PWM Inverter

CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
what is a PMW inverter, is it MSW or PSW?

this PMW inverter claims to be able to run motors and household appliances with a high startup surge:

http://www.tripplite.com/en/products/model.cfm?txtModelID=182

here is a summary:

Continuously supplies up to 2400W of 120V AC power to 2 AC outlets from any 24V battery or automotive DC source. Frequency control locks AC output at 60Hz for operating stability of motor loads. Includes a set of high current DC input terminals for simple, permanent installation. Highly reliable large transformer design specializes in powering motors and other inductive loads with high-current startup needs.
«1

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Apparently I can't see the page right for there doesn't appear to be "PMW" anywhere in what I can see.

    Nor do I see any mention of pure or true sine wave, but if they're claiming it's for motors it shouldn't be MSW - no matter how big the transformer.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Aha! Got the site to work and found the magical mystery phrase: "Maintains PWM sine wave output voltage of 120 V AC (+/-5%)"

    Since "PWM" means Pulse Width Modulation around here, this makes no sense whatsoever as that doesn't apply to waveform.

    Maybe it means something else? Like they had trouble translating from Chinese? :roll:
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    this is the only description i can find:

    Output voltage regulation Maintains PWM sine wave output voltage of 120 V AC (+/-5%)
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Went searching for further info.

    Apparently it is a misleading term meant to dupe the unwary into buying product that is unsuitable. :roll:
    In other words, it is modified square wave with a twist in that the various steps up in Voltage are varied in width to more closely simulate a true sine wave. Better than an ordinary MSW but it is not a sine wave.
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    ^^^ thanks, that is what i thought, better than MSW but not as good as PSW... I don't think this is chinese junk...
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Lots of stuff is made in China that isn't junk, but translations can still be a problem.

    I'd want to see a scope of the waveform before buying. That probably wouldn't happen.
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    here is a pretty detailed writeup on amazon:

    http://www.amazon.com/Tripp-Lite-PV2400FC-Inverter-Charge/dp/B00006HNTE/ref=sr_1_45?ie=UTF8&qid=1336697350&sr=8-45

    A frequency control feature ensures that devices dependent on tightly regulated AC line frequency, such as computers, VCRs and DVD/CD players, receive clean computer-grade power.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Almost all computer power supplies can take really poor input power without trouble. Likewise, regulating frequency even on a MSW isn't too difficult. The big issue with AC induction motors is the actual waveform, because it plays a roll in how the magnetic fields are formed (shaped) in the motor and thus how they interact.

    Definitely this would be better than some of the primitive MSW inverters. Some are just square wave, some have three steps, some have a lot more, et cetera.

    I'd like to see pics of the waveforms from lots of them. It would be interesting.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: PMW Inverter

    Believe it or not those Tripp Lite inverters are not bad. They are the ideal low frequency design. Much better for starting up motors . They will run motors ok and will run a fridge no problems.
    I n fact such designs are usually better than some of the lightweight "sine wave inverters"
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Re: PMW Inverter

    I found a Tripp Lite product line glossy and they talk about "pure sine wave" or "sine wave" product. They only have a few (medical grade and these two: APS1012SW, APS2012SW) that seem to be "pure sine wave"... The others appear to be MSW.

    We here have been pushing the TSW/PSW inverters because of reliability for off grid equipment and you can plug "anything" into them.

    With MSW you need to check that your equipment will run OK on the modified square wave output (check for overheating, strange behavior, electronic timers that don't work correctly, etc.)... Probably 80% of the equipment will work OK on MSW and 10% will have a very short life... The problem is to figure out which product is in which category. Small transformers tend to overheat, motors can run hot--But if the motor is oversized for the load--probably OK. Sealed motors (like refrigerator compressors--some may work fine, others may not).

    For those new to the discussion, here are a couple of nice FAQs:

    All About Inverters
    Choosing an inverter for water pumping

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Unfortunately they don't let you "try before you buy" with this sort of thing. :roll:

    I'll take john_p's word on this, as he knows a lot about various types of equipment and designs. It makes sense with my quick analysis.

    But I think it should be called Pulse Width Modulated Square Wave, as it is not a sine wave. Looks like a deliberate attempt to mislead because they know the buying public has caught on to "sine wave is better".
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    thanks for your help guys, looks like that Tripp Lite is what I was looking for... I am going to use a smaller PSW for the computers/tv/cell phone charging, then this larger PWM inverter for the washing machine, small window a/c, power tools, and coffee maker...

    i have read elsewhere that the Tripp Lite is a decent box if you are looking for MSW, so thanks for the confirmation...
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PMW Inverter

    as was said the tripplite is still a modsine inverter. if the total harmonic distortion (thd) is under 5% then it is considered sine wave and meets the minimum specs that utilities must also meet. if they fail to list a thd then assume it is a modsine and not suitable for inductive loads like washing machines and a/c units. i don't see tripplite listing the thd for that inverter. the washing machine, a/c, and power tools should be on a psw inverter and not this tripplite model.

    the computer and even the coffee maker along with items such as lights will do fine on modsine, but we frown on using any form of electric heat for it takes a great deal of power to produce that heat.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: PMW Inverter

    I will try give a semi technical explanation about inverters like the Tripp Lite. All low cost MSW inverters and sinewave inverters are what are best described as high frequency inverters. Meaning all the switching is done at a high frequency. The reason is cost. It uses very little copper wire to make a high frequency fransformer. But dont confuse this high frequency with the output frequency of 50 or 60hz.
    Low frequency inverters are about 50 to 100% more expensive. Mostly because of the very heavy copper in the transformer. There are other things also that increase to cost.
    Here is a simple but not totally correct explanation of the working differences.
    Lets use an ICE engine comparison between a 100kw 1litre engine and a 100kw 6 litre engine
    If each put into a 2 ton vehicle the 1 litre engine (low torque)will have a hard time getting that weight moving but the 6 litre engine (high torque)will do it easily(assume identical gearing) but both will reach about same top speed.
    Now the high frequency inverter has a high output impedance so lacks "torque" to get a motor started the low frequency inverter has "high torque" like your mains power point so can easily start a motor under load.
    The above explanation has faults I know that so dont bother to tell me. but I think it explains it well enough for most people.

    I have tested many Tripp Lite inverters and they really will work ok with any type of electric motor . Their output is close enough to being a sinewave .And their design gives very good motor starting ability. Its extremely unlikely any type of motor run from one would get any hotter or stressed than running from a sine wave inverter..

    I dont think they have tried to mislead people about what type they are. I think it is more how to say what they are simply. ie TSW or MSW are known terms but they dont quite fit either one ??Mabe im wrong? mabe its a Chinglish thing?

    All industrial battery inveters are designed the same way. Good reliability,good overload ability,.and few if any problems starting or running motors.
  • BB.BB. Super Moderators, Administrators Posts: 32,027 admin
    Re: PMW Inverter

    There is still, as far as I understand, of the non-fundamental frequencies (because of the "square edges") that has to go somewhere--typically into the motor/transformers as circulating currents--which ends up as waste heat.

    The reason I am still a bit uncomfortable with VFDs (variable frequency drives) is that they (I am guessing) still some sort of MSW type output. I have a friend that has some experiences with VFDs in machine shop and similar applications.

    He believes that motors do not last as long on VFDs, from his experiences (was not his main job--so there is always the sample size biases/issues)...

    In the end, probably 80% of "stuff" out there will work OK on MSW type inverters. Just run a little bit hotter which may cause small decrease in average life (the old every 10C rise in temperature causes a 1/2x decrease in life engineering rule of thumb).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    The situation here is that this particular inverter allegedly has its square wave "steps" modulated to the point where they are nearly identical to a true sine wave curve; within the 5% distortion of that curve which is considered acceptable.

    There's another problem which Niel pointed out and I agree with: it doesn't actually say this in the description. No mention of harmonic distortion. But it does say the Voltage is regulated to +/- 5%. Could that be a translation problem?

    I may be nit-picking linguistic semantics here. Possibly because I'm jaded from reading so many blurbs for cheap equipment from you-know-where that says things like "Best MPPT inverter for batteries from solar with AC" and such. :roll:
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: PMW Inverter

    I think you guys should dig out your silly scopes and wave form analyzers and have a look at what passes for "clean" sine waves from the grid and especially from most lower priced TSW inverters.
    You may find the waves look worse that what you get from low frequency PWMSW ??? inverters.
    Mabe this is the reason some peoples fridge motors last many years longer than others?? Suburbs with little or no industry and no large shopping centers tend to have cleaner power than those where there are commercial businesses and light industry.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    You're right on the money there, John. We've probably all seen utility power that wasn't good enough to feed a light bulb! :p

    I'm just getting too cynical, that's all. I want manufacturers to provide a picture of the output waveform with the specs. ;)
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PMW Inverter

    it doesn't matter the steps or methods as what i said holds 100% true, less than or equal to 5% thd is acceptable as sinewave. this means it can have a bunch of square wave steps with their harmonics and if within that spec it is considered sine wave. if that tripplite is that low in thd then it is acceptable as a sinewave inverter and that is at all load levels that the inverter will operate at and not just powering a scope's sampling.

    +/-5% voltage regulation is only the high and low the ac voltage will be seen at and if at 120vac this is 105% for 126vac (most likely no load) and 95% for 114vac (most likely at full rated power) and both are worst case.
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    so the +/- 5% voltage spec is not related to the THD?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter
    Caneman wrote: »
    so the +/- 5% voltage spec is not related to the THD?

    As it is stated, no.
    They don't list any THD number but John thinks it is clean enough to work and he knows what he's talking about. Perhaps Tripplite would respond to an inquiry about this?

    I'm just a hopeless cynic. ;)
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter

    I will check in to it with Tripp Lite and get back on it...

    edit: just sent tech support a question about % THD, if they don't respond I will call, they have a phone number for tech questions...

    "A confirmation of your request will be sent to the e-mail address you provided. Your confirmation will also include a case number. So we can provide fast, efficient handling of this request, please reference your case number in any future correspondence and phone calls. A Tripp Lite technical support specialist has been assigned to your case and will contact you within two business days by e-mail or phone to provide further assistance. If you require more immediate assistance, please contact Tripp Lite Technical Support at (773) 869-1234. We are available Monday through Thursday between 8:00 AM and 6:00 PM Central Time and on Friday between 8:00 AM and 5:30 PM Central Time."
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: PMW Inverter

    Cariboocoot there is a lot of reason to be a cynic about many electronic devices.
    When tested thoroughly many inverters from even so called"quality" manufacturesr are nowhere near as good as the hype that goes with them..
    China is not the only country that makes crap inverters, And it also makes some very good ones equal to some of the best available from other countries.
    Same goes for MPPT charge controllers. Many barely make it to be legally called MPPT.
    Most of the time for under 1000w systems you are better off with a PWM and buy an extra panel or larger sizes .
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: PMW Inverter
    john p wrote: »
    I think you guys should dig out your silly scopes and wave form analyzers and have a look at what passes for "clean" sine waves from the grid and especially from most lower priced TSW inverters.

    It's a shame all manufacturers don't do this, but I've put all my inverters on a scope.

    Here's a sample of the waveform from a $29 Vector 400W inverter:

    scope.jpg

    Typical MSW. I used two of these to run the indoor and outdoor lighting at my last home for a couple of years. Worked flawlessly with CFL lighting. Also used it as a power source for charging my laptop computer when on the road. Still have these as backups.

    Here's the output from my Xantrex Prosine 1800W inverter:

    1609.jpg

    Here's the output from the GRID at my last house:

    grid1634.jpg

    Note the noise at the top/bottom of the waveform.

    Here's the output from my $349 Xantrex Prowatt SW2000 inverter:

    dscn4932.jpg

    That's about as cheap a PSW 1800W (continuous) inverter as you'll find, and the waveform looks pretty good to me.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PMW Inverter

    2manytoys,
    can you adjust the screen to show only about 1 cycle for each of those like the first one with a square wave output as this will show more detail on the makeup of the waves? i don't expect to see too much difference though. this would also show people here the many tiny steps the voltage does actually take in making up a good sine wave waveform.

    i should note that for many out there that if you superimposed a sine wave to the square wave that anything added to or subtracted from the sine wave that the square wave departs from it is considered distortion and is technically wasted power on many items to be run. that waste becomes heat and not usable power.
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: PMW Inverter
    niel wrote: »
    2manytoys,
    can you adjust the screen to show only about 1 cycle for each of those like the first one with a square wave output as this will show more detail on the makeup of the waves? i don't expect to see too much difference though. this would also show people here the many tiny steps the voltage does actually take in making up a good sine wave waveform.

    Not a problem. My personal budget doesn't allow me to own anything other than an old Tektronix o-scope. The NICE one pictured belongs to my employer. I'll borrow it again before long, and capture single cycles.

    Not to get too far off topic, but I'm amazed by how many UPS units there are, and "most people" have no clue what the waveforms look like that's feeding their sensitive electronics when the grid goes down. Most of mine now are PSW. Prior to that, mine were all MSW. I even found some with square wave.

    upspanel.jpg

    upswaveform.jpg

    It's hardware like this that makes me test everything. It would have been easy to look at the name brand, and assume the waveform was above par.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: PMW Inverter

    is that the waveform of that tripplite? yikes.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: PMW Inverter

    Looks a lot like my last EKG. :p
  • 2manytoyz2manytoyz Solar Expert Posts: 373 ✭✭✭
    Re: PMW Inverter
    niel wrote: »
    is that the waveform of that tripplite? yikes.

    Same response I had!
  • CanemanCaneman Solar Expert Posts: 71 ✭✭✭✭
    Re: PMW Inverter
    2manytoyz wrote: »
    Same response I had!

    That is the Tripp Lite UPS, but is it the same type of wave form as the Tripp Lite PWM Inverter?
Sign In or Register to comment.