{"id":130,"date":"2011-07-28T12:37:08","date_gmt":"2011-07-28T10:37:08","guid":{"rendered":"http:\/\/jaran.de\/goodbits\/?p=130"},"modified":"2012-07-02T21:57:18","modified_gmt":"2012-07-02T20:57:18","slug":"building-a-mobile-usb-cell-phone-charger","status":"publish","type":"post","link":"http:\/\/jaran.de\/goodbits\/2011\/07\/28\/building-a-mobile-usb-cell-phone-charger\/","title":{"rendered":"Building a mobile USB cell phone charger"},"content":{"rendered":"            \n\t\t<div class=\"ngg-gallery-singlepic-image \" style=\"max-width: 640px\">\n\t\t\t    \t<a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/IMG_0955_small.jpg\"\n\t\t     title=\"\"\n             data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/IMG_0955_small.jpg\"\n             data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_IMG_0955_small.jpg\"\n             data-image-id=\"23\"\n             data-title=\"IMG_0955_small\"\n             data-description=\"\"\n             target='_self'\n             class=\"shutterset_3214d44af96a279197dc506fa0d6cc45\">\n            <img class=\"ngg-singlepic\"\n             src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/cache\/IMG_0955_small.jpg-nggid0223-ngg0dyn-640x480x100-00f0w010c010r110f110r010t010.jpg\"\n             alt=\"IMG_0955_small\"\n             title=\"IMG_0955_small\"\n              width=\"640\"               \/>\n    \t<\/a>\n\t\t      <\/div>\n        \n<p>Using your smartphone as a GPS tracker when biking tends to drain the battery very fast. For long tours this might actually be too fast. So I decided to build a mobile cell phone charger that runs on two standard AA batteries and extends the run-time of my smartphone. (To be honest before deciding to build my own I bought a commercially available one which unfortunately went up in smoke. Fortunately Amazon has a nice return policy and after once more killing the same model again I got my money back).<\/p>\n<p>I&#8217;ve previously experimented with the <a title=\"LT1073 - Micropower DC-DC Converter Adjustable and Fixed 5V, 12V\" href=\"http:\/\/www.linear.com\/product\/LT1073\" target=\"_blank\">LT1073<\/a> converter which is nice because it can provide 5V out of a single cell. However, this time a bit more power was needed and so I got hold of a <a title=\"LT1302 - Micropower High Output Current Step-Up Adjustable and Fixed 5V DC\/DC Converters\" href=\"http:\/\/www.linear.com\/product\/LT1302\" target=\"_blank\">LT1302<\/a> which is able to produce 5V at 600mA from a 2 cell supply.<br \/>\n<!--more--><br \/>\n<!-- index.php -->\n<div\n\tclass=\"ngg-galleryoverview ngg-ajax-pagination-none\"\n\tid=\"ngg-gallery-4c760abe68a3b1c443a09e1e4454bd61-1\">\n\n    \t<div class=\"slideshowlink\">\n        <a href='http:\/\/jaran.de\/goodbits\/2011\/07\/28\/building-a-mobile-usb-cell-phone-charger\/nggallery\/slideshow'>[Show as slideshow]<\/a>\n\t\t\n\t<\/div>\n\t\t\t<!-- Thumbnails -->\n\t\t\t\t<div id=\"ngg-image-0\" class=\"ngg-gallery-thumbnail-box\" >\n\t\t\t\t        <div class=\"ngg-gallery-thumbnail\">\n            <a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0947_small.jpg\"\n               title=\"\"\n               data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0947_small.jpg\"\n               data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0947_small.jpg\"\n               data-image-id=\"19\"\n               data-title=\"img_0947_small\"\n               data-description=\"\"\n               data-image-slug=\"img_0947_small\"\n               class=\"shutterset_4c760abe68a3b1c443a09e1e4454bd61\">\n                <img\n                    title=\"img_0947_small\"\n                    alt=\"img_0947_small\"\n                    src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0947_small.jpg\"\n                    width=\"225\"\n                    height=\"150\"\n                    style=\"max-width:100%;\"\n                \/>\n            <\/a>\n        <\/div>\n\t\t\t\t\t\t\t<\/div> \n\t\t\t\n        \n\t\t\t\t<div id=\"ngg-image-1\" class=\"ngg-gallery-thumbnail-box\" >\n\t\t\t\t        <div class=\"ngg-gallery-thumbnail\">\n            <a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0949_small.jpg\"\n               title=\"\"\n               data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0949_small.jpg\"\n               data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0949_small.jpg\"\n               data-image-id=\"20\"\n               data-title=\"img_0949_small\"\n               data-description=\"\"\n               data-image-slug=\"img_0949_small\"\n               class=\"shutterset_4c760abe68a3b1c443a09e1e4454bd61\">\n                <img\n                    title=\"img_0949_small\"\n                    alt=\"img_0949_small\"\n                    src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0949_small.jpg\"\n                    width=\"225\"\n                    height=\"150\"\n                    style=\"max-width:100%;\"\n                \/>\n            <\/a>\n        <\/div>\n\t\t\t\t\t\t\t<\/div> \n\t\t\t\n        \n\t\t\t\t<div id=\"ngg-image-2\" class=\"ngg-gallery-thumbnail-box\" >\n\t\t\t\t        <div class=\"ngg-gallery-thumbnail\">\n            <a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0951_0952_small.jpg\"\n               title=\"\"\n               data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0951_0952_small.jpg\"\n               data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0951_0952_small.jpg\"\n               data-image-id=\"21\"\n               data-title=\"img_0951_0952_small\"\n               data-description=\"\"\n               data-image-slug=\"img_0951_0952_small\"\n               class=\"shutterset_4c760abe68a3b1c443a09e1e4454bd61\">\n                <img\n                    title=\"img_0951_0952_small\"\n                    alt=\"img_0951_0952_small\"\n                    src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0951_0952_small.jpg\"\n                    width=\"225\"\n                    height=\"150\"\n                    style=\"max-width:100%;\"\n                \/>\n            <\/a>\n        <\/div>\n\t\t\t\t\t\t\t<\/div> \n\t\t\t\n        \n\t\t\t\t<div id=\"ngg-image-3\" class=\"ngg-gallery-thumbnail-box\" >\n\t\t\t\t        <div class=\"ngg-gallery-thumbnail\">\n            <a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0954_small.jpg\"\n               title=\"\"\n               data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/img_0954_small.jpg\"\n               data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0954_small.jpg\"\n               data-image-id=\"22\"\n               data-title=\"img_0954_small\"\n               data-description=\"\"\n               data-image-slug=\"img_0954_small\"\n               class=\"shutterset_4c760abe68a3b1c443a09e1e4454bd61\">\n                <img\n                    title=\"img_0954_small\"\n                    alt=\"img_0954_small\"\n                    src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_img_0954_small.jpg\"\n                    width=\"225\"\n                    height=\"150\"\n                    style=\"max-width:100%;\"\n                \/>\n            <\/a>\n        <\/div>\n\t\t\t\t\t\t\t<\/div> \n\t\t\t\n        \n\t\t\t\t<div id=\"ngg-image-4\" class=\"ngg-gallery-thumbnail-box\" >\n\t\t\t\t        <div class=\"ngg-gallery-thumbnail\">\n            <a href=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/IMG_0955_small.jpg\"\n               title=\"\"\n               data-src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/IMG_0955_small.jpg\"\n               data-thumbnail=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_IMG_0955_small.jpg\"\n               data-image-id=\"23\"\n               data-title=\"IMG_0955_small\"\n               data-description=\"\"\n               data-image-slug=\"img_0955_small\"\n               class=\"shutterset_4c760abe68a3b1c443a09e1e4454bd61\">\n                <img\n                    title=\"IMG_0955_small\"\n                    alt=\"IMG_0955_small\"\n                    src=\"http:\/\/jaran.de\/goodbits\/wp-content\/gallery\/usb-charger-lt1302-20110728\/thumbs\/thumbs_IMG_0955_small.jpg\"\n                    width=\"225\"\n                    height=\"150\"\n                    style=\"max-width:100%;\"\n                \/>\n            <\/a>\n        <\/div>\n\t\t\t\t\t\t\t<\/div> \n\t\t\t\n        \n\t\t\n\t\t<!-- Pagination -->\n\t<div class='ngg-clear'><\/div>\t<\/div>\n<br \/>\nSince no DIP version of the LT1302 was available I first soldered silver wire to the tiny SO-8 lead tips. After a successful run on a breadboard I soldered together a rather ugly but working package which is actually a bit smaller than a single AA battery.<\/p>\n<p>A first simple test run showed that two 2Ah cells could add approximately a 20% charge to my HTC Desire. That was a bit disappointing but enough for a start. Measuring input voltage and current and comparing it to the output voltage and current I calculated an efficiency of only 58% with 2 cells as a supply source which is far below the 80%+ it should actually deliver. Using a 3-cell setup the efficiency rose to 68% which was still not what I was hoping for.<\/p>\n<p>Since the only suitable casing I had lying around was a 15mm square aluminium tube I had to exchange the inductor with a smaller one (not featured on the pictures). On my <a title=\"Haard &amp; Dortmund-Ems-Kanal\" href=\"http:\/\/jaran.de\/goodbits\/2011\/07\/29\/haard-dortmund-ems-kanal\/\">first field test of the device<\/a> I realized that it kept a better charge than calculated and measured above with the old coil. A new measurement with the completed device and the new inductor showed an efficiency of 81% (2.18W input and 1.76W output) which is a very nice improvement indeed. The old coil probably had a much higher DC resistance and a core not suited for power conversion applications.<br \/>\nThe casing might receive some brushing to get rid of excess glue and some scratches.<\/p>\n<p><strong>Update (2011\/07\/31):<\/strong><br \/>\nFeeding the device with three cells reduces efficiency to about 75% (which is rather odd because the datasheet shows a theoretical increase in efficiency with higher supply voltage), so adding a third cell will increase the total available energy by less than 40% (instead of 50%). Anyway, using three instead of two cells has another disadvantage with the LT1302: If one of the cells is weaker than the other two it might run into a polarity reversal which cannot happen with only two cells because the LT1302 will not work under a voltage of 2V.<\/p>\n<p>Conclusion: if even more runtime is needed it&#8217;s likely the best solution to only use two cells at a time but to keep two more reserve cells at hand.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Using your smartphone as a GPS tracker when biking tends to drain the battery very fast. For long tours this might actually be too fast. So I decided to build a mobile cell phone charger that runs on two standard &hellip;<\/p>\n<p class=\"read-more\"><a href=\"http:\/\/jaran.de\/goodbits\/2011\/07\/28\/building-a-mobile-usb-cell-phone-charger\/\">Read more &raquo;<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0},"categories":[7,5],"tags":[],"_links":{"self":[{"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/posts\/130"}],"collection":[{"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/comments?post=130"}],"version-history":[{"count":11,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/posts\/130\/revisions"}],"predecessor-version":[{"id":388,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/posts\/130\/revisions\/388"}],"wp:attachment":[{"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/media?parent=130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/categories?post=130"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/jaran.de\/goodbits\/wp-json\/wp\/v2\/tags?post=130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}