Originally Posted by larrydavid

Greetings All,

I am currently doing some research into regenerative conveyor systems and the associated benefits, to identify potential opportunities for our clients.

I have had little exposure to conveyor systems in my career so far, and whilst researching I have come up with a few questions that I could not find answers for. If you could give me some advice, it would be much appreciated. Firstly, I am a mechanical engineer, and my expertise on electrical systems is fairly average. Please forgive me if any of my statements are incorrect.

1. It seems that all regenerative systems are applied to downhill conveyors. Has anyone had experience in a regenerative braking application on a level-ground or uphill conveyor? Or is the braking energy produced during stopping simply not large enough?

2. For downhill applications, what is the difference between the amount of power generated during normal operation and stopping?

3. Is the generated electricity most commonly fed directly back into the grid, and are there any implications with this in terms of irregular voltage/frequency/current and overloading?

4. Is it common to have to shed excess electricity through resistor banks etc?

5. Is it common to store the generated electricity in batteries? What are some of the applications of this, and are there disadvantages associated with batteries?

6. What is an example of how much power can be produced (upper and lower end of the scale)?

7. Can anyone give a ballpark figure on the cost of retro-fitting/implementing a regenerative system on an existing conveyor to feed power back into a grid or battery storage?

Many thanks in advance

If you expect to gain a FULL understanding with regard to regenerative braking and

dynamic braking and the electrics involved you need to spend some time visiting a

locomotive manufacturer to gain a full and complete understanding of it; AND

another good example of regenerative braking would be the implemetation of the "Water Twister"

to create hot water by acting as a braking device on the arresting cable sets the

United States Navy aircraft carrier fleet. ■

We have built decisively regenerative downhill conveyors but the electrical aspects of conditioning and feeding the power back into the grid have not been in our mechanical/structural scope of work. These have been electrical aspects by others. In any case I'll describe what I know.

1. In the old days, the power was not typically harnessed, rather it was burned off at huge resister banks.

2. In the early1990's we built a decisively regenerative, downhill, multi-flight overland conveyor system whose first flight was a downhill sandwich belt high angle conveyor. The drives used constant speed AC motors that acted as perfect generators when driven by the conveyor load, putting out a well conditioned power while maintaining constant conveyor speed. The braking, stopping systems were of low speed disc and caliper type. Normal programmed stops occurred after each conveyor flight was purged of the material load and the the programmed braking time was quite long so that stopping was largely controlled by the normal conveyor resistances, largely drifting to a stop. Stopping under full material load was by the disc and caliper brakes and the stopping power was dissipated as friction heat from the surface of the braking discs.

3. A few years ago we built a decisively regenerative, downhill overland conveyor system that differed from the previous only in that we employed VFD controllers to gently start and stop the conveyors. We used similar braking, stopping systems, of the disc and caliper type but normal stopping was by the VFDs and the brakes engaged only when the conveyor was stopped, acting merely as a parking brake. The braking systems were designed to bring the fully loaded conveyor to a time controlled stop and did so when power was lost. It was not clear to me whether the additional stopping power of the VFD stop, was fed back into the grid since the power frequency is not at a constant 60 htz.

I am not aware of any case where conveyor braking power alone has been harnessed for its energy value.

Hopefully someone with a strong electrical background will offer their experience and expertise on this matter.

Joe Dos Santos ■