Multiplus - AC Ignore + Overload

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paul-campbell asked May 22, '23

Multiplus - AC Ignore + Overload

Quick question, I'm struggling to find the exactly answer to.

Scenario:

A Multiplus 24/800/16 is configured for AC-Ignore = true based on battery voltage using the "Dedicated AC-Ignore" Virtual switch.

The Multiplus is inverting and supplying a 700W load.

While the battery voltage and everything else remains the same.... the multiplus "derates" due to temperature to 650W.

Does the multiplus:

Switch back to AC-Ignore = false and fail back to AC-In as it would for battery voltage (for example).

Cut out and reset, dropping the AC-Out entirely.

Something else.

If the desired behaviour was to switch AC-Ignore to False and fail back to grid until either the inverter pro-rates again or the load reduces.... Can this be configured?

MultiPlus Quattro Inverter Charger

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Answer 1 · 2023-05-22T12:02:23Z

JohnC answered · May 22, 2023 at 12:02 PM

@Paul Campbell

The Multi won't 'derate' an AC load (how would it do that anyway?). It will do as it's told and continue until it's had enough, then trip. It does have overload time tolerances though.

It could be managed with the IgnoreAC function, but you'd need to tell it exactly what you want. I'd use Assistants rather than Virtual Switch, as there you have multiple options available for Ignore-AC, like say, Voltage and/or SOC and/or ACLoad.

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paul-campbell commented · May 22, 2023 at 06:25 PM

By derate I mean that its fine for 700W and then it's not fine. Based on temperature according to the manual.

I'll have a look into assistants.

The more advanced version of the Virtual switch for AC-Ignore has many options.

and

Seem to be "OR" across the board and so all form conflicting logical mirrors and stop each other working. Not only that, but it basically requires you to invert the condition, so it becomes academic if they are a collections ORs or a collection of NANDs. Baffling, ill concieved, confusing, badly presented, absolutely.

In the above example. If the battery voltage is above 26.00V for 60 seconds then AC ignore will enable regardless of whether the load is 700W or 2400W.

I tested this when I combined "Don't ignore AC when vdc lower than 25.0V" with "ignore AC when the load under 400W". The inverter promptly enabled as soon as the load fell under 400W. Even with the battery voltage at 24V. It's a wet paper cannon.

You can make it asymetrical and put the conditions only on one side, then choose the "when no condition applies..." function. However that then makes all your values single ended and you cannot operate across ranges?

Who designed that? Have you fired them yet Victron?

The "Dedicated AC Ignore" virtual switch at least has the sense to couple the ON and OFF conditions, such that OFF condition A cannot be overruled by ON condition B.

At the end of the day I would like to use the full capacity of the inverter, however I need a way to stop it tripping out if it, for whatever reason decides it can't handle the load anymore.

I'm not taking about instant overload. I'm taking about it coping with a load perfectly well until it decides otherwise.

If I can do that, I can set it to fail back to AC only when the load hits 650W.

If I can't do that I have to set it at a load which is won't trip on ever and according to the manual that's only 400W.

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paul-campbell paul-campbell commented · May 22, 2023 at 06:30 PM

The "Temperature pre-alarm" condition might hold some value for what I want. Depending on when it triggers. If it triggers before the unit "derates" from 800VA to 650VA due to temp it might be useful.

Combining that with battery voltage and charger conditions I have tried similar and gave up in confusion and ending up with too broad a test matrix to verify it did as I thought it would.

Let me investigate the assistants.

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Answer 2 · 2023-05-22T19:52:10Z

paul-campbell answered · May 22, 2023 at 07:52 PM

Assistants....

In the dedicated AC-Ignore, it presents "coupled" or "paired" conditions.

If when accepting AC because of VDC ignore AC again when VDC is X for Y

If when accepting AC because of AC Load ignore AC again when AC Load is X for Y

The assistants do not provide this.

I am not new to this, as a software engineer, but trying to achieve the same as above in the "Programmable relay" assistant is causing much tongue poking, face making, beard scratching, and grumbling about other programmers.

I'm either missing the point or these are completely junk.

None of the conditions are inter-dependent, they are only ordered for precedence. A programmable relay can set the flag, but it cannot base a condition on the flag set from previous assistants. All conditions are non-exclusive OR. Hmmm. It's like one of the aptitude tests they give you in programming exams.

Maybe I need my coffee. I will be back tomorrow.

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Answer 3 · 2023-05-22T21:02:46Z

paul-campbell answered · May 22, 2023 at 09:02 PM

So the closest I can get is using the "Generator start stop" assistant to control the "general flag" based on paired conditions around "AC Load" and/or "Battery voltage".

That gets me to exactly where the "Dedicated AC Ignore" left me.

If I add a further assistant which, say, regardless of what the generator start stop set the flag to, over rides it with "Do not ignore AC" if the "Overload pre-alarm" is active for 10 seconds.

I will have to wait to an appropriate time to test as it involves an AC reset. My worry is it will ping-pong on and off AC because the overload flag will clear instantly when the Grid AC kicks in. The inverter will immediately enable again and cutout again after 10 seconds.

Having a "paired" condition like:

"Do not ignore AC in when overload pre-alarm is set.

While accepting AC due to overload, ignore AC again when load is less than x watts for y seconds."

Or even:
While accepting AC due to overload, ignore AC again when no overload alarm exists for 5 minutes.

If I could make one feature request it would be to have more than one general flag and for those flags to be accessible in the subsequent assistants conditions. This will allow you to chain assistants into more complex inter-dependant conditions.

Making a proper logic builder UI with AND and OR conditions and even sub grouping would be really exciting, but very expensive to do in a Windows GUI from 1995.

Even better. If victron release the documentation and SDK for "Private assistants".

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JohnC ♦ commented · May 23, 2023 at 05:22 AM

@Paul Campbell

I don't claim to be an expert with Assistants, and I usually suggest to attemptees that they just try it first to 'get their head around' how they work. There's little things that are easily missed. I can't know where you stand with them, but a couple below..

An Assistant used to Open something needs another to Close it. There may be complex ones that don't though.

They work in order, as though the series is being read continuously, over and over.

Default Time delays are adjustable.

Re the second Flag. Without looking up what relays your inverter has aboard, it may be possible to externally wire an output relay to an input relay. Then read the input relay.

Don't be too hard on the capabilities of your little 800VA jobby. Not much else out there can do anything like this.

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Answer 4 · 2023-05-23T09:17:39Z

paul-campbell answered · May 23, 2023 at 09:17 AM

That's true. It is a good bit of kit and I'm not disappointed I bough it. I'm just struggling with the user interfaces while I find a way to get under them.

Also, it's not like I'm running someone's life support on the circuit! It's a few PCs, it's not like I have never pulled the plug on them. So what if I leave the AC Accept at 650W and the inverter does indeed get too hot and quit. The PC goes off, it goes dark. The inverter re-enables, the main load (the game and gfx card) is gone, the PC reboots back up. No real hard done.

It may be the case, that as it's in an unheated garage it's unlikely to be above 20*C except on the warmest summer days and it may run at 650W for the few hours I game in the evenings and never bother. I gamed for an hour last night and no alarms recorded. It was running between 550W to 650W and did for 2 minutes drop back to grid when load spike at 710W.

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Answer 5 · 2023-05-23T12:30:57Z

sharpener answered · May 23, 2023 at 12:30 PM

I have been following this thread @Paul Campbell as it seems connected to one of mine. I too find the description of the Assistants and Virtual Switch very counter-intuitive despite having had a lot of experience with Boolean algebra and logic circuit design over several decades. I don't use them because they will not do what I originally wanted (see this thread) but Node Red proved to be the answer.

So if you have a GX device in your system that may be the answer for you too. It may then be possible to do your own stepwise derating on temperature (just as I have done on battery voltage), then the algorithm will reduce the inverter power so the trip point is never reached.

You said in the other thread your Multiplus 24/800/16 only supplies the one circuit. Perhaps you could explain what the overall goal is. Protecting your gaming sessions from grid failure? Arbitraging between peak and off-peak electricity tariffs?

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Answer 6 · 2023-05-24T17:11:09Z

paul-campbell answered · May 24, 2023 at 05:11 PM

The goal is part financial and part just "hobby".

I figured I might try and generate some of it using an off grid system.

Guilt free gaming and also doing my part as a home worker to offset my carbon use.

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sharpener commented · May 24, 2023 at 10:58 PM

Getting it to work using NodeRed as upthread should satisfy the "hobby" part then <g>.

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paul-campbell sharpener commented · May 25, 2023 at 08:05 AM

Yes. Hopefully.

Sometimes when companies like Victron try and give you the full solution, they end up giving you only 80% of it before they run out of development budget.

The annoying thing for people like me, is they often remove access to the underlying system/config in the process. So they give you incomplete highlevel solutions and block access tot he lower levels. That can be quite frustrating.

On that note. Why did they give us NodeRed block when they could just have given us the documentation for the MQTT bus.

It's ok, I should be able to reverse engineer the NodeRed blocks into Python.

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Answer 7 · 2023-05-25T08:10:20Z

paul-campbell answered · May 25, 2023 at 08:10 AM

I gamed on the inverter last night and it produced 550W without fault until the battery caused a fail back to grid.

This brings in an example where the basic "When VDC is less than X" is insufficient. SoC would be better. Under 550W of load the battery voltage is pulled down maybe half a volt. So when it hits the transfer voltage, it switches over but the voltage bounces back up to 26V and the estimated SoC was 40% still. It did switch back to solar as there was still 100W coming in, when I stopped gaming and load fell back to 100W.

SoC or load factored VDC is necessary. I think when I checked the Victron battery monitors that produce SoC are expensive. I believe the smallest smart shunt is £140 or something?

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sharpener commented · May 25, 2023 at 08:39 PM

This is where NodeRed will help because you can do it in several small steps. It helps if you work out the internal resistance of the batteries. Having said that I realise I have not updated the algorithm since adding the third battery module. The Dynamic Cut-off settings were supposed to sort this out but Victron haven't really adapted the parameters to suit Li batteries.

I have occasionally encountered the same hysteresis behaviour as you, but not frequently enough to do anything about it!

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paul-campbell sharpener commented · May 26, 2023 at 01:58 PM

I took a brief look. Oddly they exclude the most useful outputs. No direct control over the assistants or flags or ACIgnore. No direct control over charger voltages.

I have to take another look through the code and MQTT to see if I can use a combination of assistants and change values which will cause them to make the changes I want.

Is it worth enabling ModBus TCP support for use with NodeRed? Does the NodeRed context do the ModBus connection?

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sharpener paul-campbell commented · May 29, 2023 at 10:40 AM

I didn't and I don't think it does, they are separate protocols. For NodeRed you just need to upgrade the OS to the Venus Large implementation. No idea about ModBus but there is plenty of stuff in the right section on this forum.

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