Author Topic: BIG transformers  (Read 8377 times)

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Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #25 on: September 26, 2018, 05:02:55 am »
The unit you have linked to is a 24VDC (or 48/60) to 220VAC inverter. The output of that unit is 220VAC.
In fact that unit does NOT output 220VAC.  That would be AFTER the output transformer that I have been discussing.

Read the datasheet I referenced.  That board contains an IC that is basically a sine wave generator at either 50Hz or 60Hz.  This is feed to a Class D amplifier that goes to MOSFET drivers that goes to the final drive MOSFETs.  The voltage out of the MOSFETs ranges from slightly higher than the DC zero volts to something slightly less then the DC maximum positive volts.  The gain of the amplifier is adjusted mased on a voltage divider circuit that is connected AFTER the transformer.



At this point you are just being ARGUMENTATIVE.  Do some real research, like READ THE DARN DATASHEET !
 

Offline sibeen

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Re: BIG transformers
« Reply #26 on: September 26, 2018, 06:01:07 am »
You linked to a site selling a 220VAC output inverter. You also linked to the data sheet of a controller chip. The chip data sheet shows that the chip can be used different techniques for inverter operation, one of which includes a transformer option and therefore a low DC voltage can be used as the input to the output inverter switches. The other techniques show a 400 volt DC link as the driving voltage to the inverter output switches.

The inverter you linked to will be of the latter type construction. It will have an intermediate stage which takes the incoming 24VDC and converts this to a 400VDC bus, so a DC to DC converter. This 400 volts will then be fed to the output switching devices of the inverter to give the required output AC waveform. The high DC voltage is required to be at a level that is above the peak voltage of the AC waveform, which for a 220 VAC machine will be 311 volts. For a lower output voltage the designers may even use a lower DC link voltage.

So this inverter is really a DC-DC-AC style machine.

The inverter can also come with different output voltages and here is one that has a 110 or 120 VAC output.

https://www.ebay.com/itm/3000W-Pure-Sine-Wave-Power-Frequency-Inverter-Board-DC-48V-24V-AC-to-110-120V/172689320870?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3D318d3f0e24de4e35b3bcedf582717058%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D292739535438%26itm%3D172689320870&_trksid=p2047675.c100009.m1982

 

Offline sibeen

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Re: BIG transformers
« Reply #27 on: September 26, 2018, 07:40:48 am »
Actually, the 120 Volt unit that I linked to does need a transformer and it shows it on the website that I linked to, perhaps I should have read to the bottom of the page :)

The page actually  shows the calculations you'll need to build the transformer.  Now the OP makes a bit more sense. You're not switching 16 volts AC across the transformer when using this inverter board. When using a 24 volt battery for the first half (positive) of the sine wave you'll be switching the positive 24 volts from primary 1 to primary 2 (P1 to P2) with a PWM waveshape. The switching transistors are just switching the DC voltage across the primary coil.  In the second half (negative) of the sinewave that will be switched around and the positive 24 volt will connect to P2 and you'll be switching from P2 to P1 with a PWM waveshape.  So with a H bridge configuration you'll be switching transistors 1 and 3  for the positive section of the sinewave and then transistors 2 and 4 for the neagative half.

That first inverter you linked to is very confusing as it does not mention a transformer at all - as far as I can see.
 

Offline fourtytwo42

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Re: BIG transformers
« Reply #28 on: September 26, 2018, 08:01:09 am »
Oldwizard if you go to this site http://www.thebackshed.com/forum/home.asp it is almost entirely devoted to inverters built around the egs chip. They are mostly Australian outbackers running entirely off grid, 6Kw being a typical size. If you trawl through the threads or do a search there is lots of info on transformers and of course a whole host of practical experience. Good luck :)
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #29 on: September 26, 2018, 01:44:00 pm »
Oldwizard if you go to this site http://www.thebackshed.com/forum/home.asp it is almost entirely devoted to inverters built around the egs chip.
Been there, done that, asked the same question did not get a definitive source for transformers or cores.
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #30 on: September 26, 2018, 02:03:14 pm »
You linked to a site selling a 220VAC output inverter. You also linked to the data sheet of a controller chip. The chip data sheet shows that the chip can be used different techniques for inverter operation, one of which includes a transformer option and therefore a low DC voltage can be used as the input to the output inverter switches. The other techniques show a 400 volt DC link as the driving voltage to the inverter output switches.

The inverter you linked to will be of the latter type construction.
In fact, that board doess NOT step up the DC !  I am pretty certain they are EXACTLY the same board. (The description was written by someone that does not use English as their primary language, so you have to take it with a LARGE "grain of salt" !)

I have STUDIED the specs and example implementations of the EGS8010 IC. I have REVIEWED many different implementation of inverter of both designs.  The "step up" inverters use multiple E-I core transformers (mounted on the board) and a high frequency (100 kHz ?) switch mode power supply boost converter circuit (multiple PWM chips available for this application).  This design is only slightly more complex than the low frequency design but has the bonus of using smaller, easier to wind transformers.  For whatever reason, this design does NOT seem very "robust".  (The magic smoke seem to come out.)

While the link you posted did give some formulas for winding transformers it does NOT answer the original question I asked in this thread

I am willing to wind my own, but I can not find a source for large toroid cores or even silicon steel E-I cores.  Anyone ?
« Last Edit: September 26, 2018, 02:09:22 pm by theoldwizard1 »
 

Offline fourtytwo42

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Re: BIG transformers
« Reply #31 on: September 26, 2018, 03:25:16 pm »
Quote from: theoldwizard1
Been there, done that, asked the same question did not get a definitive source for transformers or cores.
Then the only suggestion I could offer is a large toroid auto-transformer with enough window left for your primary. I have used that method myself for custom grid trafo's. Also if you notice people like Oztules has stacked toroids for higher output powers. The reason I say auto-transformers is they can often be had at a lot lower price per Kw.
 

Offline ahbushnell

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Re: BIG transformers
« Reply #32 on: September 27, 2018, 12:35:12 am »
I'd try one more time.

The RMS is √ ̅2 of the peak, not the peak-peak, so 7.071 would be close enough for field work :)
I don't like to dispute anyone on line, ESPECIALLY when I can not find 100% proof, but ..

"The RMS is √ ̅2 of the peak, not the peak-peak ..."  Yes, that is the "classic definition, BUT it assumes that GROUND is in the center of the sine wave.  In this case, ground is at the bottom of the wave.

And what happens when you connect that to the transformer?  Not much DC going through. 

 

Offline f4eru

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Re: BIG transformers
« Reply #33 on: September 27, 2018, 07:09:16 pm »
For big 50 Hz transformers, I'll recommend to not wire it yourself, because it's a real pain to put the tousands of turns of wire, then interlace all the sheet metal.

For a good source of powerful transformers, i'll recommend microwave oven transformers. You can cut out the HV secondary, and wire in your 2x12V primary.
You'll have to remove the core shunt though.

Why 2x12V  ? glad you asked! I'll recommend a push pull configuration.


Offline vk6zgo

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Re: BIG transformers
« Reply #34 on: September 28, 2018, 12:48:56 pm »
I'd try one more time.

The RMS is √ ̅2 of the peak, *not the peak-peak, so 7.071 would be close enough for field work :)
I don't like to dispute anyone on line, ESPECIALLY when I can not find 100% proof, but ..

"The RMS is √ ̅2 of the peak, not the peak-peak ..."  Yes, that is the "classic definition, BUT it assumes that GROUND is in the center of the sine wave.  In this case, ground is at the bottom of the wave.

*No, RMS is peak times the reciprocal of the square root of 2, which is 0.7071.
Hence, peak voltage of a 230 v RMS ac waveform is about 325v.
 

Offline Red Squirrel

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Re: BIG transformers
« Reply #35 on: September 28, 2018, 03:56:15 pm »
You can probably skip the bulky 60hz transformer by doing everything in high frequencies using SMPS transformers, then the output would basically be a smoothed PWM genreated 60hz sine wave. I'm not an expert only read up on this a tad as I would like to experiment with making my own power stuff at some point.

I was curious and it is indeed hard to find the hardware to make your own 60hz transformers.  Suppose you could get a metal fab shop to make the parts if you wanted to.  Not sure how much that would cost though, probably a lot.
 

Offline f4eru

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Re: BIG transformers
« Reply #36 on: September 28, 2018, 04:51:02 pm »
Yes, it would cost a lot to do prototypes of silicon steel parts.
On a former job, for proto laminations for motors, we used electro-erosion on complete lamination packets for creating a shape in the full packet. Of course, you can't alternate interlaced shapes (not needed usually for a motor), but you can do the same with a transformer, the alternating is a small optimization you could skip.
I don't recommend the electro-erosion because it'S expensive.

Also, of course, the HF (100kHz) SMPS version is much more compact, less cost, and higher efficiency, but it's a hassle to develop, and not worth it for only a few pieces compared to the 50Hz bulky transformer variant.

Offline jh15

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Re: BIG transformers
« Reply #37 on: November 29, 2018, 01:01:03 pm »
Not a good idea to piss off a wizard. You are (grey) bearding the lion.
Tek 575 curve trcr top shape, Tek 535, Tek 465. Tek 545 Hickok clone, Tesla Model S,  Ohio Scientific c24P SBC, c-64's from club days, Giant electric bicycle, Rigol stuff, Heathkit AR-15's. Heathkit ET- 3400a trainer&interface. Starlink pizza.
 


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