![]() ![]() ![]() If the motor would have been in good condition, it would run perfectly under the light load meant for it. This resulted in a too small resistance that caused that the large capacity 12 V car battery able to deliver several amperes and quickly burned the poor small motor. P = V x I or P = (V) squared / R In the case of our friend FINTON above, the small motor must have been defective, most probably having some shorted windings. Therefore, power can be calculated from the following simple relations: I = V / R, V = I x R, R = V / I. ![]() POWER is the result of multiplying applied voltage times current, so that a WATT is produced or dissipated when a current of one Ampere flows pushed by one Volt. (its windings are made with a much larger wire gage, just look at the diameter of the car battery cables!). BUT if we connect a much larger motor, like the Starter Motor of a car, the same 12 V battery will flow a large current, maybe 150 Amperes! because this motor presents a much lower resistance, of around 0.08 Ohms. If we connect an electric motor, a small one, it will allow just a fraction of an Ampere to flow through it, say 250 milliamps or so because the small wire that is used in the windings will present a comparatively large RESISTANCE of about 48 Ohms. This way is all too easy to fully understand and even predict how the devices will work when the power is applied to the circuit: Let's say we have a car battery with a nominal 12 volts (in reality it could have as few as 11 volts when almost discharged, to a little above 14 volts, when fully charged ans just recently disconnected from the charger!). Now, using the unit system, the voltage is measured in VOLTS, the current in AMPERES, and the resistance in OHMS. The VOLTAGE of the circuit source or supply is akin to the PRESSURE of the water inside the piping (think PSI), the CURRENT is akin to the FLOW or quantity of water that flows in a given time (think GPM), and the RESISTANCE is akin to the friction loss or PRESSURE DROP of the piping circuit, either with a pipe that is too small or a valve that is almost closed. The amount of water that can flow thru a partially open valve will depend on how high the water tank is above the valve, but also on how big the diameter of the pipe is, and how open the fawcett valve is. Imagine a piping circuit instead of an electrical one, that will help a lot. The OHM law is not difficult to understand. Lets put it clear and more or less complete.- Understanding the most basic law of electricity and electronics can help a lot when you want to use electric motors and almost any kind of stuff. ![]()
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