Watts Vs VA when calculating runtime?

Product Discussion BLUETTI Apex & AC Series
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Hi there Bluetti community,

When calculating runtime on the AC side of things, should I be using the Watts or the VA being consumed?

I have an AC2A and as noted on a couple of posts on the EB3A, it looks like the display is showing VoltAmps instead of watts on the front of the unit and it appears the runtime calculated is closer to the amount VoltAmps consumed instead of Watts. I was using a fan earlier today with a PF of roughly .5 to draw the battery down a little so the VoltAmps are about twice what the Wattage is. While this fan is going to be replaced with a DC fan within a few days, and I tend to lean heavily towards DC only loads when I can, I’m curious just when I’m doing the spreadsheets - I should be using Watts when calculating runtime correct not VA?

Still love the unit and in most cases I’d be using the fan until the unit said “that’s enough!”. For planning purposes though I’d like to figure out roughly how long it would go to figure out it’s charge breaks in the sun.

2

The AC output meter on the display is in VA. For runtime calculation you would use the formula listed in the user manual:

Operation time = Battery Capacity (Wh) x DoD x η ÷ (Load Power + AC2A Self-consumption)

Where;

η is the conversion efficiency of the inverter (85% +/- a few)
Self consumption = 12W on AC2A AC inverter.
Example: 50W AC fan with PF of 0.5 (100VA) would show 100W on the display

So 204.8 X 0.90 X 0.85 / 50 + 12W = 2.52Hrs of runtime.

1 Like
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Ok, perfect. Thank you!

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From what I discussed something is wrong with Bluetti display that shows VA ( Apparent Power ) and not watts as units printed in him display.

  1. wrote to Bluetti about that issue - the display show about twice of the writing on the transformer to a fan that connected to AC socket of Bluetti eb3a.

  2. simulations the watts power of the load by connecting external inverter 12 volt DC to 220 volt AC.

  3. what I wrote about what I saw:

I purchased the bluetti eb3a this month.

I have question that something seem to me wrong.

Devices that consume a declared and maximum power of X watts ( 24 watts in my test - fan that work with input of 12 Volt up to 24 Watts ) appear on the device that consume almost twice as much power! 48 watts.

( 48 watts instead of 24 watts ) Is this a software problem?

For example, I gave here a transformer with a maximum power of 24 watts connected to fan. The transformer came with the fan.

But when connecting this 24 watts transformer to AC socket the watts power appears on bluetti almost double! About 48 watts.

The time that the eb3a device has left to operate till battery died is about 5 hours.

But in addition, the same load (in this case a fan) when connected directly (eb3a 12 volt DC output ) without the transformer 12 volts, you get 18 watts in the DC connection, which the real power.
consumption of the fan.

The remaining power station time is also doubled - about 11 hours.

The differences between 46 watts and 18 watts in the same fan load show that eb3a do something wrong:

It does not seem possible that there are such high differences of close to 100 percent between the same load.

One - DC output about 18 watts.

other through the transformer, the AC output to the fan about 48 watts.

And this is when the efficiency of the modern typical AC transformer is about 90 percent.

It should be noted that I tested in both situations the fan had the same power output and the power in it was the same.

The fan is New got it from store today.

Photo attached of the fan label, transformer label, eb3a display on fan load in AC and DC.

What wrong here?

Thanks.

  1. My Test I did and this is the results:

Hello again.

I conducted an experiment.

I connected an external voltage converter (I didn’t have a converter that outputs a sine wave, only a square wave, but from the results, it doesn’t seem to affect the results) to simulate the internal converter of the bluetti.

A converter that receives 12 volts and outputs 220 volts to the same transformer and the fan connected to it when that fan is operated in the same configuration of wind power that I connected to the bluetti.

The current consumption of the external converter was measured and it was 0.19 amps.

I connected the same transformer and the fan. The current consumption was 2.35 amps, meaning that in the calculation we multiply the input voltage 12 volts times the input current minus 0.19 amps and we get 26 watts.

To do a reference experiment, also to make sure that a square wave did not spoil the experiment, I connected a 17-watt energy-saving light bulb in place of the transformer. I got a current of 1.52 amps.

We subtract from this 0.19 amps the operating current of the converter itself without load and we get 16.2 watts.

A complete and correct match to the declared load of the bulb of 17 watts.

Conclusion: The power consumption of the transformer together with the fan is indeed about 24 watts, meaning the efficiency of the transformer is over 95 percent.

This experiment actually simulates the DC power consumption from the bluetti battery. So it seems that the display shown by the bluetti is incorrect, showing almost double the power of 47 watts consumed by the transformer while the fan is on.

In fact, measuring the power in DC shows that there is almost no power waste in this transformer. The efficiency of the transformer is close to 95 percent! In addition, the experiment has an image of the power consumption from the bluetti battery because this time I measure everything in direct current and not in AC by converting the AC current right from the same transformer to DC to completely simulate the current consumed from batteries.

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Hi @gilgolan48gmail.com . Look up the term “power factor”. It’s essentially waste energy created by inductive AC loads. Energy that is not consumed, but needed to maintain motor function. An example would be power needed to run the magnetic field of the motor itself, requires juice. Apparent power is essentially real power + this waste power together. The ratio of real power consumed to this “waste” power is your “power factor”. Your power factor is just around 0.5, meaning half of the energy is wasted due to the crappy AC motor. Run a DC brushless motor (that runs over AC) and you’ll notice the power factor is far greater (closer to 0.8-1) meaning you’ll lose less waste energy. TLDR - Your AC appliance “uses” 24 watts but “requires” 47W to run

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According to the experiment I did with the same transformer and the same fan, the transformer’s efficiency is over 90 percent, meaning the power factor is close to one. The transformer is also an electronic transformer, similar to an economical lamp. The transformer weighs only about 72 grams and was manufactured in the last year. Note that I measured the real power consumption of the transformer with the load. Real power consumption, which in order to see, I converted all the power consumed in the circuit to DC. You can’t say that there is another component to DC current that I don’t see. All AC PARTS INCLUDED IN THIS DC. And when the measured current is 2.35 amps with a voltage input of 12 volts, the total power of the system, including everything, is about 24 watts.

You wrote: “Your power factor is just around 0.5” But where did you determine this? After all, the question is whether the device displays correctly, and when you write like that, you are relying only on the device. I conducted the experiment to know whether the device does indeed display correctly, and not to say without researching. You need to research to know this. Explore.

Do you agree with me?