question

mito avatar image
mito asked

Configuring Multi II Internal Transfer switch

Having several MPII 48 x 5KVA systems, working in DVCC off grid configuration with Generator, when load exceeds Multiplus II 5 KVA Nominal Power, pex 10 KVA, and Power Assist is not able to achieve load demand (when SOC % is too low) is supposed that internal Power Switches should get into action connecting 10 KVA Generator ACIN to serve loads bypassing to ACOut 1 or 2 , disconnecting Inverter (but still allowing charging) , as Multiplus II 5KVA specs allow constant 11 KVA in this bypass mode (220 v @ 50 amps).

Question: is this behaviour description correct? has to be programmed or it is automatic ? How? Is there any link to understand how internal bypass switches work or programmed?

Multiplus-IIquattro 10kvaswitch
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6 Answers
derrick thomas avatar image
derrick thomas answered ·

Turn off power assist and all power will be supplied by ac input and not the inverter. As long as power being used is below the input current limit you set, the batteries will continue to be charged.

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Kevin Windrem avatar image
Kevin Windrem answered ·

When the AC input is present and within specifications (voltage, frequency, stability). The AC input relay closes and power from the AC input becomes available at the AC output(s). The inverter an assist this passthrough of power if the incoming AC isn't sufficient.

For a generator, you want to enable wide frequency and possibly increase the acceptable AC voltage range for the AC input.

You also want to set the AC input current limit so the generator isn't overloaded.

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michael66 avatar image michael66 commented ·

When the MPII in ESS mode normally and grid is lost than the MPII will automatically create an island on AC out1. If I now want to recharge the batteries by temprary conecting an emergency generator to AC in, do I have to change settings to reduce current in AC in or will the MPII automatically detect that this is not grid and act accordingly?


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Kevin Windrem avatar image Kevin Windrem michael66 commented ·
Quattros have a second input that allow separate settings to be used for grid and generator but not the Multiplus. You need to manually change the input current limit for the generator.
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mito avatar image
mito answered ·

Thanks evrybody.
In fact , configuring offgrid systems that most of the time run below Nominal Inverter Power, when load demand extra power that exceeds Nominal Inverter Power but still is below maximum Transfer Switch Power spec, I understand that bypass switches ACin with ACout1, declining Power Assist when SOC% is very low. When loads request far more power than can be provided by Multiplus 2, not only as inverter but as bypass, and assuming Generator has the capacity to serve this high loads, an external bypass should be needed, with the negative impact of a short blackout period, that should be minimized.
If there is experience on this scenarios, welcome to post.

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mito avatar image
mito answered ·

Making a twist in my question about transfer switch power serving scenarios.

In MP2 datasheet shows 4KW maximum Inverter Power (220 Volts x 18 Amps), and 11 KW for Maximum Transfer Switch Power (220 Volts x 50 Amps)

So question is: When ACout1 loads exceed Inverter Maximum Power 4Kw, but still are below Internal Transfer Switch specs 11 Kw, means that Load scenario can be served entirely by ACIn1 Power and Inverter can be stopped during heavy demands short periods (less than one or two hours bypass) of power shuting inverter off but still charging batteries? Is there any Assistant that can make Inverter shut down instead of power assiting when load is higher than X amps load current? And still charge batteries from grid or generator?. I see that with VE-config in the Inverter section is possible to shutdown inverter on SOC conditions (needs to enable battery monitor, normaly disabled in my cas I use Cerbos). Is not 100% what I need (disabling inverter under load power conditions when Grid is present) but should be a shortcut in case there is no other.

Hope need is more clear now.

Question relates to my MP2 instalations, but also apply for my Quattro instalations

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Kevin Windrem avatar image
Kevin Windrem answered ·

What you describe is exactly how the system works. AC loads are satisfied by available AC input until the AC input current limit is reached, then power assist kicks in to add additional power to the loads while keeping the AC input current below the set value.

If the AC output load is below the AC input current limit, the additional power on the AC input will charge the batteries.

Lets say your loads are 10 amps and the input current limit is set to 15 amps. Then all load power is supplied to the loads. If the batteries need charging, then 220 x 5 = 1100 watts is available to charge the batteries.

If the load increases to 18 amps, then the input current will max out at 15 amps and the remains 5 amps (660 watts) will be drawn from the batteries. The batteries will not charge in this condition.

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mito avatar image
mito answered ·

Thanks Kevin
But..., the scenario I tried to describe is the opposite. The load at certain moment , for a couple of hours a day is 8Kw, above than maximum Inverter spec, lets say MP2 (48 Volts 4KW) @ 220 volts x 18 Amps=4Kw, but below the maximum Transfer Switch Power, for MP2, that according to spec 220 volts x 50 Amps=11 KW normal for bypass.

Grid or Generator supports more than 15 KW. So there is not a case por Power Assist, because it is not needed nor desired. Power Control is enabled to achieve smooth ACin1 during the transient period.

The point is to find a way to disable Inverter during this extra load Power demand when Grid or Generator is available, and still keep grid charging bateries.

I see that we can disable inverter @ SOC% in Inverter Section, but this feature works with or without ACin1 available. That is not what we need.

I was rather looking for disabling inverter through an Assistant when load was above maximum and ACin is available, so batteries are not discharged, as is the case when Power Assist

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Related Resources

MultiPlus-II Product page 

MultiPlus-II Manual

MultiPlus-II 230V Datasheet 

VE.Bus Error codes

Additional resources still need to be added for this topic