Fridge & a Capacitor for a inverter good/bad?

toxsickcity
toxsickcity Registered Users Posts: 5
Hello

My old post about fridge and inverter and surge,
I wired it up and used my meter and seen a 50A 24v DC spike at surge.

the fridge started fine. and everything runs great, but I'd like to minimize the spike.

Would a few Large 220v+ AC capacitors near the fridge reduce spike?

thanks Fellas!
Shaun
«1

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge & a Capacitor for a inverter good/bad?

    I am not quite sure what you are proposing...

    Placing AC caps in the 220 VAC circuit near the fridge? No, that will probably not help and may make things worse. There are "Motor Run" caps you can put between the L1/L2 to adjust power factor from 0.5 to near 1.0--which reduces current (VA is reduced) but Watts (power from battery) remains the same. Many modern refrigerators are already running with PF~1.0 anyway. Adding caps will not reduce the starting current.

    I would not bother with an AC side unless you have problems with the fridge starting... And if there are problems starting, you would have to look at the compressor and see if it uses a starting capacitor. The starting cap could be bad/undersized (larger staring cap gives the motor higher starting torque--but there would be even more starting current).

    If you are thinking placing caps on the DC input side of the inverter--they probably would not store enough power to make any difference (and I would worry that the inverter could become "electrically unstable"--your electrical wiring/inverter could "ring" like a bell -- or at least the electrical equivalent of an oscillator/"tank" circuit)

    If you have starting problems, make sure your DC wiring is heavy enough to handle the 50+ amp surge (short, heavy wiring) and that the battery connections are clean and sized correctly. Too small of battery bank can also cause issues with trying to draw high starting currents.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    BB has just about said it all .You cant reduce the starting current as it is caused by the compressor starting under load. its not a motor problem its just how compressors are.When they stop its with the piston just before top dead centre so when it starts again its at the hardest to turn position.
    Adding caps anywhere will cause more problems ,, and solve nothing
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    in thinking about this there are 2 sources of surge power in a frig and the compressor already mentioned is the biggy, but the circulating fan(s) will also surge to a smaller degree. it may be possible to use a delay on the fan(s) to spread out the surge even though it won't be eliminated.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    the fans draw an insignificant amount of power compared to the compressor. even eleminating the fans would save very little.. at start up they use about 40 w total. I have measured it many times.
  • toxsickcity
    toxsickcity Registered Users Posts: 5
    Re: Fridge & a Capacitor for a inverter good/bad?

    I dont know if I was clear, and sorry for that.

    My main idea was to help the 220v & 24v circuit.. reducing Surge of the Inverter

    I was thinking about car audio. having a large CAP makes BASS great because the fast access to MUCH POWER! I also noticed that starting the engine was also Amazing. 1 Farad Cap delivering to starter motor.. it turns over so fast.

    I was thinking same with a fridge.. The fridge's compressor must overcome a huge event starting up.. much like an engine there are huge compression placed on the piston.

    I own an electronic parts shop and have many types of Starting capacitors, some made in germany being the highest quality ones we sell.
    customers buy them for anything to is required to make a motor start, ( Drill Press, Compressors, Air conditioners) they rated at 200mf whats small compared to 1FARAD
    So in theroy when the inverter turns on it will charge the Starter Capacitor(s) if I use 2 or 3 of them!?!?! dunno
    The caps would be close to the fridge, so when the compressor turns on, it will look for closes source of power I.E. the cap(s) then goto the inverter, I know it will be a small amount but I wanted to know if anyone had experience.

    I truly think surging an inverter will make the inverter live a short live. or give erroneous problematic 220v circuit.


    Lastly
    I read somewhere putting Capacitors would HARM a inverter. whats your ideas?

    thanks guys again This forum is great, the user activity is great. I have always wanted to be green.

    so far I only have a Server permanantly on 12v. using a 12v dc PSU.
    next step is install 24v->12 converter and hook up new inverter to my
    500Watts panels. soon to be 700 watts and MORE with the Ebay find of a century...

    200$ u.s. for approx 200watts.. DIY :) love it
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    A little info about AC induction motors and start/run capacitors. You don't just stick on the biggest capacitor your can find, okay? It's not the same as with DC circuits. The motor will usually have whatever is the best choice for it already, unless the manufacturer is a cheapskate. We're talking about 370 or 440 Volt caps of 70 microfarads and up. Too big a capacitor will actually make the motor less efficient. Exactly how to size a cap for a motor is debated within the industry, with different companies using different formulas to calculate their specs.

    As for harming an inverter, no; a proper motor cap won't. But an improper one will reduce the motor's efficiency and make the current draw uneven (it actually distorts the internal electro-magnetic field rather than smoothing it out). It's possible to take a motor with a poor PF of 0.50 and make it even worse.

    There's all kinds of people out there who'll tell you otherwise and try to sell you "whole house capacitors." Since I'm not paying for your equipment, whether you believe them or me is no skin off my nose. :p

    In this case, it's best to accept the limitation of design and deal with its consequences.
  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Toxsickcity.. completely forget about adding caps to either the DCV or AC side of the inverter or in or near the ref. it a waste of effort and as you have ben told by everydody it wont help and it may make things worse.

    Ihave no faith either in using any caps to supply power to a car audio system..if the amp is wel designed it will not be depending on extra caps before the amp to "help" the bass.. most improvements can be made by using low resistance wires and battery connectors and a good low impedance battery such as the Hawker odyssey. same goes for starter motors,,
    I have some knowledge of amplifiers as have been building them and desiging them for over 40 yrs. if most car audio "experts" stopped using crappy sounding class "D" amplifiers,, they would not be trying to fix the sound with add on caps to the input power supply

    Back to the fridge if you having problems starting it you can do either of these 2 things.
    1 buy a low frequency sine wave inverter at double the price of a "normal " sine wave inverter
    2 modify the fridge so it can start up easy on very low input current,, it can be made to start and run ok on a 4oow inveter.. I have done it.
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Hi there in your shop you will have soft starts for heavy tools like grinders use these. to control the start up current.

    But as stated before a good quality low freq. sine wave inverter does not have any problem. I have two refrigerators and murphys law has showed me right i have seen them starting at the same time and if i run on generator ( 10 KVA ) i see the lights flash if i run normal on my inverter (4 KW pulse 8KW) there is no problem.

    p.s. a capacitor connected to your AC line is consuming electricity.:blush:

    Greetings from Greece8)
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    the only other way besides another larger inverter will be to lessen the surge by a more efficient fridge. what is your surge power and max surge rating on your inverter?
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    We installed motor run capacitors on our two furnaces.

    Even with the SW plus inverters the furnace mother boards and hot surface ignitors wouldn't cycle properly without them.

    After the electricians installed caps on the blower motors everything runs perfectly now. No problems after 4 years. I don't understand the technical reasons but everything works right.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Mangas . Your case is based on long or parallel wiring creating a more inductive load and that is compensated by capacitors. It is possible that your inverter is to perfect and that your furnace needs more dirty power ( with a lot off disturbances ).

    But a capacitor is using electricity so it is wasting a little of your energy.
    Plus special the cheaper capacitor by time and heat are drying out and stop working , short cut or burnout ( a ferry bad smell).
    So be aware if installed inside the furnace. my advice check them any sign of disclouring or cheap country production replace them.

    Greetings from Greece
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge & a Capacitor for a inverter good/bad?

    If I understand your thoughts correctly... No, a capacitor on a Induction Motor is not there to store energy to help start the motor. The "starting" capacitor is there to create another "phase" for a single phase capacitor start motor to create a rotating field internal to the motor which provides the starting torque. Once the motor is near full speed, the start capacitor is turned off and the main field(s) continue to run the motor (the math--what little I remember--regarding a single phase rotating induction motor is very interesting... But well beyond my capabilities now to properly explain and probably not really useful on this forum).

    A small sized start capacitor will start a motor with low(er) surge current for the starting windings. A Larger capacitor will provide more starting torque and require more surge current--however, the motor overall will spend less time near "zero" RPM and therefor may provide a shorter surge load on the inverter (if there is an optimum capacitor).

    The Motor Run capacitor can reduce current (VA, Volts*Amps) because a motor is "inductive" (think coil)... Remember that the current "lags"/follows the current by "90 degrees". An AC motor is inductive + does useful work--so the current "lags" the voltage (which is "hard" on an inverter and the wiring).

    Since for a capacitor the current "leads" the voltage (again, for a perfect cap) by 90 degrees... One can put a motor + appropriately sized cap together... The Lag of the inductor + the lead of the cap can "correct" the Voltage and Current to where they are both "in phase" or Power Factor = 1 (note cos 90 degrees = 0.0 power factor).

    Normally, Power Factor is only corrected for large motors (such as a refinery) where the utility charges based on VA=Volts*Amps. The typical large motor that is doing Work is defined by P=V*A*PF...

    If PF=0.6 for the refinery, they are "throwing away" 40% of their money because they are charged by VA=V*A. Putting a capacitor bank in with the motor(s), they now get P=V*A*1.0 or nearly 100% of they money is paying for the work they need done.

    For residential billing... In the US the utility actually charges for Work or Power... And you do not pay more for PF that does not equal 1.0

    Because bad power factor wastes money (more current flows than is needed, therefor there is more wasted energy lost as heat) many of the modern appliances out there now are power factor corrected (motors, by a "run" capacitor--and electronics now are designed to have PF near 1.0 by various laws and regulations).

    Note: For motors (and inductive devices)--PF is a "phase difference" between voltage and current. For many electronic devices, bad PF is not a phase difference--it is the results of the electronics only taking current at the "peak" of the sine wave voltage (specifically it is the voltage/current profile of a diode rectifier charging the input capacitor of a power supply/converter which causes current to flow only near the voltage peak). It is a "non-linear" poor PF that cannot be corrected by adding a "motor run" type capacitor to the wiring. It requires a redesign of the electronic product / internal power supply itself.

    And it even gets more complex in that many of the "Energy Star" rated refrigerators now use variable speed compressors which and an electronic front end to control the motor's operations. So there is no traditional motor start / motor run type capacitors to play with.

    For an Inverter--you are concerned about both VA and VA*PF. VA because there is a maximum AC current that the inverter can output. And VA*PF because that is the amount of "work" you are going to draw from the batteries/solar panels/etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • peterako
    peterako Solar Expert Posts: 144 ✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    I agree bill.

    I have seen more than ones at my work that when there are a lot of parallel wiring that the power factor becomes inductive and critical designed or electronically controlled motors are protesting, but when the power supply is not clean ( a lot of power switches or voltage sweeps) it finds the correct point and starts.
    And if you have a good full wave inverter your power is perfect clean. But parallel wiring is creating a small inductive response meaning current wave is before voltage wave. This seems to be the problem a capacitor solves this easy.

    But as my warning before if the capacitor is cheap or in a heated area it life time is limited.

    p.s. the same trick is used in factory`s using high speed machines like making the thread cable etc. one row normal light one row having a line connection and one using parallel connection. the result there is a small difference in flashing order but on work level it is smooth and you can see the machines moving.:D

    greeting from Greece8)
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Thanks Peterako and Bill. The SW Plus' are very good inverters and the caps corrected the problem. As mentioned everything works perfectly.

    Caps are located at the bottom of the air handler away from the furnace. They are quality name brand caps. No discoloring and they look like new.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Fridge & a Capacitor for a inverter good/bad?

    Mangas,

    These are connected as "Motor Run" type caps and are they only "energized" when the motor(s) are running? Do you remember how many MFD per HP you used?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Bill, forgive my electical limitations.

    The box I saved says a 50uf 370 VAC Motor Run capacitor. Each furnace/air handler unit has one.

    I'll take a look at it tomorrow and post.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Cap is wired to each blower motor circuit. My understanding is they help smooth small low voltage fluctuations which can confuse motherboard cycling without them.

    Once installed never had a problem since.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    You are talking about three different cap proposes.

    A motor run capacitor is not there for PF correction. It is used to create a current lag between two run windings in the motor to keep it running under mechanical load. Sort of like a carrot daggled on a pole, in front of horse by a rider.

    Run caps are usually oil filled since they are continuously energized while motor is running.

    A start cap is temporarily connected to another motor winding to get motor up to speed. Once up to speed the start cap is disconnected, by a speed actuated switch or by motor design where the voltage across the start cap drops to a low value. In older conventional refrig, this is accomplished by a disc thermistor in series with starter cap that goes to high resistance when warm, initially by current through starter cap, then by heat of running compressor motor.

    Starter caps are commonly made by two electrolytic caps put in series with reverse, end to end polarity in same package. They have a rubber vent cap hole to vent the electrolytic material if they fail, to prevent cap from exploding. Reason they are electrolytic is they need to be high capacitance value and electrolytic makes size smaller. They cannot be continuously energized like an oil filled run cap as they will overheat and fail. They are lower cost then oil filled run caps.

    Finally, an oil filled cap put across the motor terminals to cancel out its inductive load is a power factor correction cap. These may not be used on all motors. Putting a power factor correcting cap across motor improves power factor but it is hard on actuation relay contacts and can make them erode faster.

    The SW series are multi-step, 'near sinewave' inverter. There is up to 27 steps on the SW for a full sinewave but typically it is in 20-24 step range depending on battery voltage. Roughly, 12 to 18v jump per minimum step, double or triple this near zero crossing. You will hear the buzz in a ceiling fan. The problem is probably with the ignitor which in turn has a feedback safety feature to not allow the blower motor to start unless ignitor is first working. I doubt the motor would have trouble with the SW inverter output. A filter solely on the ignitor power line would likely fix it. SW series inverters are okay with capacitive loads.

    To original post, never put a large valued cap across a modified sinewave inverter. It will cause the MOSFET switches to overheat and possible failure of the inverter.

    As to cap on battery line, you can not realistically make an impact on battery slump due to surge load. The cap value would be astronomical. Say your refrig start surge was 15 amps from 120vac. Battery line surge current, with inverter efficiency tanking under the heavy load, on 24v battery would be like 150 amps. To restrict the battery voltage drop over a quarter cycle to 1 volt drop would require a 625,000 uF, 35 vdc rated cap. Not impossible, but not realistic as you could get a bigger battery for less cost and probably less space.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Bravo RC.

    It is posts like that which make this forum SO valuable. I hope this forum gets archived and never goes away.
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Bill, RCnFla and Peterako

    "Sort of like a carrot daggled on a pole, in front of horse by a rider."

    Thanks guys for putting the various cap applications into words I can figure out. I always wondered why putting a couple of caps on the HVAC fixed everything so easily.

    Agree, your explanations were great and thanks!
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • GreenerPower
    GreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    For > 3/4 HP PSC motor, I would say use a hard-start booster rather than install higher cap. The higher cap would increase the starting torque and lower the surge current but at steady state, it would reduce the motor efficiency i.e. uses more electricity. With a hard-start booster, a "cap" is temporarily attached (electronically) to increase the starting torque, reducing the surge starting current and then disconnect when the motor is running.
    GP
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Many of the compressor hard start booster are nothing but an extra starter capacitor put in parallel with existing start cap. It puts extra current in the start windings. You have to be careful because the start windings are wound with lighter gauge wire and too much boost current can blow the windings open.

    These would actually increase the starting surge current. It may last shorter in time.

    As to soft starters and trying to stay within surge limits of a battery powered inverter, as general nature rule, you don't get something for nothing.

    Soft starters lower the effective voltage on the motor during its starting period to reduce the peak surge current. There are various versions, one way just fixes a lower voltage for a short period, another type provides a voltage ramp up versus time. They are triac based, like a light dimmer.

    What I mean by 'you don't get something for nothing' is usually lowering the voltage will mean lower starting surge current but it last longer in time. You can maybe cut the surge current by half to two thirds but that reduced surge current last 2 or 4 times longer in time.

    I did some experiments trying to get stacked SW4048's to run a 3 and half ton central air conditioner. It would trip inverter overload on compressor startup attempt.

    I bought a high quality closed loop hall effect current sensor. These are very accurate and have a bandwidth of 300 KHz allowing examination of every pertubation. The compressor was a Lenox scroll type compressor. I was amazed to find the start current to be 120 amps lasting for 300 msecs (@240vac). The run current was only about 15 amps, well within capability of stacked SW4048's.

    I bought an adjustable soft-starter and made incremental adjustments while measuring the start up current. I was able to get the start up current down to 45 amps but it lasted over a second. Still outside the capabillity of stacked SW4048's.

    I ended up putting in two stacked SW+5548's which ran the compressor with no soft starter. The SW+ software allows a longer overload period then the regular SW series before shutting down inverter.
  • Mangas
    Mangas Solar Expert Posts: 547 ✭✭✭✭
    Re: Fridge & a Capacitor for a inverter good/bad?

    Interesting.

    I was told our new high efficiency seer A/C units start at much lower surge amperages and idle along pretty low. I don't think I've ever seen them running over 16-17 amps at the higher speed.

    Our two 2.5 ton A/C compressors are on different inverter banks and on different A/C breaker boxes (i.e. we ahve two 100 Amp boxes splitting the house loads) to spread the surge amperages of all the additional appliances.
    Ranch Off Grid System & Custom Home: 2 x pair stacked Schneider XW 5548+ Plus inverters (4), 2 x Schneider MPPT 80-600 Charge Controllers, 2 Xanbus AGS Generator Start and Air Extraction System Controllers, 64 Trojan L16 REB 6v 375 AH Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar Panels, Cummins Onan RS20 KW Propane Water Cooled Genset, ICF Custom House Construction, all appliances, Central A/C, 2 x High Efficiency Variable Speed three ton Central A/C 220v compressors, 2 x Propane furnaces, 2 x Variable Speed Air Handlers, 2 x HD WiFi HVAC Zoned System Controllers
  • Dr. Old School
    Dr. Old School Registered Users Posts: 1
    Re: Fridge & a Capacitor for a inverter good/bad?
    Hmmmm.... You own a store that sells electronic parts??? I came here to be lazy. Instead of transferring my notes onto computer, they are buried in moving boxes....
    .........
    Cheers,
    The Doc is out!

    Here is another idea and dozens of variations come to mind. Simplest would be to have a current limiting switch with a cheaper relay that would kick the resistance out. Electronic timers have also come down to add further control. Chances are the wattage on the resistance's wattage ratings could be a lot lower than normal as the bump last less than a couple of seconds.

    The notion that one could buy something better is a no starter. Most equipment is designed to be marketable. John Q Public has no idea and usually has never even heard of a demand meter. However your home AC power has a capacitor bank somewhere so the worry about capacitors and AC is unfounded. Our SCE found a way to scam its customers. Once a month we would have a four second power failure. Even the refrigeration that wasn't running would trip and everything would restart causing the demand load to double and we had to pay a penalty rate. About $200 for our commercial business. We were a really small business by design. My guess is the utility raked in about $250g/m pure profit. I found a secret way to reset the demand meter and I only did it once after each power outage so I know what we saved. I paid contracted rates but not the overcharge penalty. I am implementing a plan to go off grid by DIY. Not going to pay the sucker rates for wind and solar devices either.

    Cheers,
    the Doc is out....
  • CorySiple
    CorySiple Registered Users Posts: 1
    Ok, I know this thread is old.... But I almost threw away 3 inverters because they wouldn't run my 100w wine fridge / refrigerator.
    Simply compensate the Power Factor with a capacitor across the motor, and now it works. 
    You need a Kill-A-Watt or similar device to measure your Power Factor (and parameters of the inductive / motor device), then simply put them into this website, and place the size capacitor determined in the circuit... https://www.rapidtables.com/calc/electric/power-factor-calculator.html
    If you need me to make a YouTube video, let me know
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited March 2022 #27
    Cory,
    Your link looks interesting... Everyone notice that Power is in kWatts... So, make sure you enter the decimal point (i.e., 750 Watts => 0.750 kWatts).
    Generally with induction motors, do not correct beyond 0.95 PF (i.e., don't try for 1.00 PF)... As I understand, the higher capacitance will self excite the induction motor when the AC power is turned off and lots of momentum (such as a saw, flywheel, etc. that will keep the motor spinning (the motor+capacitor will generate >>120 VAC and blow capacitors/switching geat))--So I have read.
    The whole idea of using motor run caps to adjust PF... Is not a simple subject and can interact with other AC loads... Induction motors are "linear" loads that have known/correctable behavior. Other loads such as electronic drives, electronic power supplies (microwave oven, computers, etc.) can cause "bad power factor" by injecting harmonics into the AC power line. These harmonics cannot be "fixed" by adding a capacitor--And can cause harmonic resonance.
    A very nice and informative paper on Power Factor issues and Capacitors to correct power power factor.
    Table 9. Negative Consequences of Harmonics
    on Plant Equipment
    Equipment Consequences / Current Harmonic Distortion Problems
    Capacitors: Blown fuses, reduced capacitor life
    Motors: Reduced motor life, inability to fully load motor
    Fuses/breakers: False/spurious operation, damaged components
    Transformers: Increased copper losses, reduced capacity
    Voltage Harmonic Distortion Problems
    Transformers: Increased noise, possible insulation failure
    Motors: Mechanical fatigue
    Electronic loads: Misoperation
    If adding a Motor Run capacitor to your motor helps it start with your PSW/TSW inverter--Great. Just remember the motor and capacitor should be switched on and off together... You do not want the run capacitor to be "on" without the motor running (causes unneeded current flow from the AC inverter).
    But these are complex issues--And experimenting with smaller capacitors and working up to the recommended capacitor would be a good idea... More or less fixed loads (such as refrigeration compressors) can be corrected this way with a single capacitor. Motors with variable loads (such as a saw and such) are variable loads and may need variable PF correcting capacitor(s) to work properly.
    Be careful.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NANOcontrol
    NANOcontrol Registered Users Posts: 260 ✭✭✭
    My fridge just connects the start winding to the line thru a thermistor, not thru a start capacitor to additionally change phase.  I played around with adding a capacitor and also electrical time delay to replace the thermal delay. I never saw any change worth implementing either modification.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    NANOcontrol,

    Are you sure there is no motor start capacitor on the outside of the compressor housing? I looked through some wiring diagrams with a quick search, and did find some that show ONLY a PTC connected directly to the compressor start winding--Which does not make sense to me, absent a start capacitor (some may have both motor start and motor run capacitors).

    In general, as far as I know (certainly no expert), all single phase induction motors need a "start capacitor" of some sort. The capacitor is there to shift the AC current and create a rotating field inside the field coils to "drag" the rotor around (starting torque). (There are shaded pole motors, below, that do not use start capacitors)

    https://circuitglobe.com/starting-methods-of-a-single-phase-induction-motor.html

    A "two capacitor" start/run motor diagram:

    https://circuitglobe.com/capacitor-start-capacitor-run-motor.html

    https://circuitglobe.com/capacitor-start-capacitor-run-motor.html

    Once the motor is up to speed, there is some relatively complex (and neat) math as to why the motor keeps running without a capacitor in the circuit.

    I could see a thermistor used instead of a mechanical (or other electronic) switch to the aux start winding (powered by the phase shifting capacitor).

    However, the only other type of single phase induction motor I am aware of is the Shaded Pole type. These do not use a capacitor to shift the phase of the the starting field--They do it with a shorted copper band around a section of the field poles... The "inductive" copper band/wire delays a bit of the magnetic field timing to provide (a small) starting torque.

    https://circuitglobe.com/shaded-pole-induction-motor.html

    Shaded pole motors are very inefficient and typically used for applications where small motors are needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NANOcontrol
    NANOcontrol Registered Users Posts: 260 ✭✭✭
    Absolutely no capacitor.   It is quite common.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Learn something new every day!

    First, a nice read on the various types of refrigeration compressor motors:

    https://www.tecumseh.com/globalassets/media/north-america/files/marketing-brochures/tecumseh-service-handbook.pdf

    And this one is a Resistance Start--Induction Run. A more detailed explanation on how this works:

    http://www.hvacspecialists.info/electric-motors/resistance-start-induction-run-motor.html
    The rotating magnetic field of the resistance-start induction-run motor is produced by the out-of-phase currents in the run and start windings. Since the run winding appears more inductive and less resistive than the start winding, the current flow in the run winding will be close to 90 degrees out-of-phase with the applied voltage. The start winding appears more resistive and less inductive than the run winding, causing the start winding’s current to be less out-of-phase with the applied voltage, as shown in Figure 11–5. The phase-angle difference between current in the run winding and current in the start winding of a resistance-start induction-run motor is generally 35 to 40 degrees. This is enough phase angle difference to produce a weak rotating field, and consequently a weak torque, to start the motor. Once the motor reaches about 75% of its rated speed, the start winding is disconnected from the circuit and the motor continues to operate on the run winding....
    This type of motor is typically used on smaller hermetically sealed compressors up to ~1/3 HP max.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset