Posted by ads on April 4, 2019, 10:40 am
On Tue, 02 Apr 2019 14:47:18 GMT, Johnny B Good
>On Sat, 30 Mar 2019 08:12:55 -0500, ads wrote:
>
>====snip====
>
>>
>> The power the co-op delivers isn't as clean as that delivered by the
>> 2000 watt pure sine wave inverter on my solar-charged "Wait until
>> daylight" backup power system that can provide 10 to 24 hours of limited
>> power (fridge, furnace, some LED lights, internet) depending on the
>> season. The AC waveform was checked with a battery powered scope in an
>> all-plastic case so it's totally isolated. The co-op power has a slight
>> jog on the trailing edges of the peaks (positive and negative).
>>
>
> If you're trying to describe the flat topped peaks[1], typical of
>utility power worldwide, that's just the result of all the countless
>smpsus used in TV sets and desktop computers and USB wallwart chargers
>and laptop charging bricks and... well, let's just say there's a hell of
>a lot of mains powered kit that rectifies the mains supply to generate
>whatever dc voltages are needed (whether it be directly at full mains
>voltage or on the low voltage secondary of a stepdown isolating
>transformer such as an old school battery charger.
>
> Yes folks! Even ancient 70 year old battery chargers assaulted the mains
>supply with narrow conduction angle rectified current pulses which causes
>this 'flat topping' effect. It was just that, back in the day, such loads
>were in the minority.
>
> This flat topped appearance of the mains supply waveform has been
>present on utility supplies for well over three decades to my knowledge
>and probably existed to a lesser degree ever since the whole world and
>their dog started watching TV as a national pastime.
>
> The advent of the home computer and subsequent electronic gadgetry has
>no doubt exacerbated this situation to the point where this "Signature
>wave trace" can now be relied upon to identify when you're running off
>utility power rather than from a UPS or standby generator source.
>
>[1] You may notice a downward slope on the 'flat tops' on the positive
>peaks of each cycle of mains voltage and mirrored in the negative peaks.
>This is the high pass filtering effect when using the AC coupling option
>on a 'scope or else seen in audio recordings made from a low voltage
>mains transformer winding (6.3v heater voltage winding attenuated down to
>the hundred millivolt level to avoid overloading your sound card's line
>input buffer, for example).
>
> Selecting DC coupled, will reveal the true wave shape, an option I
>didn't have with my 5MHz BW boat anchor CRO nor with my CoolEdit Pro
>recordings of mains voltage supplied by my generator and pure sine wave
>UPS to compare against the utility supply, until I finally treated myself
>to a brand new DSO some five months ago.
Link to picture of scope screen:
http://www.jecarter.us/files/co-op-AC.jpg
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
>..............
> Link to picture of scope screen:
> http://www.jecarter.us/files/co-op-AC.jpg
>
> 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.
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"
><ads> wrote in message
>>..............
>> Link to picture of scope screen:
>> http://www.jecarter.us/files/co-op-AC.jpg
>>
>> 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.
>
>Does it have single sweep triggering good enough to capture a motor
>starting current surge?
>
>
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
converter).
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:
> On Tue, 02 Apr 2019 14:47:18 GMT, Johnny B Good
>
>>On Sat, 30 Mar 2019 08:12:55 -0500, ads wrote:
>>
>>====snip====
>>
>>
>>> The power the co-op delivers isn't as clean as that delivered by the
>>> 2000 watt pure sine wave inverter on my solar-charged "Wait until
>>> daylight" backup power system that can provide 10 to 24 hours of
>>> limited power (fridge, furnace, some LED lights, internet) depending
>>> on the season. The AC waveform was checked with a battery powered
>>> scope in an all-plastic case so it's totally isolated. The co-op
>>> power has a slight jog on the trailing edges of the peaks (positive
>>> and negative).
>>>
>>>
>> If you're trying to describe the flat topped peaks[1], typical of
>>utility power worldwide, that's just the result of all the countless
====snip====
>>[1] You may notice a downward slope on the 'flat tops' on the positive
>>peaks of each cycle of mains voltage and mirrored in the negative peaks.
>>This is the high pass filtering effect when using the AC coupling option
>>on a 'scope or else seen in audio recordings made from a low voltage
>>mains transformer winding (6.3v heater voltage winding attenuated down
>>to the hundred millivolt level to avoid overloading your sound card's
>>line input buffer, for example).
>>
>> Selecting DC coupled, will reveal the true wave shape, an option I
>>didn't have with my 5MHz BW boat anchor CRO nor with my CoolEdit Pro
>>recordings of mains voltage supplied by my generator and pure sine wave
>>UPS to compare against the utility supply, until I finally treated
>>myself to a brand new DSO some five months ago.
>
>
> Link to picture of scope screen:
> http://www.jecarter.us/files/co-op-AC.jpg
>
> 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.
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
> On Thu, 04 Apr 2019 05:40:55 -0500, ads wrote:
>
>> Link to picture of scope screen:
>> http://www.jecarter.us/files/co-op-AC.jpg
>>
>> 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.
>
> 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
The input voltage ramps up as the rectifier current decreases.
https://electronics.stackexchange.com/questions/51320/how-to-calculate-real-power-and-power-factor-using-an-oscilloscope
XML site map
>
>====snip====
>
>>
>> The power the co-op delivers isn't as clean as that delivered by the
>> 2000 watt pure sine wave inverter on my solar-charged "Wait until
>> daylight" backup power system that can provide 10 to 24 hours of limited
>> power (fridge, furnace, some LED lights, internet) depending on the
>> season. The AC waveform was checked with a battery powered scope in an
>> all-plastic case so it's totally isolated. The co-op power has a slight
>> jog on the trailing edges of the peaks (positive and negative).
>>
>
> If you're trying to describe the flat topped peaks[1], typical of
>utility power worldwide, that's just the result of all the countless
>smpsus used in TV sets and desktop computers and USB wallwart chargers
>and laptop charging bricks and... well, let's just say there's a hell of
>a lot of mains powered kit that rectifies the mains supply to generate
>whatever dc voltages are needed (whether it be directly at full mains
>voltage or on the low voltage secondary of a stepdown isolating
>transformer such as an old school battery charger.
>
> Yes folks! Even ancient 70 year old battery chargers assaulted the mains
>supply with narrow conduction angle rectified current pulses which causes
>this 'flat topping' effect. It was just that, back in the day, such loads
>were in the minority.
>
> This flat topped appearance of the mains supply waveform has been
>present on utility supplies for well over three decades to my knowledge
>and probably existed to a lesser degree ever since the whole world and
>their dog started watching TV as a national pastime.
>
> The advent of the home computer and subsequent electronic gadgetry has
>no doubt exacerbated this situation to the point where this "Signature
>wave trace" can now be relied upon to identify when you're running off
>utility power rather than from a UPS or standby generator source.
>
>[1] You may notice a downward slope on the 'flat tops' on the positive
>peaks of each cycle of mains voltage and mirrored in the negative peaks.
>This is the high pass filtering effect when using the AC coupling option
>on a 'scope or else seen in audio recordings made from a low voltage
>mains transformer winding (6.3v heater voltage winding attenuated down to
>the hundred millivolt level to avoid overloading your sound card's line
>input buffer, for example).
>
> Selecting DC coupled, will reveal the true wave shape, an option I
>didn't have with my 5MHz BW boat anchor CRO nor with my CoolEdit Pro
>recordings of mains voltage supplied by my generator and pure sine wave
>UPS to compare against the utility supply, until I finally treated myself
>to a brand new DSO some five months ago.