Safest Method to Lock a Fan on a Fin Fan Cooler from Rotating Due to Wind

Wait for the wind to subside!

decelerate - a braking system

locking - a lockable braking system

The safest way is to have someone else do it, who knows what they are doing.

If the fan is large and I had to do it myself, I'd slow the fan down with a broom and then put C-clamps on both sides of one of the blades so it can't rotate. If the c-clamps can't reach the blades, I'd insert blocks of wood or metal bars and clamp them in place.

What is the most safest method to decelerate and lock a fan on a Fin Fan Cooler that is rotating freely due to wind, after electrically isolating the motor to change the belt.

Choosing a braking system depends upon the motor power: for instance on power of few kWs you can inject DC into stator winding provided a suitable DC source is available.

The principle is DC creates a magnetic field around the winding which penetrates the rotor and locks it. Should DC be low you get a deceleration while a higher DC produces stop. The problem is how to find the suitable value for a given assembly: fan and motor.

WARNING!!! Do that ONLY AFTER MAINS IS DISCONNECTED!

DC injection brakes don't work after mains are disconnected, and they don't hold the rotor locked after stop, these are only dynamic brakes.

If the O.P. needs to hold the fan, he should think of mechanical means based on the characteristics of his installations, which we can't see from here.

That doesn't work if the belts are broken as stated

bump the power for a moment and start the fan.before it gets to speed, de-energize it

I would think this should be sufficient.

After all, how large will this equipment be if belt driven?

So it's disconnected from belt drive and the motor...so no motor control at this point is going to slow the fan from windmilling...right?

Are there any dampers you can close? Can you cover the intake/exhaust with sheeting of some type?

Vertical or horizontal blades? If horizontal, you could try blocking the airflow with a wet towel laid on the blades, but if this a gigantic fan which would resist the effort I wouldn't try it. Safety is paramount here, so don't get in close if it's that big...Hollywood is a bad influence for slipping through large exhaust fans.

A sturdy rope can be made to twist once fouled in the blades. Caution! Don't be holding the other end of the rope...anchor it...or you might pull back a degloved hand or a nub!

After you get it done, you might want to install a spring loaded idler/drag wheel tensioner/braking assembly to use in the future. You should get that done for all of your units...much easier.

Does anybody remember what those idler/brakes are called? I am failing at google right now.

Put a brake and VFD on the motor. Slow the RPM with the VFD to a point the brake can stop and hold. Then lock the fan with your hand or a rope or a stick. That seems the safest way to me. Well, you asked.

I forgot to say to leave the motor in the circuit until the fan is 'locked'.

You don't indicate what size this unit is other than v-belt drive so hopefully it is a rather small unit.

For V-belt drives, especially on fans that are exposed to another air stream, you can obtain a v-belt brake pulley. This is similar in appearances to an idler pulley but with a mechanical break or an electrical brake usually located near the shaft. When the drive is turned off and the fan is rotation at it's lowest possible rotational speed the brake is initiated and slows the pulley down which slows the fan down. When rotations have stopped either the brake is left on or another device is placed between the blades of the fan. Many items are specified for this, but a handy 2x4 is normally used. These devices can be home built by mounting another pulley on the v-belt and putting a brake on the shaft of this additional pulley.

Another option would to get the drive brake from a table saw and use it. They are required to stop the blade with a short time or rotations in order to reduce damage to the fingers if they get in the way.

Good Luck, Old Salt

Thanks gentlemen.......

The cooler is overhead with horizontal blades. The rotation circle diameter is approx. 6 meters. The blades will have considerable momentum if freely rotate due to the winds and it will be risky to hinder the blades while rotating.

What mechanical means/ installations are available in the market to serve the purpose??

Do an internet search on fan brake systems.

Also read this: http://en.wikipedia.org/wiki/Dynamometer

If the brake is seperate from the motor ciruit it could be used also for locking, but mechanical locking seems easier for this application.

I had similar problem with a radial induced draught fan which continued rotating for days due to natural air flow created by the stack. A bit bigger than your fin-fan (800kW drive) but same principle. Solution was to install a shaft extension on the non-drive side with a disc rotor and caliper like an automotive brake (in fact I think the caliper assembly was an automotive one). Brake could then be applied (after isolating motor of course) by hooking up a portable hydraulic hand pump to the caliper and pressurising to bring the fan to a halt. The shaft could then be secured by wooden wedges or, more likely in your case, pinned. Don't forget to include the brake as a tag on your isolation system to be released before start-up, or else bad things happen......