Inrush Current

[JohanG]

I  have noticed other topics on the affect of inrush current

How does one cater for this when you have two fridges, a dishwasher, washing maschine, dryer etc

Should one size your inverter for this or does it not pose a real problem?

Should this subject not be more comprehensively be discussed?

[Jaco De Jongh]

31 minutes ago, JohanG said:

Should one size your inverter for this or does it not pose a real problem?

The inverter must be able to handle the startup current while the others are running . The changes of any two starting up at the same time is very slim. 

Dishwashers has little inrush current but draws a lot of power. Tumble dryer will have some inrush when the motor starts, but after that the element will just cause a pretty big load while the motor drops the Power factor. Those two I never run through the inverter unless its an off-grid installation. 

Washing machine will demand  a bit more from the inverter with the constant inrush current as the motor stops and starts the whole time. Does not affect bigger inverters, but smaller ones struggle to keep up. 

So to answer your question, Yes you should definitely size your inverter for this and yes it will play a big role, less so when using a hybrid, but if the loads are to big with the Axperts, it will switch back to grid more and you will end up using more Eskom power than you planned to. 

[___]

41 minutes ago, Jaco de Jongh said:

The inverter must be able to handle the startup current while the others are running .

I agree. If you can start your largest motor while the dishwasher is running, you should be okay. A dishwasher uses about 2kw when it heats water. Assuming a non-energy-efficient fridge with a 250W compressor, those need around 5x the nominal power to start, so to be completely safe, say you need another 1.5kw on top of that. So 3.5kw peak. Then also keep in mind that most inverters have some peak capability, eg a Victron Multiplus can peak at 200% Pnominal. So a 3kVA Multi is going to be sufficient to start a fridge while the dish washer is running.

 

[Tacet]

As I understand it, when you connect the Multi in the mode where it ties to the grid (functionally parallel to the grid), physically you still connect the grid to the Multi's input, and the load to the Multi's output, meaning that the Multi still has to be able to handle the full inrush current, even if part of that inrush is supplied by the grid rather than by the Multi.  This is the simplest way of getting the Multi to do the anti-islanding while still tying to the grid.  Is my understanding correct?  If so, how much can the Multi safely pass through (Multiplus II 48/5000)?  The info should be available, but I can't seem to find it.  Seems like a simple way to cater for inrush currents without oversizing the inverter terribly.

[Guest]

On my 3kva:
1) I run the dryer daytime, at other times the geysers come on.
2) The fridge / freezer start in between.
3) Need some coffee ever now and then.
 ... the grid tied inverter happily provides the max it can to the main DB - saw peak loads this past weekend of 10kw - inverter gave the max it could at the time, +-350w, as it wa pouring with rain.

Here is the dryer on yesterday - it does push a teeny weeny back now and then.

Next second ... literally a second:

 

I don't think, IF you are grid tied, that one needs to worry about startup currents. The main DB absorbs that spike in split second BEFORE it gets to the inverter.
And I could be wrong?

[Tacet]

Bingo, I found the answer in the Multi's user manual.  It can supply a total of 45 A, meaning that you should be fine with a load of up to about 10 kW.  That should be more than enough to cater for any inrush I'm likely to encounter in my house.

[Jaco De Jongh]

2 hours ago, Tacet said:

how much can the Multi safely pass through (Multiplus II 48/5000)? 

That would be 50 Amp plus its own Output rating. 

In your example above, the 3000 va model will allow through 32 amps from grid and add to that 13 Amp from  PV or battery, but when grids fall away, it can only supply 13A.  

[Tacet]

Ah, so the 5000 VA model has a larger input rating.  Good to know, thanks!