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Riaad Abdulla avatar image
Riaad Abdulla asked

MultiPlus-II 48/3000/35-32 (ACOut2 switchable) Configuration/Questions

Hello,

I would like to find out the answers to these questions - would greatly appreciate any assistance:

- Can I connect many high load items to AC OUT 2? Like 2 water heaters, 1 oven and a few aircons... is there a limit? I understand that these will be switched off when there grid fails which I am fine with but I want to install solar and hopefully use some of that power to take care of some of the load when it's active

- Once I get solar and there is a grid failure, will the solar continue to charge the batteries to keep the critical loads on AC OUT 1 up? Or will solar stop working and I will depend fully on battery which won't be charged until grid is back up?

- I see my battery is showing in a constant charging state even when it's at 100%... is this normal or am I overcharging it? Which I hear is bad


Thanks!!

My site on VRM is called "RIAAD ABDULLA"

Inverter = MultiPlus-II 48/3000/35-32 (ACOut2 switchable)

Battery = Pylontech US3000 + US2000

Multiplus-II
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2 Answers
marekp avatar image
marekp answered ·

@Riaad Abdulla 

- Can I connect many high load items to AC OUT 2? Like 2 water heaters, 1 oven and a few aircons... is there a limit? I understand that these will be switched off when there grid fails which I am fine with but I want to install solar and hopefully use some of that power to take care of some of the load when it's active

There is a total AC-in current limit at 32A for MP-II/3000.

- Once I get solar and there is a grid failure, will the solar continue to charge the batteries to keep the critical loads on AC OUT 1 up? Or will solar stop working and I will depend fully on battery which won't be charged until grid is back up?

If you connect your grid-tie inverter on the AC-in side of MP-II, grid-tie inverter will turn off when grid is gone.

If you connect your grid-tie inverter on the AC-out side of MP-II there will be no disruption when there is a load higher than PV production. Grid-tie PV inverter connected this way cannot be bigger than MP-II. (for 3000VA MP-II it can be no bigger than 3000kW)

There is no power limit on MPPT chargers connected on the DC side.

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Riaad Abdulla avatar image
Riaad Abdulla answered ·

Thanks @MarekP - I don't fully understand but I just found a youtube video which seems to explain the solution I want. This should allow me to lose grid power and continue on batteries (along with solar still charging the batteries)... is this what you were explaining? I have ordered the MPPT already (250/70)

Video - See from 7:18

system-diagram.jpg


As for AC OUT 2 on the Multiplus unit... hopefully 32A is enough for all my needs. I will need to chat to my electrician.


system-diagram.jpg (57.7 KiB)
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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

It is an limit of the input relays (transfer switch) AC OUT 1 + 2 can't exceed 32A.
1637078156719.png

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Riaad Abdulla avatar image Riaad Abdulla Matthias Lange - DE ♦ commented ·

Thanks for clarifying!

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marekp avatar image marekp commented ·

@Riaad Abdulla

This picture shows MPPT charger connected to DC side. (your 250/70 for example)

There is also available grid-tie type inverter that connects to the AC side. (Fronius for example). It can be connected in two different ways I described in my first answer.

screen-shot-2021-11-16-at-52446-pm.png


The 32A limit is for TOTAL AC draw from grid (AC1 plus AC2).

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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·
Thanks @MarekP
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Riaad Abdulla avatar image Riaad Abdulla Riaad Abdulla commented ·

@MarekP would I be able to use something like the Fronius Ohmpilot connected to AC-OUT-2 on the MP-II to power loads (2 water heaters 3000w each) or will that still be limited to the full system 32A?


I am trying to find a way to power the water heaters using solar primarily if possible and only grid as last resort (never battery).

Something like this:

fronius.jpg

Link to forum post

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marekp avatar image marekp Riaad Abdulla commented ·

@Riaad Abdulla

If Ohmpilot is connected to AC-out2, it is still be limited to 32A max AC draw, but if you have single phase system, than Ohmpilot is only 16A device anyway.

You will not be able to load it with 6000W water heaters.

For 3 phase system is a different story since it can control 16A on each phase.

In the single phase system you can only connect those two 3000W heaters on the AC-in side of MP-II/3000.

If you change your MP-II to 5000 model you will get 50A AC limit in the single phase system.

You can also add second MP-II/3000 in parallel to the one you already have and get 64A AC limit.

P.S.

You can replace your 6000W resistive water heater with one based on heat pump and lower your power consumption down to 2000W.

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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·

Thanks @MarekP - that's a great suggestion... I agree that a solar heat pipe solution or a heat pump might be better then trying to power existing water heaters with high power elements.


Maybe something like this could run on AC-OUT-2 (1 that will cater for both water heaters - 2 x 150litre)?

ITS 5.4KW (input power required = 1.26kW)

Do you think this might be a good solution? Thanks for all the advice so far!

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marekp avatar image marekp Riaad Abdulla commented ·

@Riaad Abdulla

Solar heat pipe is great but only in hot climate area.

If you have cold winter not so much.

The heat pump from your link is for heating the whole house (and water in the tap).

I have heat pump heating my house and water, but my house was build with this method of heating in mind. Surface (floor) heating is the best for heat pumps. If you have radiators on the walls it can be done but is less efficient.

My suggestion was to install heat pump based water heater. It is much cheaper and easier to install.

https://www.energy.gov/energysaver/heat-pump-water-heaters

screen-shot-2021-11-17-at-102214-am.png

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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·

Thanks @MarekP - I live in South Africa (Johannesburg) and it is relatively warm here compared to the rest of the world... winters are definitely cold but no snow etc.


The heat pump I referenced will plug into my geyser (or water heater as it is commonly referred to around the world) and basically replace the high power element:

heat-pump.jpg


I cannot find a supplier locally that sells what you have mentioned (which looks like a heat pump and storage system in 1 unit)

Is that correct?

Also, I just spoke to my electrician and he mentioned that the best way for me to power non essential loads would be to connect the solar to AC IN with a power meter to ensure electricity does not get sent back to the grid (if not allowed). I assume this will still allow me to charge my batteries via solar when the grid is offline?

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Riaad Abdulla avatar image Riaad Abdulla Riaad Abdulla commented ·

Also @MarekP , in the diagram you sent through below is the MPPT and PV inverter connected to the same solar panel array or different solar panel array?

diagram.jpg

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marekp avatar image marekp Riaad Abdulla commented ·
@Riaad Abdulla

Different solar panels for on-grid inverter and MPPT.

The best is to have both.

The on-grid inverter has 96-97% efficiency in converting DC from panels to AC. This AC you are consuming directly without loses.

MPPT charges batteries directly from PV panels with 99% efficiency, but to get AC from this energy you have to convert it using MP-II. Efficiency of this conversion is at 90-94%.

So, if you have only MPPT you are loosing energy on constant conversion from battery DC to AC for your house loads if there is no grid.

There is also advantage of having MPPT charger when there is no grid, sun is shining and battery is empty. Without MPPT your system would be down even with sun shining.

AC-coupled on-grid inverter (connected to AC-out) would not start producing because MP-II is not creating micro-grid because battery is empty. Only active MPPT can recharge the battery and bring back your system.



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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·

Ok I think I understand @MarekP!

My main reason for wanting solar is to decrease costs (limit what I pull from the grid) so I think I need a PV inverter and solar panels. This will allow me to power all loads including charging the MP-II batteries provided I get enough solar power... the balance will be pulled from grid.

What this won't help me with is if the grid is down for an extended period and I run out of battery power... I will need to wait for grid to come back online (so that solar can start working again and powering loads/charging batteries)

Later on I can invest in a few panels and MPPT to keep batteries charged even during grid failure.

Is that correct?

Thank you so much for your help and guidance - I really appreciate it.

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marekp avatar image marekp Riaad Abdulla commented ·

@Riaad Abdulla

Yes, it is correct.

Take notice that the grid-tie inverter can be connected on the AC-in or on AC-out (AC coupled).

The AC-in connection is simple and can be any size if you can feed back to the grid, but there will be no PV power when grid is gone.

The AC-out (AC coupled) connection has a limit. There cannot be more power from PV that the MP-II size (1 to 1 rule).

AC coupled solution will work when there is no grid and sun is shining. If you choose the compatible inverter it will cooperate with the MP-II and adjust its power according to your house needs when there is no grid and battery is full. I have a Fronius inverter.

Before you install MPPT, you can charge batteries with gas generator when they get empty to jump start the system during the sunny day or to power your house at night.

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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·
Thanks @MarekP but will AC coupled (AC-out) solution allow me to power or supplement loads that are not connected to the MP-II with solar? e.g. if I generate 2000w of solar and I have a water heater that is not on the MP-II that starts and uses 3000w... will it use 2000w from solar and then 1000w from grid?
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marekp avatar image marekp Riaad Abdulla commented ·
@Riaad Abdulla

In my country, Polnad, we have winters with -25 C sometime. :)

So definition of "cold winter" is relative.

Yes the heat pump, I mentioned, is on top of the water tank (geyser) and takes heat from surrounding air.

The added bonus is that in the summer air around it is a bit colder.

If your winters are not very cold it can take air from outside the house and still be efficient enough.

The unit you mentioned is ok too when is used only for water heating and your water tank has big enough internal heating coil. Just make make sure the there is enough flow from H-P to your geyser. Your installer should know that.

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Riaad Abdulla avatar image Riaad Abdulla marekp commented ·
Wow! -25C ... yes I am not built for that weather... our coldest day ever was probably -7C

Poland is definitely on my list of countries to visit though. Very beautiful

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marekp avatar image marekp Riaad Abdulla commented ·
@Riaad Abdulla

You can visit in the summer. :)

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