[RE-wrenches] Power Factor

boB Gudgel boB at midnitesolar.com
Thu Jul 30 16:26:42 PDT 2009


Matt wrote:
> Unh - hunh, but it will run on the generator. If it didn't, I would go for the bad starter or motor, but it "seems" like the PF could be an issue??
>
> Matt T
>   

Well, an inverter is just (supposed to be) a low impedance Voltage 
Source and the current does whatever it is going to do... And what that 
current - voltage
relationship is, is definitely related to power factor.

Is the generator (which works fine) passing ~through~ the Magnum and out 
to the loads and pump ?  If so, then you know it's not a high
resistance circuit or loose terminal block screw I guess.   If the 
generator goes around the Magnum AE internal relays then I would
suspect a high resistance connection somewhere.

I would measure the voltage at the pump and note what it does when the 
pump is switched on from the inverter.
I bet you a drink, (next time I see you), that the voltage drops to zero 
or at least very low.

boB







> ---- boB Gudgel <boB at midnitesolar.com> wrote: 
>   
>> Matt wrote:
>>     
>>> Possibly a PF question, or maybe one for Magnum - boB,
>>>
>>> One of the guys at work is (almost) running a 3/4 hp sub pump with a Magna AE 48. Or rather, he isn't. According to him when he first fired it up, it operated the pump just fine. The next time he tried, though. he couldn't even get a buzz out of the starter. No workee.
>>>   
>>>       
>> Sounds kind of like a "pump is broken or worn out" problem, doesn't it ?
>>
>> If there is enough ac voltage applied to the pump, the it should do 
>> ~something~, or lights should dim or some
>> kind of sign should show itself, wouldn't you think ?   Otherwise, I 
>> would suspect it might be a surge problem.
>>
>> Is there a pilot light or something ?   Maybe a fuse blew or breaker 
>> tripped somewhere ?   (when the pump went off?)
>>
>> Doesn't sound like a PF problem though... However,  since you mention 
>> it, with loads that are not a 1.0 power factor,
>> at least for displacement power factor, when reactive phase shift is 
>> involved, the inverter must be able to "sink" current
>> from the stored reactive energy as well as be a source to the motor.   
>> The Magnum does that just fine, as does any other
>> decent inverter.
>>
>> Maybe Tony, Eldon or Gary at Magnum has seen this before ?    425-353-8833
>>
>> boB
>>
>>
>>
>>
>>
>>
>>     
>>> The inverter runs all the other loads in the house fine, just not the pump. He can run the pump directly from a 7 kW generator with no issues.
>>> So, do you think we're looking at a power factor deficit,(I think not), a motor starter problem or an inverter issue? I have to admit to being somewhat baffled by this one because it ran the pump once, but not after.
>>>
>>> Matt T
>>>
>>>
>>> ---- boB Gudgel <boB at midnitesolar.com> wrote: 
>>>   
>>>       
>>>> boB Gudgel wrote:
>>>>
>>>>  >>So, because of the different ways of specifying PF, it is always best 
>>>> to think of Power Factor as being the ratio of real (in phase) power, or 
>>>> VA to reactive power >>(VARS or "Volt Ampere Reactive").   That will 
>>>> work in all cases.
>>>>
>>>>
>>>> OOOps !   See, this can get confusing.   Reverse what I just said  Power 
>>>> Factor... " Definition: The ratio of true power to apparent power"  as 
>>>> David Brearley had just posted.  Otherwise, that calculation can give 
>>>> you an answer that is GREATER than 1.0 and you don't want that !
>>>>
>>>> Had to eat some of my words.  I just wanted to point out that the phase 
>>>> shift method was called DPF.   Didn't Ian Woodenden do an article on PF
>>>> recently too ?  If not, he or someone probably should in one of the two 
>>>> HP magazines.
>>>>
>>>> boB
>>>>
>>>>     
>>>>         
>>>>> R. Walters wrote:
>>>>>       
>>>>>           
>>>>>> Power factor expresses the time difference  between voltage peak and 
>>>>>> current peak on each of their sine waves. If both current and voltage 
>>>>>> waves are "in time", (their wave peaks match up) power factor is 1. 
>>>>>> If one is ahead or behind the other, it's not. Think about an 
>>>>>> electric motor: we hit it with a voltage wave, and a fraction of a 
>>>>>> second later, it actually moves, and the current wave happens. There 
>>>>>> is a little lag there. Resistive loads like lights have very little 
>>>>>> lag, and big electric motors coming up to speed can have horrible PF.
>>>>>>         
>>>>>>             
>>>>> This definition of power factor only applies for linear loads with 
>>>>> only inductance or capacitance (with resistance) and is called 
>>>>> "Displacement Power Factor (DPF) and you will  see that on some power 
>>>>> meters.
>>>>>
>>>>> For non-linear loads, like battery chargers or computer power supplies 
>>>>> without PF Correction,  the current waveform (on an O-scope) looks 
>>>>> nothing like a sine or cosine wave.   The current "spikes up" at the 
>>>>> AC voltage peaks.  It actually *looks like* it might be in phase, BUT 
>>>>> the current and the voltage do NOT look the same.  It's non-linear.  
>>>>> Lower than 1.0 power factor for sure.
>>>>>
>>>>> For a grid tie inverter, resistive heater or any load that has a PF of 
>>>>> 1.0,  the current and voltage waveform will both look exactly the same 
>>>>> AND there will be no phase shift.   They are both linear and all 
>>>>> current and voltage is in phase at every point in the AC cycle.
>>>>>
>>>>> So, because of the different ways of specifying PF, it is always best 
>>>>> to think of Power Factor as being the ratio of real (in phase) power, 
>>>>> or VA to reactive power (VARS or "Volt Ampere Reactive").   That will 
>>>>> work in all cases. (Real Vs. Apparent power is the same thing).   
>>>>> Apparent power is what you get when you multiply
>>>>> your RMS meter's Voltage by the RMS current and is called VA Volt 
>>>>> Amperes)   V x A will be the highest measured number, that is unless 
>>>>> the PF = 1.0 in which
>>>>> case both will measure the same.
>>>>>
>>>>> Some of that measured VA, or apparent power will be "in phase" and is 
>>>>> the "real" or "true" power.  Some of that VA may be reactive, 
>>>>> (inductive or capacitive that is) and is the "out of phase" portion.  
>>>>> Capacitive and inductive reactance is ALWAYS 90 degrees out of phase 
>>>>> in current and voltage.... It's just a matter of how MUCH of your 
>>>>> power is 0 degrees phase shift and how MUCH of that VA is  + or - 90 
>>>>> degrees out of phase.  If  ALL of the current is in phase with the 
>>>>> voltage, then
>>>>> the power factor is 1.0.   That is, if you lay them on top of each 
>>>>> other, they will look the same on an oscilloscope if power factor = 1.0
>>>>>
>>>>> It can get way more complicated that this too, but that's basically 
>>>>> it.  Feel free to add to this.
>>>>>
>>>>> boB
>>>>>
>>>>>
>>>>>
>>>>> power meters.
>>>>>
>>>>>
>>>>>       
>>>>>           
>>>>>> There is much more to it, with reactance, "real" and "imaginary" 
>>>>>> numbers?!, etc. but basically, we wrenches need to know that 
>>>>>> everybody wants  Power factor to be close to 1.
>>>>>> Obviously there isn't PF on DC, and it is my understanding that most 
>>>>>> inverters can operate at most power factors. Not 100% sure, but I 
>>>>>> think GT inverters would help not hurt the PF problem in most 
>>>>>> situations.
>>>>>>
>>>>>> Correct me on any and all of this, Oh fellow wrenches,
>>>>>>
>>>>>> R. Walters
>>>>>> Solarray.com
>>>>>> NABCEP # 04170442
>>>>>>
>>>>>>         
>>>>>>             
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>       
>>>>>           
>>>>>> On Jul 30, 2009, at 9:19 AM, boB Gudgel wrote:
>>>>>>
>>>>>>         
>>>>>>             
>>>>>>> Ron Young wrote:
>>>>>>>           
>>>>>>>               
>>>>>>>> Ok, so all seem to be in agreement more or less. How do I break it 
>>>>>>>> to British Columbia Hydro? :-|
>>>>>>>>
>>>>>>>> I think they must be misunderstanding what they are asking for but 
>>>>>>>> the question is in the section for PV and on the same line as the 
>>>>>>>> total output in Kwh of the PV. Power Factor %
>>>>>>>>             
>>>>>>>>                 
>>>>>>> It was most likely just  a trick question.
>>>>>>>
>>>>>>> You're gonna fool them, though !   :)
>>>>>>>
>>>>>>>
>>>>>>> boB
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>           
>>>>>>>               
>>>>>>>> I'll contact them and see where this goes but I don't fully 
>>>>>>>> understand what power factor is which will make it hard to argue my 
>>>>>>>> case. My understanding is that it is the difference between what 
>>>>>>>> the utility supplies to a residence vs. the actual loads being used 
>>>>>>>> by that residence expressed as a percentage. I came across the 
>>>>>>>> following course offering by SEI that discusses Power Factor with 
>>>>>>>> reference to PV:
>>>>>>>>
>>>>>>>> POWER FACTOR AS IT RELATES TO SOLAR INSTALLATIONS Presented By: 
>>>>>>>> Michael Smith of Alpine Management Systems  
>>>>>>>> This session will deal with power factor: What is power factor?  
>>>>>>>> What causes low power factor?  Why improve your power factor? This 
>>>>>>>> session will explain the role of power factor correction as it 
>>>>>>>> applies to solar installations. There are currently over 67,000 
>>>>>>>> KVAR installations in 26 countries resulting in phenomenal energy 
>>>>>>>> savings with a corresponding reduction in greenhouse gas emissions. 
>>>>>>>> Session includes several KVAR installations and the resultant 
>>>>>>>> savings. 
>>>>>>>> http://www.solarenergy.org/workshops/docs/industry08_trainingdetails.pdf 
>>>>>>>>
>>>>>>>>
>>>>>>>> Ron
>>>>>>>>
>>>>>>>> On 30-Jul-09, at 7:43 AM, Wind-sun.com wrote:
>>>>>>>>
>>>>>>>>             
>>>>>>>>                 
>>>>>>>>> There is no such thing as a power factor for DC or for panels.
>>>>>>>>>  .................................................................................................. 
>>>>>>>>>
>>>>>>>>> Northern Arizona Wind & Sun - Electricity From The Sun Since 1979
>>>>>>>>> Solar Discussion Forum: http://www.wind-sun.com/ForumVB/
>>>>>>>>> .................................................................................................. 
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>     ----- Original Message -----
>>>>>>>>>     *From:* Ron Young <mailto:solareagle at solareagle.com>
>>>>>>>>>     *To:* RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org>
>>>>>>>>>     *Sent:* Wednesday, July 29, 2009 5:45 PM
>>>>>>>>>     *Subject:* [RE-wrenches] Power Factor
>>>>>>>>>
>>>>>>>>>     Can anyone point me in the direction to find the power factor for
>>>>>>>>>     Sanyo HIT N 205 panels? The utility is requesting it on a net
>>>>>>>>>     metering interconnection application.      Ron Young
>>>>>>>>>     earthRight Products - Solareagle.com
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>     
>>>>>>>>> ------------------------------------------------------------------------ 
>>>>>>>>>
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