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Reduce off grid freezer startup current?

Discussion in 'General Electronics Discussion' started by cygnusv, Feb 28, 2018.

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  1. cygnusv

    cygnusv

    76
    14
    Oct 7, 2014
    I've been reading on various websites about reducing the startup current required by freezers for off grid use.
    My freezer is

    Beko 'A' class Model ZSA 436 W
    230 volt
    50 Hz
    55 watts and .25 amps.
    The freezer is about 12 years old

    I've just installed a Victron 1200 watts pure sine wave inverter. When the freezer kicks in, the inverter shows the red overload light for less than a second and then carries on 'in the green'. The inverter fan does not kick in.

    Is there a relatively easy method to make a 'soft start' for the freezer? I don't want to damage the inverter.

    Many thanks in advance for your collective advice. Stu

    Just thought. We also have a small table top fridge. Might be a good idea to do both. Thanks
     
  2. AnalogKid

    AnalogKid

    2,393
    665
    Jun 10, 2015
    I'm not familiar with your freezer, but

    a. only 57.5 VA total power consumption seems way too low

    b. if the running power really is only 58 VA, there is no way the startup current would overload a 1200 W generator.

    ak
     
  3. Hopup

    Hopup

    253
    36
    Jul 5, 2015
    By fast google search NTC inrush limiter and extra capacitance in form of capacitor was recommended as DIY solutions for this problem.
     
  4. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    I agree. I don't see the current stated in the manual, but it's fused at 13amps and the model #436 hints that its 436 watts, or 1.9amps. Start up current is probably about 12amps.

    They do have electronic soft starters for motors but I don't know much about them.

    If the above is accurate, your inverter is likely a bit undersized, but read the manual to find its peak current and Rms current. It may be ok with a short sipke in current.

    Do make sure you use wiring/cords that are heavy gauge to minimize voltage drop.
     
  5. Externet

    Externet

    744
    162
    Aug 24, 2009
    The nearest I could suggest is :
    [​IMG]
    In use for the last 10+ years with my refrigerator, has never failed, and seems to do its work.
    Do not know if exists for 230V, or if works at start/run/both.
     
  6. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    I hate to say it, but I believe this is a scam.

    If you open it up there's nothing in there but a capacitor. It helps with power factor correction but doesn't actually save you anything.
     
  7. cygnusv

    cygnusv

    76
    14
    Oct 7, 2014
    The numbers shown are directly off the label inside the top shelf of the freezer.
     
  8. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    I believe you. If that's the case, the inrush current to start the motor should never be over 2amps and your 1200w inverter should have no problems with starting it.

    You may want to double check the actual draw with a clamp on amp meter. Maybe the compressor is on its way out?
     
  9. debe

    debe

    253
    65
    Oct 15, 2011
    This is what I did to a small fridge to get it to start on a 240V 400W generator. I added a 18uf start capacitor in the start circuit. This worked with this compressor, but was a trial & error exersize. Wont work on all compressors. Been working for about 12 years now. SANYO COMPRESSOR.jpg
     
    kellys_eye likes this.
  10. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    Good idea, but most small fridge compressors already have a ptc circuit built in. It's usually behind the black insulation block where the motor wires terminate.

    It should be shown on the wiring diagram too. That is, if there is one.
     
  11. Externet

    Externet

    744
    162
    Aug 24, 2009
    P1010719.JPG
    Well, curious about your comment; with no need to defend the item, opened it for the first time. A substantial finned heat sink for the MT2 - 3 pin TO something semiconductor, vented case back, and a not simple circuit board with no 'capacitors' makes it an elaborated scam.
    I do not know what it does, but I did notice low electric bills and been carrying it along 3 house movings.
     
    Tha fios agaibh likes this.
  12. debe

    debe

    253
    65
    Oct 15, 2011
    The PTC unit was already in the fridge, just put the start capacitor in the circuit so it would start on a 400W generator. Which it would not do before.
     
  13. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    Thanks for pulling it apart Externet.

    I did a quick web search and some say it works but also many think it's a scam.
    I'm not sure, but here's what a few people said;
    It allows full start up current and then chops the sine wave like a dimmer to save energy. This could be beneficial but also could cause your compressor to eventually fail. It is said to only works on older inefficient refrigerators that should probably be replaced anyway. Others said it doesn't save any energy but only temporarily lowers amperage. (Like I was thinking)

    I guess using a watt meter would prove if it actually saves energy or not, but I don't think I would trust my fridge to a device that puts out a pseudo-sine wave.
     
  14. kellys_eye

    kellys_eye

    4,275
    1,146
    Jun 25, 2010
    I'm not even sure the method actually works either.

    I can see how they might be able to reduce the start-up surge (which, to me, is the most important issue) but as far as 'energy saving' is concerned any messing with the compressor simply means it doesn't work as efficiently as it should and that the 'energy saver' box is doing what YOU could do i.e. turn the thermostat down a bit!
     
  15. Externet

    Externet

    744
    162
    Aug 24, 2009
    Whatever the trick method is; there is maaany on the market, also 230V

    ----> https://duckduckgo.com/?q=power+saver+&t=canonical&iax=images&ia=images

    Read the abundant comments on the web also. The thing is I started using the gadget when living in a small apartment with gas heating. That made me sense in a better way the electrical billing decreased like 30% !
    In a dwelling with lots of electrical appliances, would had been harder to evaluate if actually does something.
     
  16. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    Many get away with it by using ambiguous language like, "It may improve your energy usage" Or, they show videos of the amperage before and after their device being plugged in.
    A 30% reduction is very impressive.
    I would love to see the actual numbers on a watt meter.
     
  17. DickN

    DickN

    1
    0
    Sep 8, 2015
    I believe the "Green Plug" is probably a power factor controller. They're specifically for induction motors and this one might be specifically for the induction motor in a refrigeration compressor. The rationale behind the device is that motors have to be designed to start up and run on the lowest expected supply voltage. At nominal or greater voltage, the motor is over-driven. The back-EMF is limited by the RPM, which can't increase very much because an induction motor requires some "slip" to produce torque. The excess supply voltage therefore appears across the motor's equivalent load inductance and therefore contributes reactive current - hence the increasing phase lag and lower power factor. The extra current is not purely reactive, however, because it also increases the copper and iron core losses, so power consumption is increased. Reducing the supply voltage to not much more than necessary to run the motor thus improves efficiency.

    I had a device about 30 years ago called the "Watt Wizard" which I used on my refrigerator. It was damaged by an electrical storm (which also took out a lot of other electronics in my apartment), and when I opened it up to repair it I found the markings on an IC had been removed. I wound up tracing out the circuit to identify its function (it was a quad op-amp). It had a manual adjustment to tweak it for whatever motor it was powering. Without the Watt Wizard, I could hear a whine from the compressor - sounded to me like 360 Hz (I'm in the land of 60 Hz power) but I never confirmed that. With the Watt Wizard operating, that whine disappeared. The device monitored the phase lag of the load current and reduced the RMS voltage by delaying the triggering of a Triac until the phase lag relative to the applied voltage was reduced to match the manual adjustment. If the phase lag decreased rapidly (due to e.g. increasing mechanical load), the unit would immediately apply full voltage to prevent stalling. This would happen when I opened the refrigerator door and the incandescent lamp lit. It can only control a single motor properly - fortunately the small fan motor could run just fine on lower voltage than the compressor could.

    As you would expect from the above, the Watt Wizard did nothing to reduce the startup current. It did reduce the running current. I believe, however, that the startup current could be reduced substantially by using a voltage/frequency controller. The start winding would probably have to be supplied a controlled current at 90 degree leading phase angle. This would also eliminate the start capacitor and thermistor. Without matching the voltage and frequency of the supply to the speed of the motor as it's starting up, the motor is terribly inefficient during startup.

    It must be noted that the mechanical load on the compressor increases rapidly as the refrigerant is compressed. This may limit the startup current reduction which can be achieved.
     
    Last edited: Mar 3, 2018
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