Modified sinewave to pretty good sinewave?

[Harald Kapp]

Mind if I ask what program/app/simulator you did this with?

This was done using LTSPICE (free) from Analog Devices (formerly Linear Technology, hence LTSPICE)

 

[HANKMARS]

This was done using LTSPICE (free) from Analog Devices (formerly Linear Technology, hence LTSPICE

Thank you. In the simulation you were considerably more generous with the waveform shoulders than my inverter. The attachment is a very near replication of power out.

 

[crutschow]

I am working with will power an 1100 W microwave oven and a 1000 W toaster oven. Not simultaneously of course. The toaster oven will be fine I'm sure but I am concerned that the long duration of peak voltage will burn transformer windings. Do you consider that a valid concern?

Microwaves normally aren't operated for more than a few minutes at a time, so that may be okay.
Measuring the microwave current/power with both the mains sinewave and the inverter will tell you if it is drawing excess current with the inverter waveform.
A power measuring device, such as the Kill-A-Watt, is very handy for this purpose.

Can you measure the output voltage of the inverter with a "true RMS" meter (a meter labeled as such)?

 

[crutschow]

The attachment is a very near replication of power out.

Can you approximate some times for the various step levels?

 

[roughshawd]

Mosfet amps and PWM give off two differn't signal sets...
yer sine wave is not such a good idea cause it's not respected as a proper circuit in electronic brain cavities..
If a true sine wave is what you are talking about, well it is a signal that will fry everything if allowed to go on its' own.

PRO RULE OF THUMB... STAY AWAY FROM SINE WAVES!

This is why electronic musical instruments are sucking hind tit... You should know that PWM is what they came up with to replace the sine. left hand rule ===> ^|^^ <=== other rules not included in this study.

 

[roughshawd]

About your off grid sitrep---- The type of power you want is power that is created, not power that exists in gravity or otherwise... the day off grid starts between 7 and 9 and requires constant care. "TV and Movies" are considered the 'highest' on the list of un-needed entertainment. You will need a popcorn popper, so start there. When the genset gives out, you hope its daylight, the weather is good and you have a spare, or a backup plan that works. Has little to do with PWM and MIDI...

 

[crutschow]

PRO RULE OF THUMB... STAY AWAY FROM SINE WAVES!

I have absolutely no idea what you are rambling on about.
Makes no sense.
Standard AC mains power is a sinewave.

 

[crutschow]

Also can you provide the measured voltage at each step of the quasi-sinewave?

I did some simulations for a 4-step quasi-sinewave with equal 1/3 voltage steps, and with 1/2 time at the peak and 1/4 time at each step (below).
For the same RMS voltage value, the peak voltage of the quasi (green trace) was 5% below the sinewave (yellow trace), and the currents into equal value inductors (simulating a transformer load magnetizing current) were within 1% of each other (quasi--red trace and sine--blue trace).

This indicates to me that a properly configured 4-step quasi-sinewave should work okay with transformer powered appliances, and likely work properly with most electronics.

 

[HANKMARS]

Microwaves normally aren't operated for more than a few minutes at a time, so that may be okay.
Measuring the microwave current/power with both the mains sinewave and the inverter will tell you if it is drawing excess current with the inverter waveform.
A power measuring device, such as the Kill-A-Watt, is very handy for this purpose.

Can you measure the output voltage of the inverter with a "true RMS" meter (a meter labeled as such)?

I do have a kill-a-watt meter. I found that it keeps the landlords a little more honest. I do not have a true RMS meter. I will scope inverter output and include it in an attachment.

 

[HANKMARS]

Can you approximate some times for the various step levels?

Glad you asked. The following attachments are 1. Inverter power out. It appears that this inverter has been seriously damaged. Scope setting is 5 V per division. The signal is about half right. The high side shows +10 V. Low side looks like about -7 V. Also 0 V has been dragged down about 5 V. Maybe the Metal Oxide gate has burned shorted. I am not sure. I just discovered this situation. 2. This is a figure directly from the owners manual. Modifying this inverter is not currently an immediate concern until I repair this unit, if I'm able. I bring power to my inverters directly from the battery bank and not thru the charge controller. That may not be such a hot idea and may have contributed to this device's failure. The first charge controller I used was cheapo. At the moment I do not recall actual configuration I had but due to some shortcomings in cheapo design of charge controller, I think that my PV panel's no load voltage of ~36 V got presented to the power buses. Kind of frightening.

 

[HANKMARS]

Can you approximate some times for the various step levels?

Net connection flaky. Fortunately funky inverter pwr out from other day was faulty power cord. Here is actual waveform. 50 V per division, time base 5 ms per but skewed to get 2 cycles on display.

 

[HANKMARS]

Second attempt

 

[kellys_eye]

That's about as bad as a 'modified sinewave' can possible get! Only two steps (pos and neg!)

What does it look like under load?

 

[HANKMARS]

That's about as bad as a 'modified sinewave' can possible get! Only two steps (pos and neg!)

What does it look like under load?

The power out seems pretty stable. V/D = 50 V. A non-true RMS meter reads inverter voltage out as 100 VAC. Inverter supply voltage is 12 VDC. Photos: #1. Inverter Vout no load. #2. 6 Amp belt sander start up. #3. Belt sander free running. #4. Belt sander running loaded.

 

[HANKMARS]

Here is an update on my theory as it relates to my earlier suspicion that because of the long duration of the power wave supplied to a transformer primary winding, sitting at a constant voltage (modified sinewave), would induce a greater rise in temperature of the winding than normally occurs. That notion implies that if no energy is transferred from the primary to the secondary winding, the supplied energy needs to be dissipated solely by the primary winding. As I try to visualize the energy transfer of a sinewave which is not clipped and continues upward to the nominal peak voltage of a normal sinusoidal waveform, compared to a lower voltage sitting static, my conclusion that my theory is incorrect, keeps flip flopping from correct to incorrect to correct and in turn my personal little bag of gray matter is feeling a rise in temperature. Does anyone have a couple formulas on hand that will give the definitive solution to this quandary?

 

[HANKMARS]

The latest info I just heard about the overheating problem that seems to accompany the modified sinewave (modified square wave?) inverters is that when trying to "regulate" the ac voltage with a capacitor, this is when overheating is going to be quite obvious. Devices like a motor with a run capacitor, electric blankets, and so forth. I don't understand it fully but I somewhat understand the idea that a capacitor valve is calculated by its device's parameters and those calcs are based upon the power in being a sinewave. I'm losing momentum with the thot of making minor modifications to what is supplied by the non-sinusoidal inverters. That's ok, I'll use the one for devices which don't demand a good sinewave. I guess the days of a device's max ratings being able to exceed those ratings are gone. It seems if a device's max ratings can be used without failing, it is an atypical event today. Make it cheap is the landscape. Trash the failed unit and buy new. I would guess an economics savvy person would explain to me how repairable goods are bad for the economy.

 

[kellys_eye]

I would guess an economics savvy person would explain to me how repairable goods are bad for the economy.

Not so sure that theory will stick for too much longer! Given the supply chain issues and economic consequences I reckon 'repairs' will start making a comeback.

 

[HANKMARS]

Not so sure that theory will stick for too much longer! Given the supply chain issues and economic consequences I reckon 'repairs' will start making a comeback.

It is indeed a sad state of affairs. I think it was Switzerland that mandated the hours that one could charge their EVs and the electric cars are to be driven only in the case of extreme emergencies. Hopefully our paper currency will maintain a value greater than that of kindling and wall insulation. Think I'll go up to the attic and look for my old buggy whips.