The Basics
Table of Contents
Table of Contents
Introduction
Some basic concepts
Volts
Amperes (A) or Milliamperes (mA)
Watts (W)
Amp Hours (Ah)
The water flow analogy
Batteries in Series and Parallel
Batteries In Series
Batteries In Parallel
Introduction
Ok, so lets start with some very basic concepts that are essentially used in pretty
much anything you will do related to electric powered RC.
I’m going through this material because I know there are a lot of people out there
that are like I was when I first started with electric powered RC. I had a vague
recollection of what Volts, Amps and Watts are, but I didn’t really have a good
understanding of the relationship between them. This is the foundation you will
need for everything you do related to electric powered RC so I thought it would
be good to start at the beginning so we are all on the same page. Please note that
I am not a physics major or an electrical engineer so I humbly apologize if I make mistakes. If you find
any, please feel free to let us know and we will update the information.
Some basic concepts
Volts
In short, Volts (Symbol: V) represents the electric potential difference.
Amperes (A) or Milliamperes (mA)
Also refered to as Amps, Amperes are represented by the symbol A or by mA for
milliamps. Amps represent the current or flow rate.
Watts (W)
Watts represent the power being generated as a combination of Volts and Amps.
Amp Hours (Ah)
Amp Hous (or milliamp hours - mAh) represent the capacity of a battery. 1 Ah (or
1000 mAh) means that you can draw 1A from the battery for a full hour before the
battery is completely empty.
The water flow analogy
This is a good analogy used to explain the relationship between Volts, Amps and
Watts. Imagine a basin of water where Volts are represented by the pressure difference
between the pressure inside the basin and the pressure outside the basin (higher
inside than outside). This determines how fast the water (or electrons) will travel along the
output water channel (or circuit). Now imagine an opening in the basin from which the water can flow. The
current (in Amps) is a measure of volume of water flowing through the opening per
unit of time (per second for example) or flow-rate. In this example, the total power
(in Watts) generated is represented by the total amount of water that has exited
the basin within the same amount of time. This is a factor of pressure difference
(Volts) and flow-rate (Amps). So Watts = Volts x Amps.
You can even go a little further with this example to help you visualize other
properties of an electric circuit. Imagine the size of the opening (or pipe) leading
out of the basin represents the size (or gauge) of the wire that forms the circuit.
Now, the bigger the pipe (or wire), logically the greater the current (flow-rate
as gallons per second or Amps) can flow through the pipe. So the greater the Amps
can pass through the pipe and therefore generate greater power (total gallons in
one second or Amps).
Now, imagine the water is a really abrasive liquid which generates heat with
friction. Now imagine the same amount of current (Amps or Gallons per second) flowing
through a small pipe and through a large pipe. There will be much more heat generated
from the current going through the small pipe than there will be from the current
going through the large pipe. The same holds true for passing current through small
wires and large gauge wires. The smaller the gauge, the hotter the wire will get
assuming the same current.
Also, imagine that the output pipe can have varying amounts of resistance (Ohm’s)
which can vary between very little resistance (completely hollow pipe with no obstructions)
to high resistance where the pipe has lots fine wire-like obstructions inside the
pipe. Now, imagine the same current going through a pipe with low resistance and
one with high resistance. The pipe with low resistance will be cooler, will have
more current (Amps) and consequently more power (Watts). Conversely, the wire with
more resistance will be hotter, will have less current (Amps) and consequently less
power (Watts). The pipe could also melt! This is bad!
Resistance is a factor of the gauge of the wire as well as the material that composes
the wire.
Just remember that the Water-Flow analogy is exactly that, an analogy. It is meant
to give a very general visualization of how electricity works and is not 100% complete
but is a good tool for the basic understanding of electricity. To find out more,
you can learn all about electricity from any number of textbooks and from online
websites like Wikipedia.
Batteries in Series and Parallel
Ok, now that we have a good understanding of Volts, Amps and Watts, I would like
to talk about what happens when you take two batteries and put them in series or
in parallel.
Batteries In Series
This is when you take two (or more) batteries and you put them in-line with each
other. To do this you connect the negative pole (usually the black wire) of the
first battery to the positive pole (usually the red wire) of the second battery.
You then use the positive pole (red wire) of the first battery and the negative
pole (black wire) of the second battery as if it was one single battery. The result
is that you are adding the voltage of the two batteries together and the Amps
(and Ah) stay
the same. For example, if you take two 3.7V batteries that each have 4000mAh, the
resulting “battery” will have 7.4 Volts and 4000mAh.
So remember, in series means that you are adding up the Voltage of all the batteries
that are in the series.
In this example, it is important that all the batteries have the same mAh rating.
The voltage can differ. It's probably a good idea for all the batteries to
have the same output C rating as well. I'm not sure what would happen if the C
rating is different, but I would think that the current in your circuit would be
limited to the lowest C rating (or to the maximum Amp output of the battery with
the lowest C rating).
Connecting batteries in series is normally done by connecting them to a Y-Harness
(or Y-Cable). Here is a diagram of a Y-Harness with Deans connectors:
Here is what a Y-Harness looks like (with XT-60 connectors):
Batteries In Parallel
This is when you take two (or more) batteries and you connect all the positive
poles (red wires) together and separately, all the negative poles (black wires)
together. The result is that you are adding the mAh of the batteries together and
the Voltage stays the same. So with the two battery example above, if you configure
them in parallel (instead of in-series), the resulting “battery” will
have 3.7V but the resulting mAh will be 8000mAh.
In this example, it is important that all the batteries have the same Voltage
(V). It is also recommended that the mAh and output C rating be the same for
all the batteries. I'm not exactly sure what would happen if they aren't
matched, but I would assume that the battery with the lowest mAh rating or the
battery with the highest C rating would drain faster than the other batteries.
You will have to do your own research if you want to know exactly what happens,
but I would recommend using matched batteries for a parallel battery setup.
Connecting batteries in parallel is normally done by connecting them to a Parallel
Wiring Harness (or Parallel Wiring Cable). Here is a diagram of a Parallel Wiring
Harness with Deans connectors:
Here is what a Parallel Wiring Harness with XT-60 connectors looks like:
