Recommendations for through-hole transformers - Page 1
Forum section: electronics / beginners

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 02:42:29 pm
content: Looking for any recommendations for through hole transformers. I can find a ton on digikey that match the specs i need: 115v primary, 15v/30v(parallel/series), 1-2A(tho this is the spec that i'm having a little trouble matching). How do i know if it will fit on perfboard? What about form-factors; i've noticed there's the traditional square shape, then flatter rectangles, and round type(like this one:https://www.digikey.com/product-detail/en/talema-group-llc/70073K/1295-1078-ND/3881390... i mean, this one could work if it would mount properly on a perfboard).This is the project that i'm using this for:https://www.eevblog.com/forum/beginners/4-output-(but-very-basic)-power-supply/Thank you

author: jaromir
author_rank: Unknown
timestamp: November 17, 2017, 03:01:25 pm
content: PCB mount 50/60Hz transformers above something like 50VA are not common, because of weight. If you have troubles finding 30V/2A transformer, you can still use two separate 15V/2A transformers (easier to find) and connect the secondaries in series.Don't forget to properly secure the PCB, as it's going to carry a lot of mass.

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 03:11:32 pm
content: Quote from: jaromir on November 17, 2017, 03:01:25 pmWell they only need to be max 30v, 1A or 2A. But they'll be on perfboard, not a PCB so mounting may be more difficult due to hole spacing and what not(all though, im sure designing a PCB to mount the transformer on and route its pins to a phoenix header wouldn't be that difficult, even for a novice like me.

author: SeanB
author_rank: Super Contributor
timestamp: November 17, 2017, 03:34:56 pm
content: Why do you want to mount a large heavy transformer to a thin flexible board. At 50VA plus the most common transformer mount is a chassis mounted transformer with either flying leads ( mostly toroidal units) or with terminal lugs you solder flexible wires to for connections. the chassis mount is more usable, as it uses no expensive PCB space, can be mounted using either bolts and nuts, screws or even rivets, and you can easily attach a grounding connection to the mounting for protection. PCB mount is generally reserved for low power and small space, where you only want to have the minimum amount of off board wiring, and all has to fit on the same board. Even there a small transformer with flying leads is very common as it saves board space and can be fitted into a larger variety of positions in a case.

author: Zero999
author_rank: Super Contributor
timestamp: November 17, 2017, 03:43:43 pm
content: Quote from: SkrillBill on November 17, 2017, 03:11:32 pmWhen you mean perf board? What sort is it? Does it have any track or spots to solder the components to or is it for wire wrap or to solder hookup wire to?This doesn't sound like a good idea, especially if it's strip board or has copper pads. The creepage distances between the primary an secondary are unlikely to be big enough to be safe.

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 04:06:21 pm
content: Quote from: Hero999 on November 17, 2017, 03:43:43 pmSomething like this:https://www.makerlab-electronics.com/my_uploads/2016/09/small-protoboard-5x7-1.jpgyou bring up good points about weakness of the board, maybe i'll give a go at Designing a PCB for it with some proper hookups.

author: Zero999
author_rank: Super Contributor
timestamp: November 17, 2017, 04:39:25 pm
content: Quote from: SkrillBill on November 17, 2017, 04:06:21 pmThat's probably about the worst thing to put mains on!At least with stripboard, it's possible to cut the tracks, to allow enough creepage but with that stuff, the pins need to be much further apart. A 6mm gap is generally accepted as the minimum allowable creepage distance, between the primary and secondary of a mains transformer, on a PCB. The gaps between those holes should add up to 6mm, between the shortest path from the primary to secondary.

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 05:09:22 pm
content: Quote from: Hero999 on November 17, 2017, 04:39:25 pmSo using a chassis mount is how i want to go right now? Any drawbacks to doing so, other than a bold sticking thru the project box it will temporarily be housed in for prototyping?

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 17, 2017, 05:19:23 pm
content: Perhaps we don't understand WHY you think you want to "mount it on perf-board"?That seems like an unfortunate decision on several levels.Can you explain what you are trying to do here?Perhaps we can identify a more suitable solution.

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 07:56:04 pm
content: Quote from: Richard Crowley on November 17, 2017, 05:19:23 pmMaking a small bench powersupply for powering smaller projects. 30v/1A. I had plans to mount it on a perf/protoboard just so it was all on a single board // i didn't know it would be so bad to do. I think going into this i thought that 'thru-hole' mean the pins would be far enough apart on any components to not cause a problem, but i've since learned that may not be true. I'm very new at this all.

author: Cliff Matthews
author_rank: Unknown
timestamp: November 17, 2017, 08:59:20 pm
content: Why not use a low cost smps as a pre-regulator? Mean Well has the LRS-75-36 (adj. 32-to-39v @2amp 75w) for $14https://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeyLRS-75-36

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 09:05:31 pm
content: Quote from: Cliff Matthews on November 17, 2017, 08:59:20 pmI could do that, but i also want the experience of building the circuitry to convert AC to DC and regulate the output(s). From my understanding of the smps you linked, it does everything except step the voltage down(as its already been rectified and filtered). I'm essentially building a linear power supply with a range of output DC voltages.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 17, 2017, 09:21:03 pm
content: Quote from: SkrillBill on November 17, 2017, 07:56:04 pmIf you are designing a custom PC board, they ARE far enough apart. But, by definition, perf-board has NO "far enough apart" pads, because they are all 0.1 inches apart. And furthermore, a transformer of that size will very likely have pins that are too big to fit into typical perf-boards. You might consider that using a conventional bolt-mounted E-I transformer (or a toroid transformer) is more appropriate for one-off circuits. You can mount the transformer directly to the enclosure and save a lot of PC board space which would otherwise be wasted under the transformer.

author: Cliff Matthews
author_rank: Unknown
timestamp: November 17, 2017, 09:23:09 pm
content: Quote from: SkrillBill on November 17, 2017, 09:05:31 pmThere's not much circuitry to a transfo, 4 diodes and filter caps. Besides, buying smps as packaged, is safer and leaves more $ for good stuff, like led metering, multi-turn pots and current limiting so projects don't blow-up too fast

author: rdl
author_rank: Super Contributor
timestamp: November 17, 2017, 09:27:50 pm
content: I've used Tamura transformers for pcb mounting in the past, but I don't think they have any in the size you need. Mouser sells them, you could try searching there. For my own projects I mostly use Avel Y23 series toroidal transformers. One place to get them is Parts Express.http://www.avellindberg.com/transformers/y23_range.htmhttps://www.mouser.com/Power/Transformers/_/N-8u9moZ1yzvvqx?P=1z0z80nZ1z0z63x

author: SkrillBill
author_rank: Regular Contributor
timestamp: November 17, 2017, 09:28:27 pm
content: Quote from: Richard Crowley on November 17, 2017, 09:21:03 pmI have come to the same conclusion on using a chassis mount toroidal transformer.By saying 'thru hole' the novice me thought that meant that they all fit on perfboard regardless, which was my primary mistake.Quote from: rdl on November 17, 2017, 09:27:50 pmThat is likely the direction i will be going in now. Ive done some research on the toroidal transformers, they should suffice for this one-off project.

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 17, 2017, 10:21:37 pm
content: This is what happens when you combine a transformer (actually two transformers) with a stripboard:

author: Cliff Matthews
author_rank: Unknown
timestamp: November 17, 2017, 10:58:10 pm
content: FR-4 strip board is available at Walmart.. Not tothere's more power per inch sq. using a pre-regulator.