Bridge rectifier soldered directly to secondary wires hanging in "open air"? - Page 1
Forum section: electronics / beginners

author: dentaku
author_rank: Frequent Contributor
timestamp: June 13, 2014, 03:12:57 pm
content: I'm wondering if there's any reason why a bridge rectifier needs to be on the circuit board taking up valuable space when it could simply be soldered onto the wires of the secondary of the transformer and left out in "open air"?I seem to remember seeing old transformers with little rectifiers attached directly to them.My center tapped transformer has about 30cm of wire coming out of the secondary and I'd like to save some space on the circuit board of the power supply I'm building (the caps take up allot of space so I want to waste as little as possible) by moving the 3N257 bridge rectifier out of the way.

author: SeanB
author_rank: Super Contributor
timestamp: June 13, 2014, 03:25:58 pm
content: Nothing wrong with it at all, often you find higher power ( typically over 3A with a mounting hole in them) mounted off board often on either a metal chassis or a dedicated heatsink to cool them. The capacitors can also be off board, and if you have some really big ones ( I have some 4700uF 450VDC ones near me I found in a dumpster) you will be mounting them anyway using a clamp, often the board is only there to arrange connections and hold a PCB mounted fuse holder and a discharge resistor and possibly a LED and resistor for power on indication. I have seen some power supplies where the PCB is held by the bridge rectifier mounting bolt and the tags.

author: IanB
author_rank: Super Contributor
timestamp: June 13, 2014, 03:32:07 pm
content: Quote from: dentaku on June 13, 2014, 03:12:57 pmIn general, what you are describing is "point to point" wiring. It was done a lot in the old days, and it still has a place for appropriate circuits.Here's an example:

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 13, 2014, 03:34:46 pm
content: 1) Since the AC input terminals are the two center terminals, you would save no board space by "flying" them off' board.2) If you are talking about just hanging the 3N257 out in open-air, at least glue it down to something to prevent it from flopping around.3) Those straight-wire terminals are designed for PC board mounting. Connecting them in open-air will be more challenging to make them physically secure and properly insulated and isolated.4) Note that "point-to-point" requires a POINT at each end of the component. You seem to be describing wiring a component with 4 leads, and ZERO "points" of attachment.

author: rob77
author_rank: Super Contributor
timestamp: June 13, 2014, 03:47:49 pm
content: fully agree with Richard above.but if you'll mount that bridge open-air, then at least use heat-shrink tubing to insulate the leads with the wires. and glue it down somewhere in your enclosure/case (for example with hot-glue).

author: IanB
author_rank: Super Contributor
timestamp: June 13, 2014, 05:17:08 pm
content: Quote from: rob77 on June 13, 2014, 03:47:49 pmJust to mention, if you have a component that gets hot in operation such as a rectifier, it might not be a good idea to mount it using hot-melt glue...

author: dentaku
author_rank: Frequent Contributor
timestamp: June 13, 2014, 05:19:25 pm
content: Quote from: rob77 on June 13, 2014, 03:47:49 pmYup. I'm planning to heatshrink the leads and attach it to the case.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 12:18:49 am
content: By the way.I can use a nice small 3N255 (even smaller than the 3N257 I've been experimenting with) OR I can use a giant/overkill KBU 605 6.0A 600V bridge rectifier that seems to perform exactly the same when I use it in my breadboarded LM317/LM337 +/- 20V power supply.Would there be any reason NOT to use the huge one other than the space it uses?It has a nice hole in the middle of it that I could use to screw it to the plastic enclosure I'm going to use.http://datasheetcatalog.com/datasheets_pdf/K/B/U/6/KBU605.shtml

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 14, 2014, 12:29:50 am
content: I recall seeing photos of old tube TV sets that had the rectifier (socket) integrated into the transformer covers!Tim

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 14, 2014, 12:39:56 am
content: No real reason other than money. The hole can be reason enough.For a solution to connecting flying leads from a component to a wire, use a solder lug terminal strip like this:http://canada.newark.com/cinch/56c/terminal-strip-lug-type-8pos-0/dp/29F593'Course no-one would freak out to see wires directly soldered to flying leads in a homebrew project, especially if heat shrunk & well secured. Shouldn't be in something professional though. Also you can get square types that are meant to be soldered to or use a spade crimp terminal. Definitely overkill in that they're usually rated for 25-35A. A caveat though is that you'll need a fairly large soldering iron or gun to solder to it. 35W pencil won't cut it.Like this:http://canada.newark.com/fairchild-semiconductor/gbpc3510/bridge-rectifier-1ph-35a-1kv-qc/dp/18C6691

author: Shredhead
author_rank: Regular Contributor
timestamp: June 14, 2014, 01:13:13 am
content: Quote from: IanB on June 13, 2014, 03:32:07 pmWhoa, is that an old guitar amp?

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 01:17:40 am
content: Quote from: Paul Moir on June 14, 2014, 12:39:56 amWell, I'm using almost all recycled and free parts so I'm leaning towards the KBU 605It has the same voltage drop across each diode as the 3N255 so it's really no better or worse. It's just easier to solder to and it has the handy hole through the middle for the screw.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 14, 2014, 01:54:56 am
content: Oh yeah if you have one already!My happy hunting grounds are old PSUs and old CRT monitors. Lots of nice power components and single layer boards which make removal much easier. If you want to order parts Digikey gets them to me (East Coast) in 1-2 days for under $10. Mouser is a bit slower. Don't remember how Newark is. For in-Canada, ABRA has been good to me but you gotta call and see if they actually have stock.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 02:38:36 am
content: Quote from: Paul Moir on June 14, 2014, 01:54:56 amI've gotten stuff from Newark/Element 14 before but mostly I get my stuff on "big garbage day" where people put their old electronics on the side of the road along with other big things like furniture and rusty barbequesPeople still haven't figured out that they don't take electronics (at least not in NS) so you always see old TVs and satellite receivers left over after the pickup day.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 14, 2014, 02:46:05 am
content: Ah, I know what you mean. I'm in NS too. Dartmouth area.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 03:16:30 pm
content: Quote from: Paul Moir on June 14, 2014, 02:46:05 amSpeaking of Dartmouth, is there anywhere else in the HRM that sells electronics stuff like Jentronics in Burnside? I see they have Arduino clones, power supplies etc.I've only seen that place once but it was closed. I rarely ever have a chance to go to the Halifax/Dartmouth area.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 03:19:08 pm
content: I just stumbled onto this ancient video Dave did before he had any kind of lighting and it shows a big bridge rectifier with a hole in it bolted to the chassis with heatshrink and the leadshttp://www.eevblog.com/2009/09/11/eevblog-30-jaycar-bench-lab-power-supply-review/

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 14, 2014, 07:03:05 pm
content: RAE industrial is also in Burnside. I find their prices a bit better, and their electronics knowlege & focus a bit more keen. They also seem to have some Rigol gear and some Hanatek on the shelves if you want to try stuff out. IIRC their Rigol prices were actually pretty good. For a long time these shops were strongly focused on industrial and repair electronics, but it seems like both have somehow figured out about the hobbyist electronics renaissance lately. Just in the last few years you started seeing a lot more interesting stuff on their shelves rather than just yet another DIN mounted octal base relay socket.I buy a fair amount of stuff in Burnside as part of my job but I only use them occasionally. If they have to order, I can get stuff faster & much cheaper from Digikey, etc. Jentronics sells CSA approved wire by the foot, while RAE sells neither (!). I tend to use them only when they add value.Oh, I noticed RAE has some Wiha drivers on sale. I strongly suspect someone there is an EEVBlog fan!

author: dentaku
author_rank: Frequent Contributor
timestamp: June 14, 2014, 09:20:45 pm
content: That's good to know and they're both along Akerley Blvd. very close to each other. Maybe someday this Summer I'll have a chance to head over there again.I love the precise look of those screwdrivers Dave uses