Without going into long winded explanations at this stage, can someone just give me the formula for calculating this or just the value I should plug into the website.
The explanations that website gives for power factor calculation is so long winded that I am confused as to what the end result formula is.
Without going into long winded explanations at this stage, can someone just give me the formula for calculating this or just the value I should plug into the website.
Only if you tell us what you are trying to do with the results.
However I don't no what the power factor is.
Power factor is the phase relationship between voltage and current. It depends on what you are driving into, that is if you have a capacitave or an inductive load. See this Power Factor
If you have a purely resistave load then you power factor will be zero. For a pure inductive load or capacitave load then you have 1 or -1. Anything in between is a power factor in between.
boylesg:
Without going into long winded explanations at this stage, can someone just give me the formula for calculating this or just the value I should plug into the website.
Whole formula is just: VA * PF = W. So the main point for you I guess is that wattage drawn by a device is always less or equal to the volt-amperes. Googling for usual power factors for solenoid valve shows that PF usually could be 0.7 - 1, but you've got to find the specs for the valve you're using or maybe just consider PF=1.
antti_s:
Whole formula is just: VA * PF = W. So the main point for you I guess is that wattage drawn by a device is always less or equal to the volt-amperes. Googling for usual power factors for solenoid valve shows that PF usually could be 0.7 - 1, but you've got to find the specs for the valve you're using or maybe just consider PF=1.
Solenoid valve says 24VAC / 8VA
The plug pack I have at present is 24VAC 1A max
But this power supply also supplies the DC for the Arduino and relay board etc.
The solenoid would draw 8 / 24 = 333mA?
But I would have thought the Arduino etc would be drawing enough to exceed the 1A max.
As long as I have my solenoid connected to one of the relays and trigger it, my arduino resets itself.
I assume the DC voltage is dropping too low as soon, as the solenoid valve 'goes', and my arduino resets itself.
Either my calculations above for the solenoid are wrong and the solenoid is drawing more current than that.
You're calculations seem correct to me, but I'm just the beginner myself. So you could try getting a more powerful PSU, looks like the easiest solution.
Without seeing a schematic of just how you have it wired, it is not clear what issue you are running into. You indicate the power supply is also supplying the Arduino, however, the Arduino can't handle 24vac, so what is the missing block between the 24vac and the Arduino? As far as the solenoid causing a reset of the Arduino, it may be a supply issue of too much current dropping the voltage, or it may be the inductive kick you get when you remove the supply from an inductor (like the solenoid) that is causing the reset. We need to know just how that 24vac is powering the Arduino.
gpsmikey:
Without seeing a schematic of just how you have it wired, it is not clear what issue you are running into. You indicate the power supply is also supplying the Arduino, however, the Arduino can't handle 24vac, so what is the missing block between the 24vac and the Arduino? As far as the solenoid causing a reset of the Arduino, it may be a supply issue of too much current dropping the voltage, or it may be the inductive kick you get when you remove the supply from an inductor (like the solenoid) that is causing the reset. We need to know just how that 24vac is powering the Arduino.
24VAC is not supplying the arduino drirectly - it goes through a bridge rectifier and one of these first:
I am now using one of the relay boards with opticoupling, so it should be the result of kickback from the relay.
But then again there will be also kickback from the solenoid valve itself.
However the bridge rectifier should protect the DC to DC converter......unless the voltage level of the kickback exceeds the capacity of the DC to DC converter?
The solenoid valve is in parallel with the bridge rectifier .
If it was a voltage spike exceeding the input limit of the DC to DC converter (about 40V I think) then how would you suppress that?
I know how to do it in DC circuits but not so clear with AC circuits.
The initial inrush of current into a solenoid when it turns on is much higher than the steady "on" current.
There is usually quite a high voltage spike created on the supply when a solenoid turns off. A diode is usually wired across the solenoid to reduce the spike (check the polarity required).
Run separate power supply wires to the solenoid and control PCB. Of course the solenoid wires will usually be thicker than the PCB supply wires. The "negative" wires will have a common connection at the PCB. Run these pairs of wires all the way back to the power supply. The hope is that the power supply will absorb any glitches caused by the solenoid operating.
Grumpy_Mike:
Only if you tell us what you are trying to do with the results.
Power factor is the phase relationship between voltage and current. It depends on what you are driving into, that is if you have a capacitave or an inductive load. See this Power Factor
If you have a purely resistave load then you power factor will be zero. For a pure inductive load or capacitave load then you have 1 or -1. Anything in between is a power factor in between.
Power factor is 1 for resistive and 0 for purely reactive, -1 for non-reactive power source, its the cosine of the phase difference for sinusoidal waveforms. Its defined as rms power consumed divided by
(rms current x rms voltage)
Its the phase angle whose sign tells you whether capacitive or inductive.
It varies from -pi/2 to +pi/2 depending on whether capacitive or inductive. I'm not sure
which way though!
The initial inrush of current into a solenoid when it turns on is much higher than the steady "on" current.
There is usually quite a high voltage spike created on the supply when a solenoid turns off. A diode is usually wired across the solenoid to reduce the spike (check the polarity required).
Run separate power supply wires to the solenoid and control PCB. Of course the solenoid wires will usually be thicker than the PCB supply wires. The "negative" wires will have a common connection at the PCB. Run these pairs of wires all the way back to the power supply. The hope is that the power supply will absorb any glitches caused by the solenoid operating.
The diode across the coil to suppress the inductive kick only works for DC - he indicates it is being driven from AC (24v). You can use something like a transorb or something similar to clip the kick with either polarity of the AC depending on when the contacts open on the relay. Also, as indicated, run all grounds back to a common point on the supply otherwise, you do get strange transients happening when loads turn on and off. I have also found that supply ratings (especially of the cheaper variety) tend to have a bit of "advertising" factor added in. Running them close to the "advertised" rating is often too much for the supply (when they say it is rated 12v 2A, it may put out 12v OR 2A, but not both at the same time )
boylesg:
I know how to do it in DC circuits but not so clear with AC circuits.
You do not have any AC circuits. Once you get to the bridge rectifier it is a DC circuit. You should have a large capacitor on the output of the bridge rectifier as well.
I have still no idea why you want the power factor in all this.
The OP indicated the solenoid was 24VAC, 8VA. It sounds like he is controlling it with a relay, so that part may or may not be AC but without a schematic it is hard to tell. He did say it was 24vac though so I assume it is being powered before the bridge and controlled with a relay. The OP needs to provide a schematic (even if drawn by hand) so we know exactly how this is all wired.
The initial inrush of current into a solenoid when it turns on is much higher than the steady "on" current.
There is usually quite a high voltage spike created on the supply when a solenoid turns off. A diode is usually wired across the solenoid to reduce the spike (check the polarity required).
Run separate power supply wires to the solenoid and control PCB. Of course the solenoid wires will usually be thicker than the PCB supply wires. The "negative" wires will have a common connection at the PCB. Run these pairs of wires all the way back to the power supply. The hope is that the power supply will absorb any glitches caused by the solenoid operating.
The power supply is a sealed plug pack so I can do this only as far as the end of the wire coming from the plug pack and where it plugs into my little black box containing all my electronics.
The thing is the commercially made irrigation controllers only have one pair of wires from the wall socket to where you attach the ends of the wire to the input terminal block with the irrigation controller:
The arduino resets the instant the solenoid turns on. So it must be that the initial current in rush is causing the voltage to drop for my DC power supply thus shutting the Arduino down. When the AC current in the solenoid becomes steady then the DC power is restored to the Arduino.
But the thing is the above Holman irrigation controllers use the same 24VAC 1A power supplies and you can attach the exact same solenoids to them.
So they must have some means of storing charge to cater for the initial momentary current in rush of AC power into the solenoid valve.
How would this be done?
Could it be as simple as a low value resistor, of suitable wattage, in series with the solenoid valves to limit the current to 8 / 24 = 300mA or so?
I just read that in rush current to solenoids can be 3 times the normal current. So if the initial in rush current is around 900mA then I can see why the there might not be enough current capacity left over to power the DC electronics.
boylesg:
The arduino resets the instant the solenoid turns on. So it must be that the initial current in rush is causing the voltage to drop for my DC power supply thus shutting the Arduino down. When the AC current in the solenoid becomes steady then the DC power is restored to the Arduino.
You tried putting a relatively large electrolytic capacitor (eg. 100 microFarad) across the 5V pin and the GND pin of the arduino board?
The arduino resets the instant the solenoid turns on. So it must be that the initial current in rush is causing the voltage to drop for my DC power supply thus shutting the Arduino down.
You can not draw that conclusion without taking measurements. There are lots of things that could be causing the reset.
Southpark:
You tried putting a relatively large electrolytic capacitor (eg. 100 microFarad) across the 5V pin and the GND pin of the arduino board?
Well I do have a 3300uF electrolytic cap on the bridge rectifier before it goes into my DC to DC converter, you would think that that would be enough to take care of it.
Perhaps another cap on the output of the DC to DC converter?
boylesg:
Well I do have a 3300uF electrolytic cap on the bridge rectifier before it goes into my DC to DC converter, you would think that that would be enough to take care of it.
Perhaps another cap on the output of the DC to DC converter?
Try putting a large cap between the 5V pin and the GND pin of the arduino, and put it as close to those pins as you can get.
Southpark:
Try putting a large cap between the 5V pin and the GND pin of the arduino, and put it as close to those pins as you can get.
What do you mean by large? 10s of uF, 100s of uF, 1000s of uF?
P.S. My resistor in series with the solenoid idea has no effect, so it therefore must be the in rush current on the relay coil itself that is causing the problem, which is why you have suggested a cap on the arduino.
But then why does the same thing not happen if I disconnect the solenoid valve?
boylesg:
What do you mean by large? 10s of uF, 100s of uF, 1000s of uF?
Five or six posts back, I had provided a value of capacitance (as an example).
But then why does the same thing not happen if I disconnect the solenoid valve?
I haven't got the gift (or curse) of clairvoyance. But if a capacitor does help, then could always speculate that the coil might have some kind of snubbing circuit for handling disconnection.
)