DPDT switches commonly use polarity reversal. That is why some variations of the DPDT switch, such as the cross-over switches, are internally wired for that purpose. The cross-over switches have only four terminals or connections, as opposed to six that you see on DPDT. There are two connections used for the outputs and the other two for the inputs. The switch then selects either normal or reversed polarity when connected to any DC source such as the battery.
A DPDT Relay has a single coil with two arms that move simultaneously. Inside of the DPDT relay, there are two separate SPDT (Single Pole Double Throw) switch mechanisms. These are being used for signal switching applications more often than not, but can also be found in high power switching applications.
A DPDT can be used on any application that requires a NO (Normally Open) and NC (Normally Closed) wiring system, an example of which is Railroad Modelling or Model Railroading, a hobby that makes use of small scaled trains and railways, even small scale cars and bridges. The NC allows for the system to be "on" at all times while NO allows for another piece to be turned "on" or activated through the relay.
DPDT can be used in such cases for block control due to the ease and flexibility of wiring, as well as, coil voltage and coil amperage capabilities. In block controls, it is important to be able to take the higher power due to multiple turn ons and turn offs on the system.
Block control allows the relay coil to be triggered remotely, while another relay is controlling another block. It is important to assess the priority needs when employing the block control, which accessory or application would need to be prioritized that would be turned on while the other one is turned off to make way for it.
There are different types of DPDT . There is a wide selection of DPDT Relay boards that can be used for different applications. There are DPDT Relay boards used for low power signal switching, there are also DPDT Relay boards used for high voltage switching used in high current applications. There are ranges of channels to choose from, from a two-channel DPDT Relay Controller to a 32-channel DPDT Relay Controller. One may choose whichever fits the configuration that is needed. Other options would be either Ethernet DPDT Relay, USB DPDT Relay and BlueTooth DPDT Relay.
Dual 1-Amp DPDT Small Signal Relay Controller Board- 2-Channel 1-Amp RS232 DPDT Relay, is used with low current, low signal switching applications. Examples of applications are: telecommunications, networking, video and line-level audio. This relay is soldered to the controller to connect the relays to the board, which is a cheaper and space saving alternative to terminal blocks.
Dual 3-Amp DPDT Signal Relay Controller Board- 2-Channel 3-Amp RS232 DPDT Relay. This is similar in application to the Dual 1-Amp DPDT except that it uses higher amperage.
Quad 1-Amp DPDT Small Signal Relay Controller Board- has 4-Channel 1-Amp RS232 DPDT Relay. Similar in application to that of the first two, except it has four channels. This controller board or relay is also available in 3-Amp and 5-Amp. Also available in eight channels with 1-Amp, 3-Amp and 5-Amp.
Other types using higher channels and amperages, such as 8-channels, 16-channels, 24-channels and 32-channels with 3-Amp and 5-Amp are available in the market.
As you can see, there are different types of DPDT switches that can be used for different configurations. They are significant in ensuring that the applications they are applied to perform the type of switching that they are intended to perform. From computing and networking, to video and audio level switching, as well as, hobbies such as Model Railroading.