• EVERYBODY: As a general rule of thumb, do not connect any of these experiments to any high-voltage source -- nor to any device connected to high voltage (such as a manufactured TV, radio or lamp, or any electrical appliance).

• KIDS: Do NOT mess with the high-voltage (110 volts or more) power from wall outlets, light sockets and extension cords. Just don't. Stick to voltages at or below 12 volts. And still be careful. Runaway current, even at low voltages, can cause burns, fire and explosions. Be sure to arrange things EXACTLY as instructions indicate (unless you see a hazard in them). Always be ready to disconnect power INSTANTLY.

• ADULTS: Be extremely cautious with the high-voltage (110 volts or more) power from wall outlets, light sockets and extension cords.
  • NEVER assume you're safe when working with high voltages. ONE mistake can be catastrophic, even fatal.
  • Wear rubber gloves.
  • Keep your LEFT hand in your pocket, to reduce the risk of making an electrical contact that passes through your heart -- and use only your right hand (a traditional electrician's technique).
  • Know where the circuit breakers (or fuses) are, and how to use them to interrupt current.
  • Have another adult nearby trained to do just that if you get shocked. They should not attempt to touch you, but rather shut off power from a safe place, and then push (or kick) you away from it with something not metal -- or push away the electrical item you're in contact with. Pulling is more hazardous.

• READ THEM FULLY BEFORE ACTING: Don't assume you know what you're doing until you've read ALL of the instructions (multiple times, if necessary). Then procede to follow them.
• FOLLOW THEM: Be sure to arrange things EXACTLY as instructions indicate (unless you see a hazard in them).
  • BEFORE you start:
    • Follow the SAFETY instructions.
    • Make sure you have the correct...
      • INSTRUCTIONS
      • WORKSPACE (clear, clean, dry & secure)
      • TOOLS
      • PARTS
      • POWER SOURCE (adequately charged)
  • WHILE WORKING:
    • Follow the SAFETY instructions.
    • Make sure devices are ORIENTED the correct way. (assembling things backwards could damage things, even start a fire or tiny explosion).
    • Make sure POLARITY is correct for all items -- ensure that Positive (+) and Negative (-) contacts are made correctly -- not just with batteries, but also with electrolytic capacitors, diodes, transistors, integrated circuits, LEDs, and everything connected to them.
    • ASSEMBLE things in the prescribed ORDER.
    • MEASURE, TEST and OPERATE things in the prescribed ORDER.
    • If something is wrong, STOP, and go back and fix it, before moving ahead.
  • IF SOMETHING SEEMS to be RISKY or HAZARDOUS -- DON'T DO IT.

For best INITIAL results,
  buy NON-rechargeable alkaline batteries

 
Long-life, good-quality, 1.5 volt alkaline batteries are the most effective batteries for most experimenting. (Do NOT try to recharge them; they can blow up if you do -- mine did.)
 
Many electronic devices and kits, today, like most of those of the 20th Century, assume your batteries are of the NON-rechargeable types -- common 1.5-volt batteries. ( Two of these, combined, produce 3.0 volts. )
  (The small rectangular alkaline batteries produce 9.0 volts.)
 
By comparison, nearly all rechargeable batteries produce just 1.2-volts per cell. ( Two of them produce only 2.4 volts, which can make a significant difference in the behavior of some circuits.)
  (Most small rectangular rechargeable batteries produce 7.2—7.4 volts; a few produce 8.4 volts.)

Rechargeable batteries are the most expensive batteries for an initial purchase (especially since you must also buy a recharger), but they rapidly pay for themselves as you use them up, and then recharge them, then use them again, over and over.
 
ONE good set of rechargeables does the work of DOZENS of "cheaper" NON-rechargeables -- quickly saving you a ton of money, and lots of needless trips to the store. One of the most quickly-profitable investments anyone can make.

---


 
About RECHARGEABLE BATTERIES:
There are various types, but...
The BEST (for normal use, at present, in 2018) are:
• "NiMH" ("Nickel-Metal Hydride) batteries.
AVOID:
• "Li-on" ("Lithium-Ion") batteries -- as they are unusually prone to fire;
• "Ni-Cad" ("Nickel-Cadmium) batteries -- as they are suceptible to "memory" issues that can limit their rechargeability - and to "thermal runaway" that can cause explosion or fire.

---


About battery RECHARGERS:
When you buy rechargeable batteries, also buy the exactly-matching recharger(s), of the same brand(s). (Recharging a battery with the wrong recharger could cause explosion or fire). NEVER use a "rapid charger" with a battery it wasn't specifically designed for.

---

• BEST batteries:
  "Duracell," followed by "Energizer."
  Sunbeam's "gold-top" alkaline batteries seem adequate, too.
  The relatively cheap green rechargeable "Thunderbolt" batteries, from Harbor Freight, seem to be worth the money, though not as effective as these other brands.

• WORST batteries:
  Sunbeam's cheaper red-and-white batteries. Also avoid "Ray-O-Vac," "Eveready" and "Radio Shack" brand batteries. They're cheap, short-life, weak batteries, and the Ray-O-Vac seem prone to nasty, destructive leaks. Any off-brand battery is likely poor quality, or outright junk.

Battery capacity is, essentially, how long a battery can continue to put out a given amount of current -- measured in Amps ("A") or milliAmps ("mA" -- one-thousandth of an Amp) -- before it is completely discharged. Obviously, more is better.
 
a 1.0 Amp-hour ("1 Ah") battery
-- more often called a 1,000 milliAmp-hour ("1000mAh") battery
-- can, at best, supply
1 Amp of currrent for 1 hour.
or 1 milliAmp (1 one-thousandth of an Amp) for 1,000 hours.
or 2 milliAmps for 500 hours.
or 20 milliAmps for 50 hours.
or 200 milliAmps for 5 hours.
And so on.
 
While NON-rechargeable batteries aren't usually marked with their capacity, nearly all rechargeable batteries are marked with their capacity, in mAh -- telling you how much energy the battery can hold at full charge.
 
Typical values in AA-size batteries range from weak 50mAh batteries (sometimes installed in cheap solar yard lights) to powerful 2600mAh batteries (top-brand consumer rechargeables). Some industrial batteries are even higher.
 
Most rechargeable AA batteries, today, can store between 1100 and 2500 mAh. It's far better to spend the little extra to get the higher-capacity batteries. They do more, longer -- and seem to survive longer in heavy use and recharging -- before burning out altogether. (Yes, even rechargeables eventually weaken, and find it hard to fully recharge -- and finally quit permanently -- but only after you've gotten more than your money's worth out of them.)

• The electrical current rates, of the various small electronic devices and projects, range from a few milliAmps, to (momentarily) a couple of amps (2000 mA), or more.
• Typical current rates, for most kit projects, are probably between 20 and 500 mA.
• The higher-current circuits -- one Amp (1000mA) and above -- probably only pull that current momentarily, or until you release the "key" or other momentary switch contact.

REALLY SPEND TIME with ONE PROJECT at a time:

• read the instructions (if any) fully before beginnning,
• check out the components before putting them in the circuit,
• carefully note the outcomes, and reflect upon them, and
• consider alteratives and practical applications.
• Talk it over with someone.
• Let the lesson really soak in, and truly enrich your knowledge.

  If you can afford it, buy one of each type ("analog" with a moving needle -- and "digital" with a digital display) -- they each have advantages and disadvantages. Combined, they're really handy.

•   STUDY THE METER'S INSTRUCTIONS, THOROUGHLY, and
    EXPERIMENT CAREFULLY with each feature.
•   ASK AN EXPERT FOR ADVICE on using the meter.
•   SET FUNCTION SELECTOR to LEAST-SENSITIVE SETTING FIRST, when measuring a completely unknown energy or resistance:
  • Volts (V), start at the highest voltage setting, then work your way down, until you get a proper indication.
  • Amps (A)--- current -- start at the highest Amperage setting, then work down (towards milliAmps -- mA).
  • Ohms (Ω)-- resistance -- start at the LOWEST resistance, and then work your way UP (from Ω.to KΩ to MΩ)

•   IF THE METER FAILS,
  CHECK...
  • THE SETTINGS, then
  • THE FUSE and
  • THE BATTERY.
    Don't freak out just because your meter isn't working.
  • Is there an "ON" switch? Is it "ON"?
  • Did you set the function switch to the correct function?
  • Did you set it to the correct maximum-range setting? (Don't test 115 volts on the 10-volt setting. Don't test 0.2 volts on the 1000-volt setting)
  • Is the battery dead, or dying?
  • Fuse blown? Normally, meters also have very sensitive small FUSES inside them, to prevent you from blowing up the meter. If the meter fails, check the fuse. If the fuse is not intact, replace it (exactly) from an electronics, hardware, or automotive store. (The fuse has its part number or specifications stamped or engraved in the metal parts of the fuse; hard to read, but extremely important).

Just keep in mind that most components have a certain amount of "slop" in them:
Their component's official or marked ratings may be very precise,
but the component, itself, will probably only be approximately that value.
The range of acceptable or intentional variation of a component, or a circuit, is called its tolerance. Many resistors, for instance, have a "tolerance" of plus-or-minus (+/-) 20%. (A resistor marked as "100 ohms" may actually be anywhere in the range between 80 and 120 ohms.)

REPLACEMENT PARTS are available (usually cheaply) from:

• LOCAL STORES: Electonics hobby or pro shops, like some Radio Shack stores (yes, a few still exist), and some industrial-supply distributors. Ask a local electronics technician, ham radio operator, electrician or appliance repairman where to go.

• ONLINE retailers and distributors (industrial pros turn to Mouser Electronics, DigiKey, Grainger Supply, and others).

• BASICS -- Wire, switches, bulbs and other such basics -- can be found in hardware and auto-supply stores (and the staff can be helpful in finding the items), and sometimes in such departments at department stores. And these devices can be great basic experimenting tools to add to your kit.

• RECYCLE: Some parts can be "cannibalized" from junk equipment, or from cheap, new stuff. I've scavanged low-power rechargeable batteries -- and solar panels, and LEDs -- from cheap two-dollar yard lights sold at the local dollar store. Just be sure to test these scavanged parts, before using them, to ensure they'll work as you hope. Don't replace faulty parts with more faulty parts.