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they have a coupling transformer built in for 1to1 , 10 to 1 etc. or what ever the ckt rating is...
we have several so they have different ratios depending on what we are checking.

we have them for both ways so we can look at super small voltages as well as up to 100kv.
 

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they have a coupling transformer built in for 1to1 , 10 to 1 etc. or what ever the ckt rating is...
we have several so they have different ratios depending on what we are checking.

we have them for both ways so we can look at super small voltages as well as up to 100kv.
So I need another part before I can measure waveforms from the generators?
 

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do what you like....
isolation transformer probes are cheap insurance for the scope.
and for the items you are checking.
 

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do what you like....
isolation transformer probes are cheap insurance for the scope.
and for the items you are checking.
I'm just trying to figure out how the probes interface with the power outlets so they can be measured. It looks like only one probe is needed, but I don't know how it connects to the generator. Presumably, you have to find a way to connect to the outlet somehow, but I don't know how that's done.
 

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In one of the videos I saw, the guy had the probe clipped to what appeared to be one of the blades of an electrical plug. It was difficult to tell. The clip doesn't fit on the ground part of the plug, so it had to be clipped either to the hot blade or the neutral blade. I guess the ground clip on the probe would clip to the ground rod on the plug? Or would it clip to the other blade?

It seems there has to be a simple way to get a waveform reading.
 

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One thing to keep in mind when you measure your home AC is that your scope probe likely has its ground lead (the one with the alligator clip) connected to the earth ground that the scope is powered by. They are tied together in the scope. So if you connect the ground clip to the hot of your AC, then you have shorted hot to ground and something is going to give. You normally have to use both leads on a scope to measure a V potential difference, but since your scope is likely connected to earth ground and earth ground is connected to your house neutral in your breaker box, you already have your scope ground clip connected to neutral and can use just the non-ground clip on your scope probe to measure the hot line. If you get the neutral line, you just won't see a signal.
I like to use a ground cheater plug (about $1 at home Depot or Lowes) to plug my scope into to disconnect the earth connection from the scope so I don't have to worry about the probe ground connection.
As far as where to measure, I have an AC breakout box for the power analyzer that gives me an easy connection however with great care you can use a cutoff AC cord (with the insulation stripped some to expose the wires) plugged in to your power source, but then you have exposed live wires. Just be very careful if you go this route.
 

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LaSwamp: There really isn't anything too difficult about using a scope and viewing a waveform, However, there are a few things you should be aware of when doing so. If interested and this hasn't been suggested in an earlier post, I would strongly suggest viewing the following video:


Note: you can certainly view the waveform output of your generator in the same manner as you would the electrical system in your home. If your generator supplies 240 VAC as well as 120 VAC, I would suggest against connecting your scope to the 240 VAC without the use of a small stepdown transformer, unless you are using the appropriate probes. Not knowing your particular scopes input rating, you should certainly ensure your current probe is set to the 10X setting when viewing the 120 VAC source .......... using a high voltage differential probe kit would certainly be the safest method, but not completely necessary if one is very careful and ensures everything is done correctly. I'll stop with that!
 

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I'm just planning on testing the 120VAC outlets, nothing 240VAC. The main reason I got the scope was to try to figure out strange readings I was getting with my multimeter when testing Hz on my Wen GN400i inverter. It should have read a clean 60Hz, but the readings were all over the place. Something seems odd with the signal and I was hoping to nail it down with the scope.

I have one of those bonded-neutral plugs. Can I clip the scope probe to one of the blades and use that? Or will that be a Bad Thing? I can always clip to a power strip (or something like that) and plug it in, right? I'm just going to snap a pic of the waveform so I can post it. I'm not going to be doing a lot of experiments with it, at least not yet. It really seems like a cool device, though. I'm not an electrical engineer, so I don't understand a lot of how it all works, or the terminology.
 

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LaSwamp:

I'm going to stick my neck out and try to help. It's obvious you're inexperienced with a scope, but it's also obvious you're wanting to learn and it seems you're determined to use your newly acquired tool. In the interest of safety and not doing any harm to yourself or the scope, I will make a suggestion that should work fine for your IF you make certain everything is connected properly before applying power:

Note: the following method is not the only way to take a measurement, but I feel it might be the simplest for you!

1) Get yourself a regular power strip
2) With the power strip NOT CONNECTED OR PLUGGED IN to your generator or any other 120 VAC outlet, connect one of your oscilloscope's probes to the hot terminal of one of the power strip's receptacles (the shorter of the two open slots). You can use a dummy plug as you mentioned in your post, ensuring you connect to the proper blade or whatever other method you feel comfortable using. Also ENSURE the probe is set to 10X attenuation! Do not connect the probe's ground clip to any terminal - better yet, completely remove the grounding clip from the probe!
3) Once steps 1 & 2 are complete, the scope's probe is now connected and ready to take a reading, but obviously there's more! At this point and before proceeding to the next step, please do ensure the power strips ON/OFF button is set to OFF!
4) I believe you mentioned your generator has a floating neutral and you have made or purchased a bonding plug. Is this correct? If so, push the bonding plug into one of your generator's 120 VAC outlets. This will bond your neutral to ground.
5) Again after ENSURING the power strips ON/OFF button is set to OFF, plug the strip into one of the generator's 120 VAC outlets.
6) Now is a good time to also plug your oscilloscope into one of your generator's 120 VAC outlets
7) Start your generator and allow time for it to stabilize
8) Once stabilized, power on your oscilloscope. If this step and all previous steps have been followed correctly, the scope is now ON with one of its probe's connected to the hot terminal of a receptacle on the power strip AND the ground clip has been removed OR is NOT connected to anything.
9) At this point, if you're certain all steps have been followed correctly, everything is connected properly and the scope's probe is set for 10X attenuation, you can now power ON the power strip.
10) You should now see the waveform you have been looking for and also get the other measurements you wanted - such as frequency.

Disclaimer: You're doing this at your own risk. I will not be responsible for any damage to you or your equipment. This certainly isn't rocket science, but anything can go wrong if one is not extremely careful and observant. I'm just trying to help, but was very hesitant to do so!
 

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Thank you, TVL. That worked perfectly. I finally got some waveforms!

I first tested wall power. As you can imagine, it was a perfect sine wave. Very smooth and consistent.

I was going to wait until the weekend to test the generators, but the suspense was simply too much. So I pulled out the Wen and fired it up. That's the generator that was giving me wonky Hz readings, so I was very curious to see what the waveform was going to look like. When I pulled it up, the waveform looked... good. It had a very slight distortion around the peaks, but it looked almost identical to the wall power waveform. It was what you'd expect from a gas engine inverter. I was pleasantly surprised. I feel a lot better about it now. I'm not sure why I was getting weird Hz readings.

I decided to pull out the Coleman Powermate from 2005 that's in my collection. I wasn't expecting a very clean signal and it wasn't. It had the basic shape of a sine wave, but it was very jagged. I would not want to run anything on it for very long. I was going to snap pics of the waveforms, but I'm still trying to figure out how to do it. I was looking to see if I could get it to display Hz and VAC on the screen with the waveform but I could not figure out how to do it. I found Hz on another screen, but I could not find VAC anywhere. There has to be a way to do it, I would think.

I'm going to post pics of the waveforms when I figure out how to get the pics. I was going to try today, but it was Swamp People hot outside. I need to do it when I have more time to tinker with how all of that works.
 

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super super expensive to buy one...
a broad spectrum analyzer for elf to lets say 1ghz... (they are super pricey to buy at that wide range.and certified)
we rent them for the smaller jobs where we have to look at interference or trash in the air or power.
they rent for 5K per week....
way way out of line on price for this small home hobby stuff... but that is the kinda of instrumentation you need to chase super weird power issues.
we had purchased one back in 2014 for $60k (lease to own on a job) it did not take too long to pay for it out of the rental!
but it was stolen from storage along with lots of other cool items back 4-5 years... wow time flies!

that was the tool we went to for looking at inverter gens!
nice to be able to see the whole band scope feature and see the trash if there was any spikes!

we found 2 bad transformers in the close in area to me and reported them to the utility.
they promptly replaced them and no more hash noise on the hf radios!

depending on the scope they can work for some things like this if you have the proper probes and special band pass filters.
some of the HP scope units had plug in features for this.

yea i have a couple of good books on the scope pages that help with complex scope operation.
pm if you need links.
 

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For what I needed to find out about the signal from the Wen, I didn't need anything radical. I was happy to see that the scope recognized the the signal as a sine wave. The waveform looked pretty good, all things considered. I no longer have reservations about using the Wen to power anything. It looks almost identical to wall power. OMH was right that there was likely nothing to worry about.

As for the Powermate... yeah, not so much. It looked like a sine wave wearing a fur coat. It's definitely not a generator to use for anything sensitive. I don't know what to expect when I scope the Firman, but I'm not expecting anything very clean. It's a typical worksite generator. I suspect the Champion inverter I have will look like wall power, similar to the Wen.

The scope has a USB port that can download waveform images onto a thumb drive. As soon as I get that figured out, I will post them all on here. Now I want to test the built-in inverter in my truck. It's probably not clean, but we shall see. So stay tuned, waveforms will be incoming.
 

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Discussion Starter · #93 ·
Glad you got it figured out. You can always take a picture of the monitor and upload it. All good either way.
 

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Glad you got it figured out. You can always take a picture of the monitor and upload it. All good either way.
There's a way to save the image, but if push comes to shove, I can always just snap a pic of the scope itself. Since I have tomorrow off, I am planning on getting out there early and catching some waveforms.
 

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Okay, here some waveforms I promised.

Here's the basic calibration form:

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I had to adjust it a bit, but that looks about as close to perfect as I could get. First up for testing is the Coleman Powermate. It's from about 2004-05, last used extensively during Hurricane Gustav in 2008.

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I'm not sure how bad that is, but it doesn't look great. As waveforms go, that may not be too bad.

Next up, the waveform I've been wanting to see since I bought it, the Wen GN400i open frame inverter:

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That seems to look pretty good to me. Maybe a bit of distortion near the top of the wave, but I'm presuming still plenty fine for powering anything. I'm not seeing what was giving my DMM so much grief, but maybe I'm missing something?

Next up, the Firman P03602. I've been curious about this one, although it's not a secret that THD is high for this model. Just how bad is it?

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I know that's not inverter power, obviously, but how bad is it? It's rated at 25% THD. Does the waveform reflect that?

I'm going to scope the Champion 200913 this afternoon since it's at another location. It's an open frame inverter. I'm expecting it to show similar to the Wen.

Let me know your thoughts, opinions, and observations, guys!
 

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Discussion Starter · #96 ·
The old powerate is no surprise, they notoriously had sawtooth waveforms.

The WEN generator looks good. No complaints. Would like to see your grid readings for comparison.

The fireman is way worse then I would have expected. There are basic generators in same price range have cleaner outputs.

I wonder how close to the same image my little pocket scope would produce.
 

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I wasn't really expecting very clean power from the Coleman or the Firman. Clearly, they are both worksite generators. I'll use them as backups and loaners should one of my neighbors need power in an outage. It's better than no power. I'd imagine using them for a short period of time won't hurt anything, which is typically how outages go when weather events knock it out. People usually just need power for a few days to run a fridge, some fans, or a window shaker.

So, I had a chance to sit down with the Champion inverter, my newest generator, to see what kind of power it put out. It was a strange afternoon with some odd surprises. I powered it up and let it warm up. I then set up the scope. No matter what I did, the following results happened below.

First, the generator itself:

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The waveforms:

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I was not expecting that. I tested the power from the outlet itself, then through an extension cord, and then through a power strip. No matter what I used, that was the waveform I got.

Baffled, I decided to plug in the bonded-neutral plug I got, the one I use to cure the open-ground fault on the Isobars. As soon as I plugged it in, this is what I got:

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I was really surprised by that. I removed the plug and reinstalled it a few times to make sure it was actually the plug that was making the difference. It was indeed the plug. What I don't understand is that my Wen inverter, which also has a floating neutral, made clean sine waves right out of the box, no bonded-neutral plug needed. I was expecting the same from the Champion, but no. It produced what looks like very dirty power out of the box. The bonded-neutral plug is needed to get it to make clean power. What's up with that? Has anyone seen that before from an inverter?

The other strange thing was that when I turned off the fuel valve to burn off the gas in the carb, I was expecting it to run for about a minute or two and then sputter out. Well, that did not happen. After about 20 minutes, the Champion was still running strong. I had to manually shut it off. I pulled the fuel line and discovered that even with the valve closed, it was still allowing enough gasoline to flow to keep the carb full and the engine running. That's not so good. I'm guessing I can contact Champion and let them know the fuel valve is leaking? It should be an easy part to replace, as long as the fuel tank is empty.

Just for Schlitz and giggles, I decided to test my truck. It has a built-in inverter that puts out 400w of power. I've never really used it. It's not all that useful except to charge a a phone or laptop. It's not enough power to run anything intensive. First, the truck:

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This is the waveform it outputs:

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Clearly, it's a modified sine wave. That looks like a typical budget-friendly vehicle inverter. Unless I just have to have power someplace remote, I'm not sure if I will ever use it.

It was an interesting afternoon. I'm glad I caught the problem with the fuel valve on the Champion. I'm not sure why the signal is so distorted without the bonded-neutral plug installed.

Thought?
 

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Discussion Starter · #99 ·
I’m not sure what to make of the champions improved waveform with a neutral bond. Good thought To experiment with the bonding plug.
 

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I’m not sure what to make of the champions improved waveform with a neutral bond. Good thought To experiment with the bonding plug.
I was very surprised to see that, given that Champion is an inverter. I was expecting the power to be very clean. Unless there's a ground loose somewhere, I am baffled over the scope readings.
 
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