Induction motor - generator conversion

[RogerAS]

Done correctly, power-factor correction decouples load from input line but there are switchmode power circuit losses.

Capacitive PFC schemes to make motors & A/C-refrigeration compressors run more efficiently may have good acceptance down south where heat pumps, A/C, or large whole house house fans - swamp coolers - etc. are the rule. $70-90 off eBay, and if it makes the utility power play nicer...

Would such a device help an off grid modwave inverter power an AC unit? By "help" I mean run the AC unit smoother and with less "torque" on the inverter.

R

[rcavictim]

Done correctly, power-factor correction decouples load from input line but there are switchmode power circuit losses.

Capacitive PFC schemes to make motors & A/C-refrigeration compressors run more efficiently may have good acceptance down south where heat pumps, A/C, or large whole house house fans - swamp coolers - etc. are the rule. $70-90 off eBay, and if it makes the utility power play nicer...

Would such a device help an off grid modwave inverter power an AC unit? By "help" I mean run the AC unit smoother and with less "torque" on the inverter.

R

Roger,

It well might.  Is your setup such that you could actually measure a small drop or increase in DC current flowing into your inverter if you happen to tune the load to be more or less efficient?  If you have such a meter then you might try adding 50 uF or so of motor run cap rated higher than your system AC voltage right across the outlet where the AirCon unit plugs in (while the compressor is running) and see if that makes any drop in DC current from the batteries into your inverter.  You can fine tune how many microfarads you will need this way by trial and error.  You might need 100uF or more.  I really don't know because it depends on the rating of your AC and the voltage.  110 or 220 or   Once you have found the best size capacitor wire the cap right across the compressor terminals in the aircon so it is only across the output of your power inverter when the aircon compressor is running. Reason I suggest this is that your inverter may not take kindly to seeing just the big capacitor alone as a load and there is a real chance it (the inverter) might blow up.  There is always an element of risk to experiments like this.

What inverter do you have?  What AC voltage?  What DC voltage?  Sorry for all the damned questions.   

[DanG]

if anything, makes the meter read most correctly the actual or true power flowing through it

The unspoken assumption so far has been 'perfect' utility power is evenly supplied to us all. With corrected PFC having every motorized device start up easier (shorter surge period)  run cooler and throw off less distortion to everything on that side of the the 240 house feed is a win. Refrigerator - freezer - A/C - well pumps -  fans - blah blah... Add-on Cap bank (eBay) is a passive PFC but may help if you and the neighbors are all spinning A/C's and the like on the downstream side of the supply xfmr with crappy power to begin with.

The modulation I spoke about was probably a side benefit of a municipal street light cost-cutting scheme, degrade the power quality to run lights 8-12 hours a night. At the time that County in Maryland was the wealthiest in the Country with enough pull to get favors like that from utilities.

Would such a device help an off grid modwave inverter power an AC unit? By "help" I mean run the AC unit smoother and with less "torque" on the inverter

There are add-on soft-start start-run capacitor kits for RV A/C units, and there is a danger of over-size mismatching where the motor/compressor never gets to full speed. Opening your A/C unit and seeing what they've provided as start-up circuit would be first, then see what's what for add-in values. Since square-wave inverters came out folks have been trying to clean them up or make inductance motors run cooler and if there were a set of cures it'd be common knowledge and built in by now... heavy cables, short wire runs, lots of battery for surge, over-sized inverter, pure-sine oh wait you don't want to hear that one..