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Posted by ads on April 4, 2019, 10:40 am
On Tue, 02 Apr 2019 14:47:18 GMT, Johnny B Good

Link to picture of scope screen:

Not a great picture but it shows the waveform.  It's a handheld shot
of a $0 DSO138 battery powered scope in a plastic case - not a very
bright screen - but with a 10:1 probe, it's a great little scope for
checking AC waveforms from line, inverter or generator.

Posted by Jim Wilkins on April 4, 2019, 11:09 am
<ads> wrote in message  

Does it have single sweep triggering good enough to capture a motor  
starting current surge?

Posted by ads on April 4, 2019, 11:15 pm
 On Thu, 4 Apr 2019 07:09:58 -0400, "Jim Wilkins"

Most of the Chinese sellers have the scope or a copy of it ;-)
The original company was JSY and here's a link to one listed as a JSY:
https://www.gearbest.com/testers-detectors/pp_009471063829.html?wid 33363#goodsDetail

You'll need the scope ($0), a case ($), a probe (BNC connector), a
source of 9 volts (I use a 5000mah USB powerbank with a 5=>9 boost

It's a very basic scope with triggered, free run and one shot modes
and 1 million samples/sec (12 bit).  The one shot might work to catch
the motor start surge but the speed may not catch the full pulse - I
haven't tried that yet although it's on my list of things to check. If
doing that, I'd trigger the scope with the power to the motor and the
(very short) time for the ramp up of the motor might be enough delay
to capture the motor's spike.  Having storage means you can keep a
trace up a long time.  On the other hand, 12 bits of resolution might
not be enough for some things.

I'm usually more interested in how good the waveform is and how much
"garbage" can feed back on the AC line from the inverter.  I did some
inverter testing using a 300 watt halogen lamp with a dimmer (probably
triac) to generate "noise" and see how much the noise was damped by
each inverter.  The 2000 watt pure sine wave (PSW) inverter damps the
noise much better then the 500 watt PSW inverter - no surprise there.

The ideal thing for checking motor surge might be my Tek 4 channel,
100MHz scope but it's somewhat large to ensure the entire case is
insulated when I'm doing AC power work ;-)

Posted by Johnny B Good on April 5, 2019, 12:11 am
 On Thu, 04 Apr 2019 05:40:55 -0500, ads wrote:


 The trace is similar to what I was describing. However, it appears to be  
a reversed trace in that the sloped tops are inclined upwards going from  
left to right, the opposite of what you would normally see when using the  
AC coupled option on a 'scope.

Johnny B Good

Posted by Jim Wilkins on April 5, 2019, 5:07 pm
The input voltage ramps up as the rectifier current decreases.

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