PF correction for washing machine

[dnix71]

I have a relatively new one-speed washer made by Roper. No computer controls. Hot and cold water have to be adjusted from the tap side. One cycle, as basic as it gets.

I can't run this from my small 1kw generator, even though the "watts" used is 750.

The power factor is .45 to .55 according to my Kill-a-Watt meter, so the VA varies from 1100 to 1200. The motor pulls the same power through the whole cycle of wash/rinse and spin.

I can't change the motor itself because it's sandwiched between the transmission and water pump direct shaft driven.

There is a large start capacitor, which seems to work. There is no abnormal power draw on startup.

Would a capacitor in series with one motor feed help with the PF, and if so, what size would be useful to try. The motor is 120vac US 60Hz.

Most caps are rated for intermittent use. This would have to work for 30 minutes or so to be safe.

[bob g]

you might wanna contact roper and ask for their engineering dept

my bet is they make a pf corrected model that uses the same motor

it is common to delete the capacitor to shave a few bucks wholesale off the cost

of the unit, 5 bucks saved in manufacturing cost equates to perhaps 20 dollars or more at retail.

they will tell you what capacitor to use, and it will have to be a "run" type cap

not an intermittent duty "start" capacitor

they probably have a part number and one on the shelf to sell you too.

bob g

[Ungrounded Lightning Rod]

Also:  The capacitor isn't necessary for making the machine run correctly or efficiently (in itself - the inefficiency shows up in the transmission lines).  And it isn't necessary for keeping the power bill down on residential metering (which could care less about power factor).  In fact you burn a little extra power in the cap and have to pay for it.  So why put it in for ordinary consumers?

A big industrial operation with a lot of these, and perhaps a laundromat, would have metering that penalizes for rotten power factors.  So these users would want a power factor corrected motor.  Thus (as was noted) the manufacturer probably either has it as an option or makes another model with most of the same parts that includes the correction.

People trying to start motors on smaller-than-inrush-current inverters is a much smaller market.  But leveraging off the big guys' existing engineering rather than doing your own is convenient.

[oztules]

ULR, Me and most of the planet have trouble with this PF stuff.

Suppose we use a rope, and pull start the 750 watt motor to avoid the inrush start currents and the inverter could now support it.

The VA at the motor will be about 1150VA, the watts at the motor will be 750 watts..... assuming 100% efficiency in the inverter, will the DC VxA=750 watts?

Now we place a run cap on the motor (in series with the start field), and our AC VA comes down to 750W (PF=1), our motor watts is about the same .. 750 watts (forget cap losses... small) does our DC VxA change at all?... I expect it to remain about the same (unless there was a lot of line loss in the AC side).

Not entirely sure here.. I suspect the DC current will barely change with the changed PF, and then only to reflect line losses on the AC side from higher A in the VA... but ??

.........oztules

[Flux]

There are 2 issues here. You could correct the running power factor and this would reduce the running demand on your generator a little bit. That would need a reasonably small capacitor across the motor main run terminals ( basically incoming line and that is easier to find).

This may not cure the starting problem as the powerfactor during start may be down to 0.2 or lower. Most small generators, particularly the capacitor excited brushless ones are dreadful at motor starting, usually worse than similar sized inverters.

You may be able to start it with a much bigger capacitor across the generator to force the generator to keep its excitation up.

I would try the correct capacitor across the washing machine to get to about .95 pf lag and this certainly needs to be a non electrolytic motor run capacitor. If it doesn't start then, you can switch in a larger capacitor across the generator for the duration of the start. This could be a motor start electrolytic but you mustn't leave it in long.

Watch it if you have sensitive loads on at the time as the volts will go way up when you switch in the boost capacitor before the washing machine. Try to do the washing when you don't have critical loads.

At 240v I suspect you are looking at something about 8uF for the running correction and probably 100uf for the boost start. At 110 v you will probably need nearly 4 times this.

Fridges and freezers are the worst to start, a washing machine may not be so bad.

As the others said it's down to cost, on mains the simple motor is more than adequate, but for these applications a single phase capacitor start motor is a pain but cost prevents them using any other motor.

Flux

[Flux]

Oz you don't connect the power factor correction capacitor in series with the start capacitor.

The start capacitor is designed to produce the necessary phase shift for starting. There is no single value that does the best start and best run. Some machines just use a big cap for starting and switch it out but others use a compromise that will start it and help running performance and power factor.The best use 2 capacitors and switch the start one out and leave the second.

You have little chance of doing much with power factor here without messing up the start or running properties,

The place for running power factor correction is across the run winding, it does nothing for the motor but neutralises the inductive reactance as seen by the line. In reality apart from the transmission loss that the utilities are concerned with it does little to help the user. With an inverter or a small generator you may see some improvement from pf correction especially in regards to maintaining terminal volts on generators. Inverters are not so bothered about pf unless the VA gets way too high and it current limits.

MSW inverters present special challenges as they hate capacitive loads with their fast rising edges but sine wave inverters and generators are happy with it.

Most inverters are not too fussy about pf correction as long as the bulk of the load is near resistive and you will probably see little drop on the dc input current if you correct. Same for generators, the engine is not particularly bothered about the reactive component and correcting will not save fuel to any extent but you can get more from the alternator if you keep the pf up.

Usually with small generators you need to add a lot of capacitance during the motor start  but it is normally much more than can be used during running as pf correction. Some alternators take off with leading power factor and you loose control of the volts.

Unless it is it can be started with a small extra capacitor that can be left in place as a pf correction it is best to ignore correction on the load motor and devise a way to switch in this big capacitor as a boost during starting and then remove it.

Inverters sometimes respond to this trick but be very careful with the ones based on square waves. The main thing with inverters during motor starting is to maintain the input volts, that means short leads and a huge electrolytic across the terminal may help.

Normally you have to maintain the terminal volts fairly well on a motor to get it started but you can tolerate some volt drop. With alternators your problem is keeping the drop to reasonable limits. Some inverters can hold the volts but trip on over current, this is the case where deliberately dropping the motor volts can help ( long extension lead). For generators any extra cable drop is normally working well against you.

Three phase motors will start at reduced volts and reduced frequency ( generator engine speed)but single phase motors get their starting capacitors off resonance if you mess with engine speed.

Flux

[TomW]

How about the old gimmick where you spool up an unloaded induction motor on the line before firing off the washer? Some claim it helps get fridges and freezers rolling along. Could work here too but not sure.

Just an early morning thought.

All this Pf chatter makes my head hurt because it is a tough one to get a thorough understanding of. And it is seldom comparing apples to apples as it were.

Now, out to do chores in the balmy 6 degrees F it is outside due to this global warming stuff. Hehe country living ain't all sitting on the porch smoking your pipe and drinking a Fat Tire. At least not around here, anyway.

Tom

[oztules]

I said "Now we place a run cap on the motor (in series with the start field), and our AC VA comes down......"

And you correctly said "Oz you don't connect the power factor correction capacitor in series with the start capacitor."......... but I said start field.... not start capacitor.

If I place a run cap in series with the start field. This gives us a sort of two phase motor instead of a single phase one ... almost 90 degrees out of phase to the main field with a true rotating field (if the start windings can handle it.... particularly if the motor has a start capacitor in the first place) It would be in parallel with the start capacitor when the start cap is switched in.... and on it's own in series with the start winding (not in series with the start capacitor) and parallel with the main field when running.... standard cap start cap run arrangement. This will give the motor a rotating field..... and....

I have noticed that this brings the PF from around the 65% up to 90% and beyond.... It's not quite what you would call dedicated power factor correction, which as you stated is caps across the run field... but seems to have that effect as well as making the motor smoother.... so I think a better way of doing it..... if the windings can handle it of course. If the motor has no centrifugal start mechanism, then a triac starter could be effected or current relay perhaps.... or even the PTC (positive temperature coefficient resistor) from a TV degaussing circuit.

That aside, thanks for your in depth explanation, and it would appear that if we effected PF correction ......somehow, the only relief we would get in the DC amps into the inverter would probably be more related to efficiencies from the polyphase effect of the run cap (if we did it that way)... maybe a  few% and almost nil from the improved power factor.... and same for the diesel fuel... no real change for a 40% improvement in PF.

This was the bit I was intrigued by.

Thanks again

oztules

[Volvo farmer]

Roper is made by Whirlpool.

I have seen hundreds and hundreds of these washing machines. All that I have seen have a start capacitor and no run capacitor. I would be extremely surprised to learn that a run capacitor version of this motor is available from the manufacturer.

[Flux]

Sorry I missed your point. You are proposing converting a capacitor start motor to start and run. Yes that is worthwhile with most motors, as I said the optimum starting and running capacitances are different. On small motors the improvement is not great but larger motors run much more smoothly and with better pf and efficiency if run with a carefully chosen capacitor.

 This type of motor was rare when only electrolytic capacitors were cost effective but in demanding cases we used to see huge paper capacitors. With modern polypropylene motor run capacitors being quite cheap this mod is well worthwhile doing. Sometimes it doesn't work so well, as the start winding of some capacitor start motors are more optimised for best starting torque with a compromised size starting capacitor, but generally most modern motors have a decent start winding so that the same frame can be used for capacitor run in low torque applications.

One thing to watch, these run capacitors are resonant as you suggest and the voltage across the capacitor is way higher than a normal pf capacitor across the line. Not a big issue these days as suitable capacitors are readily available.

I agree with you that in most respects pf correction is not going to bring you any great benefit but in this particular case the improvement in running and reduction in vibration alone is a step in the right direction.

Flux

[Flux]

Interesting point Tom.

What you are proposing seems to be basically an adaptation of the Ferraris Arno phase converter. If you run a 3 phase pilot motor single phase it will develop 3 phase across its terminals and will then start other 3 phase motors connected to it.

I doubt that the scheme works single phase and the idle running motor will already be at low power factor and will hinder rather than help the undersized alternator. It may possibly help a little on a long line where the local energy recovery may mitigate the line drop but most things seem to be stacked against it.

Yes indeed all this is a black art and what starts one motor may fail on another.

Flux

[Opera House]

The series capacitor comments reminded me of a trick I have used and is a good teaching lesson.  I have a number of new really nice German metal muffin fans, but they are 220V.  Most if the used test equipment I buy have old noisy fans.  I place around a 3uF capacitor in series with the motor running off 120V.  This boosts motor voltage to about 180V and is a nice quiet running speed.  A capacitor in series usually reduces voltage, but near LC resonance the voltage on both components dramatically increases.

[dnix71]

I just ordered a 35uf 440v oil filled run cap from ebay. It looks like the kind used in air conditioners. The seller is close enough to walk to (Lauderhill, I live in Sunrise). I'll let you guys know when it comes in. I plan to hook it up across the run windings.

[huntedheads]

Imagine purchaseing a million cap's shipping and storeing them, then stamping out all the clips to hold them, then building all the jumper wires to connect them wow!

End result 10 people benifit and only 5 even know what it is, not very consumer centered manufactureing is it? We don't install it unless it benifits the mass consumer. (keeps cost down) The motor is made by Emerson electric they may be ones to contact?

[bob g]

not sure how the addition of the cap is going to affect starting, but

i have done the math to determine relative increase in system efficiency

with improvements in powerfactor, and its not a one to one gain.

iirc it is something on the order of 1% gain in system efficiency for each 10 points in power factor improvement, bearing in mind that these calc's were done on my system

and your results might vary, however

i would not expect them to vary by much!

also something to keep in mind is this, power factor will change as the load increases on the motor, so you probably want to recheck its power factor under its heaviest load condition and be conservative in correction in my opinion.

best to sneak up on the correction to maybe .95 under max load, the last thing you want is to over correct anything attached to an inverter,

if overcorrection is done, and the motor gets enough load to go over unity powerfactor

the voltage will start to climb and in some cases soar, this happens and it is up to the inverter to protect itself and shutdown. something i would not count on happening

myself, because it is doubtful that anything other than high end inverters will have built in overvoltage protection schemes.

Utterpower.com sells a book by Bill Rogers, that is excellent as it pertains to

this specific topic, Bill explains power factor and its correction, and how a diy'er can make corrections in a proper manner that will result in a properly done and verified job.

just simply grabbing a cap and throwing it at the problem might work, might not, and might damage something in a worst case scenario

if for no other reason Bills explanation of power factor and it correction make the purchase price of the book a real bargain in my opinion.

tell George, mobile_bob sent you!

bob g

[bob g]

almost forgot the most important thing

make sure to connect the capacitor across the motor run windings, right at the motor

not across the line, where it will remain connected even if the motor is not running

it must be switched off line with the motor, otherwise the cap stays online and the system pf could go well over unity and smoke your inverter

bob g

[rossw]

Unfortunately, there's no such thing as a free lunch.

If you had a COMPLETELY inductive or capacitive load that had a powerfactor of 0 (I know, it won't happen, but we can get close).... and lets say it's pulling 5 amps at 240V for 1200 VA but 0 WATTS, that 5 amps current still has to come from SOMEWHERE.

The short answer is: take your inverters load IN VA, divide by your inverters efficiency and that will give you near as damnit, the power the batteries need to supply.

In the above case, 1200 VA, lets say the inverter is 85% efficient (0.85), that gives us an INPUT power requirement of 1200/0.85 = 1411 VA DC (since at DC VA=Watts, 1411 watts). So at 24V, thats 59 amps.

Doesn't matter that there's no "useful work" being done with it, you're still pumping electrons.

[bob g]

this is not the case with a generator supplied load, wherein the reactive component

circulates to and fro between the generator and the load, once established the

reactive component produces no useful work, and only has to have a bit more power injected to overcome resistance, but certainly not 59amps like your example would suggest, however

i don't have a clue if this is the case with a system where an inverter is the generator, it doesn't seem likely that the reactive component could circulate from inverter to load, to and fro as is the case for the generator supplied load, so

is it truely the case that the inverter has to continually supply the reactive component, if so that 59amps makes a strong case for power factor correction.

anyone know this for a fact? witnessed and measured the effect?

bob g

[Ungrounded Lightning Rod]

You can understand it without actually testing it.

For an inverter consisting of a DC - to - DC converter followed by an H bridge, the reactive current (at least for an inductor) will spend part of its time discharging the converter's output filter capacitors and then (after the switch to the other half-cycle) another part of its time recharging them.  (For this to work right with MSW, which has two fixed-voltage periods separate by zero-voltage periods, the zero-voltage part of the waveform has to have some of the bridge transistors turned on in a way that leaves the output shorted, allowing the current to freewheel until it's time for the other half-cycle to be applied.  If the inverter tries to open the output with an inductor connected the voltage across the transistor will rise high enough to drive the current through it anyhow - and dissipate much of the energy in the transistor.  So they don't do it that way, lest it pop the first time you plug in a motor or wall-wart.)  After a few cycles when things have stabilized the first half of a half-cycle catches the energy from the inductor and the second half feeds it back in the other direction, leaving the raw power supply to feed only the resistive load and losses.

(H-bridge inverters don't like capacitive reactance because that amounts to closing a switch across a charged capacitor - or one connecting two capacitors charged to different voltages.  The burst of current will be limited only by the wiring resistance and will fry the transistors.  It's the compliment of trying to open the switch when there's an inductor drawing current.)

The situation gets more complicated with true-sine inverters, and depends on how the sine wave is accomplished.  But generally the story is similar - catch and re-throw the energy from the reactive current.  With true-sine you also don't get the current spike on caps and if done right the inverter can also do throw-then-recapture on capacitive reactance, rather than dissipating the energy every half cycle as heat in the inverter and then regenerating it from the DC supply.  (Some of 'em can even feed power back through to the DC side, potentially supporting unconverted induction motors as generators for hydro or the like.  B-) )

[bob g]

thanks for the explanation, and it makes sense to me

now lets see if i got it right

the reactive component, that power which does no useful work at the load end

recirculates between the power source and the load (motor), in a generator system

this reactive component returns to the gen stator inductance where it is returned to the motor in the next cycle, after adding just a pinch more power to it to offset for

resistance losses.

from what i gather the inverter can do the same in that it can accept the return flow of the reactive component, add back a touch to cover resistance losses and return it to the motor in the next cycle, wash/rinse/repeat.

it seems reasonable that those inverters that use large transformers as the final drive could accept and return reactive current easier than the smaller/lighter switch mode style inverters that don't have a large inductance to work against?

maybe that is why inverters like the 130lb xantrex units have such high surge ratings

and are able to tolerate worse power factor loads than the much lighter switchers like those made by some other inverter manufactures who shall remain unnamed.

the reference to some designs being able to accept the returning reactive component and push that power back to the batteries is an interesting concept, do you have reference as to which manufactures and models are capable of this?

thanks

bob g

[dnix71]

Yeah, it's going on the motor as a run booster. The motor runs one speed and is on the full wash/rinse/spin cycle. The hard part will be dragging it out of the laundry room to pull the shell off again.

My generator has a circuit breaker on it, it's brushless, I think.

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200313480_200313480

It's this one.

[oztules]

Ross, It can't work that way..... A load that pulls no watts for a 1200VA costs no power (other than transmission loss). the 5A is not at 240v.... it has in fact no in phase voltage component.. and so no potential for work (no volts) We need only input the power from resistive losses in the circuit.

How else would a tank circuit work? Enormous currents and voltages can slosh back and forth between the cap and the inductor... for only resistive losses. It would oscillate forever otherwise. Big V and big A... but no work being done.

You have a decent RE setup there. Try a known poor pf load that you know the KW not just the VA for. Check the DC VxA against the AC watts (perhaps a kilowatt meter that gives you the watts and the PF would be the go..... and use a clamp meter and multi meter to measure the AC VA.) they should be nearly the same. If you were to add a cap and reduce the PF of the load to say .93, the DC amps should hardly change.

This should prove it once and for all for you. I recall Volvo farmer did this actual test a few years ago and was astounded to find it was true. I'll try to find the post.

.............oztules

[bob g]

ok we got the reactive component sloshing back and forth, each cycle between the source and load, with the addition of a bit more from the source to offset losses due

to resistance.

that good so far?

now a cheap inverter that has virtually no iron, because it is a high frequency switcher, how and where does it catch/store/and return the slosh?

i can understand a heavy inverter using final drive transformers having the iron and inductance to catch/store and return the slosh, but not so much the lighter high frequency switchers,

would they because of their inability to store and return this reactive component have to make up more power to send back to the load?

it seems like the high freq units would consume more battery power for a given load at a given power factor than would one of the heavier lower frequency inverters for the same given load and powerfactor. is this not the case?

if not why not? where is the high freq switcher catching/storing and returning the reactive component in any significant amount?

is this why small lightly built, high frequency switcher type inverters cannot provide

power to very poor pf, highly inductive loads as well as the heavier transformer type units?

just trying to get my head fully wrapped around this issue.

bob g

[Ungrounded Lightning Rod]

Suppose we use a rope, and pull start the 750 watt motor to avoid the inrush start currents and the inverter could now support it.

The VA at the motor will be about 1150VA, the watts at the motor will be 750 watts..... assuming 100% efficiency in the inverter, will the DC VxA=750 watts?

It's not DC VxA.  It's in phase (with the voltage) current versus 90 degrees out-of-phase current.

(The resistive/reactive analysis is for pure sine waves.  For other waveforms you can sometimes treat them as a sum of harmonics and sometimes just have to throw up your hands and integrate everything across the whole waveform.  B-(  So I'll stick with the simple sine-wave interpretation from here on - as power engineering guys tend to do because it usually dominates all the other stuff.)

The in-phase portion of the current represents the resistive load (or source, if it's negative, i.e. 180 degrees out-of-phase).  The 90 degrees out-of-phase ("reactive") component of the current represents the current into the inductive or capacitive part of the load.  This occurs a quarter-cycle ahead of the voltage ("leading") if the load is capacitive, a quarter-cycle behind ("lagging") if the load is inductive.  Because they're 90 degrees out-of-phase their product integrates out to zero over a full cycle and for a lot of things you can treat the restive and reactive current as separate.  "Real power" - the product of the in-phase RMS current with the RMS voltage - represents the resistive load - power delivered from the supply to the load on every cycle.  It's measured in Watts.  "Imaginary power" or "reactive power" - the product of the reactive RMS current with the RMS voltage - represents energy swapped back-and-forth between the supply and the load every half-cycle.  It's measured in VARs (Volt Amps Reactive).  Capacitive and inductive reactive currents are opposite in sign, so which is "gerating" and which is "consuming" VARs is arbitrary.  Because most of the parasitic loads on a power grid are inductive, then convention is to chose the sign so that that inductors "consume" VARs and capacitors "generate" them.  (The power company has to either hang extra capacitors on the line to "generate" VARs, and any they don't generate with capacitors are generated by out-of-phase currents in the actual generators.)

(The "real" versus "imaginary" nomenclature comes from mathematical treatment of the magnitude and phase of a current as a complex number.  The "imaginary" part of the current is just as real in the ordinary sense as the "real" part, which can cause confusion when talking about it.  So while academics use the confusing nomenclature and embarrass new students, people working in the field tend to stick with "reactive" when referring to the 90-degree currents.  When talking about a current-voltage product they'll still use "real power" for the in-phase, producer-to-consumer flow and sometimes say "imaginary power" rather than "reactive power" when talking about the out-of-phase, ping-pong flow.)

Losses in wiring and transformer windings are resistive losses - proportional to the square of the current and unrelated to the voltage between the conductor and anything else.  (That's why transformer "power" ratings are in VA rather than Watts.)  The "they're separate" approximation doesn't hold when you want to compute the overall current in the wiring from the combination of real and reactive current.  Instead you have to add the resistive and reactive current using vector addition.  Think of the resistive current as the length of an arrow from left to right, reactive current as the length of an arrow from that one's tip and pointing up for leading (capacitive), down for lagging (inductive).  Then draw an arrow from the base of the first to the tip of the second.  Right triangle:  Compute it's length with the square-root of sum of squares rule.

Power factor is the ratio of the amount of the in-phase current to the overall load current (that vector sum of the resistive and reactive current).  It represents the fraction of the power that you'd expect from looking at the current to the amount you actually get delivered, rather than playing ping-pong with your supply.

Back to your motor:  Yes.  The real power will be 750 watts.  The VA will be 1150.  With a little trig we can see that the reactive power (which is inductive) will be sqrt ( 1150^2 - 750^2 ) =~ 872 VAR.

Now we place a run cap on the motor (in series with the start field), and our AC VA comes down to 750W (PF=1), our motor watts is about the same .. 750 watts (forget cap losses... small) does our DC VxA change at all?... I expect it to remain about the same (unless there was a lot of line loss in the AC side).

(Again changing "DC VxA" to "V x in-phase A", "real power", or "Watts"...)  Yes, the real power into your run coil is still 750W.  However you've just added another coil...

The reactive current in that coil is phase shifted more leading by the capacitor, so it will cancel some of the lagging reactive current of the run coil.  But the resistive losses in the coil - from coil resistance, eddy-current losses in the core, and rotor load, along with the resistive losses in the capacitor, still show up as an additional resistive load current on the input.  (Rotor load showing up on the start coil will have been lifted from the run coil's load but the rest will be new loads.)

So adding an always-on run cap to the start coil does help significantly (in addition to reducing vibration in the driven shaft).  But hanging a capacitor directly across the run winding, as Flux described, will do a more pure job of canceling that coil's reactive current while only adding the capacitor's internal resistive losses to the main load.

[Ungrounded Lightning Rod]

The power factor doesn't go over unity.  It's always sqrt(in-phase current / total current) and in phase current can equal total current but never exceed it.

But the reactive portion of the current CAN go leading (capacitive load), which is much harder on many inverter designs than lagging (inductive load).

[Ungrounded Lightning Rod]

now a cheap inverter that has virtually no iron, because it is a high frequency switcher, how and where does it catch/store/and return the slosh?

In the output filter capacitors of the DC-to-DC converter upstream of the H-bridge.

The fancier high-frequency switchers can store it in the inductor of the switcher.

[12AX7]

Last time I heard these two terms in one sentence, a friend and I were playing with a Spark-Gap Transmitter.  

And if I recall correctly it had plenty of slosh!

(talk about bandwidth)

ax7

[oztules]

Ax7

It is 3hrs and 50 odd minutes to new year here.

I strongly suspect that tanked and sloshed will be used in the same sentence fairly soon here.........

..........oz (whoops spilt some) tules

[oztules]

Sorry ULR,

I deliberately used DC VxA (as opposed to DC VA) to give what we usually measure to find watts on our DC side. I foolishly thought this would resonate better with the folks that usually measure their dc volts and amps to find their watts..... obviously I created uncertainty instead.... best laid plans etc.

Thanks for the dissertation on  this. Somehow information on this type of thing is clouded in mystery. Your thoughts are clear and concise. Much appreciated.

............oztules

[Flux]

This seems to have been a very comprehensive discussion and seems to have covered a great deal.

The conclusion probably is that normally pf correction for an individual is not worth the bother. If you have one major load with very poor pf then it may pay to correct it if you are near or over the kVAr rating of an inverter or alternator.

You gain little as long as the alternator or inverter can actually drive the load but you may drive a little more with correction.

Failure to start motors is not normally cured by normal correct pf correction. You can often get things started with  a large leading pf especially on small alternators but this may be risky if over done with inverters. This needs to be treated as a temporary condition during the start and any capacitors used for this need switching out.

Any individual pfc capacitors need to be switched with their appliance so you need to get in beyond the internal switch or you will get a build up of leading power factor when these appliances are off.

Correction on msw inverters is questionable as the normal definition of power factor based on cos phi doesn't work with non sine waves. You can't correct the inherent power factor of a distorted waveform with capacitors but you can correct bits due to an inductive component so it may help a bit but the inverter probably won't stand much direct capacitance across its terminals. Msw inverters often come unstuck driving fluorescents with magnetic ballasts and are best kept away from this duty, they also screw up many electronic ballasts unless rectified to dc first.

Flux

[12AX7]

Reading the replies to this thread brought memories of some poor schmuck trudging across a glacier.   Then the poor old fella had a name,  Eli.

and then finally " ELI the ICE man"

http://www.electronicstheory.com/html/e101-31.htm

for those that have an interest..

ax7

Mark

[TomW]

Mark;

Met ELI myself about 50 years ago. He ain't chanmged a bit, either.

Remember a couple ribald methods to remember the resistor color code, too.

Thanks for the blast from the past.

BTW to the uninitiated ELI means Voltage [E] leads current  in an Inductive [L] circuit.

ICE means Current Leads Voltage [E] in a capacitive [C] Circuit.

Thats why you have VA in AC circuits. The real time voltage and current do not align perfectly thus you get power factor. I think.

The resistor color code phrase you are on your own!

Tom

[12AX7]

Bad boys repair our young girls, but violet gives willingly..  get some now!

black = 0

brown = 1

red =   2

orange 3

yellow =4

green = 5

blue =  6

violet =7

gray   8

white = 9

gold =  1%

silver 5%

none   =10%  (or was it 20?)


oh,  and it wasn't repair.  


and then there was the one for G I'm a tree.


Susan can't tell Oscar had a hunk of apple


where   S

        c

        t

and then     O/H

and          A/H

and          O/A


or...      Sine = Opposit/Hypot

           Csin  Ajacent/Hypot

           Tan =  Opposit/Ajacent

and it was never an apple!