Sunday, April 26, 2015

Day 92 Ohms, Voltage, and Amps in Maker projects

Yesterday I started to share that my mental model around volts, amps, and ohms was finally emerging to a point where I felt that the fog had lifted. While that post was a reflection of the learning process by which this happened, today I thought I’d do a quick explanation of that mental model using the explanation provided in this Sparkfun tutorial and apply it to some of the project we have been making in our Girls Make IT sessions and see if it might resonate for some of you.  

By the end of this post, it is my hope that you might have a better understanding of why the words (volts, amps, and ohms)  might impact  your project design.  It will not be the goal of this post that you be able to calculate the ideal solution by which to power your project,  but you will be tuned in to how these materials might impact the design solution.  It is my goal that as you notice these words in the future you will be less likely to ignore them and start to create your own data points of how materials rated with different values (volts, amps, ohms) might impact your project design. 

First of all a mental model is built around our experiences and current understanding of the world. Water is s something most of us have experience with. Most of us have experience with garden hoses, water faucets, water towers, and with the experience of letting the current in a river carry us downstream. These experiences can help us better understand amps, voltage, and ohms.


The amount of energy that an electrical current is often measured in something we call AMPS (or ampere). To put it in perspective, an oven might use 10 - 20 amps while a clock radio would need only 1 amp. Amps is the total amount of current that is available or needed to power an object. 

Water example from Sparkfun

Let’s say you have a 55 gallon water tank in your home for hot water. The design of the water tank including how much water it can hold will determine the flow of the water to your sink or shower.  The design of your battery will determine the flow of the current from the battery to your project. The flow of the current in electricity is measured in a unit called AMPS.  

 The number of AMPS a battery has (if fully charged) is only one part of the equation of whether it is a good solution to power your project. 


Let’s say you connect your water tank to a hose laying flat on the ground. Chances are the water would trickle through the hose and be available to you, but there would be very little pressure behind it. On the other hand, if you raise the water tank up and place it up higher than the hose, the water pressure will increase and the water will come out the other end of the hose with enough pressure to be useful. You’ll definitely want more pressure to power wash your house than you will need to rinse off your dishes or take a shower. 

When working with electricity, the design of the battery can also provide more pressure behind the current making it useful for different types of tasks. The force by which the current is being pushed out towards us is measured in volts. The more volts, the more pressure or force is behind the current as it moves through your circuit. To put it in perspective, check out the difference between the clock radio and oven in our diagram above; an oven needs a power source that sends electrical current at 220 volts, while the clock radio only needs 12 volts to work.

Although we might have a lot of ‘water’ available, we are familiar that water can have a much different impact if it is flowing slowly or trickling through a hose laying flat than it can if you left one end of the hose higher. Consider the impact that a water coming through a hose has in the picture of the power wash hose above versus the impact that the water being being poured in this glass has. The water coming through the hose would knock the glass right out of your hand. Just as water pressure can increase the impact of the water has when it comes in contact with an object, so can electrical current. When it comes to electricity, we use a measure called voltage to measure the pressure of an electrical current. 

We need a measure of for this type of pressure when it comes to electricity The same is true for electrical current. Just because we have enough ‘electricity’ does not mean it is coming through the wire with enough pressure to power the project. An oven needs a power source that sends electrical current at 220 volts, while the clock radio only needs 12 volts to work.


Finally sometimes we have a power source with a lot of water and a lot of pressure, but the amount of current and speed of the current coming at us at once can be slowed down by adding some resistance to the hose or pipe through which the water is traveling. Have you ever bent a garden hose to slow down the flow of the water, while you grab the hose to aims it. When you did this you were adding resistance. Another way to add resistance would be to change the size of the hose. A narrower hose offers more resistance as water does not flow through it as easily as it does the wider hose.   Perhaps your shower has a shower head that allows you to adjust the pressure.

Your shower head can add more resistance thus slowing down the flow or increase the pressure by reducing the resistance.   The same is true for electricity.

In your maker project you select various materials for electricity to pass through based on the resistance it has. Some materials offer little or no resistance, while others materials have a lot of resistance.   Most metal or wire has very little resistance and connecting them to your battery allows the current to pass through at full force. If you have a 3 volt battery, your current passes through at 3 volts, while if you have a 12 volt battery the current has 4 times the pressure behind it. The amount of resistance is measured in Ohms or Ohms per meter.

Some materials like conductive threads are created with material that have more resistance and thus conductive thread allows the current to flow through with much less force/pressure than a piece of copper tape or a wire.  One of the benefits of this is that you can use conductive thread with power sources without frying your LED's because of too much voltage. 

For example silver coated conductive thread may have 300 ohms of resistance per foot while stainless steel conductive thread may have 28 ohms of resistance per foot. When you compare that to the .009 ohms of resistance you might find in a foot of copper tape, you can see that the materials you use to design your project make a huge difference in the way the project works (or doesn’t work).

In some future blog post, we'll put this knowledge to use with some practical examples of maker projects.  We'll even learn to use ohms law to calculate the amount of current needed for our maker projects. 

But hopefully your vocabulary will include the words, amps, voltage, resistance, and ohms and you will start to pay attention to the number of volts and amps as well as the resistance from using various power sources and materials as you design your  projects.  

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