One of the most common items found in every electrical circuit and commercial electronics are switches. These come in many different shapes, sizes, and functions, They are a necessary component as they are used to open or close a circuit. The problem with switches is that they all have mechanical parts in them that move. These mechanical parts can wear, bend, and break. Without a functional switch your circuit and possibly your entire device can be out of commission. I think every member of the team here has received a call stating “the switch in my shop vac has failed. Do you have one?” Many times, we can find a switch that will work for the customer once we can find the specifications of the switch itself. This post is going to go through the steps that our technicians and engineers use to help find switches that will work for our customers.
First, we need to identify what kind of switch that is needed. If you are not familiar with the terminology this can be a task as well since DigiKey has many switches and accessories to look at.
One of my co-workers Pat Sagsveen wrote a Switch Tutorial that can help you identify types and features of these switches if you are not familiar with them.
Today I am going to take a quick look at one of the most common switches we deal with which is the Rocker Switch. Although I will be going through this specific section, you will find that the way I narrow down my required specifications will often be the same steps I would use if I was looking for a toggle or pushbutton switch as well.
Just selecting rocker switches can be a little overwhelming with over 10,000 different options. When looking for a replacement switch we start with 3 main attributes or specifications.
- How does your switch function?
- What is the size of the Panel cutout or hole that the switch mounts in?
- What are the voltage/amperage ratings on the side of your switch.
So, the first thing I am going to do is select in-stock as I am looking for options that can ship today. If you are not in a hurry or don’t find any options, you can deselect this at any time during your search. This step takes my options from 10,000+ down to 1,500.
- What is the switch function. My switch today is very simple. The function is on-off and it will stay in the individual position when chosen. Here I have selected on-off and narrowed my options to 500.
Note: One of the most common errors we see in the function category is on Momentary switches. If you have a switch for a starter that you rock in one direction when starting and then it rocks back when switched this would be a momentary switch. Since it is normally in the off position this would be an off-mom switch. For more information on functions and circuits Click here!
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What is the size of the panel cutout? Since this is measured in mm I am measuring mine and it appears to me 30mm long and 22 mm wide. Knowing there is some room for error I will normally look at any switches that are within 10% of my measurements. I will also ask my customers if there is room to make this cutout larger if we have an available switch.
By selecting all options with a length or 27-33mm and a width of 20-24mm I have narrowed down to only 100 options.
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What are the voltage and current ratings? These ratings should be found on the side of your switch. On the side on my switch I see the following numbers 20A 125VAC and 16A 250V-.
Since I know my vacuum is running on 110V I am going to go with the higher 20A rating on my search. I have selected all the switches with a 20A or higher rating. Most of the switches on the DigiKey site will have the voltage ratings associated with the highest current rating. In this instance, had I searched for the 250V rating it may have eliminated the switch I was looking for.
Using these 3 steps I have narrowed my possibilities down to a much more manageable 50 options.
Note: If these rating are not on the switch it may be up to you to determine what the ratings of your circuit are. If your device has a power supply, what is the max voltage and current of the power supply? You can then select a switch that meets or exceeds these specifications.
Next I want to verify the circuit for my switch. I can generally do this by looking at the bottom of my switch.
When looking at the bottom of my switch I have four .250" quick connect terminals. They are marked 1, 1a, 2, 2a. This is a quick indication that I have two circuits (Double Pole) and I know that I only have one throw as my switch is simple on-off. Using this information, I can select DPST (Double Pole Single Throw) for a circuit. I seeing that I have .250" quick connects I can also select that for my termination. In this instance, I have options on termination for just .250" quick connect and .250" quick connect terminals that are rated for solderability.
Now I am down to 42 options and most of these parts would work for my customer’s application, however there are some features that we can narrow for preference as well.
Some of these are Actuator Color, Actuator Type(Shape), Actuator Markings, and Illumination. While these will not functionally make a difference, they can aesthetically make a difference. Therefore, I wait on these until the end to eliminate these options from my search. Many customers need a replacement part to get their equipment working and if there are options that are aesthetics only we look at that last.
My customer has a black actuator, that is concave in shape, no illumination and has a marking of “I 0”.
Note: In the markings section I have chosen both “IO” and “I-” as they can be confused easily based on how they are described by the manufacturer.
Using these steps, I could narrow my customer’s options from 10,000 down to 5 and I offered the customer a rocker switch EG1529-ND that met all his requirements.