strange relay problem

[aaronik19]

A friend of mine gave me a lifter operating with 24V for repair and found that the card is faulty. I replaced the card with three relays as illustrated in the figure attached before I make a new card using PIC Microcontroller.

http://postimg.org/image/d1xs11wyx/

Please refer to the attached illustration for my circuit.

B1 and B2 are the buttons of the remotes. Each button has two auxiliary contacts. One NC and one NO. The NC is serving as an interlock. Relay 1 is used to rotate the motor clockwise and Relay 2 is used to rotate the motor anti-clockwise.

when you operate with these two relays, the lifter works correctly but when you release the UP button, it will not brake instantaneously, but continues to travel for about 3 centimeters, which is not good. Same for Down button. The lifter is equipped with Up and Down Limit Sensors for safety. Now one of our members who used to work with me discovered that to brake the motor, one needs to short the motor's windings just for a moment. That's why he puts Relay 3 in between. Infact this idea works but when the lifter is loaded, and the current consumption is higher, the MCB trips after about 5 travels. When you reset the mcb and try to activate the lifter, it trips immediately.

The funny thing is that when you remove Relay 3 from circuit and put it back again and restore the supply, it continue to work! It is very strange! I know that this problem in not directly related to PIC but I took the opportunity to post it here to learn from each other.

Really appreciate your thoughts about this.

[guy]

Maybe the MCB or some other component heats up and takes time to cool down?