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Rob Duthie avatar image
Rob Duthie asked

Hot water diversion assistant setup Mulitplus2 with overload shut off

I have some answers about hot water diversion based on SOC readings and load control with programmable relay, genset assistants with a 3kw Mulitplus2.

Answer i have found for grid tied and off grid system: Under testing 12/04/2021.

Re Diversion control of surplus PV power. EG Hot water cylinder heating, with a small Multiplus2 3kw 48v inverter with overload control, turn off hot water cylinder when other loads come on. Main house loads are top priority, hot water cylinder is second priority

This is what is have done and tested to date and it's works like this.

Start genset assistant first with inverted relay function open relay, and set loads to suit inverter type, times, watts etc.

Then add programmable relay with off function with low SOC %

Then add another programmable relay on function with high SOC % Note: not required works without the SOC high function, this might cure the overload if you exceed the high% set point?

Note1: If you have the high SOC below 100% any thing above that % will stop the over load function from working and keeps the relay on all the time, in which case you will get a overload warning alarm or shut down etc. So to stop this remove this last assistant.

Note2: If it says lower% but that logic is reversed, anything above activates the relay

Note3: With just the Genset start and the first relay assisant installed the system works perfectly, in that it diverts the excess PV power to water heater load and shuts off when the loads are to great.

Example system test:

generator start and stop (size:197)

*) Use primary programmable relay to start generator.

*) Open relay to start generator.

*) Start generator when load higher than 1200 Watt for 2 seconds

and stop generator when load lower than 1100 Watt for 2 seconds.

*) The generator is not stopped by AC input.


programmable relay (size:30)

*) Use primary programmable relay.

*) Set relay off

*) when SOClower than 78%. See Note1


programmable relay (1) (size:30) See Note: 2

*) Use primary programmable relay.

*) Set relay on

*) when SOChigher than 100%.


Regards

Rob D

NZ

Hot Water Diversion
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3 Answers
markus avatar image
markus answered ·

Hi, @Rob Duthie,

check out the Generator Start Stop Assistant:

1616925828663.png

BR


1616925828663.png (233.8 KiB)
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Rob Duthie avatar image Rob Duthie commented ·

Hi Markus

Thanks for the reply back.

So i have to use the generator start assistant at the start of the process then add in the SOC set points to turn on and off the relay. I will be using the programmble relay instead of the AC ouput2. So my logic for the power watts on and off would not work? it seems to me to be the same sort of logic, but simplier to understand, what is the reason is there any where it is written about this logic?

Update and tested on the 30/03/2021 on the Hotwater diversion control assistant setup below is the only one that works well with the gen start using the programmable relay. with no AC input otherwise its keeps the relay on all the time, I think Victron should add another assistant called Diversion control so not to confuse it with the gen start assistant, just a thought?

*) Use primary programmable relay to start generator.

*) Open relay to start generator.

*) Start generator when load higher than 2500 Watt for 5 seconds

and stop generator when load lower than 2000 Watt for 5 seconds.

*) The generator is not stopped by AC input.


programmable relay (size:30)

*) Use primary programmable relay.

*) Set relay on

*) when SOChigher than 99%.


programmable relay (1) (size:30)

*) Use primary programmable relay.

*) Set relay off

*) when SOClower than 98%.


Regards

Rob D

NZ

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justmurph avatar image
justmurph answered ·

Rob,

I originally used the generator start stop assistant in my Multiplus 5k for controlling my hot water, and that worked fairly well. In my setup I'm trying to run it only when I have excess solar power. I ended up switching to using my Cerbo GX's generator control functionality to do the same, which gives you a little more control, for example adding a time range in which it will operate.

I would love to see a dedicated HW control function that gives a bit more flexibility, e.g. heating to a lower temp on days with minimal solar available.

E.g.

- SoC < 50%, no hot water

- 50% < SoC < 90%, heat to 50º (using a temp input)

- SoC > 90%, heat to full thermostat temp

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Rob Duthie avatar image Rob Duthie commented ·

Hi

Yes that would good of Victron it they were to include that in there Assistant modes as an option as it seems to more of a thing with heating and cooling loads with surplus solar generation, As more power companies restrict export power into the grid, lets divert it more into house loads with some control.

The genset mode sort of works just that on the smaller inverters we need to be able to turn off the relay outputs and AC 2 outputs under high loads situations when another loads come on which are more high priorty loads.

It sort of works but won't always switch off the relay output? There are some condidtion it won't switch off? and inverter goes into over load warning but still keeps going?

Regards

Rob D

NZ

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justmurph avatar image justmurph Rob Duthie commented ·

In my case controlling by load worked pretty well for my use case. I have a 5k that can easily run pretty much everything in the boat, so Im not worried about inverter overload. My main driver is trying to ensure that I am predominantly running the hot water on excess solar. It's not possible to make to work only with excess power under all circumstances. It's not a perfect setup, but works very well under most conditions.

I ended up controlling it based on SoC, battery current and time.

So, time between 7am and 5pm, SoC over 90% (90% on and 88% off) and for battery current it'll start if over 0A (i.e. charging) and stop if the draw is more than 28A (750W, which is what the HW draws). So there will be situations in which the solar output drops (1.7kW system) enough that it'll be drawing on the battery. If you set it to only turn on if it's charging at more than 750W, then the system will never turn on once the batteries are full and floating.

Doing it this way ensures that you have decent solar coming in and will also shut it off if you turn loads on larger than 750W. It also means you can still heat the water on a low power day, it just cycles on and off between 90 and 88% capacity.

Could it be better, yes. But the control would get pretty complex and this does the job well.

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Rob Duthie avatar image Rob Duthie justmurph commented ·

Hi justmurph

Yes did test run on my home test gig with the folowing parameters and it works perfectly. I have clients site with a very simalar setup, but wont shut on the set points only some times intermitte very odd. So will be revisitng site and checking the settings again.

*) Use primary programmable relay to start generator.

*) Open relay to start generator.

*) Start generator when load higher than 1500 Watt for 2 seconds

and stop generator when load lower than 1400 Watt for 2 seconds.

*) The generator is not stopped by AC input.


programmable relay (size:30)

*) Use primary programmable relay.

*) Set relay on

*) when SOChigher than 99%.


programmable relay (1) (size:30)

*) Use primary programmable relay.

*) Set relay off

*) when SOClower than 98%.

Regards

Rob D

NZ

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justmurph avatar image justmurph Rob Duthie commented ·

Hmm is this an issue with the logical order of the assistants? I am forgetting exactly how it works, but the order in which you put them does matter?

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jbakuwel avatar image
jbakuwel answered ·

Kia ora Rob,

I would add some logic to VenusOS for this purpose. You'll have a lot more flexibility there compared to the limited functionality of the programmable relays.

I am using Sonoff POWR2 units running Tasmota firmware to turn loads on & off (such as HWC's) based on a number of parameters. I have to manage a whole bunch of loads that all being on would surely overload the 5KW inverter.

For example if someone wants to use the kettle, they first need to press a button that signals a control process on VenusOS. The control process knows which loads are on and whether there's room for the requested load (the Sonoff POWR2 also measures power consumption). For example if the HWC is on or the car is charging and the addition of the kettle would exceed the maximum I've set, the control process turns the HWC and/or car off, turns the kettle on and once the kettle is done (power consumption -> 0), it will turn the HWC back on. One of the many projects is derating the HWC (reducing the power it's receiving) instead of turning it off.

The Sonoff POWR2 units can subscribe to MQTT topics using the MQTT broker on VenusOS that you can publish to, to control them. You can do that with Python scripts or - much nicer - with Node-RED which is part of VenusOS large

It's a work in progress here. At some stage, the weather forecast for the next couple of hours (in particular cloud cover), the time of the day, the date and other factors will be included in deciding how much energy can be taken from the battery.

Ngā mihi,

Jan

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Rob Duthie avatar image Rob Duthie commented ·

Hi Jan

Yes i have heard of the Sonoff devices and Tasmota stuff. I see that you are local. Myself in Rotorua. Yes i have used and programmed a ESP 32 wifi modules for temp monitering etc. I have designed and built raspi HAT called a Stetson. which i am am adding a couple more analog inputs etc. Attached doc FYI.

I thougt by adding some basic logic for hotwater control this will work, but what i have heard that you have to add the generator start logic to have some control. as well.

I will be testing the different forms of logic to see what works and does'nt work. As this seems to be a common request for excess PV power for off grid and on grid applications.

Regards

Rob D

NZ

Victron Raspi Hat.pdf

Victron Raspi Stetson.pdf

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