In a comment, Metis asked:<\/p>\n
How can I reliably measure and\/or control the output voltage of the JT? I\u2019m currently trying to build a small power supply to recharge a Li-ion battery and I\u2019d prefer to be able to keep the output voltage at (or rather below) a known level rather than invest in a buck converter to regulate it.<\/p>\n
I don\u2019t have an oscilloscope at the moment, trying to find one that\u2019s affordable, but until then I won\u2019t be able to measure it directly.<\/p><\/blockquote>\n
[When I wrote this, I didn’t read the above close enough.\u00a0 Voltage was what he was talking about.\u00a0 Skip to update for more.] You can control the JT power output by changing the resistor to a pot or variable resistor.\u00a0 The 1k resistor can be increased to 3.3k or much more, depending on the amount of light you want.\u00a0 I would try a 50k pot, with audio taper so it gives finer adjustment at low levels.\u00a0 But it will be maximum light at the lowest setting, which is at the counter-clockwise end.\u00a0 I have 100k audio pots with an on\/off switch, which makes it convenient.<\/p>\n
You also might want to consider using a module that’s made for this exact purpose.\u00a0 DealExtreme.com<\/a> sells this type of module.\u00a0 It’s a PC board that’s the diameter of the cell that goes into a flashlight (torch).\u00a0 These come in various voltages and currents.\u00a0 The different power levels are controlled by quickly switching it off and on.\u00a0 Some of them are rated for connecting to a single 2.6V Li Ion cell, such as the 16450, or else two RCR123 rechargeable cells in series.\u00a0 This makes it convenient to use any of several voltages.\u00a0 you could also add it to a bike light that uses three AA cells in series.\u00a0 They are typically very efficient, much better than a Joule Thief.\u00a0 They use surface mount components and their cost is very inexpensive.<\/p>\n
You also might consider getting the whole flashlight preassembled so all you have to do is mount it on the bike.\u00a0 Some have adjustable beams, which can give you enough beam width to cover the road.\u00a0 I bought one with the reflector that is bumpy, which spreads out the beam somewhat, and gives a bright spot in the middle.\u00a0 Mine is an Ultrafire, and uses a 16450 rechargeable cell.<\/p>\n
Update Jan 3 – Upo closer reading, I see what the issue is.\u00a0 I have built and blogged a few DC to DC converters that regulate the output voltage.\u00a0 Here is one.\u00a0 Here is another.<\/p>\n","protected":false},"excerpt":{"rendered":"
In a comment, Metis asked: How can I reliably measure and\/or control the output voltage of the JT? I\u2019m currently trying to build a small power supply to recharge a Li-ion battery and I\u2019d prefer to be able to keep the output voltage at (or rather below) a known level rather than invest in a <\/p>\n
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