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harry4516 avatar image
harry4516 asked

VM-3P75CT Speed

I have the VM-3P75CT installed in an ESS system using three Multiplus 48/3000. Previously I used the EM24. The reason was to speed up line regulation as advertised for the VM-3P75CT.

The manual says:
"High refresh rateCalculating the RMS power values for each phase, the energy meter transmits them at a high rate over VE.Can orEthernet, leading to more accurate measurements for power usage, grid-import and grid feed-in, for example, in an ESSsystem."

The VM-3P75CT sends data to the cerbo at remarkable speed, several values per second which looks good. It is connected via ethernet.

But if I look to the in/out sum power, then it jumps between e.g. -60 and +60 watts (when it should be 0) in the same way as with the EM24. I cannot see any improvement in regulation speed (in the VRM grid diagram).

My expectation was to see the curve more close to 0 compared to the EM24.

Is there anything that I have missed, any special setting or whatever?

Energy Meter
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larry avatar image larry commented ·

I have a small system and am using ESS to optimize/automate the system. One of my goals is to keep a low profile and not feed the grid at all. My Grid Set-point is 100W, but I still get an occasional spike feeding the grid after a sudden drop in consumption. These spikes seem to be 1 second or less as measured on a fast monitor (Eyedro) with 1 second resolution.

I was thinking of replacing the Eyedro with a VM-3P75CT as a way to prevent feed-in to the grid, but it appears that this will not improve the situation since the speed bottleneck is the MP2 / firmware.

Am I concerned about something that doesn't matter? In a normal home with no inverter, couldn't inductive loads periodically cause energy to be fed to the grid anyway when switched off due to collapsing fields / back emf?








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9 Answers
JohnC avatar image
JohnC answered ·

@harry4516

What you're seeing is likely just the reporting schedule in the Cerbo. It will still continue as it always has, and even it's values don't get sampled at the same time. Switching power supplies and ac motors typically cause such reporting variations.

What's happening behind the scenes though you can't see. But hopefully your ESS is performing better..

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mysik avatar image
mysik answered ·

hi @harry4516

What is the response speed to high load change with this meter?

I was using ET112 (single phase) and the reaction speed to high load change was terrible. (I've documented it in the other thread: https://community.victronenergy.com/questions/51697/victron-ess-et112-slow-response.html).

Can you do a video how the system is behaving when there is sudden high load change (let say 2kW load change)?

After reading all this comments from Victron about speed improvement I would like to see how it is looks like in the real life. Is it really much better that the old ET112 meter? The price of the new meter is really high and I just can't justify the money spend if I won't be absolutely sure that the new meter is really good.

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harry4516 avatar image
harry4516 answered ·

Hi mysik,

the resonse speed using the new meter is still low.
However the measurement speed of the new meter is really very very high, the incoming values in the cerbo display are updating multiple times a second. So the speed of the new meter should be fine.

But even with this fast measurement speed the reaction to load changes has not improved compared to the EM24.

I think the multiplus-2 is the bottleneck, without improving the reaction speed of the MP2 its not worth to change an existing meter against the new one.

I did some records via MQTT, this is how ESS looks like if set to 0 watts:

mmeter.pngso no change to the previous EM24.
My hope was that someone tells me to update the MP2 to any future version, but no response so far.


mmeter.png (115.7 KiB)
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kerbal avatar image
kerbal answered ·

Is there any update here?
I also thinking about to change my EM24 against a VM-3P75CT to increase the speed for my ESS.

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Alex Pescaru avatar image
Alex Pescaru answered ·

All processes on a multitasking environment are based on timers and events.

Venus OS has - according to its scripts - the following timers when it processes its signals.

So, no matter how quick the "outside world" is supplying its data, it will process the variables at the following minimum rates:

Battery Data = 5 seconds
Battery Life = 15 minutes
Battery Sense = 3 seconds
Buzzer Control = 0.5 seconds
DVCC = 1 second
DESS = 1 second (default 5 seconds)
Schedule = 5 seconds
Sources = 10 seconds

DBus Updates = 1 second

Indeed, if you write your own scripts, with lower intervals, you can take advantage of the improved speed of various devices.

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kerbal avatar image kerbal commented ·

Thanks for this clarification.

In the Post

Venus OS v3.00~36 available for beta testing - Victron Community (victronenergy.com)

in the section Changes v2.92 -> v3.00~4 following is mentioned:

"ESS: increase control speed of systems using todays supported meters (ET112, ET330, EM24, and also the ABB ones) a little. But, for faster meters, such as the EM540 which is not available yet, increase it very significantly. Requires updating the built-in MK3-chip, see next bullet."

I'm wondering that there is no further information about this (from victron or victron customers). So if i switch from EM24 to the VM-3P75CT will the control speed also increase very significantly?

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disaster123 avatar image disaster123 kerbal commented ·

I would expect another OS or FW update for the 3P75CT like they did for the EM540 and others. Hopefully someone from Victron can clarify.

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kerbal avatar image kerbal commented ·

I finally bought the new VM-3P75CT and installed it.
I can't see any increased control-speed compared to the EM24.
Only the update rate of the VM-3P75CT is very high (multiple times per second).

Maybe this has something to do with the fact that only 400W per second is allowed in Germany.

But it doesn't even manage the 400W per second. Adjusting the last 500W takes quite a long time.

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rickc avatar image rickc commented ·
It is very tempting to try to update the power using a Mode 3 script running at 10 Hz.
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rickc avatar image
rickc answered ·

I’ve been doing lots of detailed measurements using an EM530, which has a 10 Hz update rate. The 1 second delay in responding is plainly visible.

img-6619.png


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kerbal avatar image
kerbal answered ·

Here is a video with the VM-3P75CT installed in my ESS.
In Germany we are limited to 400W/s.

The grid setpoint is -10W.
Why does it take so long until the grid setpoint is reached again?
The Multiplus II takes quite a long time for the last 500W.

(3 phase grid with one Multplus II and 2 US3000C)



screen-20240425-221338.mp4 (38.1 MiB)
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kerbal avatar image
kerbal answered ·

If i look into the project dbus-cgwacs/README.md at 1efddc0fe20d854b768e525d02b01eb7e16cf947 · victronenergy/dbus-cgwacs · GitHub it seems to be that the VM-3P75CT isn't supported yet.

Or does the VM-3P75CT use the EM540Protocol? (dbus-cgwacs/software/src/ac_sensor.cpp at 1efddc0fe20d854b768e525d02b01eb7e16cf947 · victronenergy/dbus-cgwacs · GitHub).

With the VM-3P75CT i can't see any difference to the EM24 that was installed before.

Is there any update in the future planed? If not, i will switch to the EM540.

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haloibims avatar image
haloibims answered ·

Hello, is there more information available now? I am currently using the Shelly Pro 3Em. On days that have a relatively constant yield/consumption, I use less than 1 kWh. But on days with strong fluctuations, e.g. when I charge my electric car and there is a strong change between sun and clouds, then the consumption rises to 4 kWh. The linked video of the VM 3P75CT reacts just as quickly as my Shelly Pro 3EM, which would be disappointing. Do you have any tips or information on whether the device will regulate as quickly as the EM540 in the future? If that is helpful: I am from Germany (regarding grid code)

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