Hi everyone,
Do you have any idea of the duration of compressors inrush current ? I know (from this post: https://community.victronenergy.com/questions/4454/peak-power-of-victron-inverters.html) that a Multi/ Quattro can hold 200% the nominal current for 600ms (30 cycles - 50Hz).
But how long does an inrush peak current last?
I ask this question because in my sizing, I am 70% over the quattros nominal capacity during the inrush current.
Thanks in advance.
There's no single answer. It will depend on the type of motor and the circuitry placed in front of it. You might be able to talk to your manufacturer, but more likely, you'll have to test it yourself.
You're powering a huge compressor with this inverter. It would make more economic sense for you to buy the right size of inverter for the steady-state demand, and then add a soft-start capacitor to reduce the inrush demand as you test and find it necessary.
Hi Ben,
Thanks for your answer. I kind of expected this answer... But is there any order of time ? Is it more like microseconds, milliseconds or seconds ?
Unfortunately, I can't test it. A customer asked me to size a system and I don't know the compressors models.
It is not just one compressor, there's AC and some resistive load, with an average power factor of 0.9 if everything start together which is OK good.
But if most of the compressors start together, the quattros will be over load during these inrush current.
The inrush current curve is complex and will have different (larger) values in each of those timeframes you mention, typically.
How many ACs do you have? Where did you get the inrush number you are using to arrive at 170% of capacity?
In this set-up, I've got these inductive loads :
I took a factor 4 for the AC inruch current and 3 for the pump, I've got these numbers from the tables on the internet.
Assuming for a moment that these are all on the same phase, my guess is that you will be totally fine unless you have something strange that might encourage a dozen units to start at the exact same time. Even a couple of units spinning up simultaneously is not going to come close to exceeding the surge capacity.
I have four smallish 1500W air conditioners in my setup. Their startup demand is roughly 4kW for about 1.5s. I'm sure in the very first cycle the current inrush is much higher, but our power supplies have "outrush" capacity, too.
I think you're going to be fine, or you're very close. Others with more experience with larger setups might chime in as well.
I also have a 11.5kW resistive load taken with a 60% bulking factor (otherwise 19kW).
The math gave me 21kVA (@60% bulking factor) in normal operation.
1.5 seconds is pretty long ! So according to the doc, I should size at 150% capacity ?
Oh, so you have a lot more loads, my bad.
I don't know what a "bulking factor" is.
What "doc" are you referring to?
I'm not sure 1.5s is that long given that the demand is only 2.5x. Most of these inrush demands are approximations, a steeply downward-sloping curve averaged over an interval.
Strictly speaking, inrush is quite complex: locked rotor rating, back EMF, stability of the driving power supply, voltage drop, other inductance in the circuit... all of these can affect the interaction, and so we just have rule-of-thumb multipliers to quickly arrive at a good sizing without putting everything on the scope.
For your size system, you need help from someone with more practical experience than I have to validate those rules-of-thumb, I think. (I don't think you're going to find the answers you really want anywhere in the Victron specs.)
Good luck!
Yes that the word I was looking for: a rules-of-thumbs (thanks to improve my english)
The bulking factor is a coefficient based on the probability that all the electrical equipments could run at the same time.
The documentation I was talking about is this one:
https://community.victronenergy.com/questions/4454/peak-power-of-victron-inverters.html
Thanks for your time
