[SOLVED] Kill-a-Watt P3 plugged into PWS inverter acting weird. Can't trust the numbers!

[PopDBop]

Just noticed strange behavior on my old Kill-a-Watt P3 plugged into BESTEK 1200W PWS inverter...

With no load plugged in to Kill-a-Watt
* Hz reporting as 13.5 (not 60)!
* Volts read higher than inverter's display... about 123 volts vs 115 on the inverter.
* slight flickering of the Kill-a-Watt display

Plugged in a lamp with 100W incandescent bulb -- purely resistive load. Kill-a-Watt reports
* Hz, still 13.5 (not 60)
* Volts even higher than 130 Volts
* Power reading 95 watts (close enough)


Lamp plugged into house power with the Kill-a-Watt looks perfectly normal. No flicker in the display either.

Why?

I'm still shopping oscilloscopes, so I can't see phase shifts or waveform distortions. It's a very old Kill-a-Watt meter, but it seems to output correct numbers as long as it's plugged into the grid power. It just doesn't play well with my inverter. Yes, I know, it's a cheapie inverter. But it is pure sine wave. And, it's 1200W output rating is much larger than even the 100 W lamp plugged into it. So I'm not pushing the limits of the inverter where I'd expect to see some funny numbers.

Is anyone else having this problem?

Seems like many people rely on the Kill-a-Watt numbers when testing inverter based solar systems (HoboTech comes to mind). But if noise, distortion and reactance are skewing the Kill-a_Watt readings, how can I trust it for measuring loads on my DIY system?

UPDATE:
I just so happen to have an older BESTEK 1000W PSW inverter. It looks identical to the new 1200W version. I checked the same numbers on this inverter and they look normal. So I'm speculating that the 1200W is malfunctioning, despite being able to power loads.

 

[740GLE]

Try powering something other than a lightbulb with it.

 

[PopDBop]

Try powering something other than a lightbulb with it.

Why? A purely resistive load has no reactance and will not affect the Kill-A-Watt in any way by back feeding a wonky signal that could throw off voltage and frequency. That's why I used it as a test load.

Besides, I already tried other devices on the inverter. I successfully ran a Midea U 8000BTU AC. It was the first thing I ran on the inverter to test it. And I still get the strange readings. That's why I double checked conditions under load with the incandescent lamp, so I could rule out any weird reading from a inductive load.

Based on my benchmark with the very similar 1000W BESTEK, I've concluded that I have a defective device and have returned it to Amazon. It's easy enough to return it and get another one and repeat the tests.

 

[schmism]

square wave inverters with light loads (percentage wise) are a recipe for erratic and inconsistent output.

 

[tigerwillow1]

BESTEK 1200W PWS

The only 1200 watt inverter I can find on their web site is said to be modified square wave, which can confuse kill-a-watt.

FAQs​

• Is this pure or modified sine power ?​

  It is a modified sine wave inverter that can meet your basic needs.

 

[PopDBop]

The only 1200 watt inverter I can find on their web site is said to be modified square wave, which can confuse kill-a-watt.

FAQs​

• Is this pure or modified sine power ?​

  It is a modified sine wave inverter that can meet your basic needs.

[SOLVED]
Good thought. You are correct sir!

I discovered earlier today that's it's a MODIFIED sine wave inverter after cross checking the Kill-a-Watt on my older BESTECK 1000w PSW and seeing normal numbers. Then I double checked the Amazon order page. The "modified" info was way down the sales page. That explains everything. Dooh!

Sneaky beastards packaged in the same case and everything as their 1000W PSW inverter. Lesson: double check descriptions CAREFULLY before ordering inverters. It's on it's way back to the jungle.

Well thanks to all who responded. Sorry I to waste your time. Maybe someone will find this in the future and learn from it.

 

[740GLE]

A lightbulb doesn’t care about a modified square wave input, but more sensitive equipment will.

 

[MisterSandals]

Sneaky beastards packaged in the same case and everything as their 1000W PWS inverter.

Are you confusing PWS with PSW (pure sine wave)?

 

[PopDBop]

Are you confusing PWS with PSW (pure sine wave)?

Nah. Just too tired to type correctly. Ha. (fixed those typos)

 

[PopDBop]

A lightbulb doesn’t care about a modified square wave input, but more sensitive equipment will.

Of course not. But I do, as well as my other loads.

 

[Tecnodave]

The better the inverter the better the waveshape, use an oscilloscope to see the waveform plus distortion on your inverter....its horrible, that is why the kill-a-watt is confused