Thread: Different switch types

General switch information that may be helpful in understanding how switches work and selecting the right switch for the job.

Some terminology when hunting for the right type of switch or coming across a switch in a package, you can tell exactly what it does without opening & trying it out when reading the information below about switches. Some manufacturers of switches have indicator lamps that are operated in different configurations such as independent (not connected to the controlling circuit) or dependent (connected to the circuit and always the same voltage). I only describe the non-lighted versions to help you better understand the configurations. Scroll down to understand some characteristics of some switches that are out there and what you'd need to be aware of.

SPST = Single pole, single throw. This is a most basic switch. The single pole can be consisted as a "single current".
SPDT = Single pole, double throw. Double throw can be consisted as "two different paths" for the current to follow.
DPDT - Double pole, double throw. In other ways, two SPDT switches joined together but with one lever activating both at the same time.

There are other variants such as 3PST (3 Pole, single throw), 4PDT (4 Pole, double throw), and so forth to describe the basics.

Switch types -
Self explanatory with different styles available, duck bill, paddle, rocker, etc. The mounting hole are usually round or rectangular. some are even square. There are rocker switches that can be mounted in round holes for ease of installation. Switches with round holes almost always have a long notch on the body of the switch which indicates the "down" position of the switch.

Switch positions -
Other things to know besides the above is these symbols which describes the method of operation of the switches and the positions offered. There are two types of SPST switches, momentary and on. To determine what type it is, look for the parenthesis "( )" to indicate momentary.

Here are a few examples...

SPDT on-on = This is a single pole, double throw switch with only two positions. No center off here.
SPDT (on)-off-on = This is a three position switch which has a center position that is off, one side is momentary which when released, it moves back to off. The other side will hold the position when released.
SPDT off-on1-on2 = Again, a three position switch but with a twist. The off position is not in the middle! In the middle position (or on1), only one side of the switch is on. With the switch in the on2 position, both circuits are activated. This is known as a "progressive switch"


Lighted switches - This gets a little more dicey to understand.
Some are dependent, which means they require connection to the circuit. Most lighted 12vdc switches are of that type where only one extra terminal is provided to serve as a ground for the lamp. While it's possible to use the switch as a ground switch (as opposed to positive) by connecting the extra terminal to positive but this only works for incandescent indicator lamps which are not polarity sensitive. If it's a LED type of lamp, it's polarity sensitive and you cannot reverse the current while expecting the lamp to work. Switches with neon indicator lamps or 120vac bulbs are designed for household circuits. Keep in mind that these lighted switches are limited to the ratings of the lamp. While it's possible to wire a neon switch in an automotive application, just don't expect the lamp to work.

Some are independent, which means the lamps don't care what circuit it's controlling. This offers more flexibility. The switch body can handle any type of rated voltage and the lamp can be wired independently.

Some have dual indicators, which means they are usually wired in such a way that one serves as an illumination lamp while the other serves as a "status" lamp.

There are more configurations that are only limited to the imagination on how they can be wired. I've wired dual indicator lamps that flash simultaneously when it is in the on position much like the TM-4's to get the idea. Do pay attention to the package what you are getting.

Switch ratings -
A switch rated 125vac, 3a - 250vac 1a doesn't mean it's only for high voltage applications. It's just shows the maximum capacity. Switches with these rating levels can handle up to 20 amps on a 12vdc system.

Hope you'll get some idea of how a switch works just by looking at the package.

Switch ratings -
A switch rated 125vac, 3a - 250vac 1a doesn't mean it's only for high voltage applications. It's just shows the maximum capacity. Switches with these rating levels can handle up to 20 amps on a 12vdc system.

This has always confused me...I thought that was the case, but I wasn't sure. Is there any way to consistently convert the rating mathematically?

Great info and thanks for posting. Do you have a source for progressive switches, particularly rotary? And how about a relay 101 post?

Can you give suggestions on good ways to cut the holes to fit the switch? I have had a tough time on more than one occasion working a rectangular hole for some of those switches.

Matt,

Take 250a, divide it by 12 (20.8 amps). I always make a point to use a relay on anything higher than 15a because the contacts can wear out when switching higher live loads (arcing).

I've searched high & low for a reliable & unbreakable rotary switch and found that it needs to be custom ordered, and only available in quantities. I will be ordering a batch to incorporate it with a new product that's in the prototype stages. There's virtually nothing available that meets the specs & durability requirements however, I do have less-rated switches that can do the job if you're careful of it (translation, personal use). I've done many rotary switches but they get broken often because the operators really abuse it and it just falls apart or spins past the stop.

Relays 101 coming up in approx a week. Got a business trip soon. Let me know what stumps you (members) about relays and I'll shine more light on it.


kinnelonfire75,

Rule #1 - When it comes to switches. Stick with the easiest switch to install, which are round one's!

Rule #2 - If Rule #1 gets broken, mark the outline, drill two starter holes with an Unibit so you can "creep" up on the edge, then use files, air saw, dremel to cut away the rest to make the square hole. Make the hole a smidgen smaller than you think and test fit / file until it gets to the size that's perfect.

Sean,

I've got relays figured out (took some time for it to "click"), thought the board would benefit. Agree on not pushing a switch to its rating.

For cutting out the switch shape, I typically start with thin cardboard to get sizing down (try to use same thickness as the material your switch will be housed in). Cut with razor knife, square-up and measure. I then cut a strip of good 3M automotive masking tape (lime green color...sticks the best, IMO) to the correct size and place it on back side of material to be cut. I then trace the edges with a silver or black sharpie and remove tape. This should leave a nice marked edge, kinda like a photo negative. Use a small drillbit to drill out corners. Now, depending on material, use a razor knife, cut-off wheel, jewelers saw, etc to cut the line. Or, use a Dremel tool with a fluted cutting bit to remove material. Go slow, keep material cool, remove debris often, do not go past your markings with the cutting tools. Once you are close, start test-fitting. Switch should mount snug, but not tight (will cause problems with actuating mechanism). Keep in mind that back-pressure from wiring and such can make loose switches pop-out or fit poorly. Keep in mind that the switch flange will help cover minor gaps. Keep in mind that the switch's locking tabs need a wee bit of extra room to fit through the cut-out. Once switch is in place, I often run clear silicone around the inside to "glue" it into position...be sure let it set before finishing install. If you over-cut, use black silicone to help conceal gaps. Small needle files, Xacto knife kits, etc. are helpful tools for plastic. Also, I sometimes use sheet ABS to replace the factory trim piece, keeping it intact for re-sale.

Originally Posted by EVModules

Matt,

Take 250a, divide it by 12 (20.8 amps). I always make a point to use a relay on anything higher than 15a because the contacts can wear out when switching higher live loads (arcing).

Originally Posted by EVModules

Matt,

Take 250a, divide it by 12 (20.8 amps). I always make a point to use a relay on anything higher than 15a because the contacts can wear out when switching higher live loads (arcing).

I've always wondered and asked many people about switch or cable ratings. For instance, household wires will usually handle 1800 watts: 120 Volts x 15 Amps. Since W=VA, could the SAME wire handle 120 Amps at 12 Volts??? Same wattage but opposite amps vs. volts.... I wouldn't think so but if anyone knows the correct answer...

Originally Posted by toon80

Originally Posted by EVModules

Matt,

Take 250a, divide it by 12 (20.8 amps). I always make a point to use a relay on anything higher than 15a because the contacts can wear out when switching higher live loads (arcing).

I've always wondered and asked many people about switch or cable ratings. For instance, household wires will usually handle 1800 watts: 120 Volts x 15 Amps. Since W=VA, could the SAME wire handle 120 Amps at 12 Volts??? Same wattage but opposite amps vs. volts.... I wouldn't think so but if anyone knows the correct answer...

Here's a link to a wire gauge chart that should take some of the mystery out of sizing wire for 12vdc applications. http://www.the12volt.com/info/recwirsz.asp The chart on the lower right hand side of the screen is what emergency equipment installers might want to use. Personally, I am a bit more conservative and would add a wire size. For example, they list 16 gauge for 15 amps but I'd use 14 gauge and so on.

Originally Posted by kinnelonfire75

Can you give suggestions on good ways to cut the holes to fit the switch? I have had a tough time on more than one occasion working a rectangular hole for some of those switches.

I also suggest masking of the area around where you are cutting. The first time I ever tried cutting a rectangular hole, I put the dremmel at to shallow of an angle and the chuck marred the surface of a project box. I covered the face with two layers of duct tape and didn't have to worry for the rest of the holes. I'm just glad it wasn't my brother's dash.

Do they make a switch that has off-on-momentary while still applying power when you trip the momentary switch?

Originally Posted by Jtsou

Do they make a switch that has off-on-momentary while still applying power when you trip the momentary switch?

Yes they do. This switch would be the same as the "siren" button on the old Federal PA15 or PA20, for example. They are 2 types I know: "Normally Open" (N/O) and "Normally Closed" (N/C).

N/O switch: when the switch is not pushed, the circuit is open and current doesn't flow. When you push it, you close the circuit and current flows. This switch is spring-loaded and the spring keep the switch "off" when not pushed.
N/C: opposite of the above.

Originally Posted by toon80

Yes they do. This switch would be the same as the "siren" button on the old Federal PA15 or PA20, for example. They are 2 types I know: "Normally Open" (N/O) and "Normally Closed" (N/C).

N/O switch: when the switch is not pushed, the circuit is open and current doesn't flow. When you push it, you close the circuit and current flows. This switch is spring-loaded and the spring keep the switch "off" when not pushed.
N/C: opposite of the above.

I am trying to wire a whelen avenger which uses 3 wires which are gnd, 12v, another wire that needs a momentary 12v to change the pattern. The switch needs to be like this:

Momentary
On
Off

That way if I wanted to change the pattern I just pull up on the momentary. But it has to keep 12v on the on position.


I'll look at what you suggested thanks.

I don't think I have ever seen a switch in the configuration. You are probaly going to need a std switch for the on/off and a momentary button/switch for the pattern. Are you looking to change patterns while driving?? If so I don't recommend that and would suggest that you find a pattern that works best for your need/vehicle and set it and forget it.

Rob

Originally Posted by Jtsou

I am trying to wire a whelen avenger which uses 3 wires which are gnd, 12v, another wire that needs a momentary 12v to change the pattern. The switch needs to be like this:

Momentary
On
Off

That way if I wanted to change the pattern I just pull up on the momentary. But it has to keep 12v on the on position.


I'll look at what you suggested thanks.

Originally Posted by Jtsou

I am trying to wire a whelen avenger which uses 3 wires which are gnd, 12v, another wire that needs a momentary 12v to change the pattern. The switch needs to be like this:

Momentary
On
Off

That way if I wanted to change the pattern I just pull up on the momentary. But it has to keep 12v on the on position.


I'll look at what you suggested thanks.

I'm not 100% certain but I think Soundoff Signal uses a switch like this. I had a Pinnacle mini bar from them and I'm pretty sure they used that type of configuration; you held the momentary to cycle through patterns. On Talons the light has to be on to change patterns and this wasn't the case for the SOS bar, so this switch might not work for your situation.

Originally Posted by rofowacker

I don't think I have ever seen a switch in the configuration. You are probaly going to need a std switch for the on/off and a momentary button/switch for the pattern.

I think what I am going to do is get a regular SPST switch and split the switched current to 1) the light itself to turn it on and 2) to a momentary switch that connects to the pattern select wire. I think that will do what I want it to do.

Originally Posted by rofowacker

Are you looking to change patterns while driving?? If so I don't recommend that and would suggest that you find a pattern that works best for your need/vehicle and set it and forget it.

Rob

Not at all. I am just trying to set it up this way since I plan on hardwiring the avenger, and will need a way to change the patterns. This has nothing to do with ease of access while driving.

You wish to use the progressive style switch so as to have ON2 to be momentary? If so, I can try to get you a switch to do that.

Like described before it needs to be


[momentary]
[on]
[off]

When [on], of course the light is on...
When you press the momentary, the light stays on, but the 12v current it sent to another outlet to change the pattern. Pretty sure it can be done, but i will probably end up just using two separate switches.