Modified Sinewave Inverter Efficiency and Refrigerators - Page 1
Forum section: electronics / general

author: jonovid
author_rank: Super Contributor
timestamp: June 06, 2022, 06:12:06 pm
content: efficiency of the inverter generally ranges from 95 to 98% as stated by some? but is this true of most cheaper modified sinewave inverters?if I have a 300 watt AC refrigerator, is a modified sinewave inverter rated at a continuous 600 watt's ok to power it, in a power outage.if say the peak or surge power is 1500 watt on start up. one site stated modified sinewave inverter efficiency was as low as 75%with inductive loads. does it matter if it is 120 volt 60Hz or a 240 volt 50Hz inverter set-up? as to the efficiency in quotation.can an AC line filter help the efficiency?-this is about powering Refrigerators in a power outage from 12 or 24 v deep-cycle battery for 1 or 2 hrs.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 07, 2022, 01:50:26 am
content: You'll ideally want V/Hz ramp up to eliminate inrush, but I'm not aware of any cheap inverters nowadays with that feature. Vector had just that in the mid 2000s, but they apparently ran into patent issues and had to discontinue it.

author: james_s
author_rank: Super Contributor
timestamp: June 07, 2022, 02:31:19 am
content: I've never measured the efficiency, but inverters will typically run motors ok, even cheap modified sine wave inverters. The motor will be noisier than usual though and I do suspect the efficiency is lower. A pure sine inverter would certainly be preferable, they are not especially exotic or expensive anymore. I think I paid around $100 for the 300W continuous model I have.

author: BrianHG
author_rank: Super Contributor
timestamp: June 07, 2022, 03:09:24 am
content: Cheap modified sine wave inverters have trouble with startup torque with most induction motors, even if the inverter is a continuous 1500 watt unit. If your fridge has a normal induction motor compressor, every time it switches on, if it is a relay type thermostat switch, you may end up in a situation where your inverter will not deliver the required torque to get the compressor running before that stalled motor's high current knocks out the inverter's over current protection.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: June 07, 2022, 03:22:09 am
content: Quote from: jonovid on June 06, 2022, 06:12:06 pmThe thing about cheap inverters and their numbers is the closer you go toward pulling the numbers it says on the box, the lifespan of the inverter diminishes.Modified sinewave inverters can have more adverse effects on electronics.Can I suggest if you want this for use during a zombie apocalypse, think about spending a little bit more for a better-rated, pure sine wave one. It wont become the weak link when the chips are down and with a bit of extra capacity may allow a phone or torch to be charged as well.

author: woodchips
author_rank: Frequent Contributor
timestamp: June 10, 2022, 08:10:02 pm
content: For many years I ran a small larder fridge from a 300W cheap inverter. Provided a 240V 50Hz power to a remote building so could just pull a cord and the lights would come on, worked very well. It ran from a 24V LA battery system with solar charging.

author: Seekonk
author_rank: Super Contributor
timestamp: June 11, 2022, 06:47:09 pm
content: I run a chest fridge at my camp with a 2000W MSW inverter for years without issue. It is a cheap Harbor Freight model I bought broken, I just wiggled out two shorted H bridge FET so you could call it a 1,000W. Startup at 12V is about 120A. H bridge section can easily Handel the power, all fans are removed to lower current. It is the inverter section which is always weak. in small units. There are some videos that demonstrated low voltage inverter sections being paralleled to handle higher current. Anyway, many of the older models used a TL494 for the H bridge. I have thought of increasing the dead time after the fridge has started to make it more efficient. NASA had some patents in early 80's that altered phase triggering in motors to reduce power consumption once load lightened. Some company made them called GREEN MACHINE. If only running a fridge, you could probably just increase deadtime to prevent magnetic saturation. My fridge only draws 78W when running so I can't see there would be much of a reduction.

author: Miyuki
author_rank: Frequent Contributor
timestamp: June 13, 2022, 06:21:51 pm
content: If you will change the refrigerator consider taking some with an inverter motor.Or use a sine wave inverter.If the fridge is not super old with a mechanical regulator, it uses zero switch SSR (does not make change with "Modified Sine"), but still has that mechanical related inrush current.Motors on modified sine are generally noisy, with lower efficiency (this can be significant) and it causes little more wear (so like shorter lifespan from 30 years to 25)But no direct damage