Invertor size for a refrigerator

Gdetrailer wrote:

westend wrote:
Knowing what the locked rotor draw is where you should start. I made the mistake of matching an inverter to a fridge where the inverter should have handled the load but didn't. I replaced that inverter with a larger one and haven't had any issues since.
The Tripp Lite inverters that are built for motor startup have a good rep but prices are getting closer with the newer sine wave inverters. I am using a Xantrex Prowatt inverter and think it's a fairly well built device.

Many of the newer inverters use a high frequency chopper like a switching power supply. The chopper often is at frequencies above 20 khz which allows for the use of much smaller high frequency transformers or diode/capacitor voltage "doubler" technique in order to arrive at 160-170V DC. The high voltage DC is then run through basically the same setup as a audio amplifier. The AC load attaches directly to the output stage.

while it works one of the draw backs with this setup is the chopper circuit has very little surge capacity, in fact most inverters do not disclose the duration of the surge which the inverter can handle. This is extremely important when dealing with high startup surges of an inductive load.

The Tripplite PV1250 is expensive because instead of using a chopper circuit, they are actually using the old school tried and true method which employs and very large and heavy 60 hz transformer taking the 12V DC to 12V 60hz AC through the transformer and the transformer is multiplying to 120V. The PV1250 weighs in at 20 lbs compared to a chopper type at just one or two pounds.

This has several advantages over a high frequency chopper, one is much higher surge capacity, two is reduction of harmonics in the output (transformer actually filters out the high frequency harmonics which takes a lot of the edges off the wave form), three is the transformer absorbs the back EMF from the highly inductive load lick a motor (this is critical in preventing the output transistors from seeing these back EMF spikes).

Expensive, perhaps but not all that expensive if you think about how much larger of a PSW inverter you would have to buy to get the high surge capacity of the Tripplite. It is hard to beat at $280 and you get 1250W continuous, 2500W surge for TEN MINUTES additionally they give a 2400W surge rating for SIXTY MINUTES.

I challenge anyone who can find a 1200W PSW inverter which makes a 2500W TEN MINUTE SURGE capacity inverter for a mere $280 (most if not all that do give a time rating will be seconds or even microseconds).

Thanks for taking the time to explain the electronic differences between the two inverters. My issues with the smaller Samlex pure sine inverter and the fridge probably existed from just what you explained, a chopper that doesn't have enough duration at higher surge.
Sometimes, there just isn't a good substitute for a large chunk of copper. :B