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Posted: 2/13/2013 2:51:10 PM EDT
a few weeks ago you scoped a mod sine wave inv.

just curious what the sine wave looks like when you use an isolation transformer. just curious if it smooths out the waveform a little bit in essence making the waveform more like a pure sine waveform..
Link Posted: 2/13/2013 2:56:57 PM EDT
I'd think not. Induction Is linear
Link Posted: 2/13/2013 5:24:27 PM EDT
Most isolation transformers don't have a super-wide frequency response, since they're just designed for 60 Hz.

The "modified" square wave produced by most MSW inverters has some pretty fast rise times (i.e., high frequency components or harmonics).

So, it's possible that you might see some rounding off of the square waves, due to the transformer attenuating some of the higher harmonics.
Link Posted: 2/13/2013 5:29:47 PM EDT
[Last Edit: 2/13/2013 5:35:39 PM EDT by SuperJanitor]
Originally Posted By Skibane:
Most isolation transformers don't have a super-wide frequency response, since they're just designed for 60 Hz.

The "modified" square wave produced by most MSW inverters has some pretty fast rise times (i.e., high frequency components or harmonics).

So, it's possible that you might see some rounding off of the square waves, due to the transformer attenuating some of the higher harmonics.


I'm inclined to agree with this, but Keith J should be along shortly!


ETA, I don't have an isolation transformer, but I do have a 10:1, 12 VAC wall wart. I might scope that when I get a chance, just for chits and grins.
Link Posted: 2/13/2013 9:14:10 PM EDT
cool beans. ive always been curious i know that most transformers that i have pluuged into msw inverters get a lil hotter when i start reaching about 80% load. skibane hit the nail on the head and i was just curious. i dont have scope to test it. but if it does smooth it out there would be a loss but i may be able to run my ups off of it if place an isolator in line. my ups's dont wanna work right running just off a msw inverter.
Link Posted: 2/14/2013 5:03:37 PM EDT
[Last Edit: 2/14/2013 5:09:05 PM EDT by SuperJanitor]
OK, here is the trace of the 150 watt inverter, no load


Here is the 10:1 wall wart


Here is the trace out of the wall wart, no load.

A little bit of change. The peaks are slightly ramped.

Link Posted: 2/14/2013 5:08:45 PM EDT
Originally Posted By SuperJanitor:
OK, here is the trace of the 150 watt inverter, no load
http://i46.tinypic.com/20iji8m.jpg

Here is the 10:1 wall wart
http://i48.tinypic.com/21mucfq.jpg

Here is the trace out of the wall wart, no load.
http://i47.tinypic.com/1zbze2v.jpg

A little bit of change. The peaks are slightly ramped.



calibrate your shitty probe!



Link Posted: 2/14/2013 5:13:05 PM EDT
Originally Posted By xwarp:
Originally Posted By SuperJanitor:
OK, here is the trace of the 150 watt inverter, no load
http://i46.tinypic.com/20iji8m.jpg

Here is the 10:1 wall wart
http://i48.tinypic.com/21mucfq.jpg

Here is the trace out of the wall wart, no load.
http://i47.tinypic.com/1zbze2v.jpg

A little bit of change. The peaks are slightly ramped.



calibrate your shitty probe!




It looks ok when on on the calibration terminal. They are cheap probes though.
Link Posted: 2/14/2013 5:41:00 PM EDT
Originally Posted By SuperJanitor:
A little bit of change. The peaks are slightly ramped.


Run it through 87 cascaded transformers, and viola - no more square wave!

Link Posted: 2/16/2013 12:54:13 PM EDT
Chained a few inductors together and ran it through again, no appreciable difference.
Link Posted: 2/16/2013 12:58:58 PM EDT

Originally Posted By SuperJanitor:
Originally Posted By Skibane:
Most isolation transformers don't have a super-wide frequency response, since they're just designed for 60 Hz.

The "modified" square wave produced by most MSW inverters has some pretty fast rise times (i.e., high frequency components or harmonics).

So, it's possible that you might see some rounding off of the square waves, due to the transformer attenuating some of the higher harmonics.


I'm inclined to agree with this, but Keith J should be along shortly!


ETA, I don't have an isolation transformer, but I do have a 10:1, 12 VAC wall wart. I might scope that when I get a chance, just for chits and grins.

Nailed it.

In the o-scope traces, it looks like this is a square wave AC, not a MSW. Meaning there is no intermediate voltages, just rail to rail switching.
Link Posted: 2/16/2013 1:06:50 PM EDT
Originally Posted By SuperJanitor:
OK, here is the trace of the 150 watt inverter, no load
http://i46.tinypic.com/20iji8m.jpg

Here is the 10:1 wall wart
http://i48.tinypic.com/21mucfq.jpg

Here is the trace out of the wall wart, no load.
http://i47.tinypic.com/1zbze2v.jpg
A little bit of change. The peaks are slightly ramped.


Very informative. I would have thought that a small transformer would be a much better lowpass filter than that.z
Link Posted: 2/16/2013 1:22:08 PM EDT
Originally Posted By zoom:
Originally Posted By SuperJanitor:
OK, here is the trace of the 150 watt inverter, no load
http://i46.tinypic.com/20iji8m.jpg

Here is the 10:1 wall wart
http://i48.tinypic.com/21mucfq.jpg

Here is the trace out of the wall wart, no load.
http://i47.tinypic.com/1zbze2v.jpg
A little bit of change. The peaks are slightly ramped.


Very informative. I would have thought that a small transformer would be a much better lowpass filter than that.z
It might behave very differently under a modest load.

Link Posted: 2/16/2013 1:26:13 PM EDT

Originally Posted By webtaz99:
Originally Posted By zoom:
Originally Posted By SuperJanitor:
OK, here is the trace of the 150 watt inverter, no load
http://i46.tinypic.com/20iji8m.jpg

Here is the 10:1 wall wart
http://i48.tinypic.com/21mucfq.jpg

Here is the trace out of the wall wart, no load.
http://i47.tinypic.com/1zbze2v.jpg
A little bit of change. The peaks are slightly ramped.


Very informative. I would have thought that a small transformer would be a much better lowpass filter than that.z
It might behave very differently under a modest load.


A resistive load. It would go bonkers under any inductive load.
Link Posted: 2/16/2013 1:31:41 PM EDT
I'd like to see a 1:1 transformer on the scope. Wonder how different it would be.
Link Posted: 2/16/2013 2:35:00 PM EDT
[Last Edit: 2/16/2013 2:46:38 PM EDT by SuperJanitor]
OK, I wanted to put a 100 watt incandescent bulb on the inverter for a load, but unfortunately, my bench PS won't supply enough current. That would be roughly a 67% load.

What I did do was to light both filaments of an 1157 bulb with the 12 VAC wall wart plugged into the inverter. Here is the trace under that load.




Maybe I'll disconnect my tractor battery sometime and hook the inverter up to it and scope it under the 100 watt resistive load.


ETA, the power trace looks nice and uniform over the whole waveform under load.

Almost looks like a kindergartner's rendition of an FBI silhouette
Link Posted: 2/16/2013 2:56:22 PM EDT

Originally Posted By SuperJanitor:
OK, I wanted to put a 100 watt incandescent bulb on the inverter for a load, but unfortunately, my bench PS won't supply enough current. That would be roughly a 67% load.

What I did do was to light both filaments of an 1157 bulb with the 12 VAC wall wart plugged into the inverter. Here is the trace under that load.

http://i48.tinypic.com/2rcltvs.jpg


Maybe I'll disconnect my tractor battery sometime and hook the inverter up to it and scope it under the 100 watt resistive load.


ETA, the power trace looks nice and uniform over the whole waveform under load.

Almost looks like a kindergartner's rendition of an FBI silhouette

Almost looks like field saturation in the transformer. Almost as if a capacitor might be a better smoothing element to quell the hard on switching.
Link Posted: 2/16/2013 5:38:38 PM EDT
[Last Edit: 2/16/2013 6:43:30 PM EDT by LePew]
The problem with trying to filter is that you're attempting to remove odd harmonics of 60 Hz from the waveform. If you remove them that energy has to go somewhere. The inverter won't like it very much if you bounce them back at it, I suspect. (ETA: as KeithJ says "go bonkers"). Some will be dissipated in your transformer which will cause it to heat up. This is actually one of the reasons some devices don't like anything but sine waves-they can't pass the energy through and so they overheat.

Some devices don't care whether it's modified sine or even square wave. Switch mode power supplies (like a laptop charger) don't care usually.

Link Posted: 2/16/2013 6:02:48 PM EDT
I think I'll plug a small fan into the inverter in addition to the light bulb also to see what an inductive load looks like.
Link Posted: 2/17/2013 8:26:41 AM EDT
Here is a 100 watt load from an incandescent bulb


Here is an inductive load from a fan


Here is a video of the fan starting up.
View My Video

I was hoping to see the inrush on the scope, but it was pretty unremarkable. A refrigerator on the other hand may show something more substantial, but the inverter wont handle it.

Notice how the power is largely missing from the vertical portions of the trace. I think Keith J was right about the little transformer being saturated.
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