Bobbin winding depth of E70 bobbin? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: April 05, 2022, 07:49:03 pm
content: Hi,The winding area of the E70 former is 389mm^2. The winding width is shown as 65mmTherefore, is the windings depth equal to 389mm^2/65mm = 6mm?E70https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32.pdf6mm seems awful shallow for such a big core?Also, how do you mount this on a PCB, it has no pins?

author: uer166
author_rank: Super Contributor
timestamp: April 05, 2022, 07:58:24 pm
content: Quote from: Faringdon on April 05, 2022, 07:49:03 pmAt ~0.6kG, you don't. You mount it to something mechanically solid, and terminate flying leads on PCB. At this weight a PCB would be a structurally unsound method of securing this.

author: Faringdon
author_rank: Super Contributor
timestamp: April 05, 2022, 10:10:07 pm
content: Thanks, also , do you know how to compress the core halves together so they stay together?The datasheet doesnt say.https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32_dg.pdfWe dont have any choice but to mount it to a PCB for our el cheapo prototype......we will just have to make sure that any delicate SMD components are mounted on daughter boards, and the only other components on the transformer PCB are eg through hole radial caps etc.....would you say this was OK?Do you think a shedload of tape would hold the core halves together?Also, do you know why the former is so shallow?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 06, 2022, 12:07:53 am
content: What's shallow about it? They give dimensions, figure it out yourself..?Oh neat, it's double stack, don't see that too often.I'd probably go with something like: fiberglass or metal brackets to mount the transformer to the board with screws; brackets are glued or tied (say with metal strapping) to the core. Varnish or epoxy secures core and bobbin, no vibration. Bobbin is loose wires, a bit of a pain to get into the board; or can be tied to tag strips or wire-to-board headers and then soldered in. Orientation vertical or horizontal, however you want to do it, and however fancy you want to get with the brackets.For something that size, the brackets should probably be tied into standoffs to the enclosure or something. It could be free on a board but the board should be much thicker say 3.2mm in that case, and still supported nearby and often.Tim

author: Faringdon
author_rank: Super Contributor
timestamp: April 06, 2022, 09:09:58 am
content: QuoteThanks, the only dimension given for a winding width on the single core set bobbin is "32.3mm". However, this cant be right, as the core spindle is 43.8mm...therefore , the winding length must be 43.3 - (2 x 1.2mm) = 40.9mm. However, this isnt at all certain...pg 4 of the below..https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32_dg.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 06, 2022, 09:52:50 am
content: Err, the winding window is (47.3 - 25)/2 x (43.3 - 1.2 - 1.2)? And 35 is the outside depth, so the mean turn length is on the order of, 11.15 * 4 + (25 + 35) * 2 = 164.6. So the, what, 7 turns you wanted? A bit over a meter, it should be.Ed: 21 and 9+9, so about 3m, and a bit under 3. Or triple stranded, ~20m total, call it 25m for safeties.Tim

author: Faringdon
author_rank: Super Contributor
timestamp: April 06, 2022, 10:12:12 am
content: Thanks, i am with you on calc of mean-turn-length of 164.6mm....however, the datasheet page 3 says 209mm...so i am guessing they just added a bit extra onhttps://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32_dg.pdf

author: jonpaul
author_rank: Super Contributor
timestamp: April 06, 2022, 11:15:01 am
content: TDK no longer makes bobbins but the E70 spec is JIS and all dimensions redialy availableThe old,bobbins had pins, later tyey were separately sold and inserted by user.In 1970s special clamp hardware brackets were availableAs E70 is seldom used now-a-days availability of bobbins and hardware is doubtfulJon