'Bank wound' transformer by hand - Page 1
Forum section: electronics / projects

author: Technical Mayhem
author_rank: Contributor
timestamp: January 10, 2024, 05:23:43 am
content: Does anyone have any advice on bank winding a transformer by hand? See attached pic for what I mean.I need a low qty of transformers with about 500T of 0.16mm on the secondary. I have a winding jig for counting turns and making the actual winding easy.The problem of course is getting the tension right so that the higher-up turns don't push the lower-down turns across.The point of this is to achieve the lowest possible intra-winding capacitance on the secondary, since this is reflected to the primary as the square of the turns ratio. So, for example, 100pF of secondary capacitance on a 1:100 ratio transformer = 1uF seen by the primary. Not exactly what you want.Alternately are there any suppliers that could offer this service?Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2024, 08:06:58 am
content: You'll have a devil of a time keeping it level and consistent, with the wire jumping around like that.I've kind of always wanted to try that style, but never had a pressing enough need to go and do it...Next best is probably using sections. If you don't mind class A insulation, it can just be sheets of cardboard:This was a 10mH choke that came out to ~80pF.Another good way is to make multiple independent layers, from left to right, and connect them in series in such a way that their capacitances cancel out. If this is a flyback supply, a diode in series with each layer puts only DC across the interwinding capacitance, while at AC it's more or less bootstrapped between each winding. Probably too special of a case, but maybe worth mentioning. Capacitance can also be used to advantage in a resonant converter, if you can deal with complexity of the control.Tim

author: jonpaul
author_rank: Super Contributor
timestamp: January 10, 2024, 10:30:20 am
content: OP: Voltage, frequency, core shape/mfg/part #?Desired L, Cp-s, Cshunt, SRF?HV transformers (CCFL, CRT, Ozone) need other wdg technique.Most EE/EI etc have avail stock sectionalized bobbins, see core mfg for bobbins,Jon

author: Technical Mayhem
author_rank: Contributor
timestamp: January 10, 2024, 10:26:31 pm
content: Thanks Tim & Jon,I think a sectioned bobbin could work but I'm unsure how to arrange the primary - could it sit in one of the sections or will this increase leakage inductance too much?The current prototype is a push pull primary at 48V (2 x 10T of 1.2mm), secondary (500T of .16mm) for 2400V at 20mA. Running at 40kHz.Currently the secondary is wound in a zig-zag configuration over 5 layers and the primary wound on top - this is the worst way to do it in terms of capacitance as I found out.Core / bobbin is an ETD39 with an OD of 29, ID of 13 and a length about 28mm. I can't find any sectioned bobbins for this size - Jon are you able to suggest something similar sized that has one available?Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 10, 2024, 11:40:02 pm
content: Quote from: Technical Mayhem on January 10, 2024, 10:26:31 pmBeats me -- what are you doing with it? Again, depends on type. It can be hard to get "too much" leakage for a resonant type, but a plain square-pulse flyback or god forbid, forward, will be less tolerant.It sounds like this is for a DC-DC converter, in which case you may want to do that, break it into sections and rectify each independently. C scales as N^2 as you note, so this has substantial effect.Tim

author: Benta
author_rank: Super Contributor
timestamp: January 10, 2024, 11:48:06 pm
content: I visited a transformer manufacturer in Scandinavia doing this kind of thing (mind you, this was 30 years ago).They had a technique of using wires coated with a special kind of varnish/lacquer that would turn sticky when heated. When winding, a kind of hot air gun (carefully temperature controlled) was aimed at the bobbin/winding, making certain the wires would stick without compromising the isolation.Very tricky operation, but when tuned correctly highly successful.

author: CaptDon
author_rank: Super Contributor
timestamp: January 11, 2024, 01:05:21 am
content: If cost is no object initially and for production quantities perhaps Peter at E.P.D. magnetics in Wendall North Carolina may be able to help. I haven't talked to Pete in many years but he did some miracle stuff for us with ultra fast turn around for prototypes. He was really good with the Litz wire stuff for S.M.P.S. transformers and good at reducing leakage inductance for our needs.

author: langwadt
author_rank: Super Contributor
timestamp: January 11, 2024, 01:52:24 am
content: Quote from: Benta on January 10, 2024, 11:48:06 pmit is called "self bonding"

author: Technical Mayhem
author_rank: Contributor
timestamp: January 11, 2024, 02:11:03 am
content: Quote from: T3sl4co1l on January 10, 2024, 11:40:02 pmYep, standard DC-DC push-pull configuration. 2400V @ 50W unregulated. Should be easy right?!?BTW the reason I'm not doing it with a 50/60Hz transformer is that I need low ripple and not too much energy storage (i.e small filter caps).The current configuration does work, but has awful switching waveforms, high no-load power draw etc.Maybe as an intermediate step I could change the secondary to an A-B style winding, where the wire is returned to the same side after each layer.Cheers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 11, 2024, 12:00:54 pm
content: Unregulated..? Like what, FWB on secondary? Like so many car amps?Yeah, that's a total-loss scenario, most likely all reactive power in the parasitics is dissipated as conduction or switching loss. The only reason those don't blow up is precisely because of leakage inductance.Leakage can at least be "stirred" at the primary side, if the primary halves are tightly coupled, and clamp diodes are used (this comes free in MOSFETs), and then PWM can be used crudely to limit inrush/fault current, and regulate voltage to a rough extent.Tim

author: jonpaul
author_rank: Super Contributor
timestamp: January 12, 2024, 01:59:08 pm
content: Hello done HV trsf for decades.My random impressions....1/ Load is? capacitive, resistive, arc/glow lamp, spark gap?2/ Usually HV DC is NOT push pull but simple flyback.Suggest to Read about HV PS topologies.3/ "Bank wound" is odd and vague.Check perfect layer, zig zag, universal, random wind4/ Sectionized bobbins can have the primary wound first at bottom of bobbin, or use a UU or UI shape with separate legs for PRI and SEC.5/ SFR and wire insulation stress first to last turn are the issues.6/ HF HV stresses all insulation, worse with heat and sharp waveforms.7/ wire type mentioned in Germany was self bonding, very special order, used mostly for speaker voice coils.8/ Commercial bobbins with sections have slots for connection between sections9/ Alternative to sec bob is singe sec bobbin, layer wound with interlayer insulation eg 3M56 mylar tape.Wind L>>R R>>L to minimize electric field.Enjoy!Jon

author: Technical Mayhem
author_rank: Contributor
timestamp: January 14, 2024, 12:46:26 am
content: Jon, can you please clarify what you mean by SFR?Also can you suggest suppliers of sectioned bobins?Thanks heaps!

author: jonpaul
author_rank: Super Contributor
timestamp: January 16, 2024, 12:07:25 am
content: Hello:" push-pull configuration. 2400V @ 50W unregulated. Should be easy right"WRONG!If DC output use Flyback. Push Pull not needed and had downsides.Study HV DC DC PS topologies. ETD39 is overkill and not ideal for HV. We use EE and EI or UU, UI shapes for HV. Flyback with P on one leg, sec on the other.SRF = Self Resonant Frequency, where the primary or secondary magnetizing L resonates with the self capacitance.See models of ideal transformer.Bobbin suppliers: Check the ferrite supplier.TDK, Siemens, EPCOS, Cosmo,Some 2 sec (split bobbin) perhaps a few multisection.Try the Chi Com suppliers you will find many like Pinshine. Look for "CCFL transformer"We had custom sectionalized turned from a delrin or nylon plastic rod on a lathe.Bon chance,Jon