Modified sine wave vs pure sine wave inverter

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i was desigining a simple ( simple as in no MPPT) PV-pump standalone system, and we decided on using an AC-pump, so while i was searching for inverters i noticed the remarkable difference in price ranges, so i started to read about the difference between the two, so far the disadvantages of the modified sine wave i found online is the relatively high THD (around 22%) and the issue with devices using 0 crossings for timing for example.
my question is: is there any other problems i should i be aware off , even if it's not related to the pump application, i want to know just in case i want to use it in any future application.
one particular thing i had in mind is the steep rise in voltage, the one pointed in the picture, is that wave form will be the same in real life, or is this just an ideal form. If this is real, will this high dV/dt cause any trouble?
 

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anorlunda
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If it causes a problem it would be overheating in the pump's motor. However, if the pump power is not close to the motor's rated power, then heating is probably less of a problem. I'm thinking that a 1/2 HP pump probably has a 1 HP motor rather than a 1/2 HP motor just to stay away from the limit, and because it doesn't cost that much more.

If you have no controller at all, then make sure that you're in the neighborhood of the MPPT point anyhow in both bright sunlight and on cloudy days. Extremes in voltage or current don't use your panels efficiently. The point is the knee of the curve.

Solar-Cell-IV-curve-with-MPP.png
 

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  • #3
davenn
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my question is: is there any other problems i should i be aware off , even if it's not related to the pump application, i want to know just in case i want to use it in any future application.

yes, just be aware of what you are connecting the inverter to ... not all equip likes a rough square wave (mod-sine).
They must be supplied with a true sine wave AC voltage.
If you had a piece of equip you wanted to use with the mod-sine inverter, just do some research to make sure it can handle it


Dave
 
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sophiecentaur
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simple as in no MPPT
Are you really so limited in your available money for this project? I can't find any mention of the ball park figure for the power you are dealing with - except for the example @anorlunda gave. The actual figures are very relevant in almost any Engineering project on any scale.
 
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Really not too many details given, but - some VFDs ( Variable frequency motor drives) allow for a DC input. You do not mention what your solar set up is, but this may the say to go as starting a pump / motor against a regular inverter's output can be difficult.
 
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jim hardy
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one particular thing i had in mind is the steep rise in voltage, the one pointed in the picture, is that wave form will be the same in real life, or is this just an ideal form. If this is real, will this high dV/dt cause any trouble?

An induction motor ought to tolerate that waveform. It's inductive so will smooth out the current wave somewhat.
Beware of non-dimmable LED or CFL light bulbs with that voltage wave - it resembles a dimmer.

See if your pump motor has a "NEMA KVA Code" letter.
Induction motors draw several times rated current during startup. 5x is not unusual and 10x is not unheard of.. the code letter tells you what to expect.
Check your proposed inverter's datasheet carefully to make sure you're buying enough 'oompf' to start your motor.

upload_2018-2-11_19-43-35.png

table courtesy these guys https://www.engineeringtoolbox.com/locked-rotor-code-d_917.html



old jim
 

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