How can I wire a snap action roller switch to a 48V DC motor?

Question

I am building funhouse type cars that are powered by a 1200 watt electric motor that is rated at 32 amps. I want to install a roller switch that will turn the car off when it comes into the loading dock and turn it back on when the car is shoved into the ride. All the roller switches I have found are 15 amps max. What is the safest, cheapest way to do this?

Answer 1

Use the roller switch to open/close a relay. Select a single-pole relay with at least a 32A contact rating, and a coil voltage approximately equal to the car battery voltage.
www.digikey.com is one source.

[REPOST] The poster below me is incorrect. You do not use a 15A switch for a 32A circuit, even if the voltage rating of the switch is 5 times higher than your app. The voltage rating of a switch is primarily according to the voltage it can stand off in the open postition, and secondarily, how robustly the contacts can handle inevitable arcing upon opening. The current rating is according to the contact resistance relative to power handling capability in the closed position, and since the switch is in the closed position, it doesn't matter what the voltage was across it when it was open, the small voltage across it closed will be only a factor of the current through it. So definitely use a relay, unless you want to be replacing switches every few weeks.

In fact, if the relay is to be opened under full motor load, you may need some sort of snubbing across the contacts and high-wattage zeners across the motor to prevent premature failure of the relay contacts. Inductance like in your motors has the property of resisting a change in current by building up a high voltage, potentially much higher than your battery voltage. Email me if you need more details.

Answer 2

Are you saying that the switch is rated for 48 volts and 32 amps? If so, wire the motor through a starter, basically a heavy duty relay, and operate the starter with the roller switch. You can buy starters wherever you got the motor or find a plane old relay that is capable of carrying the load.

If you mean you are using a roller switch that is rated for 15 amps at 120 or 220 V, then you don't have a problem. Since its the power, not the current that you have to be concerned about. 120 V times 15 A = 1800 W. If that's the case wire it directly to the motor.

Answer 3

You should use a relay to control the power tot he motor. That will get around the 15 amp limits on the switches you are finding. It will alos save you the issue of checking whether that rating is for an inductive load (which the motors are), determining what the startup load for the motors is (usually a multiple of its rolling load), and making sure the switch is rated for those amps at 48 volts DC (AC and DC rating may be different and some switches may be usable only at 12V).

To avoid maintenance issues on the switches I would suggest getting inductive proximity switches instead. They are easier to adjust for position and have no moving parts to wear out.