{"id":12135,"date":"2026-04-16T19:21:29","date_gmt":"2026-04-16T18:21:29","guid":{"rendered":"https:\/\/mathscitech.org\/articles\/?page_id=12135"},"modified":"2026-04-16T19:32:02","modified_gmt":"2026-04-16T18:32:02","slug":"electronics-3","status":"publish","type":"page","link":"https:\/\/mathscitech.org\/articles\/electronics-2\/electronics-3","title":{"rendered":"Electronics (Part 2)"},"content":{"rendered":"

<\/a><\/p>\n

C. Power Supplies (Batteries, Holders, Converters) Fuses, & Heat Sinks<\/h2>\n

Barrel Jack notes:<\/p>\n

    \n
  1. 2.1mm barrel jack – default is center positive, i.e. inside is positive, shaft is negative. Read to see if center negative (opposite polarity) is specified.\n
  2. Polarity reversing barrel jack cable 2pc. for \u00a35.60 (\u00a32.80 ea)<\/a> – useful for centre negative guitar effects pedal and other musical equipments\n
  3. 3-way barrel jack connector cable \u00a34<\/a>\n<\/ol>\n

    <\/a><\/p>\n

      \n
    1. DC Power Supply (wallwart, 110\/220V AC to DC) with 2.1mm barrel jack<\/strong>
      \nNotes:<\/p>\n
        \n
      1. wallwarts are unregulated power supplies. Use 100uF capacitors across their inputs to smooth them. E.g. 9V wallwarts measured at 9.19V and 9.13V (not bad).
        \n        Wallwarts & Brick Basics<\/a> | How Power Supplies are built: Transformer+Rectifier+Smoothing+Regulator<\/a><\/p>\n
          \n
        1. Breadboard Power Supply MB-102 – convenient form factor plugs into 400+-tie points breadboard (watch out to align +\/- with red\/blue power stripes), takes 5VDC USB power input or 9VDC wal-wart, converts down to 5V or 3.3V, or both to have two power rails, \u00a34.67 next day<\/a>, or 3pc for \u00a33.79 (\u00a31.26 ea)<\/a>\n
        2. 9V DC<\/strong> 1A 9W \u00a33.95 (two weeks)<\/a>, \u00a34.77 (five days)<\/a>, or 2A 18W for \u00a35.79, five-days<\/a>, or \u00a38 next day<\/a>. Also: Center negative 1A \u00a39.74 next day<\/a> (for e.g. guitar pedals and other musical equipment).\n
        3. 5V DC<\/strong> 2A 10W: \u00a34.03ea 1 week (ebay)<\/a>, or \u00a33.38ea (MOQ2) ebay<\/a>, \u00a33.41ea (MOQ2)<\/a>, or \u00a34.69 in 2-3 wks<\/a>, or \u00a37 next day<\/a>\n
        4. Converter cores: 5V DC switching power supply 2A, 10W, no cables, \u00a32.39<\/a> 2.8″ x 1.5″ x 1.2″ compact\n<\/ol>\n

          <\/a><\/p>\n

        5. Batteries and Holders<\/strong>
          \nReferences: <\/p>\n
            \n
          1. AA have better energy density than 9V batteries<\/a>: 4.6x more energy, for 3x worse weight and 2x worse volume\n
          2. Camelion battery information<\/a> | Table: Internal Resistance of Batteries<\/a> Used batteries have higher resistance, upto 5x | List of Battery Types<\/a> Thought all 1.5V batteries were the same? They’re not. Read to understand the properties of different types of batteries. | Zinc Carbon batteries<\/a> can be 25% cheaper per unit than Alkaline batteries (18p vs. 23p), but you’re typically getting less for your money electrically, except in low drain, intermittent use applications. | When a Lithium battery gets hot…<\/a> remove, put in open air, cover, let cool. Do not use again | Battery descriptions and stable voltages<\/a> | CR123 safety<\/a> | Manually recharging Li-ion\/Li-Po batteries with a desktop power supply<\/a> – punchline, first run at CC (constant current) and the voltage will rise, then charge at CV (constant voltage) and the current will drop trickle charging the last bit of the journey | Li-Po slim high density various shape batteries<\/a> – charging\/building tutorial\n

            Other batteries: 18650 15969<\/p>\n

            <\/a><\/p>\n

          3. Table: Power Specs of Common Batteries<\/strong>
            \n
            \"\"<\/a>

            Electrical capacity of common battery types.
            Source: https:\/\/daycounter.com\/LabBook\/Battery-Capacity-Comparison.phtml<\/p><\/div>\n<\/ol>\n

              \n
            1. Battery contacts kits for direct PCB insertion (instead of holders): Contact plate spring kits, 10 pairs for \u00a32 (20p each pair), ebay<\/a>, Leaf spring kits,\n
            2. LiPo batteries, high density, thin – example: 3.7V $12 next day<\/a>\n
            3. 9V batteries:\n
                \n
              1. Standard current: Current price: 15 for \u00a311.15 (74p ea)<\/a> 4 for \u00a35.50 (\u00a31.38 ea)<\/a> or 4 for \u00a36 (\u00a31.50 ea)<\/a> or 8 for \u00a37.50 (94p ea)<\/a> or \u00a320 for 24pc (83p ea)<\/a>\n
              2. High current: 9V battery high current, \u00a31.59<\/a>\n
              3. 9V Battery Clip Connector (Wiring Harness), RECOMMEND: Hard Plastic not Faux Leather which has poor connectivity: \u00a33 for 5<\/a>\n
              4. 9V Battery Holder (open), two types. With loose wire \u00a33.55 for 10pc (35p ea, 4 weeks)<\/a>, or \u00a35.00 for 10pc (\u00a350p ea., 4 weeks)<\/a> or \u00a35.55 for 10pc (\u00a355p ea, 4 weeks)<\/a>, or with DC barrel plug: \u00a311.50 for 10pc (\u00a31.50 ea, 4 weeks)<\/a>,\n
              5. 9V battery box with barrel plug, Lowest price: 80p ea (MOQ1). Current price: 10pc for \u00a36 (60p ea)<\/a> or \u00a34.40 ea (MOQ1)<\/a>\n <\/ol>\n

                <\/a><\/p>\n

              6. 3V Coin Cell Battery:\n
                  \n
                1. CR1220 3V coin cell (smaller), Li ion: \u00a31.65 for 5pc, (33p ea)<\/a> or \u00a31.60 for 5pc, (32p ea)<\/a>\n
                2. CR2032 3V coin cell (button) batteries (thicker than 1220), Li ion: Low: 10 for \u00a31.79 (18p ea). Now: \u00a34.60 for 20pc (23p ea)<\/a> or 20 for \u00a35 (25p ea)<\/a>, or 20 for \u00a36 (30p ea)<\/a> or 10 pc for \u00a34.00 (40p ea.)<\/a>, or 10 for \u00a34 (40p ea.)<\/a>\n
                3. CR2032 holder: open-holder lowest price \u00a31.08 for 20pc (5p ea) or 82p for 10pc (8p ea), or \u00a34.50 for 20pc (22p ea), or \u00a35.40 for 20pc (27p ea, 3 wks)<\/a>, or \u00a36 for 20pc (30p ea, next day)<\/a>, polarity: + is at the raised neck of the holder; (to see how to remove the battery from the holder later, see here<\/a>) Enclosed-holder: CR2032 holder with wire lead and button 68p<\/a> (need voltmeter to identify polarity of the lead wires as they are both white). Vertical open holder: Lowest: 56p ea, Now: 5pc for \u00a34 (80p ea.)<\/a>\n
                4. CR2032 6V double coin cell holder: Dual holder enclosed case (6V) with on\/off switch and wire leads, 3pc for 90p (30p ea)<\/a>\n

                  Using the double coin cell holder is not obvious: Cell 1 (closest to wires) goes in with + side up; Cell 2 (furthest from wires) goes in with + side down.<\/i>\n <\/ol>\n

                5. 1.5V Button Cell Battery: LR41, LR1120, LR1130, LR43, LR44=AG13<\/a> from 30mAh to 120mAh\n
                    \n
                  1. LR41 button cell (1.5V): 10 pc for \u00a31.86 (19p ea.)<\/a>\n
                  2. LR44 button cell (1.5V): 10 pc for \u00a31.85 (19pc ea.)<\/a>\n
                  3. LR1130 button cell (1.5V): 20pc for \u00a31.88 (9p ea)<\/a>, or 10pc for \u00a31.84 (18p ea)<\/a>, or 10pc for \u00a32.30 (23p ea)<\/a>, or 10pc for \u00a33.25 (33p ea) same day<\/a>\n
                  4. Holder for LR41, 100pcs for \u00a38 (8p ea.)<\/a> and alternative<\/a>\n <\/ol>\n
                  5. MN21 23A 12V wireless doorbell battery, 2 for \u00a32.28 (\u00a31.14 ea)<\/a> same day, or 5 for \u00a33 (60p ea)<\/a> 2 days\n
                  6. Li-Ion 3V Safety Precautions for Lithium batteries<\/a>\n
                      \n
                    1. CR123A (CR17345) (3V) Li ion: 2pc for \u00a32.48 (\u00a31.24 ea)<\/a> or 2pc for \u00a32.55 (\u00a31.28 ea.)<\/a> or 18pc. for \u00a317 (95p ea)<\/a> 960 mAh batteries boosted to 5V. These deliver high current and maintain stable voltage for the duration of their life (10 years), so are essential for battery powered motors, and other projects with sustained current draws of 150mA or more. Design details<\/a> WARNING: If you drop this battery you should assume it is internally damaged, and discard. If you use it, you will find erratic voltage, and it will start to get hot, and a chain reaction may start that causes it to get hotter slowly even if not connected. In this case, put it outside and cover it with a saucepan for a few hours and then you can safely recycle it in a battery recycling center.\n
                    2. Battery holders for CR123A: Best price 24p ea. (2019). Currently: 10pc for \u00a33.88 (38p ea)<\/a>, or 6 pc for \u00a32.50 (42p ea.)<\/a> or 5 pc for \u00a36 (\u00a31.20 ea.) next day<\/a> or 20 pc for \u00a310 (50p ea.)<\/a>\n <\/ol>\n
                    3. AA and AAA batteries: Zinc Carbon 30pc AA and 20pc AAA for \u00a38.50 (18p ea)<\/a>\n
                        \n
                      1. AA Zinc Carbon (14500, 14mmx50mm) batteries: lowest Zinc Carbon was \u00a34 for 28pc (14p ea). Currently Zinc Carbon \u00a34.60 for 20pc (23p ea)<\/a> or or \u00a34.00 for 10pc (40p ea.) Camelion<\/a>\n
                      2. AA Alkaline batteries: Lowest Alkaline was \u00a37.45 for 40pc (19p ea). Currently: Alkaline
                        \n                        32 for \u00a39.79 (31p ea.) Maxell (Same Day delivery)<\/a>, or Amazon Basics, \u00a313.50 for 40pc (34p ea.)<\/a>, or or high current, 74p (for 2 pc)<\/a><\/p>\n
                      3. AAA Zinc Carbon 1.5V batteries (low current capacity): Low 10 for \u00a32.07 (21p ea). Now: 28pc. Alkaline for \u00a36.23 (23p ea.)<\/a> or 10 for \u00a33.33 (33p ea)<\/a>. WARNING: Not all batteries are the same — LR03 (alkaline) and R03 zinc carbon<\/a> are the same nominal voltage but R03 have typically half the current capacity as LR03.\n
                      4. AAA 1.5V batteries Alkaline: Low: 32 for \u00a38.46 (26p ea). Now: 16 for \u00a35 (31p ea)<\/a>, or 20 for \u00a39 (45p ea)<\/a>, or 32 for \u00a312 (38p ea.) Maxell (Same Day delivery)<\/a>\n
                      5. Battery Holder with Flying Leads:\n