zebrainmotion avatar image
zebrainmotion asked

Multi II not Working as UPS (ZA)

Recently purchased and installed MultiPlus-II 48/8000/110-100 with Freedom Won 5.5 kWh battery all connected by a Cerbo. All Victron firmware is latest, v2.94 and 502. (I don't yet know how to check/update the Freedom Won firmware; I'm in communication with the company.) Settings as given on, except that for a while I had the ESS mode as Keep batteries charged rather than Optimized (with BatteryLife).

When set to ZA grid, the Multi correctly acts as a UPS when I kill the AC in at the breaker. However, the Multi shuts down and restarts during a loadshedding event. This behavior seems to be seen elsewhere, and and; people seem to say that the problem is that the grid fails too slowly, more of a brownout where the voltage drops, but not very quickly.

Following the suggestion of some of the above links, I changed the grid to Other and manually set the AC low cutoff to 215V. For the most recent loadshedding event, the Multi shutdown and threw a Low Voltage battery alarm (at 55.84V (?)). Prior to the loadshedding event, AC out draw was low--max could've been 2kW but was likely more like 250W.

I have two questions: 1) in, @Daniël Boekel (Victron Energy Staff) suggested changing the grid code to None (and thus no ESS). Since tells me explicitly to use ESS, should I change settings to try grid None and no ESS? 2) are there other idea(s) for thing(s) I can do to get the Multi + battery to work as a UPS during a loadshedding event here?

Thank you very much for your help!

EDIT: I see that when loadshedding hits, I get simultaneously a Low Battery L1 and High DC Ripple warning/alarm. Also, adding from a comment below, the system shuts down even on very low loads, most recently when the load was only 108W.

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4 Answers
nickdb avatar image
nickdb answered ·

That is way too little battery for that inverter.

The system is undersized.

Almost all these issues have been identified as systems with batteries incapable of delivering the required power at cutover.

Usually solved by adding batteries.

Especially on etowers.

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zebrainmotion avatar image zebrainmotion commented ·

Hi @nickdb, thank you very much for this response. Yes, I understand that under a full load, the battery is too small. So far, the battery handles perfectly well the loads we put on it on a day-to-day when the grid is down. And before I invest an additional ~R40K, can you please help me understand _why_ the system works as intended as-is when the AC in is killed at the circuit breaker and _how_ the extra battery will make the system work during a loadshedding event, especially when at the time of loadshedding the load is (seemingly?) well within the capacity of the battery to handle?

Just to emphasize, I can confirm that as-is, the Multi+battery work perfectly as a UPS under loads from 0.5kW to at least 2.5kW loads when the power is killed at the db using a circuit breaker. Thank you.

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nickdb avatar image nickdb ♦♦ zebrainmotion commented ·
It's simple. When you drop a breaker it is a clean cutoff, when eskom has an outage, the grid tends to brown-out, it is not clean. The problem varies by area and state of the grid.

The brownout is what creates the conditions you are experiencing, a momentary surge that is beyond what the battery/bms is prepared for.

Pace based BMS's have been a bit worse at this - so etower, hubble, bsl etc.

The DCL for that (assuming etower) battery is not good, 90A, on an inverter that can peak way, way beyond that.

Capacity is never the issue with a battery, it is the ability to delivery power, especially under transient conditions.

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zebrainmotion avatar image zebrainmotion nickdb ♦♦ commented ·

Thanks again for responding, @nickdb.

I'm very sorry for being slow, but I'm still trying to understand your answer. Why does a brown-out lead to a greater draw on the battery than a clean cutoff? And if the AC load is ~2kW, what's creating such a big current draw on the battery? Yes, the Multi II 8kVA _can_ peak at 15kW, but shouldn't the current only be ~2kW/45V ~ 45A << 90A?

Somewhat related, you seem to not like the eTower. What's your preferred battery?

EDIT: the Multi II just shut down at the start of loadshedding under 108W of AC out load, which seems bonkers to me.

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nickdb avatar image nickdb ♦♦ zebrainmotion commented ·

Nothing against the e-tower, have a few myself, it just uses a generic BMS (PACE) like other local brands, which has had a chequered history.

When the input voltage dips, the inverter tracks it downwards towards the cutoff, trying to then catch this via the battery can cause a sudden spike on the battery end, dropping it's voltage (momentarily) below cutoffs on the BMS and/or inverter (but usually the battery).

The tools you have available to you cannot show transients. There is a 1min granularity to VRM, whatever is happening is too quick for anything you have access to.

This is not a new issue, and it is always resolved with more battery.

A search here will show as much. We have members with the same issue and pylontechs, Revov, hubble etc.

No installer should have recommended this configuration to you.

You can can go double check your settings from the Freedom Won docs here

That way you can be sure nothing was missed.

An installer friend of mine recently swapped this brand for another at a site doing the same thing. Issue evaporated.

Even at my own home, I have plenty of battery, and on some grid loss events there can be a proper dip. The number of times it actually rejects the supply is an indication of how bad the grid can be in some places.

There is an install round the corner from me, also using the minimum battery (incidentally also a PACE BMS), and 9/10 outages AC out is lost briefly, and then recovers.

Even by Freedom won's specs on the battery, your inverter is too large, that won't help any support requests.

Sorry to be the bearer of bad news, but this is not an Inverter issue.

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dylan07 avatar image
dylan07 answered ·

@nickdb is right though the battery is too small, had the same issue with a 5kVa with a 2.5kWh battery (fixed when I changed to a 3kVa). For that split second the inverter is trying to power the whole street, all 8kVa and the battery BMS cuts off as this is sees this as a short (voltage tanks really fast / high current) this is the causes of low voltage and DC ripple from the disconnect. Why not set the multi up as a UPS not ESS.

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zebrainmotion avatar image zebrainmotion commented ·

Hi @Dylan07, this answer makes much more sense to me (because why would 100W of loads cause trouble?). That said, I've got a one-way meter, and (I thought!) the Multi/Cerbo system was set up to prevent feed-in to the grid.

I can confirm that under ESS in the Cerbo the AC-coupled PV and DC-coupled PV feed in excess is disabled (although I've got no PV system at the moment). I was using the ZA grid code selection in VE Configure 3, but now I'm using Other with LOM B. When I try to change to Grid None (feeding energy from DC to grid not allowed), then VE Configure 3 won't allow me to run ESS.

I hear your point on just turning off ESS--and I'm now very much tempted to do it--but I come back to my original question: in the official instructions for connecting Freedom Won to the Multi II, we're told to use ESS with very specific parameters, Can anyone at Victron officially sanction turning off ESS when connecting a Freedom Won battery to a Multi II?

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martin-delp avatar image martin-delp zebrainmotion commented ·

Please let us know whether upsizing the battery worked for you. I have exactly the same issue (high ripple/low voltage disconnect), but battery sizing is not the issue (5kva MP2 + 10kwh (100A dcl) battery, neither is LOM detection, neither is ESS/no ESS, neither is changing grid code to “other”. Also placed external voltage monitor and contactor to externally cut when voltage drops before it gets to the Multi but has not made a difference. Getting a replacement MP2 on Tuesday so hopefully this solves it, but would still like to know others successes for me to try.

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zebrainmotion avatar image zebrainmotion martin-delp commented ·

That's wild. Does your MP2+batt properly act as a UPS when you cut your main switch? I can confirm now that changing my Grid to None (feeding energy from DC to grid not allowed) didn't solve the problem for me; I had ~200W AC out loads when loadshedding hit, and the system went down again.

I'm thinking now that the solution will be to physically isolate the MP2+batt a few minutes before loadshedding begins, but it sounds like you've tried that already with your system?

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martin-delp avatar image martin-delp zebrainmotion commented ·
Yes, no interruption when mains breaker is flipped. I have a breaker on each of the MP2 AC connections (AC-IN, AC1-OUT (essential) and AC2-OUT (non-essential) so I manually flip AC-IN before loadshedding to avoid the house going down. With enough solar it gets me through the day so I can leave it down. I don't have any comment on your system being undersized which could cause similar issues, so will take nickdb's word on this. There are still quite a few things to test without having to replace the inverter (although it used to work perfectly up until September 2021 - been having this issue since then) such as battery cables, BMS, communication cables, rolling back firmware to pre v476 etc. Unfortunately my supplier has not been as vested in my issue as I had hoped. Also had CoCT out to check the meter - nothing wrong. My neighbour diagonally across from me has a MP2 5kva and has had no issues upon grid failure.
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martin-delp avatar image martin-delp martin-delp commented ·
Morning all, I just wanted to provide an update. It appears that I have managed to fix my Victrons shutting down on "low battery voltage" alarms when loadshedding hits (as discussed above). We did four things together last week Monday, so difficult to say exactly what the fix was, but thought I would share my experience for others to hopefully find relevant. 1) replaced battery cables with 50mm cables (old ones were 35mm I believe), 2) replaced Victron megafuses with alternative fuses, 3) replaced neutral busbar where eskom comes into the property (ours was quite rusty), 4) City of Cape Town fixed loose "live" cable that goes into our split meter in box outside the house (the cable just dropped out and wasn't screwed in properly). I hope this helps some people having the same issue. We have tried many things over the last 2.5 years and happy this is now resolved (we have had 6 successful changeovers since last week). Following these suggesntions are of course cheaper than increasing battery size, but I would agree with nickdb that this should be considered first.
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nickdb avatar image nickdb ♦♦ martin-delp commented ·
@martin_delp glad you came right. If you are able to remove the cause of the brownout, that will make life much easier on the system and battery, which is of course cheaper. Fortunately the issue was located on the property, where there is a broader issue then you can only really throw hardware at the problem.
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nickdb avatar image nickdb ♦♦ zebrainmotion commented ·

The setup guide is for an ESS, which is why the parameters are referenced. There are numerous installs with batteries just used for backup, or with no solar or off-grid. There is no requirement to use ESS for anyones battery, there are only requirements to configure it correctly if you do.

There is no scenario where the inverter, not setup to feed-in, will backfeed at full power at grid failure. There is always some ebb and flow of power to/from grid, with or without ESS, but since low frequency inverters don't have the fastest response times, the battery will always be first in line.

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zebrainmotion avatar image
zebrainmotion answered ·

What I ultimately did was set up a home automation to 1) track loadshedding via the ESP API, 2) automatically change the Inverter Switch to Inverter Only a few minutes before shedding, 3) automatically change the Inverter Switch back to On about 20 minutes into loadshedding. Haven't had a problem since.

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martin-delp avatar image martin-delp commented ·

That is great news! Replacement inverter didnt fix my problem so next step is a deeper analysis of the BMS (for which I require my installer to assist with). In the meantime would you be able to share the software etc you used to achieve this automation? At this point I am willing to try anything (at least as a temporary measure). Although I guess it wont help with ad hoc interruptions (e.g. street maintenance), but at least it seems to work for loadshedding which is of course far more often. Thank you very much.

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Ettienne avatar image
Ettienne answered ·

To me this only means that the Victron UPS function is not working. UPS means the system should be running from the inverted power (not pass through grid power) all the time, with grid only used for charging when required (e.g. PV not available when SOC goes below set limits, etc.), or for when loads are high. I have a 2 x Multiplus II 48/5000 in parallel on one phase, with 10kw battery backup, 6kW solar in a small house, and running on grid code for South Africa (btw. it removes the UPS function selection in the config). Leaving grid input off, the whole house runs smoothly without problems. With grid switched on, brown outs causes the inverters to dip for 3s, like above. Any other UPS and Sunsynk and other inverters functioning as UPS on the essential circuits does not do that. A UPS (uninterrupted power supply!!!) should run the essential (circuits on the Multi's output) permanently from the inverted power (that the inverter gets from battery, PV, grid or combination thereof). The output should be independent from the grid.

Currently, with the Multiplus having a fast switchover time of milliseconds, what is the use of the UPS function. It seems even with UPS on, the Multi still runs off the grid and when grid fails it quickly switches over to battery/PV. And with UPS off it does the same thing... So what is the use?

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nickdb avatar image nickdb ♦♦ commented ·

UPS's come in different flavours. A full UPS provides clean and stable power no matter the grid quality.

An inverter is not a UPS.

It has UPS like qualities, ie fast cutover from grid to invert.

First and foremost it is an ESS, to be an ESS you have to sync to the grid so power can be fed back and forth, so within the operating ranges AC out will track grid voltage/frequency,

This is clearly documented.

This post was about the battery cutting out when faced with the cutover surge it is easily resolved by following all the vendors sizing requirements.

in SA, grid failures can brownout. While the UPS cutover still works, it can result in the voltage tracking down a bit too low and sensitive gear restarting - vs power being lost altogether, which is what this topic is about.

Some of this can be improved by tightening upper/lower limits.

These inverters are low-frequency so put a greater demand on the battery at cutover vs high frequency inverters like the sunsynk, so are less forgiving of less optimal system design.

Ultimately, though, expecting an inverter system to behave like a class A UPS, is a fundamental misunderstanding of both UPS and ESS technology.

We deal with these issues from time to time, it almost always comes down to cutting corners on the battery spend - something that has been more prevalent on batteries using PACE BMS's (hubble, BSL, e-tower and others).

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rickc avatar image rickc nickdb ♦♦ commented ·

@nickdb I had a UPS anomaly today.

Setup: US Split Phase, 48V System, Dual Quattro 5k 120V.

ESS connected to grid, UPS mode, no feed-in, 400W grid set point, EM530 Energy Meter (it's fast), 15 kWh total EG4 LL batteries (3x100Ah), BMS DCL is 300A.

We have somewhat frequent power glitches here at the end of the utility run.

I normally never notice them, because the Quattro UPS mode has worked really well for us. But not today.

Like the OP above, today, the Quattos gave a high DC Ripple Warning, Low Battery Voltage Warning, then shutoff 3 seconds later, then recovered 10 seconds(?) after that. I can confirm that the DC voltage went down to 42.8V.

You were mentioning tightening up the voltage limits above. Tighter meaning switch to UPS sooner on brownouts? Like 110V for a normal 120V line?

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nickdb avatar image nickdb ♦♦ rickc commented ·
Hi, yes, select a grid code usually "other" that allows for changes, then you can spec the upper and lower AC cutoff limits and restart threshold. The inverter often has a wider range and that can lean a bit too hard on the battery. It is not a 100% fix, but may help.
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rickc avatar image rickc nickdb ♦♦ commented ·
Done, thanks.
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