Rotary Switch Help?

Question

I'm designing a fixture to test a 12vdc & 24vdc motor at different times. The fixture has a dual output (12&24) DC power supply.

The operator of the fixture needs to change the voltage between 12 & 24 vdc. The motor leads are connected to a pair of spring loaded binding post. The voltage at the posts needs to change.

Is a rotary switch the answer? Any recommendations?

Thanks

Mark

Answer 1

The type of movement (rotary, toggle, rocker, etc.) is really a secondary consideration. That's a choice best made based on factors like reliability/life requirements, ergonomics, how much voltage/current the switch must withstand, etc. I would recommend a toggle switch because they're very common, very simple and reliable, can handle a large current (motors can draw substantial currents), and are easy to install in a panel -- all you need is a single round hole.

The most important first consideration for you is the "form" of the contacts -- how many sets of contacts, and how they connect when the switch is in each position.

Here are two choices: First, the simplest: If your supply has a common ground between the 12 V and 24 V outputs (I'll assume negative ground), you can use a SPDT (single pole, dual throw) switch. An SPDT toggle switch will have three terminals on the bottom. Connect the center terminal to the (+) motor test terminal, and the power supply common ground (-) to the (-) motor test terminal. Connect each of the two outer terminals on the switch to either the 12 V (+) terminal or the 24 V (+) terminal.

If your supply has separate (+) and (-) terminals for each of the 12 and 24 V outputs (isolated outputs), you'll need to check to see if it's safe to short the two (-) terminals together to use an SPDT switch this way. This is OK on most supplies, but some can be damaged, depending on how they're designed.

If you need to keep the supply outputs isolated from each other, use a DPDT (double pole, double throw) switch instead. It's like two SPDT switches in one package, and has six terminals on the bottom, two columns with three terminals in each. Connect one column to (in order) 12V (+), the motor (+) terminal, and 24V (+), and connect the other column (same order) to 12V (-), the motor (-) terminal, and 24V (-).

If you're looking for a circuit that simply applies the voltage to the motor for a few seconds or so, look for a "momentary on, center off" SPDT or DPDT switch. It'll connect the same as described above, but it's spring loaded and returns to the center position. In the center position, no connection is made. Otherwise, with a regular SPDT or DPDT, you'll need some other switch in series to turn the power off most of the time, on only during the test.

Answer 2

What are you testing about the motors?

You can test 24V motors at 12V.

This would prevent the possibility of testing a 12V motor at 24V if the operator forgets to throw the switch.

Depending on the characteristics of the motor, you could design a device that would supply the correct voltage by sensing either the coil resistance or the impedance of the motor.

Another thought is to passively test the motor by spinning it with another motor and looking at the voltage and current signature generated by the motor leads (you are turning the tested motor into a generator). This method would reveal winding flaws, magnet mounting flaws and shorts, if there were any.

Answer 3

3 position switch sounds good 12v / no connection / 24V,

3rd position removes the chance of arcing due to stored potential.

schneider harmony range ZB4 if low current.

or another make (i cant remember sorry.)

Answer 4

I think a 3-position switch.