Anyone here experienced in reading oscilloscope sine waves?

[OnTheRoadAgain]

I have an odd one.
I have not seen one like this before and am not sure how to interpret it.

It is from a brand new Bestek 500Watt Pure Sine wave Inverter. I would say it has a problem.
Do you know how to interpret this?

 

[CaseyB]

ZB

I have an odd one.
I have not seen one like this before and am not sure how to interpret it.

It is from a brand new Bestek 500Watt Pure Sine wave Inverter. I would say it has a problem.
Do you know how to interpret this?

View attachment 44562

 

[CaseyB]

First blush it looks like the ‘scope isn’t triggering properly. Check your probe ground, and play around with the “trigger” controls.

 

[OnTheRoadAgain]

First blush it looks like the ‘scope isn’t triggering properly. Check your probe ground, and play around with the “trigger” controls.

Roger that.
But.......is it possible it would be triggering improperly for one device and not any of the others?
In other words, other items tested at the same time do not exhibit this irregularity........

Still a possible triggering / grounding issue ?

 

[Gazoo]

I have an odd one.
I have not seen one like this before and am not sure how to interpret it.

It is from a brand new Bestek 500Watt Pure Sine wave Inverter. I would say it has a problem.
Do you know how to interpret this?

View attachment 44562

Looks like something from the Outer Limits. Is that with no load?

 

[OnTheRoadAgain]

Looks like something from the Outer Limits. Is that with no load?

Yes...no load.
I have never seen a result like that.

I've had 2 people now to say it could be a triggering issue or a grounding issue and it could be.

But no one as of yet can explain why testing other inverters and other AC sources right after this test do not have any such artifacts.
I can consistently get that plot no matter how many times I do the test and no matter what settings.

So from my perspective it has to be coming from the new Inverter.

If it was an issue of setting the triggering or grounding, wouldn't it be present on all the other AC sources tested?

 

[Gazoo]

If it was an issue of setting the triggering or grounding, wouldn't it be present on all the other AC sources tested?

I would think so. Does the signal get cleaner when you put a load on the inverter?

 

[CaseyB]

Roger that.
But.......is it possible it would be triggering improperly for one device and not any of the others?
In other words, other items tested at the same time do not exhibit this irregularity........

Still a possible triggering / grounding issue ?

I think you might have a grounding issue internally in the inverter. If you can take the cover off, without breaking a warranty seal,
I would look for anything that might have come loose in shipping. Anything to do with case hounding.

 

[OnTheRoadAgain]

It gets slightly cleaner.......but......

Now the Amplitude of the wave form is slowly changing all by itself from about 120v down to about 20 volts and then back up to 120 in an endless cycle.

Just for comparisons....I just connected my Renogy 1000Watt inverter and as expected.....perfect Sine wave, better than AC grid.

It's the Bestek Inverter. Could be a bad capacitor, MOSFET....who knows.

Not sure if I'll try another....but this one is headed back to Amazon. Someone without an Oscilloscope will probably get it next and never know the issues it has.

Sad thing is that it passed my load tests. I was able to run 482 watts on it but this wave form is a deal breaker.
It means it will likely fail early. I do wish I knew what was causing it tho.

 

[time2roll]

I would at least try a small load such as 60w incandescent or hairdryer on low heat.

 

[Bud Martin]

Is this the same one as yours?

BESTEK 500W Pure Sine Wave Power Inverter

Will recently made a DIY milk crate generator using a Bestek 500w PSW inverter. I'm thinking about buying one but I have a question. There's a YouTube video where the guy uses an oscilloscope to test the waveform on this inverter. The waveform is good with no load but has "ripples" when he loads...

diysolarforum.com

 

[OnTheRoadAgain]

Is this the same one as yours?

BESTEK 500W Pure Sine Wave Power Inverter

Will recently made a DIY milk crate generator using a Bestek 500w PSW inverter. I'm thinking about buying one but I have a question. There's a YouTube video where the guy uses an oscilloscope to test the waveform on this inverter. The waveform is good with no load but has "ripples" when he loads...

diysolarforum.com

Yes. That's the one. Red and all.

Mine has a decent waveform when it's off, then I hear something inside kick on (not the fan) and that's it. (yeah, odd right?)

But develops all kinds of problems when switched on.

 

[OnTheRoadAgain]

I tried adjusting the trigger settings and the grounds. Nothing helped.

Because my homes AC power produced a consistent and near perfect AC sine wave with this same setup......

And because I just connected my Renogy 1000Watt inverter and it produced a 100% perfect Sine Wave, it must be the Bestek inverter.

I'm starting a return to Amazon now.

I wonder how many of these seem to work ok....but have serious issues right out of the gate?

 

[OnTheRoadAgain]

 

[OnTheRoadAgain]

So, I got the 2nd one from Amazon today.
Hooked it all up and connected the Oscilloscope to it.

EXACT same results.
I tested this one with a load. 499watts for 10 minutes no problem.
520watts for 1 minute, no problem.

I've contacted Bestek for information regarding the unusual Sine wave.

Meanwhile, I'm going to keep the 2nd one and take my chances.

I could not even get a definitive answer at forums that specialize in electronics. So maybe it's some kind of electronic wizardry to get the "improved" sine wave from it. I would not call it a 'Pure Sine wave" inverter. But perhaps "a good bit better than a Modified Sine Wave" inverter.
Time will tell.

This one goes in the car and is used when traveling for various things so it won't see full time or heavy duty.

 

[efficientPV]

Not a problem. You are triggering on the HF noise because the inverter has minimal filtering.

 

[OnTheRoadAgain]

Not a problem. You are triggering on the HF noise because the inverter has minimal filtering.

Don't most oscilloscopes have a way of filtering that? Or limiting the range?

 

[svetz]

Curious. From your video it was looking good for grid power, so shouldn't be a scope issue.

But, you can't have two Y values for a single X value on a single channel. Ahh... the scope is sampling in the MHz range? So really those are two different X's ... I'm guessing it's a harmonic from how they're generating a sine wave. Probably one side is slightly out of phase with the other, possibly within the efficiency of the device.

What's the waveform look like under load?

 

[efficientPV]

A scope with storage would show only one trace. Since there is a 20KHZ or so signal imposed on the sine wave, you see a double trace. Some scopes have a TV filter. If you looked at the waveform thru a transformer it would probably filter that out. As with any piece of test equipment, you should never trust what you see.

 

[OnTheRoadAgain]

Curious. From your video it was looking good for grid power, so shouldn't be a scope issue.

But, you can't have two Y values for a single X value on a single channel. Ahh... the scope is sampling in the MHz range? So really those are two different X's ... I'm guessing it's a harmonic from how they're generating a sine wave. Probably one side is slightly out of phase with the other, possibly within the efficiency of the device.

What's the waveform look like under load?

That's what I was thinking. I've tested dozens of generators and Inverters and not one ever gave me results like this. I think the scope is fine.

I will run some load tests soon and post the results.