Author Topic: How I made my SMU  (Read 8713 times)

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Offline Bansci

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Re: How I made my SMU
« Reply #25 on: December 26, 2021, 01:03:01 am »
Please find...
Thank you for such a comprehensive and well illustrated reply!

A winding machine does indeed seem like a nesscessity, six hours of winding sounds very frustrating. I'm trying to find a local (UK) transformer EI lamination supplier but I've already ordered the NK-1 you speak of. I'm really inspired to try winding myself and to learn it so thank you again. The split bobbin seems like a nice way to separate the shields!
« Last Edit: December 26, 2021, 01:42:45 pm by Bansci »
 

Online Roehrenonkel

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Re: How I made my SMU
« Reply #26 on: December 26, 2021, 01:06:11 pm »
Hi Bansci and all,

when winding a transformer yourself keep in mind not to build a short-circuit with the shield-foil.
Start and end of the foil can be lead to the outside (for test purposes), but never connected together.
Also i would highly recomend vacuum-impregnation/potting.
 
And for the very best noise-reduction run it over an UPS (sine-wave of course),
like the hardcore-hifi-freaks. ;-)))

Will post my ideas regarding the output-connectors in Daves SMU-thread.
 
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Offline cnt

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Re: How I made my SMU
« Reply #27 on: December 27, 2021, 01:26:18 am »
wow this is fantastic.  I know its never the point but what do you think the BOM cost was?
 

Offline Bansci

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Re: How I made my SMU
« Reply #28 on: December 27, 2021, 08:23:37 am »
The original design this is based off has a BOM goal of $350.
https://www.djerickson.com/diy_smu/
 
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Offline Bansci

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Re: How I made my SMU
« Reply #29 on: January 19, 2022, 09:08:08 pm »
Jaromir, I've found a UK supplier of split bobbins, EI inserts, and I'm just putting together my order. It was http://www.ascocomponents.co.uk/, who have very reasonable prices and small order quantities, you just have to email to get them. My winding machine has also arrived!

I had a few questions I was hoping you'd help me with.

(1) How did you avoid forming a shorted turn with your shielding? Did you insert paper to prevent a short while overlapping your copper tape, or did you leave a gap?

(2) I plan to use kapton as insulation. Did you do this between windings and shields? Paranoid I can see isolation being needed everywhere, but actually I think we're nowhere near the enamel breakdown voltages...

(2) I've seen this video on YouTube where the guy pots the transformer using bees wax
https://youtu.be/K4VcmJIoNBA?t=1174
I think he's winding a audio output/input transformer though.
Did you pot your mains transformer? I'm tempted not to do this as I'm worried about it melting, but perhaps my transformer shouldn't get that hot anyway.

Thanks again for all the detail you gave, I'm much more confident about buying/designing this transformer now and I'm really looking forward to developing this new skill.
 

Offline Kleinstein

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Re: How I made my SMU
« Reply #30 on: January 19, 2022, 09:46:10 pm »
Bees way is a bit low in the melting point. It may be OK for an audio transformer that on average is used only for low power.
I would avoid potting, at least for the first few tries, till you know it is for sure working. Once pottet it would be had to fix.
Oe could try something with a much higher melting point, like rosin, if needed to fix some wires in place.
Idolation on both sides of the shield may be a good idea. It would also reduce the capacitance.
 
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Online jaromir

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Re: How I made my SMU
« Reply #31 on: January 19, 2022, 10:22:45 pm »
Bansci:
I'm glad you found EI parts supplier. Those are hard to find nowadays.

1, The shielding was quite laborious task. I left small gap in the shielding to prevent short circuit. Overlapping may be easier to do, if the overlapped part is insulated.
I put one layer on insulation tape between shield and windings. Insulation of the magnet wire itself may be probably enough, but better safe than sorry. Enamel should withstand the voltage just fine, if not damaged - I was worried that can happen during hand winding.
2, I used both classic "yellow mylar tape" and kapton tape in my transformers, with good results. Mind that mylar tape was made for this application, has known dielectric strength and somehow lower thickness - so perhaps it's preferred. Be careful with insulation thickness, it adds quite a lot to volume consumed on the bobbin. When buying insulation tape, buy rolls with various width, it makes life easier. Cutting narrow slices of a tape from wider one is PITA job.
3, (you had point 2 twice). I did not pot the transformer, though I bought beeswax just for this purpose - it was fairly cheap, under 10EUR/kg at local beekeeper. My intent with potting was reducing transformer hum (by fixing parts that can move against each other in the magnetic field) and somehow improve cooling of the transformer. At the end I decided not to do this step, because mains hum was nearly inaudible (I had to drop a few drops of thin lacquer on outer EI laminations to "glue" them in place - still easy to disassemble if needed). Leaving it as is also let me back door for transformer modification - if any - as potting it makes repairs/modification difficult. Cooling doesn't seem to be a problem with my transformer.
There are also dedicated synthetic transformer varnish solutions (those are usually even more PITA to disassemble). For ideal impregnation vacuum setup is probably needed, which is something I don't have anyway.
 

Offline 8334455

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Re: How I made my SMU
« Reply #32 on: January 24, 2022, 01:29:30 am »
Hi , exciting job, is there any update in your github? I'm expecting repeat your awesome work.
 

Online jaromir

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Re: How I made my SMU
« Reply #33 on: February 24, 2022, 08:28:01 pm »
Right now I pushed new release of firmware into the repository - https://github.com/jaromir-sukuba/J-SMU

Major change is rework of USB communication, it works now via SCPI commands, unlike previous communication protocol similar to 'R2D2-talk' of older test gear. Apart from that, I refactored the code and made minor cleanups.
Next update will include user and calibration quick manual.
« Last Edit: February 24, 2022, 08:44:11 pm by jaromir »
 
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Offline RikV

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Re: How I made my SMU
« Reply #34 on: February 24, 2022, 08:52:39 pm »
Thanks Jaromir! I am anxious to see your approach on the calibration issue!
 


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