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Old 10-30-2014, 01:03 PM
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voltan voltan is offline
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Join Date: Jul 2014
Location: brisbane,australia
Posts: 107
hi dave.this is the most efficient setup i have tried so goes to mr Qantstuff for diagram A.the diode between the - rail and vr1 has a forward voltage drop around .65v( i use a fr302 and a schottky 1n5189 in series).this keeps Q1 around the conduction threshold regardless of input voltage and vr1 adjustment which controls the base current.this approach provides crude regulation and makes for hard and fast switching and higher operating frequencies than usual.
next trick is both windings and the battery supply power to the led.the red arrows show the path of emf when the field collapses.
diagram B is modified to run off small solar cells pillaged from garden lights.the output charges 4 aa nimh cells in only 1 winding and c1 push on field collapse but i got more efficiency this way because d2 is another 1n5189 with less v drop(.2-.3v), than going through d1.
input is around 1.5v when the sun is out and output is up to about 5.4v so i added another winding for diagram C.this helps a little bit. 1.5 v 50ma in=5.3v 11.5ma out.that's over 80% which is decent for a simple diy converter,and that's with 2.2 ohm meter shunts and vr1 tuned aggressively,622 ohms,for max output current.with these circuits i have measured efficiencies around 85-86% with vr1 backed off but as it's solar powered why not go for max charging current.
next step is to try diagram B with the third winding,L3 piggybacked on to L2.i need more solar cells to get say 80-100 ma at 1.5 to 2 volts.this will increase the charging current to the battery pack.
solar panels have a different voltage/current curve to other power sources.for best performance they need to be matched to the load with the right series/parallel combinations.
t1 is a mje340,hfe measures 75. c1 is 25v 4700uf,presumably low esr from a SMPS. inductor is a small ferrite torroid with 16 turns each winding.
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Last edited by voltan; 10-31-2014 at 12:47 PM. Reason: grammar
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