Explain basic electrical terms such as Volts, Amps, Watts, and Amp-Hours Using water as an analogy makes basic electricity
easier to understand. Imagine a 100 foot water tower. Its height above a
given spigot determines the amount of pressure available at that spigot. A
spigot at 100 feet high has almost no pressure, while a spigot at the base
of the tower has a lot of pressure. The difference in pressure between two
points is called voltage. Now, imaging two spigots at the base of the
tower, one with a 1/2" pipe, the other with a 1" pipe. The
amount of water that will flow from the 1" pipe is much greater than
the smaller one. The measurement of the amount of flow is called amperage.
Amp-Hours is a measurement of how much water is in the tower -- how much
it holds. Expressed another way:
Electrical
Water
Volts (potential)
Pressure
Amps (current)
Volume
Amp Hours (capacity)
Gallons
Leaving the water analogy now.. Watts is the same thing as power. It is
always calculated as volts X amps. 2 volts at 50 amps = 100 watts of
power. 50 volts at 2 amps = 100 watts of power. 25 volts at 4 amps = 100
watts of power. Simple enough, but there is a reason for different
voltages. Amps is a measurement of current flow, and current tends to heat
the substance through which it travels. It doesn't take much current to
melt a tiny conductor as in a telephone wire. Heat is wasted energy unless
you're trying to generate heat, so the larger the gauge of wire, the less
energy is wasted in the transport of current. So why don't we use high
voltage, low current, and small wires? Well.. voltage can be nasty. The
higher the voltage, the more likely it is to jump through an insulator
like the sheath of a wire or air. Lightning is very high voltage, so it
bridges the insulator (air) to get from the high voltage cloud to the zero
voltage ground. Higher voltages are also much more dangerous to humans.
That is, no one gets shocked touching the positive and negative terminals
of a 12 volt battery, yet the battery has enough power to weld steel. On
the other hand, 110 volt outlets in your house will shock the heck out of
you and can even kill. All it takes is 1 amp through the chest to stop
your heart. A higher voltage makes it easier to break through the
insulation (your skin) to get the current to flow.
Now let's look at series and parallel circuits. Suppose I have two
identical 12 volt batteries. If I connect the positive of battery 1 to the
negative of battery 2, I will measure 24 volts between the negative of
battery 1 and the positive of battery 2. This is a series circuit. Voltage
adds, but current and amp hours do not. I can run 24 volts at the same
current as either of the batteries can produce, and at the capacity (amp
hours) of either of the batteries. If I connect negative of battery 1 to
negative of battery 2, positive of battery 1 to positive of battery 2, I
will read 12 volts from either battery's negative to either battery's
positive. This is a parallel circuit. Current and amp hours add, but
voltage does not. Expressed another way:
Series
Adds voltage
Parallel
Adds amps and amp hours
What is a Watt?
A Watt is a measurement of power. It is NOT a
measurement of useful power. That is, an inefficient 600W system may not
accelerate as fast as an efficient 300W system. If a motor gets too hot to
touch by the time the battery is exhausted, it is wasting a lot of energy as
heat, and you get no benefit from that heat. The more efficient the motor,
the cooler it will run during use. You can exhaust a 12AH battery pack on
a Phoenix motor and barely feel heat. That's efficient!
In technical terms, a Watt is Volts times Amps. A 48V controller that
will deliver 40 Amps is a 1920 Watt controller (48 X 40 = 1920). This is
the rating of the controller, not the motor. Motor watt ratings are not
real useful in our application because motor ratings deal with continuous
load at continuous speed. We do not believe Watts is a good measurement to
use for comparing light electric vehicles because it is misleading.
Instead, we use charts that show you actual on-the-road performance.
A
large diameter motor, such as the Phoenix, produces a lot more torque
given the same amount of power as a small diameter motor such as the
RoadRunner. That is, for the same amount of power used, the Phoenix will
far out-perform the RoadRunner. I'm not sure why this is; I just know that
it is. Perhaps it has something to do with leverage.
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San Angelo, TX 76903
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