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nyholku avatar image
nyholku asked

Multiplus II 48/5000 automatically dropping water heater in case of overload

I'm having an off-grid solar system installed (16x415W + 2 x MPPT 250/100 + Multiplus II 48/5000 + 2 x 5 kWH LiFePo4). I'm worried about overload condition and would like to have an automatic system that drops the water heater (2kW) off line if the 5000 kW inverter output is about the be exceeded.

My question is if the Multiplus II has some features that can be used to implement this or do I have to have this implemented without help from the Multiplus? Can the relay be programmed for this application?

Multiplus-II
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Rob Duthie avatar image Rob Duthie commented ·
Hi

Yes you can, need to add a assitant in software to do that.

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nyholku avatar image
nyholku answered ·

Thanks! Where can I learn more about adding an assistant in software?


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Rob Duthie avatar image Rob Duthie commented ·

Do the Victron training courses, to learn more.

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ponzoa avatar image
ponzoa answered ·

You could also choose a larger or more powerful Multiplus II, say a 48/8000 or 48/10,000 or even a 48/15,000 (but this last would likely be overkill for your project). Alternatively, you can install 2 x 48/5000's in Parallel for an equivalent of a 48/10000.

You would also be able to use an assistance to disable that water heater if required.

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nyholku avatar image nyholku commented ·
Thanks, I'm actually working on down grading my plan from 48/8000 to 48/5000. It is very rare that the peak power will exceed 5kW but I would like that situation to be handled by just delaying the water heating until other loads are less. Sort of prioritisation of loads. My typical load will be in the 1-3 kW range so would not like to install 8 kW inverter to solve a situation where I'm using 6 kW because a washing machine, water pump and a coffee maker may occasionally be on at the same time.
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nickdb avatar image nickdb ♦ nyholku commented ·

You can add smart timers/switches like Shelly/Ewelink etc. These can be integrated via node red in the large image and turned on/off based on pretty much any metric in the victron ecosystem.

Assistants, in their current form, are a bit of a blunt instrument.

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ponzoa avatar image ponzoa nyholku commented ·
Sounds great however, from my point of view, while an off-grider needs to be aware of their power use and consumption, knowing you have the power there when needed for a small amount of money more (in comparison to the entire project cost) leads to quality of life and comfort. Remember that the investment is intended to last you a large number of years and when you break down the price difference over those years, you're talking peanuts per year or month.


Either way you go, good luck with the project! I'm sure it'll be great either way to decide to go.

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Alistair Warburton avatar image
Alistair Warburton answered ·

A couple of points...

5000VA is not 5kW unless th load is entirly resistive.
I cant remember the spec off the top of my head but I think a 5000/48 will be rated at 4000W continuous at 25C.

That asside... The AC2 output can be used, to do what you wat from a switching perspective, I think, The strategy is gennerally refered to as load shedding.

I think you can use multiple rules, on and off, to achieve this in the relay assistant but a simple single setpoint will not work because turning off the heater would reduce the load causing it to turn back on.

Avoiding this common issue requires hysteresis in the control logic.
EG. Turn AC2 off above 3.5kW and turn AC2 On below 1.5kW

You may also want to add disabling AC2 blow some SOC value.

The relay assistant accepts multiple rules and processes them in order. You can choose if processing stops when a rule matches some criteria.

The order is usually importent. In the example above the SOC check would come first and prevent load checks from taking place if it matched.
You would also want some hysteresis for that so entry 2 would enable above some slightly higher SOC.

This video is the opersit of what you want but the principles are the same.

You could also do what you want and much more with Large OS and Node Red on a GX device (Not a CCGX though)

hope that helps.

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