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Forum Index : Electronics : Buck converters.
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Just ran the data sheet thru a translator & it's now readable. 2017-09-02_212301_FM9833e.pdf Might not be the best of chips out there, but 2 of these would provide a cheap useful in many cases. They are available with 1 cell & presume 2 modules could be paralleled to use one as the charge input & the other ass the 5V out. There seems to be a fair variety out there, just a bit hard to identify the chip. Phil. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Don't have any suitable regs here ATM, so planning on grabbing something today from RS. When I look at what's available there's a huge number to confuse me. So is say an LM1117T-Adj as good as any for this task? No complex requirements, just 18650 Li-ion in & 2.0V out. Thanks Phil. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
That thought is on my radar. BUT, tried it yesterday with an 6V SLA battery. It was sitting at 6.4V & current draw was 70mA = 448mW. The birds nest consisting of the "Juice Bank" module, FM9833e, that stepped the Li-Ion battery up to 5.0V & then dropped back to 2V with an LM2596 module pulled 90mA @ 3.9V = 351mW. So even that kludge is more efficient. ATM I've got an LM1117T-Adj on the battery, It was using 125mA @ 3.65V = 456mW. The fan is drawing 103mA @ 2.05V = 211mW. Surely I can do better than the 351mW that I can get with a step up & then back down. Have tried searching for both modules & chips that will work with the 2.8-4.2V in, and able to supply 2.0V out, but it's not my field of expertise. Anyone offer up some other suggestions? Would need to use an IC that's easy to work with on bread board, IE TO-220 etc. Thanks Phil. |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
I know you don't want to build a circuit, but a tiny 2 transistor multi vibrator will give you a nice little square wave generator, By changing the r and c values on each of the trannies, you can change the mark space ratio.... so what... Because the fan has inductance, the switched pulses will turn the thing into a buck converter. This is how normal pwm DC brush type motor drivers work. The motor adds the inductance, and the pwm drives the thing, and the high start torque at low pulse width comes from the buck action... torque is amps, speed is volts in this case. I have seen 40 amps@ 2v from a single 9 amp solar panel into a solar pump motor using this system. 8 or 9 components is not a lot of complexity... something like this http://my.integritynet.com.au/purdic/square-wave-generator.htm The tight voltage range on lithium stuff will probably keep the speed regulation pretty close without feedback. .........oztules Village idiot...or... just another hack out of his depth |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
I don't mind having to build a circuit. At the moment it's on a simple linear circuit I knocked up on a 40mm board. Just an LM1117, resistor, trim pot & a couple of caps. Works fine, just very inefficient, & would not give the best runtime in bad weather. It's just I'm not finding the right IC with my search methods. Phil. |
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