question

tom w avatar image
tom w asked

Why is my Multiplus keeping the charger on when there is no solar available during the night?

Hello,

I built a small ESS which I want to use to store solar excess and run some critical loads like my electric window shutters during a power outage.

My system:

  • Multiplus 24/500/10 (calling MPP below) FW 481
  • RPi3 with Venus OS v2.82-large-30
  • Shelly 3EM as grid meter
  • Shelly2.5 as PV meter (1kWp with 600W inverter)
  • Battery Accurat T60 25.6V LiFePo battery

I configured the battery to use 55% for ESS and 45 % for critical loads:

2023-02-21-11-29-13-ess-config.png

Yesterday the battery got charged to 96% and the MPP was doing it's best to keep the grid at 0W consumption. After sunset the MPP was discharging until the minimum SOC was reached.

Now the MPP switch to BULK charging mode and started a loud humming. With this humming the MPP was consuming 20W doing nothing. The only way to stop this was to switch the MPP off or to inverter mode. With a click the humming stop the grid consumption was reduced by 20W.

Why does the MPP keep the charger on when there is no energy available for charging?

The time was 9pm , the sun set hours ago and PV meter was reporting no solar energy available.

This morning I charged the battery to 55% because I thought the Active SOC limit was set after the discharge cycle yesterday. But no difference the charger stayed on even consuming grid power even when there grid meter reports no excess feed in.

2023-02-21-11-22-38-mpp-on.png2023-02-21-11-24-28-mpp-inverting.png

The two screen shots where taken this morning. when there was barely enough solar to meet my consumption. I attached them to show the difference in grid consumption.

BTW the MPP is hooked to L3, which mess up the AC loads total. It does not affect the grid consumption of the charge mode. It will be connected to L1 when it's installed at the final location. I used an extension cord to check that L3 hook-up does not affect the charger consumption.

So why is the MPP charger not turned off, when there is no energy excess detected?

If I had kept the MPP in BULK mode over night it would have consumed more energy than I stored in the battery yesterday!

I know that there is a newer FW for my MPP but I don't want to update until I know that this issue is addressed. Unfortunately there is no change log available in public.

multiplus ve.bus
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9 Answers
tom w avatar image
tom w answered ·
  • Some update:

As stated before the issue is that the charger does not turn off when the Active SOC limit is reached. Switching to "inverter only" is not a solution because the critical loads will be powered from the battery. I figured out the solution is to go to Passthrough mode.

All relevant controls are available in Node-RED. Injecting a "Disable Charge" to the ESS by hand is switching to the desired mode reducing the power consumption to an acceptable minimum. :-)

I'm somewhat wrestling with Node-RED as this is my first encounter with this kind of programming. Having knowledge in C++ and Python is not helping, it's totally frustrating. :-(

To the Victron ESS Team:

Why do I have to jump through hoops to stop my Multiplus from wasting power?

  • I did not buy the Multiplus to learn Node-RED programming!
  • The ESS-Assistant should go to Passthrough by default if no exzessive energy from solar or battery is available!
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tom w avatar image
tom w answered ·

Hi Glenn,

Thanks for joining the community and replying to my question. I appreciate it!

I'm sure it's the system programming. For big multi-phase / multi kW(h) ESS it may make no sense switching to Passthrough because you probably never encounter a low battery state for a longer period of time. The Firmware seems to be the same for all Multiplus, so my case is not covered.

As a System-Design-Engineer I have to admin that overall function has a higher priority than tweaking the the last bit of efficiency. If it wasn't for the loud annoying hum, I would have never looked into the power numbers.

After the dust from frustration and anger has settled, I created a first Node-RED flow which turns off the humming when the battery is depleted for a good night sleep. As soon there is enough excess solar energy for charging it turns the charger back on.


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JohnC avatar image
JohnC answered ·

Hi @tom w

I would question your use of ESS at all, considering your stated use case. Like swatting a fly with a sledgehammer. Unless you're exporting power to grid from your little 500VA, then ESS isn't necessary. Just adds complexity (as you've found), and what you want could be achieved far more easily with other methods.

Your system could be more stable, not leak power, nor groan at you. There's still a few little things that need attention to set up to your preferences, but if you're prepared to flick ESS we could help point you in the right direction.


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tom w avatar image
tom w answered ·

Hi John

At the first glance an ESS with an 500VA inverter and a 1.5 kWh battery does not make much sense.

However,
that's not purpose of the system.

The main objective of my little ESS is providing an UPS for my Home-Assistant server and electric shutters. My server and the related network appliances require 50W around clock and each shutter draws 200W for less than a minute when in action. So having a 500VA UPS is a perfekt match with some headroom. I also want to add my refrigerator to the critical loads but this requires rewiring my kitchen.

To recharge the battery and cover my basic loads of 110W, I have 600W "Balkonsolar" system because it requires the least amount of legal paperwork here in Germany. 600W is more than enough to cover my basic consumption but it's not enough to power power my coffee maker. As result on sunny day I feeding 1-2 kWh back to the grid. This happened twice last week and reminded me that I forgot to unpack the Multiplus since I bought it 3 months ago.

Now we come to the second objective, Power-Assist. On a sunny day like last Wednesday I can brew my coffee after lunch for free because the Multiplus and the solar inverter combined are able to power my 1.1 kW coffee maker even in winter.

After the sun has set, the ESS can use the battery to power my home as long as it can. And when battery is depleted to the minimum allowed, I want the ESS to consume as little energy as possible.

So yes, from time to time I'm swatting flies with a sledgehammer. But I did not buy the hammer for swatting flies. I just happen to have a sledgehammer and if it is the next best tool for swatting an annoying fly, I use it.

Regards Thomas


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JohnC avatar image
JohnC answered ·

@tom w

My point still stands, I see no reason to run ESS on a ups.

Lets try an example using your 600W, but rough figures. Set an ac input limit (ACIN) to the Multi of 2.6A (600W@230V), so you can't draw more than 600W. Power Assist adds to loads higher than that. All bog-standard stuff.

Using Assistants (not the ESS one) in the Multi you can switch off (Ignore ac) the ACIN whenever you choose, and have it switch back on under certain conditions, like low SOC or loads over 600W. Job done.

Access to the Multi settings is a bit clunky, so an improvement there might be to run a signal wire pair across from a GX (does RPi have a relay?) and use the Generator option in the GX (very powerful settings).

ESS is only one of a number of Assistants, and you can build a program from multiples of the others. ESS is designed to push'n'pull at the grid, and that's where your reported issues are coming from.

This is standard stuff for offgridders and casual grid users. No ESS (banned for gensets), and no NodeRed needed..



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tom w avatar image
tom w answered ·

Hi @JohnC

Let's agree that we disagree!

Here in Germany we have a 3 phase system and I'm paying for the power balanced over all phases.

The example of limiting the input power only on the one phase connected to Multiplus does not compensate the total power consumption. Therefore an ESS compensating all 3 phases with single phase feed in is way to go in my case.

Adding more wires and making the hardware setup more complicated is not the right thing to do considering you have all the information and controls available in Node-RED for fixing the issue in software.

Admitted Node-RED has a very steep learning curve. I was thinking far too complicated and I was missing basic programming features. After realizing that I just have to think like a toddler when creating a Node-RED flow, I already came up with a basic flow that is capable of eliminating the power waste and humming over night.

2023-02-25-12-29-58-node-red-19216817870-brave.png

I'm currently fine tuning the charger off condition, so that I don't turn off the charger too early, when clouds are blocking the sun during the day.

In the end I want my UPS paying for itself by making use of my excess solar power.


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tom w avatar image
tom w answered ·

Please ignore my rant at beginning of this question!

If it haven't been for the annoying humming, I have would never look into the issue.

Now, I have some basic knowledge of Node-RED and I created a flow that works around the constant switching losses of my Multiplus.

Thanks for your patience!

2023-02-27-13-38-51-node-red-19216817870-brave.png


4 comments
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Bonhardt László avatar image Bonhardt László commented ·

after reading your post I got curious and tested this on my 3phase ESS + solar system, it does indeed looks like the multis uses less power when the chargers are off as its forced into passthru mode, but in my system this totally turns off the whole charging even the mppt-s are not charging cause of DVCC. It would work independently if it would not use DVCC.

my concern is that putting the multi into passthru mode will affect the UPS functionality (higher transfer time) but i have no ability to test this.

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tom w avatar image tom w Bonhardt László commented ·
In case of a power outage the inverter does not need to synchronize to the grid and can turn on immediately. I have not seen a difference in the flicker of 60W lightbulb on AC-Out when I yank the input power. An LED bulb does not flicker at all whether the charger is in Passthrough or Idle.

However, I did not hook up my little home assistant server, yet, because I have to do some re-wiring first to hook it to AC-Out.

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Bonhardt László avatar image Bonhardt László tom w commented ·

in my case this was super easy to do, when sun goes up I have a pv voltage over 100V, so i just force passthru if the voltage is lower than 50 ( sun is down ) and turn it on if higher than 50 ( sun is up )

will see if this has any negative impact.


1677782011325.png

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1677782011325.png (11.5 KiB)
tom w avatar image tom w Bonhardt László commented ·

I have an AC coupled PV. Therefore I'm using the total grid balance to decide if I'm feeding back or need to provide power through the inverter. As my system is small and I want the best efficiency I'm not turning on until I see 50W feed into the grid or 100W power draw from the grid.

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Marian Titieni avatar image
Marian Titieni answered ·

please help me set Shelly EM as a grid meter, I see it in Device list but not in Energy meters


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tom w avatar image
tom w answered ·

@Marian Titieni

My Shelly3EM only appears only Dashboard as well. Under "Settings>Energy Meter" I see nothing.

Neither can I see my Deye-Inverter's Shelly2.5 under "Settings>PV-Inverter" but I can see it in the dashboard:soc-working.png

The Shelly-scripts are injecting the required messages directly to the dbus and don't create a device that can be configured using the settings menu.

I'm using https://github.com/fabian-lauer/dbus-shelly-3em-smartmeter and https://github.com/Halmand01/dbus-shelly-1pm-pvinverter-mult-instance for my Shelly devices.


soc-working.png (65.5 KiB)
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