Inverter for Whynter mini freezer

MEXICOWANDERER wrote:
GdeTrailer,

Boy! I'll say! Trace boasted their inverters "Would easily operate at X3 rated nameplate" for a half hour, at 25c. I had (and sold) a 12-volt Trace 812 that tolerated a 3,000 watt motor start up. My dumb - the poor inverter survived innumerable clashes trying to fight 120 vac shore power (and auto-protected shutdown). Trace inverters were heavy. Even though they were pseudo sine wave.

Not any more. Those cheap featherweights on the market can barely meet their design wattage spec. I blew my true sine wave Samlex immediately off-line with a 2X load attempt.

Care must be taken matching an inverter to an inductive load start up (inrush). Pseudo sine wave inverters require more percentage safety startup leeway than do true sine wave inverters.

There's no benefit in spending any money to "try and save money" only to guarantee the purchase either fails to do the job or catches fire.

1. Find out the appliance run watt rating

2. Find out what type of motor is used

3. GOOGLE motor-type start up current inrush. It will be a percentage

4. This is valid only for dedicated inverter / motor connections

Trace was a well known quality inverter, thats for sure.

Tripplite does make some heavier inverters built the same way as the PV1250. The PV1250 uses and old school heavy duty 60 hz transformer in the output stage.. This 60hz transformer HELPS greatly to "match" to inductive loads. Also acts as a "filter" to help filter out some of the MSW harmonics in the waveform.

The flip side to modern inverters which makes them extremely lightweight AND CHEAP is the method of how they get the 120V.. The modern day versions use a high frequency "chopper" which also for a very small tiny transformer.. This creates a high voltage at a high frequency on the secondary of the transformer.

This high frequency AC voltage is no good to 120V 60hz appliances so it is rectified and filtered to high voltage DC..

Pretty much the same way a switching power supply works..

Then the high voltage DC is now fed to the output transistors and modulated to 60HZ 120V

Output stage is very similar to say an audio amp except for the fact that it is designed for a single frequency output.

Because of the high frequency chopper/power supply design there may not be enough "reserve" power available for the output stage to sustain large 120V surge currents..