VA versus Watt : The hidden relation!!!

va to watt

Ok, time for dumm question ( probably allready answered):

I have a solenoid valve, with 9.6VA consumption inrush current and 6.5VA holding current.
The valve is controled by a circuit witch indicated max power consumption 3Watt.
Is that correct? I believe there is a hidden mistake or a deliberate one in this manual.
What do you think?
D.

va and watt

The phase angle between V and I is quite large on reactive loads. That is why the units of VA are used. They draw large currents but the actual power dissipated is small. Watts = power factor x voltage x current. Power Factor is the cosine of the angle between voltage and current.

va versus watts

Put differently Cosθ is also the ratio Active power(W)/ Apparent power(VA)

relation between watt and va



Usually the current is defined in Amps ... However here I find in VA ?

va vs watts

mmike said:

Code:

9.6VA consumption inrush current and 6.5VA holding current

Usually the current is defined in Amps ... However here I find in VA ?

Click to expand...

It's a AC-feed solenid valve ??

Is possible draw near pure reactive power and initial in non drag state draw more reactive power depend of lower inductance compare later state and iron going in to coil and make more inductance and consume lower reactive power (but more loss i Watt depend of iron loss).

DC-coil i near pure resistive and not change current if iron draws in to coil or not

it's possible more important to display VA with know AC-voltage and measure current in industries compare to display Watt or pure current - special if VA value is much higher compare to consume Watt can make extra cost from power delivery company.

You handle only on valve, but in industri can handle hundreds of then same time and in industrial world is VA-value important value to calculating needed power distrubition, cable and control of reactive poweer compare to consume power in Watt.

va versus watt

Thanks guys.
Most helpfull.
The valve is AC solenoid. And I agree with xxargs. It is not the current that is measured in VA. It is stated that when valve is openning, the consuption will be 9.6VA, given the fact that V=24VAC.
The original question states as follows: Is the 3W max power capability , covering the specifications of my solenoid? ( the solenoid is to be controled by the circuit which is working on 24VAC.)

Thanks,

D.

va of watt

dkace said:

Thanks guys.
Most helpfull.
The valve is AC solenoid. And I agree with xxargs. It is not the current that is measured in VA. It is stated that when valve is openning, the consuption will be 9.6VA, given the fact that V=24VAC.
The original question states as follows: Is the 3W max power capability , covering the specifications of my solenoid? ( the solenoid is to be controled by the circuit which is working on 24VAC.)

Thanks,

D.

Click to expand...

Measure DC-resistance in your valve, and measure how much current valve draw on normal 24 Volt AC feed.

take measured DC-resistanse * measured AC current on 24 Volt feed and you have resistive loss in Watt, rest is reactive power.

VA^2 = Watt^2 * VAr^2

---

Wanted power level = 3 Watt load

3 Watt / 24 Volt = 0.125 Ampere (R = 192 Ohm)

measured and/or know value from valve:

9.5VA /24 volt = 0.396 Ampere (or Z=60.61 Ohm in starting moment , ignoring this in later calculate)

6.5 VA/24 Volt = 0.271 Ampere ( Z = 88.56 Ohm - on going state)



ie loads phase angle between current and voltage to load must be higher than 62.5 degree (or resistive part lower than 0.461 * 192 = 88.62 Ohm DC-resistance) to make possible using full phase compensate parallel capasitance to make 192 Ohm or higher resitive impedance in resonant mode for <= 3 Watt consume .


Question: is your driver circurit is power limited (internal power cannot delivery more than 3 watt in long term) or current limited (depend of relay/triac, thyristor heating inside etc. above 125 mA. current), can equipment give high starting peak current without problem, starting with zero crossing in period etc.

Maybe possible to using phase compensate capacitance on valve if reactive part is big compare to resistance (see above, needed capacitance in this case with 86.2 Ohm DC-resistance is 32 uF) to take down current , but for calculate this exact value I must know DC-resistance in valve or (better) phase angle between current and voltage to load ie. this case include iron-loss in valve (copper/iron loss in AC is added resistance to measured DC-resistance).

but remember - phase compensate capasitance can give very high peak current if connected outside zero-crossing area in voltage periode.


/Xxargs