Posts: 190
Joined: Tue Jan 10, 2012 12:02 am
Location: Reading.UK.EU

(AC) Power factor help needed, please.

Sun Feb 19, 2017 9:13 pm

I am tinkering with the ability to setup a freezer for use when camping running off a vehicle 12V (DC) system via an inverter.

A target freezer I have is labelled 220-240VAC, 50Hz, 0.6A at 230VAC.
According to the manual the power consumption is AC 65W.

My Brennenstuhl wall wart duly shows 240VAC, 0.63A, 80W, power factor 0.53 when plugged into the mains.

And it won't run off my 150W inverter which flashes the overload light, I expect due to the fact it wants to run 240*.63=151VA. Now I could get a bigger inverter, but ...

I have 2 questions and welcome help/corrections on my thoughts & calculations!
1) If I improve the power factor, will that reduce the load on my 12V battery via an inverter?
2) Assuming answer to 1 is yes, Dr Google coughed a formula to calculate the capacitor size required as C = Q / (2 * Pi * f * V*V) and after I converted 0.53 (cos theta) to 0.85 (sin theta) I came to 7uF for the capacitor. Would welcome an informed calculation by someone who knows this stuff rather than my really dodgy old greymatter hack!

Bottom line, will bolting one of these these across the AC input do any good?
Daily driver: Pi3B, 64GB Samsung Evo+ @100MHz, DVB-T, onboard WiFi for internet, BT/USB dongle for KB/mouse, 250GB HDD via USB for media, Raspbian Jessie Lite with Openbox desktop.
Museum: Pi B

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