Wiring a Twisted Pair or Twisted Trinity in a Transformer Secondary - Page 1
Forum section: electronics / general

author: jonovid
author_rank: Super Contributor
timestamp: July 20, 2021, 07:40:55 am
content: if make a junk box power supply for an old 120W Toshiba Satellite laptop.I have an old used 700 watt microwave oven transformerand hope to replace the 1kv secondary with my own 20 volts 6 amp secondaryby using wiring atwisted pair or twisted trinityof19 AWG copper wire Gauge 1mm in wire diameter x 2 so i can get a 6 amp secondaryon the 700 watt transformer that has a 240 volt primarymy question is wiring a twisted pair or twisted trinity in a transformer secondarya good idea? as I need current of 6 amps or more at 20 volts for an old laptop power supply.an old 120W Toshiba Satellite laptop.I do not have much in the way of 10 or 8 AWG gauge enameled copper wireso must make do with twisted pair of 2 x 19 AWGI have never seen wiring atwisted pair or twisted trinityin a 50Hz power transformerbut do see the odd twisted trinity in CRT TV pcb choke transformers. were high current is used.but this is a high hz then 50Hz.I have lots of 1mm enameled copper wire in my junk boxif my calculations are correct I will need double this for a 6 amp transformer secondary.my question is will it work? are enameled wire strandsbundled or twisted togetherin parallel a problem.if its the transformer secondary.

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 20, 2021, 08:25:32 am
content: There's no problem with using multiple wires in parallel providing they all have exactly the same number of turns and the total cross sectional area is sufficient to prevent excessive copper loss, a nominal value of 5A/mm2 is normally good enough.If there is a big disparity in length (perhaps two windings in separate layers) current distribution will follow relative winding resistances.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 20, 2021, 07:28:44 pm
content: Yup, fine. Just takes up more space and gets hotter in the middle because of all the insulation.Can also connect them in series, if you feel like saving turns. (This has a high-frequency downside of increasing capacitance between turns, but that doesn't matter here.)Multiple strands or builds are often seen at high frequency, to reduce losses; at mains frequency, there's simply no difference.Mind that the primary uses a few turns less than it should, so the core runs in saturation and gets very hot under continuous duty. You may wish to add some turns of your own.Also FYI, knock out the magnetic shunts, they make the transformer "worse"; which is good for the intended application but not helpful here (you'll be using a FWB and cap to make DC I assume?).Tim

author: jonovid
author_rank: Super Contributor
timestamp: July 20, 2021, 09:56:49 pm
content: thank you! for your suggestions.Quoteyes I may need to look at the loading and the core temperaturelooks like I be doing some rope making with my wire.electronics basket weaving

author: Red Squirrel
author_rank: Super Contributor
timestamp: July 21, 2021, 12:21:54 am
content: This is a totally offtopic and unhelpful comment but Twisted Trinity would make a pretty awesome death metal album name.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 21, 2021, 02:08:59 am
content: Or Christian rock band, but for that matter, Dee Snyder is Christian so there you have it?Tim

author: gbaddeley
author_rank: Regular Contributor
timestamp: July 24, 2021, 11:59:55 am
content: As already mentioned, MOT are not generally designed for continuous use. Run it for 10 mins without a load to see how hot it gets. They can be noisy too, running close to saturation.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 24, 2021, 01:47:26 pm
content: One trick that can be used is to phase angle cut the input so it's effectively a lower voltage. That was used in many Carver audio amplifiers back in the day. The downside is that the circuit to do it can be somewhat complex.Most likely it would be cheaper to just buy a power supply. If you instead make it a variable output high current bench supply, you might have a chance of making one cheaper than what you can buy.