Basics of Electricity
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BASICS OF ELECTRICITY
Understanding the basics of electricity will help you get the most out of your Watt's Up and
electric model. With these concepts you can intelligently compare electrical components
and conduct experiments to maximize their performance in your electric modeling hobby.
If you are new to electrical propulsion systems you may want to read through this a few
times. Experts can skip it.
We use the water and plumbing analogies to teach electrical concepts because people often
already have good intuition about water systems.
4.1
Charge
It all starts with charge.
Charge
is the basic unit of electric energy. Using the water analogy, charge is the “amount
of water”.
Charge (electrons actually) is what gets stored in a rechargeable battery by a battery
charger. Like water gets “stored” in an aquarium by a water pump a battery charger stores
charge in a battery.
Asking how much charge is in a battery is like asking how much water is in an aquarium.
A physicist will tell you that charge is measured in units of
Coulombs
(C) like water can
be measured in units of gallons. It turns out that
Amp-hours
(Ah) is also a unit of charge
and is more familiar to RC hobbyists. We’ll show why later when we discuss current.
Charge = Current
Time.
Charge can be measured in Amp-Hours by:
Amp-hours = Average Amps
hours of duration
4.2
Current
Current
is measured as an amount of something flowing per unit of time.
With electricity, the “something” flowing in a wire is charge, which is measured in
“Coulombs”.
A Coulomb per second of electric charge current has a special name. It is called an
Ampere
(abbreviated Amps or just A). A gallon per second of water flow doesn’t have a
special name. It’s just a gal/s.
So 20 Amperes or Amps flowing into a motor means it has a current of 20 Coulombs of
charge flowing
per second
.
Now we can explain why Amp-Hours is a measure of charge.
An hour is 60
60 = 3600 seconds. So an Amp-hour (meaning Amps times
hours)
= Ampere
Hour
And substituting the definition of an Ampere and of an hour this becomes
= (Coulomb/Second)
3600 Seconds which leaves 3600 Coulombs.
Coulombs are charge so there we are -- an Amp-hour (or Ah) is 3600 Coulombs
of charge.
It is common in RC modeling to discuss charge in units of mAh. The m is an abbreviation
for the Greek “milli” which means “thousandth” of something. So 1 mAh is 1/1000 of an
Ah. Conversely, 2 Ah is the same as 2000 mAh.
Here are some examples showing the important relationships between current, time and
charge.
1) Charging.
"Watt's Up" & "Doc Wattson" Watt Meter and Power Analyzer User's Manual
RC Electronics, Inc.
