Help Me Bulding Mutually Exclusive Power Switch

Hi all. I have a situation and I need your help.
Here is the current status of what I have:
Two power switches ("toggle" switches with on and off) that operates an electric motor (220V@~0.15Amp). One switch for one direction another for the opposite.
Obviously, if both switches are turned on in the same moment, the motor will get harmed. I have to build a system (I guess it will be based on relays) that will mutually exclude these two switches by either allowing only the first one or only the last one to operate (connecting only ONE switch at a time to ONE terminal of the motor).
Please HELP ASAP.
Thanks,
Evgeny

You first need to how, or if?, the motor can be reversed - if it's a normal DC only brushed permanent magnet it's simple - just a SPST switch and a DPDT switch. But at 220V it's more likely to be an AC or AC/DC motor.

Its an AC motor and it CAN be reversed (it currently works as desribed but I need to have some level of fool-protection).
The switches I use arent real switches but its a special device that has 6 channels, 220V each, which is controled by remote control.

Why is it obvious that if the two switches are turned on at the same time it will damage the motor?

Real AC motors are normally reversed by exchanging two of the phases, universal motors are normally reversed by either exchanging the connections to either the commutator or the field coil.

Hero, so what will happen to the motor if I supply the mains to both terminals?

To avoid switch contention you could wire it like this:

knfevg said:

Hero, so what will happen to the motor if I supply the mains to both terminals?

Click to expand...

So if the power is applied to one terminal, it goes in one direction and if it's applied to the other terminal it goes in the other direction?

I don't see how they could make it do that, perhaps the field coils are bifilar wound and each terminal has the coil connected with the current flowing thought them the other way. If this is the case then connecting both to the mains will damage the motor so why don't you just use a single SPDT switch to select foward and reverse by switching between the two terminals?

Hero999 said:

So if the power is applied to one terminal, it goes in one direction and if it's applied to the other terminal it goes in the other direction?

I don't see how they could make it do that, perhaps the field coils are bifilar wound and each terminal has the coil connected with the current flowing thought them the other way. If this is the case then connecting both to the mains will damage the motor so why don't you just use a single SPDT switch to select foward and reverse by switching between the two terminals?

Click to expand...

Its a normal setup for fans and other AC motors thar drive loads with a low atarting torque requirement.

There are two identical windings placed at 90º (electrical degrees, that is 90º / number of pairs of poles).

The "neutral" terminal is conected to both windings.

One winding is conected to the "foward" terminal and the other to the "reverse" terminal. There is a capacitor connected between the "foward" and "reverse" terminals.

If you apply power between the "foward" and "neutral" terminals then one winding receives the full line voltage (and has a current that lags that voltage because of the winding's inductance); but the other winding is working with the capacitor in series and so its current leads the voltage (or at least it lags less than the other winding).

If you apply power between the "reverse" and "neutral" terminals then the winding that received full voltage now has the capacitor in series (and the winding that had the capacitor in series now receives full voltage), which makes the motor change its spinning direction.

Note: This setup simplifies the switching arangrement, but it gives a relatively small current in the winding that has the capactor in series, which gives a small starting torque.

Another solution might be to use keylock switches that are keyed alike.
The key can only be removed from the power on switch when the power is turned off.
The key can be removed from the motor direction switch in either position.
Only use one key for the total operation.