question

gyrovague avatar image

How quickly should ESS switch to battery+inverter when grid fails?

I have Victron MultiPlus II 5kVA, 4x 3.5kWh pylontech batteries, 12x 395W 3s4p PV panels, 150/100 Victron MPPT, Venux GX, ET112 grid meter, all in a ESS configuration. When the grid fails (South African loadshedding, currently happens about twice a day), about 30% of the time I can see lights flicker and PC and TV and sound system etc. will reboot. The salesperson originally told me the system can switch within 20ms and will perfectly act like a UPS. The strange thing is that this happens even when in strong sunlight (basically all power supplied by sun, except for the small "grid setpoint" amount) or when already primarily using battery storage (early evening, after sunset), so in both cases everything should already be powered by the inverter, doesn't make sense to me that there would be a long enough dip in power when the grid (supplying merely a small "grid setpoint" amount of 150W) fails. At least two of the times these reboots/dips happened, there was no significant power draw, no stoves/ovens/geysers using the non-essential circuit, less than 1kW average drawn for the essential circuit,


[I have a perhaps tangentially related issue, where sometimes the system feeds back to much power into grid (while grid is working), causing prepaid grid meter to reset and cut-off the mains supply for a few seconds. There are various posts about this topic on these forums, and one of the hypotheses is that this is related to some kind of slowness between victron and the ET112 grid meter, so just mentioning that here in case that same alleged slowness could be causing this slow response to grid failure too]


Needless to say, this is extremely annoying, as the main reason I got this system was to act as backup against downtime from loadshedding. Any ideas?

ESS
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6 Answers
Paul B avatar image
Paul B answered ·

Make sure that the UPS function is ticked using ve config


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I'll pass this along to my solar installer, it's quite clear that this software is not something that I as an end-customer should be using. I installed it briefly, and saw all the warnings about how it should only be used by qualified and trained people and that it can damage your system beyond repair etc., and promptly uninstalled it. :)

Hi @gyrovague


You will be able to verify this by downloading the config through VRM and viewing it offline. That way you can double-check your solar installer.


Go to VRM-> Device List -> Remote VEConfigure -> then click download.


If you have VE configure 3 installed you can just open the file and check what has been done.


regards

Ewald



hmm, when I go to vrm.victronenergy.com website and view my installation, I go to Device List (on the left), but it just shows a list of things like gateway, Ve.bus system, battery monitor,solar charger etc.,but I don't see "remote VEconfigure" anywhere on that screen or inside any of those expanded devices.

It might be that you do not have full control of your system.

Speak to your installer about this. Seeing as its your system you should have access to it.


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in the GX. Go to settings -> VRM and make sure two-way comms is enabled.


This two-way comms did the trick, thanks @nickdb!

@EwaldErasmus Now that I've downloaded that config from VRM and loaded into VE configure, I don't see that section with the UPS checbox at all, mine looks like this:

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The way I understand it is the UPS mode only works if you are not using a grid code and an assistant requires a grid code. It is for people who only have an inverter and battery and are connected to the grid with the battery as a back up. Once you enable an assistant (ESS in this case) the UPS mode is disabled.


So you're saying in ESS mode it cannot do the fast seamless switchover? That sounds worrying ..

When you are on Solar and or battery you shouldn't see any impact when the grid fails as your critical loads are already using the inverter. You should only see this when you are not on solar and the battery has reached the cut off.

I have observed the reaction of the system switching appears to be related to how the council cuts power (or a brown out), the size of your battery and the your setup (Wire lengths, age, etc.)

The Victron can switch in 20ms but this is constrained by the grid specifications and items listed above



Many grid-tied installs (especially when backup power is a concern) have more appliances attached to them than the inverter can power on its own, with passthrough from grid covering the slack. This is a much cheaper way by avoiding massive rewiring.

Solar/batteries may only power part of the load or an ESS inverter limit is set, so it is no guarantee of a seamless failover.

The issue seems to be more about brownout as suggested before.

If you can drop the supply breaker and nothing has an issue, the problem is on the grid side.

Had some TVs restart tonight when the grid was lost . It was a noticeably larger flick of the lights when it changed to inverting. Guess the cutover isn’t always as seamless as it should be.

Ugh... :( My PC has rebooted a few times while I've been working, the main reason I got this whole expensive setup was to protect against loadshedding, and now it's not doing that.

It should not be doing that, not to that extent, so often.

Part of the problem may also be due to how the grid is being powered off. It was rare for me to notice the grid being lost, particularly on devices that have been fine previously, but it also happened to a friend down the road at the same time. Would suggest you get your installer and distributor involved to look at why this is happening so regularly.

Hi @gyrovague


I have had similar issues with some of my sensitive equipment. I have a 8kVA Quattro and although most of the equipment doesn't notice the load-shedding some of my more expensive test equipment does... I solved the problem by placing an inline UPS on those loads. I already had the UPS's so it was at no expense to me... I assume that because the equipment is rather far away (in wire length) from the inverter, there is a larger delay in voltage change over, large enough for the system to notice it and shut down...

I have been trying to read on using AC caps for low voltage ride through... but haven't had a lot of time to read on that. I cant see why it will work but I have had a few colleagues mention it, so I will have to get my oscilloscope out and test it one day.

Just as an aside, I see you have an external grid meter and that's not something your config actually needs since you can't back-feed and aren't using a PV inverter. Seems like an unnecessary link in the chain.

Maybe someone else can comment if that could throw ESS off in any way?

Think you got upsold on that one.

Yes, I'm not sure either what the purpose of having the ET-112 is... The way it was described to me was that the ET112 is necessary in order to have non-essential loads on the input side of the multiplus II, I think it essentially then feeds-in from the MP2 to those non-essential loads, and uses the ET-112 to measure the true value at the grid side. So something like:


          __________________GX
          |         ________|___________
grid -- ET-112 --+--|AC-in     AC-out-1|-- essential
                 |  ---------+----------
            non-essential    |
                             +--MPPT--PV
                             |
                            bat

(I may have some of the details wrong, doing this from memory, and I'm by no means an installer).


I think the issue is that between the ET-112 and the GX and the MP2, somehow it reacts very slowly (15 seconds or more) to large non-essential load changes (maybe due to the RS-485 to USB converter?), so ends up feeding in too much and thus leaking into the grid, which resets the prepaid meter.

What I don't understand, is how the above is supposed to be any better than doing simply this:

                            GX
                    ________|___________
grid ---------------|AC-in     AC-out-1|-- essential
                    |          AC-out-2|-- non-essential
                    ----------+---------
                              |
                              +--MPPT--PV
                              |
                             bat

As far as I can tell, the AC-out-2 is connected to the AC-out-1 (on my model of MP2) via a relay that is controlled by default based on the grid presence on AC-in (measured by an internal CT inside the MP2 I think). This relay can also optionally be controlled by assistants to allow one to have non-essentials enabled during grid failure while (say) battery is above 80% or whatever, thus also allowing non-essentials via PV+MPPT during grid failure.

The installer maintains the former is "the way the system is supposed to work" and that my 2nd drawing is "not the correct way", but from the things I've been reading in the manual and these forums, I honestly cannot see a reason why he says that, and in fact I have a feeling this configuration stems from before the MP2 with AC-out-2 came out. It seems to me this would eliminate the whole feed-in slow response problem altogether, while still allowing me to use PV+battery energy on non-essentials while grid is working, and prevent non-essentials using battery when grid fails... So essentially all the features I want/need, without any of the problems, and would've been slightly cheaper.


I'm probably missing something. Tagging @Daniël Boekel (Victron Energy Staff)

Hi @gyrovague

The second drawing is absolutely fine, it's just that if (non essential) loads are bigger than the throughput capacity of the inverter, it might be necessary to use the first diagram.

And you'll have all loads in one 'window' in the remote console.

gyrovague avatar image gyrovague Daniël Boekel (Victron Energy Staff) ♦♦ ·

Oh, hmm, OK. I was under the impression (maybe from erroneous forum posts?) that the multiplus II can automatically use extra grid power to make up for extra load required on the AC outputs, somehow. There was a specific example somewhere with somebody explaining for a 3kVA system that if the load was 4kVA, it would draw 1kVA from the grid and 3kVA from the inverter (via PV or batteries).

Edit: here is where I read about that: https://community.victronenergy.com/answers/16705/view.html


I don't mind about the remote console loads window, though I had expected (incorrectly again) that it would show AC1 and AC2, I guess it doesn't/cannot measure them separately.


I have nothing against the first drawing (esp since the system is already installed that way), if only it would work properly and not keep feeding back into the grid for multiple seconds and resetting the prepaid meter :(

Hi @gyrovague

yes it can use grid power to help power loads too heavy for the inverter, but that's something else (power assist)

Every inverter has a maximum throughput rating, the maximum current the internal relays can handle (Grid power to loads)

gyrovague avatar image gyrovague Daniël Boekel (Victron Energy Staff) ♦♦ ·

OK, not sure what you mean when you say "but that's something else (power assist)" Are you implying the power assist thing cannot work together with ESS mode, or just mentioning that it is (of course) limited? Assuming the latter, how much total load would AC1+AC2 be able to get from MP2 and grid, in other words? If it's limited to the 5kW of the inverter (so no extra power from grid, no power assist or whatever) it might be an issue for me, but if it can do (say) something like 7kW (5 from inverter, 2 extra from grid), that would probably be totally fine 99% of the time. My peak power draw is only very rarely over 5kW anyway, just when some combination of dishwasher, oven, stove, microwave etc. is all used concurrently, and that can be avoided by educating my family a bit.


My installer maintains that everybody he has asked about this recommends to NOT use AC-2, and to prefer the non-essentials on the input side with the grid meter, but nobody can tell him (or me) the reason for that... I'm wondering whether it's not just "old school" thinking from previous victron inverters that perhaps didn't have AC-2 connected via a programmable relay to AC-1 like the MP2 has? I'm not sure though, I watched a bunch of the victron videos on your youtube channel yesterday, and they all also have this non-essentials with grid meter on input side setup, I didn't find one video showing the use of AC-2 for non-essentials without any grid meter... The flexible configurations that the MP2 supports is truly amazing, but also confusing :) and I haven't found a nice resource showing examples with pros/cons of all the possibilities together (well, there was one such, but it did not have the AC2 thing without grid meter in the options, and no real pros/cons of the various setups).


Again, if that feed-in to non-essential side between grid meter and MP2 input side worked well, and didn't take 15s+ to compensate for load changes, I'd be totally fine with that too, but it seems that it's inadequately understood why it (something, whether ET-112, RS-485 to USB, GX, MP2, combination of these) takes so long to compensate, and it seems to have been an issue for months/years on these forums with no real solution AFAICT.

gyrovague avatar image gyrovague Daniël Boekel (Victron Energy Staff) ♦♦ ·

@Daniël Boekel (Victron Energy Staff) My installer got the following response from his Victron supplier support, regarding the AC-2 option:

----

The inverter can only invert to AC1, AC2 is only live when the inverter has accepted the AC input, in other words when the transfer relay is closed.


The downside of putting non-essentials on AC2 out is that the inverter will turn it off every time the transfer relay is opened, for whatever reason, and there will be a 3 second delay before AC2 is live after AC input is accepted.


It will also not solve the problem at all, since the extraneous energy that is not used on AC1/2 will still feed back to AC input. When large loads such as stove or geyser are turned off, the overshoot will still happen for a short period.


What is even more problematic is that the loads on AC2 will turn off every time the inverter behaves like a UPS and turns off the AC because the power is weak, e.g. under/over volt, Hz outside of acceptable range. This means the non-essentials will turn off even when there is grid power available. This is especially the case when the more sensitive NRS097-2-1 regulations are followed.


All systems that feed back the extra power with a limiter will have this problem because the prepaid meter is unnecessarily sensitive.


There are only two options here that will work: Either the meter needs to be replaced, or the system must be programmed to not never feed back by putting as much as possible on AC1 output, and only connecting the grid when there is insufficient solar and battery power.


The correct solution is to replace the prepaid meter, I understand the municipality is unwilling to help with this, but there is no setting that will improve this problem, only the meter is to blame for this problem.

----

I don't really agree with all above (but OTOH they are the local experts here), it seems to contradict what you said before. I thought without a grid meter and using AC2, the MP2 will not feed in to input? The MP2 diagram makes it clear that the AC2 is connected to AC1 via a programmable relay, so I'm not sure what he means regarding the transfer switch & UPS functionality. If what he says is accurate and that using AC-2 for non-essentials will cause them to often turn off, that's not ideal, similar issue that I have now with non-ess cut off when meter resets grid.

IMO the Conlog BEC23 prepaid meter tolerates perfectly reasonable overshoot (40W for 15s or 600W over 1s of back-feed before cutting off the grid, AFAIK), but the MP2 overshoots far more and far longer than that for whatever reason (I could make a video of remote console showing it, but it's been shown exactly by others on other posts on these forums, "slow response" etc.)... so it feels to me that replacing with a so-called "less sensitive" prepaid meter (at great expense to me BTW, to the tune of 400euro before installation costs) isn't really the correct solution. Am I wrong?

Did you try to use current transformer (CT) instead this ET-112 meter.

It should be faster in reacting to the direction of the current flow.

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The inverter can only invert to AC1, AC2 is only live when the inverter has accepted the AC input, in other words when the transfer relay is closed.

Yes, that's what you want

The downside of putting non-essentials on AC2 out is that the inverter will turn it off every time the transfer relay is opened, for whatever reason, and there will be a 3 second delay before AC2 is live after AC input is accepted.

I don't understand what they mean by that... why would the inverter turn off?
Yes there is a delay to AC-out2, but that's no problem as those are the non-essential loads.

It will also not solve the problem at all, since the extraneous energy that is not used on AC1/2 will still feed back to AC input. When large loads such as stove or geyser are turned off, the overshoot will still happen for a short period.

feeding loads to the output is done in the inverter firmware, thus much faster than through measurements in grid-meter etc. And also ramp up/down speed is not limited by grid-standards.

What is even more problematic is that the loads on AC2 will turn off every time the inverter behaves like a UPS and turns off the AC because the power is weak, e.g. under/over volt, Hz outside of acceptable range. This means the non-essentials will turn off even when there is grid power available. This is especially the case when the more sensitive NRS097-2-1 regulations are followed.

That is true, depending on how good/bad the local grid is this might be an issue

All systems that feed back the extra power with a limiter will have this problem because the prepaid meter is unnecessarily sensitive.

?

There are only two options here that will work: Either the meter needs to be replaced, or the system must be programmed to not never feed back by putting as much as possible on AC1 output, and only connecting the grid when there is insufficient solar and battery power.

I don't know if the inverter is fast enough for the meter, I'd say first try by not using the grid meter (thus only feeding to essential loads) and see if the grid meter likes it.

The correct solution is to replace the prepaid meter, I understand the municipality is unwilling to help with this, but there is no setting that will improve this problem, only the meter is to blame for this problem.

first try 'run without grid meter' (option in ESS menu) and see if the system is fast enough.

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gyrovague avatar image gyrovague Daniël Boekel (Victron Energy Staff) ♦♦ ·

@Daniël Boekel (Victron Energy Staff)

Can you confirm what this guy says is true?

https://community.victronenergy.com/answers/16705/view.html

and if so, what is the max power I could get to AC-out-1+AC-out-2 from a combination of the DC side (PV+bat) and the grid import? (I have the Multiplus II 5000VA version).

Yes that is correct. see datasheet for max power.

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The system isn't actually that complicated, you just need to have some electrical knowledge and understand the various mechanisms.

There is a lot of good info but it is scattered across different manuals and tutorials, It would be nice if it could all be compiled into something that is more of a digital wizard or tailored how-to for typical scenarios.

The UPS function works well, I notice the slightest flick on LED lights when eskom cuts power. Enable the grid-lost alarm on the GX, that way it will notify you when the power is cut.

Why would the South African grid code not be setup for the load shedding parameters by default? It's literally the reason we all get these systems in the first place?

Can I still run ESS with grid code other in SA?

What is the password to change it?



karel avatar image
karel answered ·

I have a 48/3000/35 MultiplusII with 1 pylontech and venus gx + 4000 W PV etc. and found similar problem. During the day when load shedding happens all appliances (TV DSTV etc) are fine i.e no rebooting at all. During night time, no sun or pv input, when load shedding happens, my TV and AV system reboots but my DSTV decoder does not reboot. Was also wondering why the resets happen at some stage. When simulating load shedding by manually switching off my main breaker I also have no resets at all.

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@Karel

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#minimum_battery_sizing_recommendations

I have seen flicker on changeover for several reasons

1 - high grid line impedance

2- battery is smaller than recommended for the system

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#minimum_battery_sizing_recommendations

3 - undersized cables feeding the AC in in the installation

4 - brownouts make all of this worse increasing the amperage drawn as the grid is failing.

5 - incorrect earthing.

6 - grid code settings and LOM can also be a related issue.

bonie-wanda avatar image
bonie-wanda answered ·

Hi

I also experience the same problem.The multiples ii 48v/3000va is so slow such that the modem and router loose network connection over and above the lights flickering.

Bonie

Johannesburg

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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi

I think the problem here is when the blackout is more like a brownout: AC voltage dropping slowly, until it finally reaches the disconnect limit.

The problem is usually that the inverter follows the input AC voltage, and when finally disconnecting it has trouble getting the loads back up to voltage.

As some grid-codes don't allow setting the disconnect limit, I'd try to run the system without a grid code (so no ESS!) and set the AC disconnect at a higher level (like 210V)

if this works: try using grid code 'other' and use an external anti-islanding device. (with grid code 'other' you can set the disconnect voltages).




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Hi @Daniël Boekel (Victron Energy Staff), Thank you this is very helpful. your explanation makes a lot more sense, so thank you, and sorry for bugging you.


I think South Africa is a difficult situation, as we have small supply interruptions as well (lasting less than 1s probably only much less) so setting that limit as high as 210 could impact other situations. I have had a few instances where the inverter kicked in but for no noticeable reason, and I can only assume it was an instantaneous voltage dip.

I am running my system without ESS, and with no grid code, but AC disconnect is set at 180V, which as you said could be the issue (slow voltage drop), coming to think about it it makes a lot of sense now, as when I simulate load shedding (dropping mains at the incoming CB) I have no issues with my loads, nothing sees the changeover, but during loadshedding when the utility turns off the supply to the mini-sub, they go off...

I would almost like to say there is an opportunity to interface the load-shedding schedule into the system and allow it to be more sensitive during the hour when load shedding is set to start, also giving users who run ESS systems the option to charge up the batteries before loadshedding...


Thank you again for your response.


regards Ewald

merlepeter avatar image
merlepeter answered ·

My MP switches perfectly , no rebooting during loadshedding.

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dylan-hyslop avatar image
dylan-hyslop answered ·

I am having the same issue, my computer reboots every time load shedding happens.

I am running a full ess system with multiplus II 3kva.

I cant see the UPS function in the VE Configure app. I have set the grid code to South Africa for the feedback function to work correctly.

I understand the brownout problem, which makes electrical sense, but how do I solve it? The main reason for me getting this system, and paying extra for Victron was so that I can work from home with Zero interruptions?

Do I really need to buy another inline up just for my computer?

Can I change the grid code to OTHER? and still have full function of ESS with push back?

I also noticed that our load-shedding has been at 5pm (evening) and my battery is often at 90% (my cut off voltage for ess) so the Inverter is primarily running from mains at the time of the ac power dropping.

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