Step 25: Power Supply Part 1
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Now, we get to the fun part. We get to play with electricity. Well, it's probably not something you want to play with. In fact, be extremely careful. I'm going to provide information that, if not treated with care and respect, is lethal. For those that do not know what lethal means, here is a definition: Lethal = Death. In this case, it's not like quick painless death, but the slow-shocking-melting kind. I've touched 110 volts of house current before, and it's a weird but ugly feeling. Your body understands what alternating current (AC) really means.
Ok, let's get to the meat of the topic. First I would like to help you understand a couple of concepts first. AC or alternating current is electricity that travels in two directions, backwards and forwards. Our goal is to convert normal AC electricity (usually found in the receptacle of the house) to DC (direct current). Direct current, as its name implies, is current running in only one direction at a mostly constant voltage (depending on how well the circuit is built, and with what components).
There are several ways to do this conversion. For the sake of simplicity, I will only be using a few components in this power supply. First, we need to convert the voltage to a level that is compatible with the driver board (the driver board that drives the stepper motors). The volts must be enough to power the motors sufficiently. The voltage is converted with a component called a transformer. Transformers can either step up a voltage, or step down a voltage. I am stepping down the voltage to 24 volts. The end result will not be 24 volts, but about 34 to 36 volts. The transformer also has an amperage rating. This rating tells you the peak normal operating current level that the transformer can handle. My transformer can handle 10 amps drawn through the circuit.
The next component through which the electricity will travel is the bridge rectifier. This doodad only allows current to travel in one direction, let's say forward. That's not all this cool component does, it also captures the backward traveling current and folds it in the forward position so there is no loss of current and it improves efficiency.
The current is bouncy now, but our goal is to have a direct flat current at a particular voltage. To flatten out the current, we need to store the energy and then release the energy when a voltage level is reached. We will do this with a capacitor (the blue cylindrical parts in the first image). The concept is simple, it's like spitting in a pool of water and when the pool hits the top level, starts to pour out the other side. Just like the name implies, the capacitor has the capacity for a certain amount of electricity. The measurement of capacity is in farads. One Farads is actually a very large measurement, so measurement are usually expressed in micro farads. I'm using two 8200 micro farad capacitors (uF). I couldn't find one very large capacitor, so two wired in parallel will do. Parallel just means that the capacitors will be wired negatives on one side and positives on the other. Getting this right is crucial. If a capacitor is incorrectly wired, mayhem will ensue.
I add a switch to the circuit also. A switch is needed to turn the power on and off. However, when the power if turned off, it's not really off. The capacitors still have a whole bunch of electricity stored in it. It stores it so well, that a resistor is needed to allow the electricity to dissipate. Even with the resistor, it bleeds very slowly. This means that handling the circuit in any way during this time should be eliminated, or you could be eliminated! Not even the motor wires should be touched because the driver chips can blow. Give yourself, like 5 minutes, to allow all of the electricity to escape the circuit.
We are not quite there yet, but we will also add a fuse. Two fuses are recommended, one on either side of the circuit. I will show that in part 2. After the power supply, get ready for the motor connections and a bit of motor basics (yes, more motor information!).