (3.8kwp and 22% efficient) which is at around 40 degrees. On a clear day there can be 2000W and 3000W coming in from the PV at any one time and feeding into 2 x 14Kwh batteries. When I'm here I can switch between them with a rotary switch. I would have bought a car with V2H or V2L instead of such large static batteries but the cost until 2023 for using a car in this way has been prohibitive e.g. around 7000 euros for an inverter to use V2H in the Nissan Leaf. Based on my measurements from my UK systems 4kwh is a good input when there's some sunlight. I didn't install generation meters here because I'm not feeding into the grid. It's the grey days that worry me. We can drop a 14kwh battery from, roughly, 100% to 25% in 5-6 days if we're here and using it minimally. I'll put a meter onto the freezer and see what it consumes in 24h. I'll update here if there's anything worth mentioning.

@Moffat thanks for helping me understand the previous inputs with your summary this morning.

1 hour ago, zennomind said:

I had two questions.

1. Will the inverter restart when PV comes back online after the battery has run out of power and stopped supplying the inverter. It sounds like the inverter should power back up. Thanks @Bobster.

2. Will the inverter be able to charge the battery after it has stopped supplying power because it's below the 95% discharge limit. It sounds like the BMS might need to be rebooted and so @Scorp007 idea of keeping the inverter's cut off rate above the battery's minimum cut out is a good one. The Axpert does have a Pylontech option and that automatically sets the inverter to stop drawing charge once the battery hits 46V. That could very well be sufficient as the Pylontech manual states that the BMS enters self protection mode at 44.5V.

Addressing some of your other questions and points. I own a small Permaculture farm in Western France but I spent my first 32 years in Durban and then 20 years in the UK and 2 years here. There's no house remotely close enough to run a cable from. The solar input varies dramatically in Winter according to how direct the sunlight is. My roof mounted system (3.6kwp but old panels) is around 20 degrees and works better when the light is diffuse. That is compared to my ground mounted system (3.8kwp and 22% efficient) which is at around 40 degrees. On a clear day there can be 2000W and 3000W coming in from the PV at any one time and feeding into 2 x 14Kwh batteries. When I'm here I can switch between them with a rotary switch. I would have bought a car with V2H or V2L instead of such large static batteries but the cost until 2023 for using a car in this way has been prohibitive e.g. around 7000 euros for an inverter to use V2H in the Nissan Leaf. Based on my measurements from my UK systems 4kwh is a good input when there's some sunlight. I didn't install generation meters here because I'm not feeding into the grid. It's the grey days that worry me. We can drop a 14kwh battery from, roughly, 100% to 25% in 5-6 days if we're here and using it minimally. I'll put a meter onto the freezer and see what it consumes in 24h. I'll update here if there's anything worth mentioning.

@Moffat thanks for helping me understand the previous inputs with your summary this morning.

@zennomind the issue/answer is:

1. If the inverter has switched off the battery above the BMS cut-off voltage, it should then switch back on when there's enough minimum PV for the inverter to run (minimum Pv required for Inverter startup). The other side of the equation is if Pv being generated is going to be equal to that which the fridge is using as well as inverter self-consumption, it won't make much a dent to the battery by way of recharging it or if your panels are producing 150w vs Self consumption of Inverter at 50w + Fridge consumption at 125w then you have a deficit of (-25w) {these are thumbsuck numbers}, which would and should have been going into the battery. The other hopeful side is that fridges don't run continuously, so when it's not running then hopefully your minimum generation can at least recharge the battery during the Pv generation time from morning to evening. No one can really give you an accurate calculation as also Pv generation is not linear and at either constant peak or constant rate, hence my erring on the side of just being optimistic and hoping for the best.

The other side of the coin is once you measure exactly what is going on now (Pv generation vs consumption) and you go on away and it's not positive, it'll leave you worried all the time you're away and you cannot change anything then, anyway but just be miserable with worry. Also as once you're away, you may have days or times of peak generation or limited generation, which you are not able to predict accurately in the future. So eat as much as you can to avoid losing too much food in the fridge if worst case happens and maybe reduce increase the fridge temperature minimum to an acceptable level so it cuts off earlier and keeps things cool.

The method we test inverter mostly these exspert inverters is set the inverter cut of volts very high like 52v + most of these exspert inverter can today set cutoff as high as 53v or 27v . 

Pull the pv  fuses 

Wait for  it to shut down push the pv fuses back in  and observe what it does .

If it does start up automatically set cut off volts higher than bms cut of volt so the inverter shuts down before bms cuts the lithium .

Get an wall  socket programmable timer for the fridge and run the fridge only through the day  as at night it's much cooler and no one opens the fridge constantly like through the day so having fridges of at night is normal not an issue even in summer times . 

 

Hope this helps 

 

Edited January 1, 20242 yr by GMAC

Thanks @GMAC that's useful information. I think that the programmable timer would use too much energy compared to what the freezer actually uses in Winter (see below).

Update:

I placed a meter on the chest freezer and it used 94W over a 24 hour period. It's in the workshop where temperatures dropped to 7C overnight with a high of 10C during the day. Looking at the freezer manual this looks like what's expected. The VM4 self consumption is around 50W/h. So if there was absolutely no sun while we're away then the inverter would power down after just over 8 days and the freezer is rated for another 4 days without dropping above freezing. My assumptions on "8 days" is based on 12.5Kwh usable power and 64W/h being used. It's highly unlikely that there's going to be a 12 day period of absolutely no sunlight bar nuclear Winter.

I'll switch off power to the house while we're away because we've cleared the house chest freezer and almost cleared the fridge. Durban here we come.

almost same problem discovered here...

wks evo max II 10kVA + 2xus5000 pylontech and 7kWc of PV

the battery can handle a night and half a day more, after that you need solar to charge them

after 2 days of snow here, the battery have come to 5% (the inverter cutoff is set to 10%) and the battery are in full idle so off as the inverter detects zero volt.

I have to start the battery manually (off then on) when solar will come back (and the PV are without snow on them...)

is there a way to restart the batteries without human action ?