Inverters Grrrrr.

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  • Panamretiree
    Panamretiree Solar Expert Posts: 278 ✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    Well, they say a picture is worth a thousand words. Only a good movie is deserving of popcorn. :D

    I could demonstrate this with the MSW inverter in our fifth wheel camper with that bench grinder. It would take a bunch of extension cords running from the camper to the shop to do it. LOL!
    --
    Chris

    So what are you doing between midnight and six in the morning, uninterrupted work time I would think.8)

    Cheers

    Ernest
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Inverters Grrrrr.
    NorthGuy wrote: »
    I searched for square waves and transformer pictures, and I found this document. Looks like a square wave put through a transformer remains a square wave with quite sharp edges - rise and fall time is only 5us. Certainly depends on the transformer, but it's not much of a smoothing by any means. They say that bad transformers would hava a slower rise and fall time at the edges.

    Transformer is certainly different from an inductive load. If no load is connected on the other end, it doesn't consume any power. When you connect a load to the secondary, I think the power factor on the primary should be the same as if the load was connected directly without a transformer (assumong it was 1:1 transformer). So that if you connect a heater to the secondary, the whole system will have power factor close to 1. If you connect a motor, you get a power factor of 0.6 or so.

    That's what I always believed, but I must confess I never could get a good understanding of the transformers.
    Close, but....

    1. The square wave you see coming out is a good indication that the transformer has a good frequency response and low phase shift at the higher harmonics. It is also possible to deliberately design a transformer that does not couple the high frequencies as well.
    2. The unloaded transformer is exactly an inductor (with an iron core). With no load there will be an "idling" or "magnetizing" current which depends on both voltage and frequency and has a power factor close to zero. As you add resistive load, the PF moves closer to 1 since the transformed load current will be purely resistive and increase with decreasing load resistance but the idling inductive current will not change in magnitude. For a very good transformer, the idling current will be low, but for an efficiently sized transformer it can get pretty high. A small motor load with a PF of .6 might appear as .5 on the input side of the transformer, while a PF=.6 motor load at the full transformer rating power will look very close to PF=.6 on the input too.
    SMA SB 3000, old BP panels.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    BB. wrote: »
    But, you can have construction/material choices that will affect high frequency performance, etc.

    Yes, power transformers with laminated silicon steel core can't operate at the frequencies that audio transformers operate it. Audio transformers have to be designed for excellent frequency response. Power transformers are designed for best power factor at a specific frequency.

    I see inetdog already mentioned this in reply to NorthGuy, but yes a transformer is an inductor too. For very well designed transformers like the Outback PSX-240 the amount power it requires to keep the core magnetized is very, very low and it's barely detectable. But there are some solid ferrite core transformers where the idle insertion loss is pretty high and they actually get warm with no load on the secondary due to high hysteresis in the core.
    --
    Chris
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    For very well designed transformers like the Outback PSX-240 the amount power it requires to keep the core magnetized is very, very low and it's barely detectable.
    But just in case somebody was not reading that carefully enough, this is not the same as saying that the VA required is also barely detectable. If you have an inverter which does not handle low power factor loads gracefully, you could still end up eating up power in the inverter even if very little of it is ending up heating the transformer.
    SMA SB 3000, old BP panels.
  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    Re: Inverters Grrrrr.

    Interesting transformer discussion guys. I'm learning a lot.
    ChrisOlson wrote: »
    Yes, power transformers with laminated silicon steel core can't operate at the frequencies that audio transformers operate it. Audio transformers have to be designed for excellent frequency response. Power transformers are designed for best power factor at a specific frequency.

    Are you saying that audio transformers can't be made with laminated silicon steel cores?
    ChrisOlson wrote:
    Interesting thing about an auto-transformer; you can hook one up to a modified sine wave inverter and get almost (but not quite) pure sine wave output from the transformer secondary to neutral
    --
    Chris

    So what's the conclusion - is this true? Would be good to know if I could use my autotransformer this way in a pinch :confused:
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Inverters Grrrrr.
    mtdoc wrote: »
    So what's the conclusion - is this true? Would be good to know if I could use my autotransformer this way in a pinch :confused:

    As they say when selling cars, YMMV.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    Edit:
    Interesting thing about an auto-transformer; you can hook one up to a modified sine wave inverter and get almost (but not quite) pure sine wave output from the transformer secondary to neutral
    Aside from the slight logical problem of what constitutes the secondary in an autotransformer.....
    A more clear statement would be that the phase opposite the driven phase looks more like a sine wave.
    The 240 volts, being a combination of the two will look better than the input 120, but not as good as the opposite phase 120. So those of you with a 240 volt motor might even want to try it.
    SMA SB 3000, old BP panels.
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    mtdoc wrote: »
    Are you saying that audio transformers can't be made with laminated silicon steel cores?
    So what's the conclusion - is this true? Would be good to know if I could use my autotransformer this way in a pinch :confused:

    No, but the lamination in high freq transformers are very, VERY thin compared to power transformers. And some even use air cores. The flux leakage is too high with an air core transformer to use one for power purposes. But they work good in high freq applications like audio and radios because there's zero core loss and zero hysteresis.

    It is a beyond a doubt fact that a transformer or induction motor can help clean up a MSW inverter's output to make it more like pure sine. But like I said, that don't mean you're going buy a $30 Cobra inverter off the shelf at Walmart, put a small transformer on it and make it work any better (assuming the inverter will even handle the inrush of the transformer when you power it up). I have seen it done with the Trace DR-series inverters and the Trace transformer. Neither are junk stuff. I have personally done it with the AIMS 3 kW MSW inverter in our camper before, and with the 2 kW Schumacher inverter I have in my service truck. The one in the service truck won't start my portable air compressor, for instance. But I plug a hand held disc grinder into it and fire up the disc grinder, then it will start the air compressor.

    So yes, it is true. There are even other "tricks" you can use on off-grid power systems, like with my Lincoln welder I mentioned before - simply using a 100 foot 8 AWG extension cord plugged in the outlet in the wall and to the welder vs having the welder plugged directly into the wall outlet "softens" the blow to the inverter from the inrush current when the switch is turned on. 8)
    --
    Chris
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    inetdog wrote: »
    Aside from the slight logical problem of what constitutes the secondary in an autotransformer.....

    Yeah, an auto transformer is indeed kind of a special unit because it only actually has one winding in it ;)
    --
    Chris
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Inverters Grrrrr.

    Outback has a nice manual discribing various ways to connect an auto-transformer to mix and match various 120/240 VAC sources and loads (and sharing of power across 120/240 VAC legs).

    http://www.outbackpower.com/pdf/archives/fw-x240_rev_b.pdf

    They are really an amazing device.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    BB. wrote: »
    They are really an amazing device.

    Yessir. They are a very versatile device. I used our T240 on the stacked inverters to balance 120V loads. Today I use it on our Champion generator to turn the gen from a 120V unit into a 240V. I used the PSX-240 to turn our 5548 into a 240V inverter. When I talked to Schneider tech support about our XW system, before we even bought it, Mike at Schnieder told me, "Don't be selling that PSX-240 transformer when you sell your old inverter - we're going to be using that on your new XW system." I had the 5548 sold before I even took it off the wall and the guy that bought it wanted that transformer. So I called Schneider back and got Wendy on the phone. I asked her, "do I really need to keep that transformer?" She and Mike conferred for a bit then told me, "Keep it - we're going to use it to prevent your generator from getting disqualified during Gen Support."

    So it's not only amazing and versatile, they're quite useful too.
    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    Yeah, an auto transformer is indeed kind of a special unit because it only actually has one winding in it ;)
    --
    Chris

    Not necessarily.
    In fact it has two with a 1:1 ratio. You can use black and white as the "primary" or red and white as the "primary:; it doesn't matter.
    Just what the transformer does depends on how you wire it up:
    Connect the two neutrals (white) and feed 120 VAC to L1 (black) and neutral and you get a mirror image from neutral to L2 (red). This is where you are seeing the "cleaner" waveform because the mirror imaging of the harmonic distortion "cancels" the primary distortion; it is not truly pure sine.
    Same connect will give 240 VAC from L1 to L2 with 120 VAC available from either to Neutral.

    It can also be fed 240 VAC across L1 and L2 to achieve 120 VAC in the same way.

    Exactly how you hook it up and to what determines what you get out of it. They are often used on Outback FX systems to provide 240 or to balance loads across two inverters, et cetera.

    I use one to power my one and only 240 VAC load, because it is far cheaper and less power-consuming than any other way of doing it!
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    Not necessarily.
    In fact it has two with a 1:1 ratio.

    You know, now that you mention that, a true autotransformer just has one winding with a center tap (or two or three) and it does not provide electrical isolation between the primary and secondary. That's the way the Trace T240 is. I have never ohmed out the PSX-240 to see if it has two separate windings. If it does, then it provides electrical isolation between the primary and secondary. And that could explain it's superior efficiency as compared to the old Trace transformer. Our Trace T240 used to get very hot. The PSX-240, I question why they even put that fan in it. I have pushed that thing to well over its 6 kVA rating on our 5548 with Gen Support going, and it never even warmed the case up.
    --
    Chris
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Inverters Grrrrr.

    I'm pretty sure the PSX240 is as I describe. I've got several OB wiring diagrams for it and that is how it is depicted. It is a very good unit, isn't it? :D
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    I have never ohmed out the PSX-240 to see if it has two separate windings. If it does, then it provides electrical isolation between the primary and secondary. And that could explain it's superior efficiency as compared to the old Trace transformer.

    How does separate windings cause greater efficiency? (not trying to argue, just curious)
    ChrisOlson wrote: »
    Our Trace T240 used to get very hot.
    Were you using pure sine wave on the Trace? If not, that could explain the heat.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Inverters Grrrrr.
    ChrisOlson wrote: »
    You know, now that you mention that, a true autotransformer just has one winding with a center tap (or two or three) and it does not provide electrical isolation between the primary and secondary.

    Two windings with opposite ends connected together is the same as one winding with center tap :D
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    Re: Inverters Grrrrr.
    vtmaps wrote: »
    How does separate windings cause greater efficiency? (not trying to argue, just curious)

    Less chance (as in no chance) of having circulating current between L1 and L2. That's the problem with the XW's Gen Support Plus where it connects the transformer center tap to the gen neutral to help keep the gen balanced. If you use too big of a generator on it (over 5 kVA) you get circulating current in the transformer winding.
    Were you using pure sine wave on the Trace? If not, that could explain the heat.

    We used to use the T240 on the dual 4024's in step down mode and took 120V off it going to a separate panel for our 120V stuff. That kept the inverters balanced so the generator wouldn't go AWOL during Gen Support. The XW is different because it doesn't attempt to charge batteries just off one leg like the SW Plus did when the amps drops below the Gen Support threshold. Gen Support in the XW is determined by the highest loaded leg. I tried to use the T240 just as a balancer with L1 hooked to the L1 inverter and L2 to the L2 inverter and that didn't work like it does with the XW because the inverters are really independent when you stack 'em. So the chargers in there don't always do the same thing. One is in Gen Support Mode and the other one isn't sometimes. So that would cause the gen to overload on one side and then it would go AWOL because the charger kicked in on the one that wasn't in Gen Support. With the XW they got the charging synchronized between L1 and L2 better than you can do with a stacked setup, so it stays in Gen Support mode until BOTH legs drop below the amp threshold.

    That's why I'm less than impressed with stacked inverter setups for 120/240V compared to a "real" split-phase inverter.

    But anyway, all our 120V stuff was powered off that transformer in step-down and it got pretty hot sometimes.

    When we went to the 5548 using the transformer in step-up mode, the T240 simply wasn't big enough. I had smoke coming out of when my wife was running the clothes dryer one day. That's when we bought the PSX-240.

    The windings in our T240 are a little discolored from getting so hot. But it still works fine on the little Champion.
    --
    Chris
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Inverters Grrrrr.
    NorthGuy wrote: »
    Two windings with opposite ends connected together is the same as one winding with center tap :D
    +1
    The Outback transformer that they call an autotransformer is physically an isolation transformer. But all of the standard uses wire it to form an autotransformer. Just in several different configurations where you perhaps could not build all of them using a single configuration of autotransformer.
    If you make a permanent internal connection between two taps, you lose flexibility.
    One example is that you can use the two windings to parallel two 120 volt inverters which are phase locked without actually making a direct DC connection between the two line outputs.
    If you had only an autotransformer, you would either have to float one inverter or have the two locked to opposite phases rather than identical phases.
    SMA SB 3000, old BP panels.
  • H2SO4_guy
    H2SO4_guy Solar Expert Posts: 213 ✭✭✭
    Re: Inverters Grrrrr.

    I have been very happy with the PSX-240 (NAWS Earth day sale) to run the air source heat pump. That is all it has done so far, but it works great and never gets even warm to the touch. I mounted it on the ceiling to save room. Made sure to hit a stud too, that thing is pretty hefty!
    12K asst panels charging through Midnite Classic 150's, powering Exeltechs and Outback VFX-3648 inverter at 12 and 48 volts.  2080 AH @ 48 VDC of Panasonic Stationary batteries (2 strings of 1040 AH each) purchased for slightly over scrap, installed August 2013.  Outback PSX-240X for 220 volt duties.  No genny usage since 2014.