kevstone122 avatar image
kevstone122 asked

How does the AC-measurement work in the Multiplus

I search in the community but didn't get the correct answer.

Main Point is to activate an electrical heater for the Boiler so store the sun power into water.

I found some "leading edge dimmer / 3-phase thyristor" like this:

Just some Thyristor for 3 phase system to fade electrical power from 0 to 100% with 0kw to 9kW for example.

Does the multiplus recognize this load also at 50% or 10% for example and try to hold the grid-feed-in at 0W?

How do the multiplus measure the AC-current? Because the current is with the Thyristor only at a short part of the sinus, or does the multiplus calculate some average?

If the multiplus recognize this, it will be really cheap to fade the load from 0 to 100%. Dont't need fronius ohm pilot and so on!

Thank you!

Multiplus-IIinverter current drawinput current
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5 Answers
sharpener avatar image
sharpener answered ·

You will need an external device to measure the net power and drive your 3 phase dimmer, the MultiPlus does not have this capability.

I have designed and built my own diverter, the chopped current waveform flows through the Multi but fortunately does not seem to affect the accuracy of its power measurements.

In the UK there are several well-known commercial devices for water heater control, look for myenergy eddi, iBoost, or build your own from a kit e.g. this one. But these are all single phase, there is also this but I don't know of ready-made three-phase one.

See also this thread.

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kevstone122 avatar image kevstone122 commented ·

Thank you a lot for the information. Which form you mean with "the chopped current waveform"

To you have thyristor or you do a PWM?

AND the multiplus still can control to Grid power to 0W, doesn't matter if you have 30% or 80% or 100%? So the AC OUT measure the load correct and multiplus can take the power from battery or MPPT and the GRID will me stable at almost 0W?
Rest is just software, if i want to take it from MPPT or also battery and so on. This i can control my own. Just PID controller to the shunt current and just activate the function if the SOC is higher then 95%. PID output from 0-100% will sent to the Thyristor and control shunt current to 0A.

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sharpener avatar image sharpener kevstone122 commented ·

It is a power controller brick which triggers a triac with a 0-10V programmable delay from the start of every cycle so the current waveform is chopped. It is on AC-Out but the waveform does not affect the power measurement by the MultiPlus. This is set to export any surplus PV but my diverter controls the grid power to <-100W just as you say whatever the water heater power 0 - 3kW* so the effect is that all surplus PV goes into the water without discharging the battery, which is your ultimate goal.

*My diverter requires an export of about 100W to turn it on fully to 3kW but the principle is the same.

If you can use your smart home system to drive your 3-phase thyristor brick with 0-10V then I think you will succeed in doing what you want. Good luck!

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kevstone122 avatar image kevstone122 sharpener commented ·

ohhhh yes. Short time forget Thyristor and Triac. Off course Triac is better because both sinus parts will work.

If i use thyristor with 100% it will effect only 50% i think because negative wave will be not used and then i am again not sure if the multiplus will measure correct if üositive sinus and negativ sinus have different current.

Better is to use Triac. I need to find this for 0-10V in best case!

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kevstone122 avatar image kevstone122 sharpener commented ·


Okay looka fine the link....It looks like an Triac! Both sinus wave is used!

So with 150€ part same function then a 1000-1500€ Ohnpilot for 9kW!

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tom4x avatar image
tom4x answered · is also a complete solution for this

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sean avatar image
sean answered ·

The Fronius Ohmpilot and the AC-Thor are 3ph surplus diverter devices.

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kevstone122 avatar image
kevstone122 answered ·

Hello together and thanks for your answers.

Maybe my question was not clear enough from my side. Sorry!

I know Fronius Ohmpilot, My PV AC-Thor but the price is to much. The part above cost only 150€, all other thing around 1000€. And i want to do how the Ohmpilot or the My PV work inside to control the 0 to 9kW. I need also 2 heaters for different boilers. So it's more important for me to pay 300€ or 2000€.

And i think all of them also just have an thyristor inside and do the same like the link above. Isn't it? I found also at Ohmpilot, that there is just an regulation for 3kW, and two relais for the other 3+3kW. So they just modulate 3kW, then switch on first relais. Then regulate 3 to 6kw, then switch on second relais. Then last 6 to 9kW with modulation. So they can fade 0-9kW.
And my question is how the modulate inside exactly. Same like a 3-Phase Thyristor, just 1-Phase thyristor?

So both information bring me to the same result.

1) If there is an thyristor inside, i know it will also work with my link above because it's also an thyristor.

2) If we know how the victron system measure the current, then we can also decide, that it will recognize the thyristor current correct and will use the PV power and not Grid Power. I am afraid that the current will be not measured correct and so the multiplus cannot regulate the Grid Power to 0W.

I have 6 Multiplus and the full house connected. So measurement over the multiplus is so far fine and they will control the grid power to almost 0W.

The control of 0-10V or 4-20mA i can do my own with smart home for the Thyristor. I have all the values in my smart home already from victron, like Shunt current, Grid Power, House Power and so on. So easy i can Ramp up the Thyristor with 0-10V according the grid Overpower and so i will "hold" the grid power again to 0W and the shunt current should not be negative.

Is it now more clear what i want? Thank you?

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janieronen avatar image janieronen commented ·
I have seen few similar DIY projects but could not find links. There is many ways to achieve your goal. I would my self activate Node-RED as Large GX feature or install NR to other server. NR you can get your grid point measurements every second from grid meter by reading values from GX-device register. Logic is easy to build in NR graphical interface. You need to find example USB to analog output 4-20mA device which you can control from NR. That way you can have live data from grid, PV and inverters when controlling loads.

I do not need that accurate load control so using NR switch on/off many different devices based on PV and electricity price.

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kevstone122 avatar image kevstone122 janieronen commented ·
Yes node red is active and i couple already over 40 values with my smart home so i know all the values.

Good idea with usb to 4-20mA, but i also want to switch it on over my smart home for worst case szenario like heat pump problem. So i can heat electrical and that's why i want my smart home as master. Also cerbo has so slow processor and is with node red, 6 multi, 5mppt and bms serial communication + VRM live view on the limit^^.

But Triac will be the solution for perfect control. On Alibaba for 50€ available!€

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kevstone122 avatar image
kevstone122 answered ·

Answer will be an TRIAC.
So positive and negative sinus part will be triggered.
TRIAC you get at AliExpress for around 100€ for 9kW inkl. Heatsink and Fan.

9kW heating bar from ASKOMA you get arround for ~400€.

So with 500€ and an existing smart home you can control the heating bar from 0 to 9000W.

Here the links:

Best regards


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