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Have installed and configured three Victron Multiplus II - 5000/48 as a 3ph System in an Off-Grid constellation. For power saving reasons I would now like to switch off the inverters for L2 and L3 during night times and connect all loads, that need to be alive, on L1.
Is there any strategy to configure the system to achieve this?
Thank you for input!
Michael.
No, the system needs to see all 3 inverters "ON" in order not to go into error mode. The only way to get some power saving is to enable AES. This can save up to 50% energy during low power periods. It helps also to keep the loads evenly balanced so the load on each inverter is less than the AES threshold.
You can add fourth smaller just inverter and use it for the night loads when main system is switched off.
Thank you very much for your input!
Michael
@Mike Dorsett
Thank you very much for your clear answer.
Anyway, are you sure, that AES works in 3ph-systems?
Due to the handbook, it's said, that this only works in single mode.
Could you confirm this?
Thank you very much!
Michael
For that freezer you can install "slow start" unit to take care of the inrush current.
No, unfortunately, from all what I know, you can't.
Every heat pump or compressor (and a freezer is nothing else) has to overcome the pressure against the dead center point on start.
A slow start unit does nothing else than limit the power to the load on start. However, limiting the power in the moment of utmost power energy demand of the motor against the gas pressure on dead center point means, that either the motor will get stuck and burn down, or, in case the slow start unit is a good one, the motor will NOT start to rotate at all, or, if the freezer motor has protection, its current limiter will respond. Some heat pumps have a mechanical decoupling in the moment of start, combined with a mechanical flywheel mass, however, freezers have to stay affordable units and therefore the expenses for such gimmicks are too high.
Test it yourself! Stop your freezer when running by interrupting the power supply and then plug it in some seconds later. You will have a good chance, that the thing refuses to start for some minutes, until the coolant has released its pressure via the expansion valve. This is usually the case during normal operation, but not, when the plug is briefly pulled. It may well be, that the motor protection will respond for quite a while, until even the background power of a public grid is strong enough to overcome the rest pressure inside the coolant system for just this one particular millisecond.
In case of electric motors built in bigger electric angle grinders, for example, that do not have to overcome any dead points on start, a slow start unit works perfect. And in case of most inverters, they have that inbuilt anyway.
Thank you for your input and if I missed something in my statement or put something wrong, please let me know.
Michael
There are 2 types of a slow-start units.
1. based on power limiting that use thyristors. Motor gets less power at the beginning and full power at the end. This method is the one you are describing.
2. based on frequency adjustment. Motor gets full power from the beginning but at lower frequency, therefore motor is rotating slower. When frequency is slowly raised up to the nominal value motor is slowly increasing its RMPs up to nominal.
I have a Heat Pump at home that uses that second method at startup.
I am not saying that that second method will work for your freezer. You should ask someone who knows your freezer for opinion on this mater. There may be a problem if the motor is a single phase type.
Thank you for your correction! Very much appreciated.
But the point is: In a compressor-like heat pump you have to have the torque to overcome the counter force at the moment of start. In addition, you have the mass inertia of the accelerating motor.
No matter in which way you try to "fade in" your energy fade up, either frequency or pulse width manipulation, both has the same result: In the moment of utmost power demand the mechanic doesn't get the energy to overcome the dead center point.
Because that's the way my freezer is constructed. After that first moment, the rotation motor has built up enough flywheel mass to overcome the next dead center point, that the freezer runs using 70W only.
But in the moment of start, it needs way more than 2000W (an inverter of that size, having inbuilt startup capabilities, can't move the thing, I have tested that before.)
Let's take an example: If you pull a nail into wood, you can either press the nail in using a leverage press (which would be according to a soft start unit) or you can use a hammer (which compares to a electrical grid with endless power reserve). Let's assume that we need a force of 1000kg (which is physically not correct, but just for easier imagination) to drive the nail in.
What will happen with the nail, if your leverage press only has 800kg max. available? It can't provide more, because the lever of that press would brake otherwise (According to our electrical motor, that would burn down, when receiving that much energy without being able to turn). Would it help to soft-start the leverage press up to that maximum point? No, for one millisecond, your load (the nail) will need a force greater than 1000kg and if you can't get this from your energy background, the nail will not move.
What do you think?
Michael
If you keep the door shut you could probably use a timeswitch to turn off the freezer for the whole night. It will probably last eight hours or more. Maybe you would need to lower the thermostat a bit but worth doing the experiment.
