Pulse-Wave Smoother?

Given an old inverter with single, vertical rise pulse wave, (no step wave feature which was popular later), with intervals of 0 volts or so....

Would a surge capacitor help smooth out the wave or reduce the harmonic content? Thus reducing stress to plugged in electronics?

Thanks for any opinions or insights.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,730 admin
    Re: Pulse-Wave Smoother?

    There is no practical way of filtering a MSW (modified square wave) type inverter (that I know of) and have a reasonable TSW (true sine wave) output for your loads.

    Sometimes, adding a second load (like a filament light bulb) may stabilize the output enough to run some equipment (sometimes useful on gensets)--but that is a waste of power.

    If you need TSW for running your smaller electronics (wall mount transformers, computers, devices with timers, embedded motors, etc.)--Get a small (and less expensive) TSW to run those loads and use the inexpensive large TSW to run your power tools, large lights, etc.

    All About Inverters
    Choosing an inverter for water pumping

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Pulse-Wave Smoother?

    one of the problems with filtering the square wave of the older msw inverters, and even many of the newer ones, is that there is a great deal of power held within those harmonics that would need to be dissipated by the filter. most filters won't dissipate very much power and if it does it can lead to a short life for the components in the filter.
  • RCinFLARCinFLA Solar Expert Posts: 1,280 ✭✭✭
    Re: Pulse-Wave Smoother?

    You can damage a MSW inverter putting a large cap, like a motor run capacitor, on output.

    The capacitor will increase the rise and fall time of the output MOSFET's causing them to get hot. There will be a high surge in current on each transition as the cap is charged and reverse charged.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Pulse-Wave Smoother?

    Trying to "improve" the quality of the output of a modified squarewave inverter is a futile waste of time,money and effort,, And is likely to do a lot more harm than good.. Save your money sell the MSW and buy a REAL sine wave inverter if you really need one.. end of story..:cool:
  • soulersouler Registered Users Posts: 12
    Re: Pulse-Wave Smoother?

    Thanks people. I really appreciate the cautionary emphasis. Well, i doubt it is wise trying to sell it, to some unwitting soul. I'll figure it must be fine to run bunches of incandescent bulbs and some compact fluorescents.... I might occasionally have this need where i do some lighting in remote, big tent celebrations. Where background noise interferes with environmental soundscapes. (This part involves already existing fixtures, not some dream package of LEDs run straight off batteries). Even one such job pays for losses.

    My hold up on the inverter choice is to choose between a 1100w version or a 2000w. Where most of the time 1100w is plenty and where once in a blue moon, i might need to fill water tanks. My wife can't start generators, in case i'm working far away. From what i gather, a 1100w inverter might or might not start up a typical 240 VAC (4-5 amps average running) well pump. While a 2000W inverter might still just barely start the pump on four 225AH, well connected batteries. Ideas here? Thanks a million, as usual, to the wizards here.
  • BB.BB. Super Moderators, Administrators Posts: 29,730 admin
    Re: Pulse-Wave Smoother?

    Be careful when powering "inexpensive" things like LED's and some small electronics (like some battery chargers for electric drills, etc.) with MSW inverters.

    They may use a capacitor as a "ballast" or other simple regulator circuits that the MSW (modified square wave) will just wipe out.

    Regarding motors, they can take upwards of 5x their rated current when starting. Possibly adding a VFD (variable frequency controller for 3 wire or 3 phase motors) can add soft start--But running one of those off a MSW inverter may have its own issues too.

    If water is critical, and it sounds like it is, you might need to look at an electric start genset... A Honda eu3000i or one of the Yamaha's may be a good solution. Depending on your specific needs--you may need a backup genset anyway if you run a streak of cloudy/bad weather, have heavy loads in hot weather with a grid outage, water for fire fighting, etc...

    Do you have an alternative fuel (such as propane or natural gas) available?

    You might find a nice Onan type genset at an RV wrecking yard for reasonable money too.

    In the end, there is no "cheap" alternative power for off-grid/emergency backup power usage. "High" upfront costs, maintenance, fuel storage, battery replacements, electronic inverters/chargers that last 10-15 years or so before they need replacement, etc. all hurt.

    That is why we recommend conservation / spending money on low power DC capable pumps, etc.... The more you can reduce your electrical needs, the less you need to spend for your emergency power systems.

    If water is critical for your needs, and you have a cistern/storage pond... A nice compromise may be a DC pump motor that can run directly from solar panels. Basically, let the pump run whenever the sun is up and save you money the 99% of the time when you have grid power available by keeping your surface water storage bulked up... And use a smaller pump for irrigation supplied from storage that is powered by your battery bank/genset.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 8,471 ✭✭✭✭✭
    Re: Pulse-Wave Smoother?
    souler wrote: »
    ....
    My hold up on the inverter choice is to choose between a 1100w version or a 2000w. Where most of the time 1100w is plenty and where once in a blue moon, i might need to fill water tanks. My wife can't start generators, in case i'm working far away. From what i gather, a 1100w inverter might or might not start up a typical 240 VAC (4-5 amps average running) well pump. While a 2000W inverter might still just barely start the pump on four 225AH, well connected batteries. Ideas here? Thanks a million, as usual, to the wizards here.

    Starting surge for a well pump is at least 4-8 times running, for about 3 seconds. And it all depends on your well depth and pump motor size.
    Most inverters are only 120V, not 240.
    Maybe a 2,000W inverter will work, maybe not, best to test ahead of time, and also have a class on starting generator, if wife gets thirsty and drinks all your beer, what will YOU drink when you finally get home?
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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