Long ago I built DC-DC converters using a toroid made with tape wound core. The cores were about 2 inches O.D. and we used regular 12 AWG solid insulated house wire for the primary windings. Even so, these cores vibrated a lot at several hundred Hz, making a screeching noise.<\/p>\n
I saw some very small tape wound toroid cores for a dollar each from Surplus Sales of Nebraska. They have the part number 50B12-1D printed on them and Surplus Sales adds ICH- to the front of that for their Item number. The cores are 0.56 inch O.D. They were made by Magnetics. A link to the data sheet is in the advert.<\/p>\n
I cut two lengths of 30 AWG wire each a foot (30 cm) long, and started winding them bifilar, together at the same time. As I wound, I measured the inductance with an LC meter. The inductance increased with each turn, until I got to 190 uH, but I still had enough wire for another turn, so I wound a thirteenth turn. The inductance jumped from 190 uH up to 10 millihenrys! So I removed that turn and it went back down to 190 uH. I thought that was really odd. I wound the thirteenth turn again and it went back up to 10 mH again. Strange.<\/p>\n
Oh, well. I left it that way and soldered the rest of the parts to it to make a conventional Joule Thief. I used a 5 mm white LED, 1k resistor, BC338 NPN transistor and a 10 uF capacitor from plus to minus to bypass the ripple from the JT. The LED lit up brightly at 1.5 volts, and the frequency was 100.6 kHz.<\/p>\n
According to the data sheet, the -1D suffix means the core is wound with 0.001 inch thick Square Permalloy 80 tape. The case is nylon. <\/p>\n
These tape wound cores work great for a Joule Thief<\/p>\n
Update May 27 – I bought a few toroid cores from China, and since the packages are in Chinese and they send no invoice or any documents, I really can’t tell who they were. But the cores are about 7\/8 inch or 22 mm O. D. and are painted green. I wound one with 13 turns and I got almost 500 uH. So they are high mu, and should work good for a Joule Thief.<\/p>\n
I decided to look for more, so my search came across some green cores on eBay. I ordered ten of these smaller ones, and they cost only 99 cents, shipping included. I think they are 9 mm O. D. I’m taking a risk, because they say nothing about the permeability, the cores could be made out of baked clay and painted green. I would expect that at this low price. I’ll just have to wait until June to find out. I received this in an email order confirmation, but I don’t know Chinese.<\/p>\n
Seller:
\n\u6df1\u5733\u5e02\u827e\u59c6\u8bd7\u6570\u7801\u79d1\u6280\u6709\u9650\u516c\u53f8
\ndigital.mart899@gmail.com<\/p>\n","protected":false},"excerpt":{"rendered":"
Long ago I built DC-DC converters using a toroid made with tape wound core. The cores were about 2 inches O.D. and we used regular 12 AWG solid insulated house wire for the primary windings. Even so, these cores vibrated a lot at several hundred Hz, making a screeching noise. I saw some very small <\/p>\n (Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[78,4],"tags":[],"class_list":["post-11147","post","type-post","status-publish","format-standard","hentry","category-inductors","category-joule-thief-smps-dc-dc"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/11147","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=11147"}],"version-history":[{"count":6,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/11147\/revisions"}],"predecessor-version":[{"id":11163,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/11147\/revisions\/11163"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11147"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11147"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11147"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}