High Frequency Inverters with Split Phase Capability and High Surge Capacity?

Basspig
Basspig Registered Users Posts: 71 ✭✭
I'm weighing the pros and cons of low frequency vs high frequency inverters.

There are several 12-15kW LF inverters that output split phase 240 VAC on the market. They have relatively high idle consumptions of 180 or more watts, are 85% efficient and weigh over 160lbs. Many are rated for 3X continuous as a surge capacity up to 20 seconds.

Hi frequency inverters are more efficient, some use only 30 watts idle consumption and boast up to 95% efficiency.

Then there are high frequency inverters. I haven't seen a split phase version however. And one manufacturer told me the surge is about double the continuous and recommended a low frequency inverter for big motor start surges.

I understand that two high frequency inverters can be paired to make split phase 240 VAC.

I also have a rather technical question about these inverters and it arose from something I discovered while running on generator power: what is the output impedance of LF vs HF inverters? Specifically, which is more resistant to distortion/harmonics injection due to poor power factor loads? My genset suffers badly from this. It's pretty clean with 1.0 PF loads, but through on a switching power supply and the distortion goes up drastically. Essentially, the harmonics pollute the entire system, not just the circuit with the poor PF load. So ideally, the inverter should be almost as perfect a voltage source as possible. Which type comes closer to this ideal?

Comments

  • mahendra
    mahendra Solar Expert Posts: 177 ✭✭✭
    Well you still have to look at the reviews. While some brands boast those features the real test is still the verdict. 
  • Tecnodave
    Tecnodave Registered Users Posts: 437 ✭✭✭✭
    edited May 2021 #3
    Low frequency vs high frequency.......

    Low frequency inverters provide far more surge capability, are at an advantage  with hugely inductive loads such as electric motors, welders, etc  that use a low frequency transformers, in shops, etc. Often they use massive wound core transformers which store huge amounts of energy in their core which makes them capable of reusing energy reflected by the loads. This is particularly true when a low frequency inverter which has a huge wound core feeding say an arc welder that has a wound core, or an electric motor of the wound core type. The load will reflect that energy back to the wound core of the inverter transformer which then recycles that energy back to the use(load). They achieve higher efficiency than a high frequency doing this.         They have much higher idle currents

    Hi frequency inverters use a very small usually toroidal transformer which does not have the mass (energy storage) of a wound core transformer and therefore cannot use the reflected energy from the load. When driving a hi-frequency load such as a switch mode power supply the high frequency inverter has the advantage of more efficiency. High frequency inverters have much lower idling power than wound core low frequency inverters. Power factor correction will make a bigger difference with a high frequency inverter than it will with a low frequency inverter

    So it all comes down to what is your use for the inverter. 


    On the issue of using two 120 volt inverters to make 240 volts...yes it can be done....BUT...the inverters MUST communicate with each other so that they share the start wave shape timing with each other...this is done by many manufacturers such as Cotek in their SD series, they are built in 110/120 volt versions and 230/240 volt versions but not 120/240 volts.....to get 120/240 you but two SD inverters and link them much the same as if you buy say a 2 Magnasine 
    MS4048PAE inverters and pair them, they have a communications protocol between them “so everybody starts at the same time / wavelength...

    on the EMI/RFI issue......that depends on the particular design....I have a Exeltech inverter which is the quietest inverter out there....they specialize in communications inverters as RFI/EMI is a deadly foe to high frequency communications.

    I have several inverters, which I use will depend on the load....listening to music on my high end music system (All Carver) I use only the Exeltech, same for radio communications, there are fewer “birdies” from the Exeltech than any other inverters that I have used. When I pump water with my 1930’s  deep well pump I use a Brutus which is only 120 volts feed through a Trace autotransformer to get the 240 volts for the pump.  The Brutus is only 3200 watts but has a whopping 11,900  watt surge capability. It has no problem with the water pump but my MagnaSine 4000 watt continuous  /5800 watt surge stumbles trying to run that pump.  The trade off......Brutus idles at 96 watts, ....MagnaSine idles at 40 watts.  MagnaSine is a beast, very heavy but Brutus is heavier than the MagnaSine the transformer core is way bigger.....whopping 11,900 watt surge.....very heavy low frequency transformer 

    There is no one inverter that is best at everything...

    Before you buy figure out what your loads are going to be. 

    Dave
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • clockmanfran
    clockmanfran Registered Users Posts: 94 ✭✭✭
    Modern design of LF Inverters that have a large toroid are now designed for a 30 to 40 watts idle.  A 30kg/66lb toroid can handle up to about 50kW of surges.

    HF types are direct FET drive and there is no room for those start up surges. 

    For the past 6 years I have been watching MIDNITE's new inverters with great interest as they are HF types in a modular design. There latest results look very promising.

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (12 years running).  ... 5kW PV on 3 Trackers, (8 years) .... 14kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    XW is still the back buster in low frequency design. An 80 pound Toroid. I too wish Midnite well. It has been more than 6 years BTW.
    It is not easy to support Inverter/chargers. I think they will find out that many offgrid people can deal with solar problems. When they lose power, that is where the feathers get ruffled. Starting big fire pumps, everytime, is where I want excellence.

    Surging for a "normal" load and how the inverter deals with it is the key. If the load generates a fault and shuts down power until the user can intervene, it is a poor deign to me. There is a 12KW out there doing that now from another new player. Maybe they will fix it?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • clockmanfran
    clockmanfran Registered Users Posts: 94 ✭✭✭
    edited June 2021 #6
    Yes, i also do a 90lb toroid version, but at this size lots and lots of issues raise their heads, and yes we can still keep idle power below 40 watts.

     However in a true practical reality situation, a hand wound toroid at 66lb would cope with most things, and would really run at 6kW all day if required and handle 15kW for 10 minutes or so, and easily cope with plant/equipment start up surges.

     The other thing that i find is the H Bridge design allows to AC Couple and therefore excess energy from GTI's linked to our MINI GRID'S flows backwards and charges the batteries, so we do away with DC chargers and DC cables that are the common standard that most folk use to day... 

    Its also an issue in today's society where unscrupulous manufacturers, and some should no better, claim kW ratings of their power Inverters that are fanciful, I am being polite with that sentence.

    One of the best Toroid designs i have seen is from 'Warpspeed', Tony in Australia. Its a fair bit more work as you need to wind three differing size of toroid's, but extremely efficient and very clever in the way it works.

    My thanks to Tony, 'Warpspeed' for allowing me to write up his projects.   WARNING, its a mind blower .........

    I have posted it here as a PDF.

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (12 years running).  ... 5kW PV on 3 Trackers, (8 years) .... 14kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,728 ✭✭✭✭✭✭
    No disrespect meant. DIY electronics are a great passtime.

     I need a system of networked chargers, cloud monitoring/config, closed loop charging, and a company that has been there all the way back to Trace. Support worldwide and a new unit if one fails in a ten year warranty. I have or know of 500+ XW's that have my hands on them in one way or another. I have already seen the best. Make something better for Offgrid, and in 3 years I may be convinced ;)
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • MichaelK
    MichaelK Registered Users Posts: 234 ✭✭✭
    Basspig said:
    I'm weighing the pros and cons of low frequency vs high frequency inverters.

    There are several 12-15kW LF inverters that output split phase 240 VAC on the market. They have relatively high idle consumptions of 180 or more watts, are 85% efficient and weigh over 160lbs. Many are rated for 3X continuous as a surge capacity up to 20 seconds.

    Hi frequency inverters are more efficient, some use only 30 watts idle consumption and boast up to 95% efficiency.

    Then there are high frequency inverters. I haven't seen a split phase version however. And one manufacturer told me the surge is about double the continuous and recommended a low frequency inverter for big motor start surges.

    Actually, I think you have the evaluations backwards.  It's actually the high frequency inverters that have high background idles, and the low frequency inverters that are more efficient.  I have an XW+6848, and it's idle consumption is about 30W.  Yes, it is very heavy though.  The mounting bracket is designed to be screwed into a wall with 16" stud spacing.  You screw the bracket into the wall first, then heft up the inverter onto it.

    In the evaluation of any inverter, don't just focus attention on the surge wattage, but focus attention on the surge time.  Some will claim they surge to 200%, but you find out that is for only for 20 milliseconds.  My XW had 200% surge for 60 seconds!
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
  • Basspig
    Basspig Registered Users Posts: 71 ✭✭
    Some years back, I was pondering the DiY route, thinking in terms of a 3 state PWM inverter, running off of +/-175V battery banks. No iron cores, etc.
    An earlier idea I had kicking around in my head was to build what was essentially a 40kW audio output stage, whose DC rails were +/- 175 V battery strings.
    Age and failing eyesight are causing me to change my strategy to look at available commercial options.
    In my research, the HF inverters have shown the lower idle consumption numbers. The LF inverters are typically the higher consumption, based on manufacturer spec sheets.
    LF inverters have one other issue, which is transformer hum. I would have to have this stuff operate in an outdoor building to keep the noise away. The other issue is 12-15kW (36-45kW surge for 20 sec) inverters I've looked at are just too darned heavy and big to move and would need a dedicated outbuilding to house them.
    My interest in the output impedance of various types of inverters stems from an experience while running on generator, which sports a 3% THD sinewave output, however goes to 50% when I switch on my Carver M-500 magnetic field amplifier. That distortion was on all branch circuits throughout the house.
    Mains power is 200A service, which gets used to capacity when my 20 KW sound system and home theater is cranking bass-heavy content. The specs on the QSC amplifiers state 126 amperes line draw at full output power and there are several in the racks. System draws a kilowatt idling. It gets used about once a week for an hour or two.
    The other loads are a high capacity deep well pump, and then electric range and cloths dryer.
    Aside from that, 8-10 desktop computers, two of which are super graphics workstations with GPUs that draw 300 watts each, massive disc arrays, large display monitors, and most of the equipment you would typically find in a recording studio.
    Static continuous load is about 4kW for everything in the house, when no water is being used and no cooking/washing being done.
    I need high surge capacity to deliver power when the pump starts, or when the main sound system is cranking loud.
    At this point, I'd settle for being able to keep the computers and networking and the pump working.
    The A/C is gradually being converted to mini split units. We still have two conventional units upstairs. Studio/theater/sound room has a mini split.
    There are some toroid LF inverters on the market, but most are from China. They weight a ton, most are 65kg or more. While the prices are attractive, I don't trust the reliability.
    Toroids typically have a stiffer voltage regulation, so that's favorable. Weight and size are still an issue though.
    I'll check out the "Warpspeed" inverter. Looks like a four-state technology. Very interesting. But I don't think I have time to DiY something of this scale. They way things are going, the grid could go down any time.
  • clockmanfran
    clockmanfran Registered Users Posts: 94 ✭✭✭
    I am no longer bothered about supplying any one, infact i will not supply complete machines. Yes i do a 'How to book' and supply the PCB's.

    Hundreds of our type of Inverters running with  co-operatives in Africa and hundreds around the World. 

    Commercial products are not always the best solutions.

     But as it has been said here, folk want stuff out of a box and working, and there is nothing wrong with that. 

     We here, and other discerning folk from around the World want better, and in the last 6 years we have slowly just got on with it and oh boy do the commercial guys get miffed with us.

    I Only do the best Inverters for friends, like this one for Dimitri ........ https://www.youtube.com/watch?v=5s9B3RTF1QA

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (12 years running).  ... 5kW PV on 3 Trackers, (8 years) .... 14kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Clockman, is your inverter bi-directional ?
  • clockmanfran
    clockmanfran Registered Users Posts: 94 ✭✭✭
    Hi boB,

    Yes it is, but we set the DC range on back flow to about 60vdc by hand winding are own toroids to a given voltage formula.

    Everything is possible, just give me Time.

    The OzInverter man. Normandy France.

    3off Hugh P's 3.7m dia wind turbines, (12 years running).  ... 5kW PV on 3 Trackers, (8 years) .... 14kW PV AC coupled using Used/second hand GTI's, on my OzInverter created Grid, and back charging with the AC Coupling and OzInverter to my 48v 1300ah batteries. 

  • Basspig
    Basspig Registered Users Posts: 71 ✭✭
    It's been years since I started this discussion, but finally some stuff happening..

    I bought this 14kWh Lifepo4 battery bank (48V) from Treeline Power Systems and the 6kW split phase inverter from Sun Gold Power. This is my smaller scale plan to get us essential power. It won't run my stereo system or other heavy draw appliances. I chose this inverter because the idle draw is only 80 watts and the weight was just under 100lbs. The 18kW inverter I'd like to have weighs in at 197lbs and used 270W idle which would draw down the batteries too much for a 4kW average load. That will have to wait.

    The first phase of this project is to back up the generator. Since we can't run it over night, I am wiring this so the generator is on the mains side of this inverter and the output of the inverter will feed the house electrical system, instead of the generator directly feeding the house electrical system as it was till now. This new configuration, when completed, should enable me to shut off the generator at night and then switch over to battery power for the overnight.

    Eventually, I want to have solar panels charging the battery bank during the day.

    I almost hit the buy button on thirty 260W used panels from SanTan Solar at $38 each, but then I saw the shipping cost and it was more than the total cost of the order, so I backed out. I looked for other solar panel suppliers, but they all seem to be in AZ or CA, too far to ship economically to CT. So the solar panels are still on hold. They also require the most planning. I need to clear trees that are on property not owned by me in order to get sunshine in the mornings and afternoons on my lot.

    Eventually, I hope to build a bank at a time of solar panels and add capacity over time. At first, enough to trickle charge the batteries. Later, enough to power basic necessities 24/7.

    So without further talk, here is what I've got setup yesterday. Tomorrow, I will wire in the generator and panel. Quite a bit of grunt work lies ahead. Hoping to test fire this into a real load tomorrow night.


    No photo description available
  • Basspig
    Basspig Registered Users Posts: 71 ✭✭
    I don't know what happened, but the tab I had this forum open on closed by itself for some reason, and now I cannot find the part of the discussion where I posted photos of the battery bank and inverter and the connectors that are on the solar panels I took delivery on today. Seems like the last dozen posts on this thread vanished.

    Oh well, I have forty 240W panels sitting in my driveway on two palettes now. Connectors seem to be MC-4 and I need to order combiner connectors to wire them in series pairs x 10 pairs per bank x 2 banks of 20 panels to wire up each bank in a 2x10 array for approx 50V nominal output. Then I need 100' of cable to carry that current to the house.

    My estimation is that at high noon, I might get 150 amps (in Arizona, 185 amps would be the panel rating but I'm way up north) of current. Since my estimated nominal power consumption at the battery is around 30A at 48V, in each hour of full sunlight, I would be storing 5 hours worth of electricity. So 3-4 good sunlight hours would give me 15-20 hours of reserve to get through overnight demand.

    I unpacked the first panel and flipped it over so the cell side faced up. This was an hour before sunset and no direct sun. No load voltage was 33.35 volts. For kicks, I put a 5 ohm resistor across it and the output dropped to 1.3 volts. About 1/3 of a watt in indirect light. I've a lot of work ahead. Have to build structures to support the panels, order connectors and cable and start putting this monstrosity together.
  • Basspig
    Basspig Registered Users Posts: 71 ✭✭
    That Exeltech inverter looks similar to Midnight Solar's modular rack mount inverters.

    I'm considering Sungold Power 18kw inverter for my permanent system.  It is 195lbs due to the big transformer. 
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited June 2022 #16
    Not so much HF vs LF, as it is good design/good quality vs bad design/bad quality,

    Many of the high freq inverters are very low cost, and low quality.  There are only a couple of good quality models.

    As to U.S. split phase, many of Chinese inverters, either HF or LF are just poor design showing a poor understanding of split phase requirements. 

    Their designs select parts spec'd with little to no design margin.  Battery input line caps have 63v rating for 48v inverter,  HV DC filter caps and PV input caps are 500v rating, with max PV input voltage specs on inverter of 500vdc.  There are very small value filter caps on HV DC node so there is a lot of 2x AC out freq ripple voltage on them which heats up electrolytic caps reducing their lifespan.  It also gives them little to no surge capability.  PV input caps are very low in capacitance so there will often be ripple getting through to PV panel loading which reduces panel maximum power point output current.  AC connect relays are cheap water heater relays rated for resistive loads.  On higher wattage inverter models they put two of these cheap 40A resistive load rated relays in parallel to handle higher AC current.

    High no-load idle current is mostly the result of poor design, lacking the knowledge of how to minimize switching losses, and/or allowing more switching crossover tolerance slop to allow for random part substitutions in manufacturing.

    HF split phase have two individual inverter circuits operating in series similar to 240/120 vac inverter-generators.  Although could be a single inverter circuit, most HF inverters use an H-bridge PWM chopping sinewave generating output stage.  This means their high voltage DC supply must be independent between the the two split phases with two separate PWM output stages.

    Most of the Chinese HF all-in-one inverters do not have their PV inputs isolated from AC output.  This means the PV panels wiring are riding on top of the inverter PWM high voltage DC polarity switching from the PWM AC output H-bridge.  You must use double pole DC breakers to PV panels to disconnect both positive and negative lines to PV panels.

    True bi-directional battery to HV DC converters are difficult to design and control.  Many Chinese HF inverters do not attempt to do it.  They just put a parallel buck converter circuit change-over to charge battery from HV DC node.  This takes some switchover time which limits the functionality of many HF hybrid inverters.  For example, they cannot do load shaving or load supplimenting by inverter with grid or generator AC input.  When connected to AC input they only allow AC pass-through and battery charging from AC input.  They cannot suppliment a generator with limited power output.

    Many of the recent low freq inverters from China do not have the management/control of split phase grid neutral voltage imbalance and cannot be connected to grid neutral in a code complient install.  They don't provide for split phase AC input grid neutral connection making them non-code complient.

    With single center tapped output transformer low frequency inverters, there must be grid neutral management to prevent output transformer from trying to correct for grid L1-N to L2-N voltage imbalance that can cause high currents in output transformer.  Lacking the safe guard to check for this, the low cost LF inverters cannot safely be connected to grid neutral.  

    Be careful of HF inverter surge claims.  2x surge capability for a couple of msecs is no surge capability.  Single phase induction motors startup surge is 400 to 500 msecs long so any surge spec less than at least a half a second is pretty much useless.

    Also be careful of believing specs.  With All-in-One inverters there are many ways to stretch the true.  For example a HF all-in-one inverter specs, "DC to AC conversion efficiency = 96%" and is only efficiency spec listed. Intent is to make you believe this is inverter battery to AC output efficiency.  It is not. 

    It is PV DC input, when PV voltage is close to inverter's internal HV DC node so PV SCC boost is barely required to boost PV voltage up to HV DC node so its efficiency is very high, like 99%.  Most of the 96% efficiency number is just the high voltage DC to sinewave PWM H-bridge switching loss and L-C output filter loss. 

    Battery to HV DC boost converter, which is about 94% efficient by itself, is not involved in this path.  Optimum battery to AC out efficiency is about 93% which is about the same as LF inverters.

    One manufacture finds a way to stretch the truth and all other manufacturers follow in order to be competitive.  Most of the Chinese HF all-in-one inverters are just copies of the same basic circuit with individual manufacturer's effort put into pulling a few more pennies of cost out of bill of material.  Build lot, to build lot, of a given inverter model will have different parts depending on what parts are available at the lowest cost.







  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    WOW !!   RCinFLA, what an informative post !!

    Thank you very much for taking the time to create the abovr meaty reply, complete with detailed schematics, too!  SO,  there IS no free lunch ??!

    Had been considering cheap Chinese Inverter/chargers, to interface a backup LiPO battery bank, to/from SW+ 5548s,  backing up old FLAs.

    Might start a new Thread for that,  thanks again!  Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.