how does elevator door open in total power failure?

does anyone know how the elevator comes to a stop at the nearest floor and door opens when there is a mains power failure and the backup generator does not start? or will it get stuck between floors as the emergency brakes will operate?
thanks

I think its done mechanically not with electronics.

1. If the elevator is old and uses steel ropes, it will stop at the point the power was cut. Brakes wont operate because it will just stop, not fall. Then u have to go at the top of the building and rotate the big wheel by hand (ask an expert how to do it) until the cabinet move to the nearest floor, then use a special key for the door to open. Have in mind, in some elevators the door does not open with this key until cabinet is exactly on the floor level.

2. If the elevator is new and uses oil pressure system, thing are easier. Brakes wont operate because it will just stop, not fall. The elevator control system when power is down usually open a valve and let some fluid to pass, causing the cabinet to move slowly to the nearest floor or mainly move to ground floor. This system has also valves that you can manually use in order to move cabinet to a lower floor or ground floor, if it does not happen automatically.

In both cases, its advised to consult an expert before trying things.

Hope it helps.

Elevator Safety System
http://www.electrical-knowhow.com/2012/04/elevator-safety-system.html

If the elevator is new and uses oil pressure system, thing are easier.

Click to expand...

I think the statement only applies for a small number of elevators (new and limit height).

@tpetar
thanks for the link to the site
its a brand new Korean made elevator for 6 persons installed in an apartment building, i was wondering if there was a standby automobile battery connected to an inverter kept in the control room upstairs to meet such a situation and electrically bring the elevator to a stop at the nearest floor and open its door

its a brand new Korean made elevator for 6 persons installed in an apartment building, i was wondering if there was a standby automobile battery connected to an inverter kept in the control room upstairs to meet such a situation and electrically bring the elevator to a stop at the nearest floor and open its door

Click to expand...

Why don't you check respective manufacturer information? I don't believe that a small automotive battery would be able to operate a motor driven elevator. But I'm not in this business and would be interested to get qualified information.

The description of safety systems posted by tpetar doesn't cover emergency operation in case of power fail, except for the well-known provisons to open the door by a special key etc. But there may be special designs, similar to the emergency operation of hydraulic operators described by xbase.