installing a 150 MFD start capacitor for chest freezer

Hi, looking for some advice how/where to install a 150 MFD start cap for a freezer that is having trouble starting with a 1400i xantrex PS 12vdc inverter - waynefromnscanada if your out there please help as I saw an earlier post that does explain it but im no expert on freezers.
100kWp GT / 4 x 25kW SMA STP25000, 25kWp, 5kWp, 6.76Kwp all GT - making the local electric company quake in their boots...


  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    What is the brand/model number of freezer? There are a lot of different configurations out there.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chrisvibeelectriccomchrisvibeelectriccom Registered Users Posts: 2

    Hi Bill, Thanks its a cheapo Premium PFR96W-220v, the compressor is Huaguang ASD65 220v-240 50hz single phase (im in St Lucia in the Caribbean so we have 240v/50hz standard supply voltage). seems to have no cap and I have had the compressor starting on occasion but most it just goes into low voltage alarm, sometimes it goes into overload alarm also. the supco items look to be the solution but not exactly sure how to wire correctly thru the relay or the best value for the cap?? rgs Chris

    100kWp GT / 4 x 25kW SMA STP25000, 25kWp, 5kWp, 6.76Kwp all GT - making the local electric company quake in their boots...
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Best I could do was find a simple electrical diagram:

    Service Manual - Premium Appliances

    Many refrigerators and freezers use an "integrated" start relay+capacitor and it may not be easy to change the capacitor for a different value.

    In general, refrigerator/freezers are not really designed to operate on a limited power output off grid power system. They are design assuming you have utility power that can supply very high starting current.

    Assuming you have a starting capacitor on this refrigerator (from the manual, apparently not all of them do)--You may be able to remove the existing capacitor and try a smaller value. Which may, or may not help.

    Two other things I would try... First, look at your DC battery to inverter connections. You need very heavy wire/cabling, kept short so that you have very little voltage drop from the battery to the inverter. Also, the battery bank needs to be large enough (and in good condition) to supply enough surge current. For a 12 volt battery bank (guessing), a 1,400 watt inverter that can supply 2x surge power for a few seconds, the DC current would be:
    • 2,800 Watts * 1/0.85 AC inverter eff * 1/10.5 volts battery cutoff = 314 Amps worst case surge
    And you would need to have less than ~1.0 volts drop (11.5 volts minimum battery voltage, 1 volt drop, for 10.5 volts minimum at the inverter).

    If you do not have enough available power/current on the DC side of the inverter, it will cutoff/shutdown during compressor starting. A 1,400 Watt AC inverter should be enough to start that freezer (all things being equal).

    And the minimum size (AH) battery bank would be roughly 2.5x the starting current: Assuming 12 volt battery bank (24 volt would be 1/2 the current & AH capacity):
    • 314 amps * 2.5 battery capacity factor = 785 AH @ 12 volt battery bank
    And lastly, a trick that sometimes work. The freezer compressor/starting capacitor is designed to start in worst case power conditions (low line voltage, poor wiring, etc.). Get a long extension cord (15 to 30 meters) and plug the freezer into the inverter using the extension cord. In some cases, the extra resistance of the cord is enough to reduce the starting current--Preventing the inverter from shutting down, but still enough current for the compressor to start.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stillchillinstillchillin Registered Users Posts: 44 ✭✭✭

    Supco makes a 3 in 1 start relay, capacitor, and overload. it replaces all the start components its easy to wire common, run, and start. wiring diagram is on the package. you just have to figure out which connections are which one the compressor, that can be done with an ohm meter if a wiring diagram is not available. the start winding has the highest reading. the top terminal is almost always common. make sure you get the 230V kit.


    18- 235 W Kyocera panel, 12- 4-KS-25PS Rolls 1350 Ah, Magnum MS4448PAE, ME RC50, ME AGS, Outback FM 80, Generac 8KW LP generator, 6.5 Honda Portable generator
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