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The VA readings same as AMP readings


Khalil
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Dear all,

I have installed Axpert MKS Plus 3KVA 60A MPPT 24VDC Solar Inverter. During the day I have noticed that the VA redings the same as AMP readings. The normal is VA reading should be less the AMP reading (VA=0.8 AMP).

And during the night there is high AMP while the watt is low. For example, when I read 167 watt as a load, the consumption is 10 AMP which it should be 6 AMP.

Regards,

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Hi Khalil

The difference between VA (apparent power)  and real power (Watts) is due to inductive loads. An inductive load is a load where a magnetic field is induce due to field windings. This magnetic field cost electrical energy to create. With the removal of current  an inductor  has a reverse current that flows due to the collapse of the magnetic field. So with AC where this magnetic field is being created and collapsed 50 times a sec the Amps measured will always be higher than the true work being done (real power) some of the energy "hiding " in the  creating and collapsing magnetic field. Fortunately we pay the utility company for real power and not apparent power.  It is more complicated than I have said but all you need to remember is that with resistive loads real power is nearly equal to apparent power and this does not hold for inductive loads.

All your observation tell me that you run mostly resistive loads during the day and more inductive loads at night.

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58 minutes ago, Khalil said:

The normal is VA reading should be less the AMP reading (VA=0.8 AMP).

No, VA (apparent power, volt-amps, V * I) will always be equal to or more than the W (symbol P, measured in watts, real power) because for a sinusoidal AC signal W = V * I * cos(theta), where theta is the phase angle. Since the cosine has maximum values of -1 and 1 (at 0 and π radians, or 0 and 180 degrees), W is strictly less or equal to VA.

If your VA is the same as your watts, it means your loads have a unity power factor, that is cos(theta) = 1, or theta = 0. This is typical for resistive loads.

About the 0.8 power factor thing you get with the Axperts: All it means is that at full power it can do 5000VA (the rated capacity of the final stage of the inverter where it makes AC from DC), and 4000W (the rated capacity of the boost stage). This means it can reach 5000VA if your power factor is 0.8. Which is rather arbitrary, confusing, and only useful to the marketing dept who has no idea what this is about anyway.

That's a bit like advertising that you can manage a 5000VA load at 0.8 PF. Then the customer asks: But what if my power factor is better than 0.8? Oh,... well sorry... then you won't be able to reach 5000.

:-)

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Oh, and as @Chris Hobson said, power factor is determined by your loads. It is not a constant/static factor.

Heating elements and incandescent lamps typically have a power factor of 1. Inductive motors with a good correction capacitor on around 0.9. Small induction motors without such a device, around 0.8. Cheap switch mode power supplies, some LED lamps with the same, and iron transformers not properly loaded down can have power factors as poor as 0.3 (turning your 5000VA inverter into a 1500W one).

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27 minutes ago, Khalil said:

three ceiling's fan at night

That would explain why your power factor changes at night :-)

It seems to be working perfectly normal, no need for concern.

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2 minutes ago, Khalil said:

So how can I check the factor ?

There are meters that can measure it, for example the modbus meters we use with Victron equipment. You also get some cheap plug-in meters (similar to the kill-a-watt) that can do this sort of thing. But mostly... I simply wouldn't worry about it.

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