Author Topic: BIG transformers  (Read 8376 times)

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Offline theoldwizard1Topic starter

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BIG transformers
« on: September 24, 2018, 03:33:25 pm »
So I am researching the cost of build an inverter.  The cost of bare bones inverter boards, on eBay, capable of several kW of power are ridiculously cheap (<$100).  The trick is purchasing/winding a transformer that will take an approximate 16VAC @ 60Hz output and transforming it into 120VAC.

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 ?

Are custom wound transformer (maybe 2-3 kVA) with in the price range of a DIYer.
 

Offline MiDi

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Re: BIG transformers
« Reply #1 on: September 24, 2018, 05:06:56 pm »
Think there is very low demand for this, nobody, except the manufacturers go to design and build such big transformers and test and get certified them.
Why not buy one that fits?
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #2 on: September 24, 2018, 05:20:27 pm »
Think there is very low demand for this, nobody, except the manufacturers go to design and build such big transformers and test and get certified them.
Why not buy one that fits?
There is nothing "off the shelf" that would work and I am afraid to even ask for a quote on a custom made one !
 

Offline MiDi

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Re: BIG transformers
« Reply #3 on: September 24, 2018, 05:23:39 pm »
There is no 120V to 16V awailable?
Only to make sure: you simply swap input and output, transformers work both ways...
 

Offline ahbushnell

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Re: BIG transformers
« Reply #4 on: September 24, 2018, 07:25:54 pm »
So I am researching the cost of build an inverter.  The cost of bare bones inverter boards, on eBay, capable of several kW of power are ridiculously cheap (<$100).  The trick is purchasing/winding a transformer that will take an approximate 16VAC @ 60Hz output and transforming it into 120VAC.

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 ?

Are custom wound transformer (maybe 2-3 kVA) with in the price range of a DIYer.

Why would you run an inverter at 16 volts at 2 -3 kva? That's 190A. 
 

Offline edpalmer42

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Re: BIG transformers
« Reply #5 on: September 24, 2018, 08:07:49 pm »
So you're going to take a low DC voltage and turn it into mains voltage?  The perfect source for such a transformer is an old UPS.  You're doing the same thing they do.  Dead UPSs are available cheap or free if you're lucky.  If you look for a 2U rackmount unit, you have a good chance of getting a toroidal transformer if that's what you really need.  In fact, it might be practical to rebuild the UPS into an inverter with better cooling so that it can run at full power continuously.  A UPS typically isn't designed to do that.

Ed
 

Offline T3sl4co1l

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Re: BIG transformers
« Reply #6 on: September 24, 2018, 10:21:26 pm »
Toroidy.pl?  Wind-your-own option, basically.

Transformers are perfectly symmetrical, so if you can find a 120:16V transformer, just run it backwards and you're done.

You may find it's, well, lighter or more compact, certainly; most likely better, but probably not easier, to do it with multiple DC-DC stages (wired in parallel, phase interleaved for lower ripple), to make a high voltage rail, then inverter-ize that for AC output.  Here's an example:



Left: 12 to 170V converter (about 1A max output) and 12:12 DC-DC (for isolation); middle board: PWM controller; right: mains generator (controller, including current limiting, drivers and inverter); breadboard: filter chokes; other bits of wire and outlet: AC output going to the lamp illuminating the scene, actually (~50W load).

A 170VA transformer is sized about the same as the whole assembly, just for this poorly built prototype.  The real downside is, unless you're doing this for the academic exercise (as I did), you're better off buying one.  This is a $40 value, at best.  And it doesn't even have a shiny extruded aluminum housing! ::)

Given that 2kVA inverters range from laughably shitty to actually-good, eh, you might not find one that's actually 2kVA and a reasonable price (say circa $300?), but if you need one, it's a far, far better deal than anything you can make (sadly!).

Tim
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Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #7 on: September 24, 2018, 11:06:07 pm »
First, I HAVE been around the block a time or 2 and I do know that transformers work in both directions.  (The "old" in my name isn't there for no reasons !)

The 2-3kVA rating is for a 24VDC to 120VAC inverter that is capable of 2000W continuous.

The 16VAC come from a peak-to-peak voltage of about 20V.  (RMS voltage = PP voltage / √ ̅2)
« Last Edit: September 24, 2018, 11:09:54 pm by theoldwizard1 »
 

Offline sibeen

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Re: BIG transformers
« Reply #8 on: September 24, 2018, 11:46:10 pm »


The 16VAC come from a peak-to-peak voltage of about 20V.  (RMS voltage = PP voltage / √ ̅2)

Cough You may want to look that over once more Cough
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #9 on: September 25, 2018, 04:52:46 am »


The 16VAC come from a peak-to-peak voltage of about 20V.  (RMS voltage = PP voltage / √ ̅2)

Cough You may want to look that over once more Cough

OOPPSS !!   √ ̅2 is 1.414  NOT 1.212 !  So more like 14VAC !

Old guy with CRS disease (Can't remember SH!T)!
 

Offline sibeen

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Re: BIG transformers
« Reply #10 on: September 25, 2018, 07:53:10 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 :)
 

Offline T3sl4co1l

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Re: BIG transformers
« Reply #11 on: September 25, 2018, 09:08:22 am »
First, I HAVE been around the block a time or 2 and I do know that transformers work in both directions.  (The "old" in my name isn't there for no reasons !)


Just checking. We have lots of newbies and oldbies here alike, good to know :)

Tim
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Offline mariush

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Re: BIG transformers
« Reply #12 on: September 25, 2018, 09:49:03 am »
You should be able to easily find 110v -> 15v AC  or 120v -> 15v AC ....  or 110v AC -> 18v AC (6.11 ration)  / 120v AC -> 18v AC  (6.66 ratio)

If you reverse it and put 16v AC on the 18v winding, it should still work, but instead of getting 120v, maybe you'll get  only 100v AC  ( with same ratios above, 98v ac or 106v ac )... and pretty much everything on the market should still tolerate it. 
 

Offline ahbushnell

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Re: BIG transformers
« Reply #13 on: September 25, 2018, 01:17:17 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 :)

So now the inverters needs to produce 3000/7=428 A RMS. 
 

Offline CJay

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Re: BIG transformers
« Reply #14 on: September 25, 2018, 01:51:23 pm »
An old APC UPS would do exactly what you need but if you really want to roll your own, I'd think about using low voltage DC to power a high frequency switcher to convert it up to higher voltage DC and then convert to AC
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #15 on: September 25, 2018, 02:40:15 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.
 

Offline T3sl4co1l

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Re: BIG transformers
« Reply #16 on: September 25, 2018, 02:59:42 pm »
Well, good luck transforming an offset sinewave. ;D

Also to be perfectly specific, note that's sine wave only, and other ratios for other waveforms (of note, triangle is sqrt(3), square is 1, rectangle wave is sqrt(D)*sqrt(1-D), etc.).

Tim
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Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #17 on: September 25, 2018, 04:34:22 pm »
Well, good luck transforming an offset sinewave. ;D
A "generated" sine wave (electronically or mechanically) does not know "ground" until it is connected to it.  It "floats".  You are just used to the fact that US mains have neutral and ground "bonded" typically at the first disconnect after the meter.
 

Offline T3sl4co1l

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Re: BIG transformers
« Reply #18 on: September 25, 2018, 05:53:40 pm »
Hmm?

I meant more to the point that, if it's going through a transformer, the average value (across the transformer) is either zero, or the transformer is a charred wreck of molten copper.  Transformer don't care about ground. :)

Tim
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Offline Gregg

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Re: BIG transformers
« Reply #19 on: September 25, 2018, 09:44:25 pm »
 

Offline sibeen

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Re: BIG transformers
« Reply #20 on: September 26, 2018, 12:53:01 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.

I think I'll stick with the classic definition :) Really, I also think you need to look at how an inverter will produce an output AC waveform. I'm assuming here that you are looking at a standard H bridge, PWM controlled inverter. If you had a waveform where the sinewave was offset in such a manner that the bottom peak was the ground of the system then I'd call that wave DC because it certainly ain't AC, and as Tim pointed out putting something like that through a transformer is going to ensure a world of hurt.
 

Offline Gregg

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Re: BIG transformers
« Reply #21 on: September 26, 2018, 01:19:35 am »

[/quote]
I think I'll stick with the classic definition :) Really, I also think you need to look at how an inverter will produce an output AC waveform. I'm assuming here that you are looking at a standard H bridge, PWM controlled inverter. If you had a waveform where the sinewave was offset in such a manner that the bottom peak was the ground of the system then I'd call that wave DC because it certainly ain't AC, and as Tim pointed out putting something like that through a transformer is going to ensure a world of hurt.
[/quote]
The transformer primary input could care less where earth or other ground is referenced; it is just a coil of wire wound around a core, as is the transformer secondary.  Plus the secondary can be totally isolated from the primary which means one could attach the ground anywhere appropriate for the desired output.  In other words, an input sine wave or modified sine wave input 0 to 16 volts won't make a difference to the transformer from the same wave input plus and minus 8 volts.   |O
 

Offline sibeen

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Re: BIG transformers
« Reply #22 on: September 26, 2018, 01:41:20 am »

I think I'll stick with the classic definition :) Really, I also think you need to look at how an inverter will produce an output AC waveform. I'm assuming here that you are looking at a standard H bridge, PWM controlled inverter. If you had a waveform where the sinewave was offset in such a manner that the bottom peak was the ground of the system then I'd call that wave DC because it certainly ain't AC, and as Tim pointed out putting something like that through a transformer is going to ensure a world of hurt.
[/quote]
The transformer primary input could care less where earth or other ground is referenced; it is just a coil of wire wound around a core, as is the transformer secondary.  Plus the secondary can be totally isolated from the primary which means one could attach the ground anywhere appropriate for the desired output.  In other words, an input sine wave or modified sine wave input 0 to 16 volts won't make a difference to the transformer from the same wave input plus and minus 8 volts.   |O
[/quote]


Sure, all true, a transformer doesn't care about a reference, swap the active and neutral around on a transformer, no biggie; ground one of the primary legs which is what is done in a TNS-C system, the transformer will merrily operate. But in these cases the hot wire compared to the cold wire goes up positive 10 volts and then it goes down to negative 10 volts. The overall voltage across the transformer is zero.

That's not what the OP is suggesting. He's got a waveform where the hot to the cold goes up to positive 20 volts and then down to zero volts. The average is a 10 volt offset. Put that through a transformer and you'll generate a shedload of heat and not much else - until the smoke gets out.
 

Offline theoldwizard1Topic starter

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Re: BIG transformers
« Reply #23 on: September 26, 2018, 03:37:19 am »
That's not what the OP is suggesting. He's got a waveform where the hot to the cold goes up to positive 20 volts and then down to zero volts. The average is a 10 volt offset. Put that through a transformer and you'll generate a shedload of heat and not much else - until the smoke gets out.
I think you need to do your home work !  This is not somewhat off design.  It is a well proven design that has been around for MANY years, used heavily in the RV/Marine/trucking industry.

What is new is, how inexpensive the implementation has gotten to be.  Ebay - 3kW inverter board -$80

Basically, add a housing, cooling and an output transformer and you are there.  The whole design revolves around the EG Micro EGS8010 chip  Datasheets
« Last Edit: September 26, 2018, 03:47:04 am by theoldwizard1 »
 

Offline sibeen

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Re: BIG transformers
« Reply #24 on: September 26, 2018, 03:57:28 am »
That's not what the OP is suggesting. He's got a waveform where the hot to the cold goes up to positive 20 volts and then down to zero volts. The average is a 10 volt offset. Put that through a transformer and you'll generate a shedload of heat and not much else - until the smoke gets out.
I think you need to do your home work !  This is not somewhat off design.  It is a well proven design that has been around for MANY years, used heavily in the RV/Marine/trucking industry.

What is new is, how inexpensive the implementation has gotten to be.  Ebay - 3kW inverter board -$80

Basically, add a housing, cooling and an output transformer and you are there.  The whole design revolves around the EG Micro EGS8010 chip  Datasheets


WAIT....WHAT??????

The unit you have linked to is a 24VDC (or 48/60) to 220VAC inverter. The output of that unit is 220VAC. This means it will have a peak voltage of 311 volts above and below the neutral or reference line, or 622 volts peak to peak. You don't need a transformer unless you want to change the 220 volts into a 110 volt system. If you want to do that you'd be far better off just buying an inverter that will output the 120 volts.

I really don't understand where your 16 volts from the OP comes into it?
 


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