The Battery LED Build Kit

The battery read fresh, on the label and spent, the LED resistor sized at the worst corner and rated for twice its heat, the light checked at the spent voltage, and the battery life budgeted so it never flatters the build

VoltLab's free tools each answer one question, and a battery-powered LED build asks them all at once. The LED Series-Resistor Calculator sizes a resistor from one supply voltage, the one on the label, though a battery reads above it when fresh and far below it when spent, and the LED in your hand may sit a little under its typical forward voltage. The Battery Life Calculator then asks for a current that nothing on the site worked out. This kit puts the tools in order for one build. It reads the battery at three voltages, sizes the resistor at the worst corner (fresh cells, the lowest forward voltage, a 5% resistor 5% low) and rounds up to a real part, rates it for twice its heat, and checks the LED is still lit when the cells are spent. In the worked example, a lantern of three white LEDs on four AA cells, the label sizing's 150 ohm part can pass 23.86 mA; the worst-corner part, 180 ohm, never passes more than 19.88 mA, and the battery budget, derated and rounded down, is 28.49 hours from 2,000 mAh. Every figure is computed by the site's own calculators; the lantern, capacities and meter reading are examples, and the per-cell voltages, spread, margin and derating are named rules of thumb. Low-voltage battery circuits only, with the safety lines for lithium and coin cells, soldering and clipping leads. Included: 23 printable pages with 7 steps, a build sheet, a battery budget sheet, a bench log, a resistor reference with color bands, and a personalised sheet worked from the numbers you enter in the calculators.

What’s inside

The full contents of The Battery LED Build Kit: size it, power it, and the working pages

Step 1, The Three Voltages Rule: an example lantern's AA and 9 V batteries read fresh, nominal and spent

The Three Voltages Rule: the battery read fresh, on the label and spent, for alkaline and NiMH cells
The Worst-Corner Rule: the resistor sized for fresh cells, the lowest forward voltage and a resistor at its low tolerance, rounded up to E12
The Twice-the-Heat Rule: the power at the worst corner, doubled, and the standard rating that clears it
The Headroom Rule: whether the LED is still lit when the battery is spent, and the voltage it goes dark
The Own-Resistor Rule: how many LEDs a string can hold on your battery, and one resistor per string
The Floor Rule: the battery budgeted with the worst-case current, derated and rounded down
The Meter Rule: the current checked with one reading across a resistor, and the safety lines for batteries and soldering
Three working pages: a build sheet, a battery budget sheet and a bench log with a pre-power checklist
A resistor reference: the worst-corner part, its color bands, rating and spent-voltage check across common batteries and LED colors
A personalised sheet worked from the figures you enter in the LED and battery calculators

Plus a second PDF, worked out for you

Run one of the free calculators first and buy from that page, and this sheet is computed from your own figures. Buy from here and the pack still arrives complete — the sheet simply has no numbers of yours to work from yet.

14-day refund, no questions asked. If the pack is not what you needed, email support@graburl.com and we refund you in full — you do not have to justify it or delete the file. Full policy.

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$19.00 including any taxes · PDF, 23 pages · instant download, link valid 7 days and 5 downloads.
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