I was reading a post from a school teacher about wanting a subject for the class project.\u00a0 Bingo, I thought of something that had not really come up before: “How much does it cost to make a Joule Thief?”<\/p>\n
I guess it would be best to start with a BOM, or Bill of Materials.\u00a0 The prices are based on retail at an electronics store, but somet parts such as wire and batteries are not available in single quantities, you may have to buy a larger quantity.<\/p>\n
<\/p>\n
Qty — Item Name ——————————- Cost $ (retail \/ large qty)<\/p>\n
1 — LED, white or Blue ———————– 2.00 \/ 0.15*<\/p>\n
1 —- Transistor, NPN PN2222A ———– 2.30 \/ 0.05*<\/p>\n
1 —- Toroid, Fair-Rite 267324002 ——– 1.00 \/ 0.12*<\/p>\n
2 – Wire, 24 AWG, 10 in. or 25 cm long — 1.00 \/ 0.30<\/p>\n
1 — Resistor, 1000 ohms, 1\/4W, 5% ——– 1.30 \/ 0.02*<\/p>\n
1 — Battery holder, AA cell, with leads — 0.99 \/ 0.70<\/p>\n
1 — Battery, AA cell, Alkaline pkg of 4 — 2.00 \/ 0.20<\/p>\n
<\/p>\n
*The LED, transistor, resistor, toroid can be purchased in a quantity of 100 with a steep discount.\u00a0 For instance, if the transistor is purchased from a retail store, it may cost a dollar or more.\u00a0 A ‘bargain pack’ of 15 may cost $2.30 US.\u00a0 But if 100 are ordered from a distributor, the price per transistor may be only 5 cents or even less.\u00a0 The same applies to resistors and toroids.<\/p>\n
The Coil<\/strong> – The coil is the more expensive part of the JT.\u00a0 Larger cores can cost a dollar or more apiece, but can be reused,\u00a0 The cores from a PC power supply can also be used, so it\u00b4s a lot cheaper if you scrounge some coils from old equipment, especially dead CFL lights. \u00a0 I gave the part number of a toroid available from Mouser.com<\/a>. Other similar toroids are available from surplussales.com<\/a>.<\/p>\n Wire<\/strong>\u00a0 The wire for the toroid can be bought from a home improvement \/ hardware store for less than a dollar a foot, but make sure it is small enough – 24 AWG or 0.5mm – so you can get about ten turns through the small core.\u00a0 There is speaker wire that is thin, and bell wire or thermostat wire. I’ve found that solid conductor telephone wire makes good JT coil wire.\u00a0 Another source for small wire is keyboard cable or similar cable – the price being free.\u00a0 That brings up the point that there is wire all around your.\u00a0 I took the bobbin out of an old table fan, and it has a lot of 28 AWG wire, useful for winding coils.\u00a0 The windings in motors can overheat, so make sure the wire\u00b4s enamel insulation is in good condition and does not crack when the wire is bent.<\/p>\n The LEDs<\/strong> don’t get discounted as much, but an easy way to buy a lot of bright white LEDs is to get the four pack of 9-LED flashlights on sale for under five dollars (I’ve seen them for less\u00a0 than four dollars US – a dollar each). That gives you 36 LEDs for about ten or fifteen cents apiece.\u00a0 The only problem is that they have short leads, and have to be removed from the flashlights and unsoldered from the PC board.\u00a0 The whole PC board with 9 LEDs can be used as it comes from the light, but it takes a lot of current to light all 9 LEDs up brightly.<\/p>\n The battery holder<\/strong> is about 70 cents apiece if ordered from a distributor in quantities of 50 or more.\u00a0 However some improvising can be done.\u00a0 I recently designed a circuit board a bit longer than AA cell, and put holes in each end to accommodate a loop of steel cut off of a paper clip.\u00a0 These act as a battery holder, and can be adjusted a bit for a tight fit.<\/p>\n Another way<\/strong> to hold the wires to the battery is with a magnet on each end.\u00a0 I soldered a small steel screw to each end of the positive and negative wires, and put some heat shrink\u00a0 tubing over the joint to prevent the wire from breaking.\u00a0 A small 1\/4 inch or 6mm diameter neo magnet holds the screw to the ends of the AA cell. I obtained the small disk\u00a0 magnets, 1\/4″ diam by 1\/16″ thick from Amazingmagnets.com for $13.00 for fifty magnets (see note below).<\/p>\n Very strong magnets can be obtained from defective hard disk drives.\u00a0 They are too large for a battery but they can be broken and the pieces used.\u00a0 NOTE: The magnet material is very sharp, almost like glass so it poses some safety hazard.\u00a0 Also these magnets are very powerful and can hurt you if you get your skin between them.\u00a0 And if you let\u00a0 two magnets pull together violently, there is a good chance that one or the other will break (I’ve already had this happen).<\/p>\n Conclusion?<\/strong>\u00a0 When I started this blog I thought I could pin down the price pretty easily – not\u00a0 The problem is that there are many ways the experimenter can save, and save a lot of money.\u00a0 If the parts buyer is purchasing enough parts for a hundred JTs (say for a classroom project), the total price of the parts could be reduced to a fraction of retail prices.\u00a0 The price of 30 AWG wire is about 10 to 12 dollars US for a quarter pound roll – that will make hundreds of JTs.\u00a0 But just about anyone can get wire free by removing some old telephone wire from the baseboard in a room, and strip off the jacket, leaving wire that looks like new.\u00a0 Or take apart an old motor and unwind the wire.<\/p>\n The one rule that every experimenter should obey is before starting a project, obtain all of the parts.\u00a0 Before you pick up any tool, you should already have all of the parts.<\/p>\n Back to experimenting…<\/p>\n","protected":false},"excerpt":{"rendered":" I was reading a post from a school teacher about wanting a subject for the class project.\u00a0 Bingo, I thought of something that had not really come up before: “How much does it cost to make a Joule Thief?” I guess it would be best to start with a BOM, or Bill of Materials.\u00a0 The <\/p>\n (Read More…)<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,4,12],"tags":[],"class_list":["post-928","post","type-post","status-publish","format-standard","hentry","category-electronics","category-joule-thief-smps-dc-dc","category-led"],"_links":{"self":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/928","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=928"}],"version-history":[{"count":23,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/928\/revisions"}],"predecessor-version":[{"id":4711,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=\/wp\/v2\/posts\/928\/revisions\/4711"}],"wp:attachment":[{"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=928"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=928"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rustybolt.info\/wordpress\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=928"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}