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Old 6th Jan 2021, 10:01 pm   #1
dougietamson
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Default Transformer calculations app

I’ve dusted off my (limited) coding hat to make a new version of an old simple transformer designer program by Silvio Klaic circa 1999.

Input is the EI tongue width, stack height and the mains voltage/frequency. Then add the desired secondary voltage and mA.
Today I did the core design and winding turns calc, will add the wire gauges tomorrow.
Anyone want to check I’m not making any major mistakes/add suggestions?

To calculate the core power limit I used:
Power in Watts = (core area in square cm / 1.152) squared
To calculate the turns per volt:
Turns/volt = 1/(0.000444 x mains freq in Hz x Flux Density in Wb/m2 x core area in cm)
Primary winding current:
Primary current in Amps = (Secondary V x Sec I) / (Primary V x Efficiency factor)
Primary winding turns number = Turns/Volt x mains primary V
Secondary winding turns number= Turns/Volt x Secondary V (optional loading factor can be added here)
For the wire gauge, this will be used:
Wire diameter = 1.128 x sir root (Current/Current Density in amps/sq mm. Standard density for copper = 3.5A/sq mm.

I've added some screen shots of the original and macOS / Windows10 versions of the new one.

Doug
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Old 6th Jan 2021, 10:36 pm   #2
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Default Re: Transformer calculations app

I have never seen the origional program!! It looks like a very nice piece of software!! I do hope you will compile a Unix/Linux version if you dont release your coding under a free licence.

EXCELLENT work. As far as correcting your math, I learnt my transformers in inches and lines/sq inch so I cannot help there.

All the best for now

Joe
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Old 6th Jan 2021, 11:05 pm   #3
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Default Re: Transformer calculations app

Quote:
Originally Posted by joebog1 View Post
I have never seen the origional program!! It looks like a very nice piece of software!! I do hope you will compile a Unix/Linux version if you dont release your coding under a free licence.

EXCELLENT work. As far as correcting your math, I learnt my transformers in inches and lines/sq inch so I cannot help there.

All the best for now

Joe
Thanks for the feedback, especially as I know you build good xformers.

In doing some reading, there's lots of info out there (RCA manual). I was brought up on feet/inches/pounds/oz but having worked in research labs SI units lust work better.

I usually run the original program with Wine, works well but there isn't an option to set the laminations type. Good news for a linux and a web app version, I just need to add a single check to an option when building

It's a niche app for me to wind a few tranformers and free to anyone who wants it.

Doug
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Old 7th Jan 2021, 12:11 am   #4
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Default Re: Transformer calculations app

Quote:
Originally Posted by joebog1 View Post
I have never seen the origional program!! It looks like a very nice piece of software!! I do hope you will compile a Unix/Linux version if you dont release your coding under a free licence.

EXCELLENT work. As far as correcting your math, I learnt my transformers in inches and lines/sq inch so I cannot help there.

All the best for now

Joe
Works on Ubuntu16

Doug
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Old 7th Jan 2021, 12:33 am   #5
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Default Re: Transformer calculations app

I've hand wound transformers over the years but that was when you found more of them that were 'un-dipped' and could be disassembled easily. Getting hold of decent quality EI lamination's seems impossible these days.

That program would be very useful if you could post a copy? The original designer has taken his down due to wanting to update it but, as of 2005 there hasn't been one!
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Old 7th Jan 2021, 1:18 am   #6
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Default Re: Transformer calculations app

kellys_eye

Laminations that I use are freely available from India, and are a good price.
The quality is excellent!! I used John Sankey ( a part of BHP before Billington took over) iron for many years, but like all other manufacturing in Australia, they closed some years ago. Buying iron is still a bit of a problem from the point of view of the vendors as they want to sell in large quantities. Even John Sankey would not do less that 25 kgs of a single type. Although it wont match
"old radios/stereos", I would recommend 5% silicon Grain oriented steel. AKA 5%SiGO. because it can run quite high flux densities in the case of slight miss design, and in the case of output transformers distortion is lower and frequency response is better simply because the leakage is somewhat less if basic design rules are followed i.e. sectioning even to a small degree.

I am watching this thread with great interest

Joe
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Old 7th Jan 2021, 9:31 am   #7
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Default Re: Transformer calculations app

I've never wound a transformer, but it's something I have been thinking about for some time. This looks like a very useful app!
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Old 7th Jan 2021, 10:29 am   #8
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Default Re: Transformer calculations app

Quote:
Originally Posted by sortedradio View Post
I've never wound a transformer, but it's something I have been thinking about for some time. This looks like a very useful app!
On Tuesday I ordered a hand winder/lathe for £18.99 inc delivery (sale price). Dual speed via 2 gears: x1 and x8 (use x1 for heater windings), a 5 digit counter and plastic gears. Should be good for infrequent use as a starter winder.

Doug
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Old 7th Jan 2021, 10:54 am   #9
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Default Re: Transformer calculations app

Hi Doug.
Congrats on the app Dougie, it looks great.
I was just about to ask a question on this forum about this very thing, as I am toying with the idea of re-winding an Oscilloscope power transformer, and that would be just the thing.
Funny how these things happen innit?
I would like to take you up on your kind offer. Please may I have a copy/ link or whatever. ( for Windows)
Thanks
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Old 7th Jan 2021, 11:56 am   #10
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Default Re: Transformer calculations app

Quote:
Originally Posted by Tim View Post
Hi Doug.
Congrats on the app Dougie, it looks great.
I was just about to ask a question on this forum about this very thing, as I am toying with the idea of re-winding an Oscilloscope power transformer, and that would be just the thing.
Funny how these things happen innit?
I would like to take you up on your kind offer. Please may I have a copy/ link or whatever. ( for Windows)
Thanks
Hi Tim, I chose the custom transformer route to rewind one of the many transformers I've collected over time.
My 1st one is a rewind of a 24V 1200mA mains adaptor/wall-wort to use in a 2W pp amp using EF80's...

I'm still in the planning stage so I was thinking about the number of secondaries, I've only added scope for 2 so far but will add scope for more.

More features to be added, eg a save feature to store settings, some EI templates for cold rolled grain orientated (and non grain orientated) laminates, this would allow for tongue width and flux density settings to be filled in.

I need to tidy up the number formatting (too many decimal places) and turns need to be rounded up to whole numbers. Needs a sanity check on the total current rating of the secondaries vs the max power capacity of the core...

Should have most done this week.

Doug
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Old 7th Jan 2021, 12:46 pm   #11
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Default Re: Transformer calculations app

Sounds fabulous!

Will it be able to work out if the desired number of turns of users chosen size of wire would actually fit selected core/widow size?
I’m thinking of winding a 240 to 950 which then gets “ doubled” to produce EHT for an Oscilloscope. It doesn’t need to be very big, as the current requirements are very little, but a high number of turns will be required for the secondary. This means ridiculously thin wire
will have to be used in order that it all fits in the space available. I presume the varnish insulation will also be thinner, not ideal for such a large voltage.
I’ll try a bigger version first, to see if I can run up the scope( I can produce the other voltages required) just to make sure all my efforts won’t be wasted.
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Old 7th Jan 2021, 1:14 pm   #12
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Default Re: Transformer calculations app

Fitting the wire into the space...that's the skill part!
So far I've wound 2 small EI transformers, actually, I've only wound the secondaries!
I took apart the laminations (wasn't too hard) The bobbins were the 2 part plastic types inside a sort of plastic holder that also isolates the primary from the secondary.
I left the primary as is, the power rating was known as per the spec.
I unwound the secondary (best not to use this wire for another wind but you can use it to try honing your winding technique).
I wound a multi-tap secondary with 1st tap at 840 turns (for 120v), then 2nd tap at 1008 turns (144v), 3rd at 1176 turns (168v), 4th at 1260 turns (180v), 5th at 1344 turns (192v), 6th at 1512 turns (216v), 7th and last tap at 1680 turns (240v).
The wire was 0.14mm, quite thin but still able to get a good tension (more tension = better winding density).

Doug
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Old 7th Jan 2021, 1:41 pm   #13
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Default Re: Transformer calculations app

Hi Dougie.
Yes, it’s probably better to use a “ known” primary as that bit( the bit that scares me) is done for you.
I have a couple of mains transformers I can re-purpose and also a number of old telecoms transformers and inductors ( all E-I)I would like to re use.
I get the core size and volts per turn business, but the bit that bothers me is will resistance/inductance of my newly wound primary be right or will I just produce a smoke generator!
Ready made primaries are presumably good from safety/regs point of view too.
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Old 7th Jan 2021, 1:51 pm   #14
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Default Re: Transformer calculations app

Dougie. Let me know how you get on with that hand winder, as I might get one too.
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Old 7th Jan 2021, 3:21 pm   #15
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Default Re: Transformer calculations app

Quote:
Originally Posted by Tim View Post
Dougie. Let me know how you get on with that hand winder, as I might get one too.
Sure, I'll put it through its paces, delivery is estimated for next Thursday 14th Jan. I have some NUMA stepper motors, lead screws and a controller board from an old project to reuse to upgrade it to an automated winder...

My DIY winder is an old 12v NiCd (battery long dead) electric drill motor and chuck mounted in a wooden frame, a 10mm threaded bar with nuts and large washers to hold the bobbin. Powered by an old 12v ATX PSU, for the counter I rigged up a 3 digit tape counter with a bodge job to get 1:1 turns/counter digit.

See pics below, also shows free (gumtree) laminates from a microwave oven, 32mm tongue x 80mm stack and 3.3kg, should be good for 850W

Doug
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Old 7th Jan 2021, 6:06 pm   #16
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Default Re: Transformer calculations app

Quote:
Power in Watts = (core area in square cm / 1.152) squared
Could you explain that? It is at odds with my understanding of how one would calculate that.
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Old 7th Jan 2021, 7:08 pm   #17
dougietamson
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Default Re: Transformer calculations app

Quote:
Originally Posted by GMB View Post
Quote:
Power in Watts = (core area in square cm / 1.152) squared
Could you explain that? It is at odds with my understanding of how one would calculate that.
I think it's been used by transformer builders as a fudge factor/magic pixie dust to sprinkle onto their designs. I've been wondering where the 1.152 comes into this too, I'm using it just to get the app up and running.

I' thinking it's a way to get real world estimates of efficiency losses from an ideal transformer.

I'd rather get some real world core material differences built into my app, the old app I was using doesn't have any setting to change the core material, eg cold rolled grain oriented vs no grain oriented

Core plate material__________flux density [Wb/m2]_____Core efficiency
Grain-oriented silicon steel______1.2_________________ 0.84
Non grain-oriented silicon steel___1.1_________________0.82

I think this page might be better to use for the calculations:https://www.giangrandi.org/electroni...tml#core_table

I need you guys to help to get it right, make suggestions for features etc.

Doug
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Old 7th Jan 2021, 10:39 pm   #18
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Default Re: Transformer calculations app

Here is another way to calculate the recommended max power available from the core.

power = (efficiency x (square of the core area in mm))/14000

efficiency examples are CRGO=0.84 and CRNGO=0.82

When calculating the turns/volt the flux densities are CRGO=1.2 and CRNGO=1.0

Does this look better?
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Old 8th Jan 2021, 7:24 pm   #19
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Default Re: Transformer calculations app

Got the app looking a bit better, added space for 6 secondaries and some buttons with preset settings to load.

I'll try a transformer build next week once my new winder arrives and compare theory to real world.

Doug.
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Old 9th Jan 2021, 11:05 am   #20
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Default Re: Transformer calculations app

My understanding is that the power handling capability of a transformer is not about the core itself at all. The core just determines your best turns/volt.

You then have to consider how much space there is for the windings - and the core affects it a bit but only in as much as the turns have to go round the core thus affecting the length and hence resistance of the winding. The key factor is the space you have available for the windings because the more space there is the thicker the wire can be and that very directly affects the power handling.

Any formula just using the core area must be making a massive load of assumptions about the shape and dimensions of typical cores.

BTW why do an "app" with all the attendant concerns when this stuff is easily calculated in a web page? And Google seems to find quite a few already.
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