Elevator Modernization Project

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We are working on an Elevator Modernization Project for a hospital. The hospital is a high-rise (19 and 6-story) buildings.

The M-G Set and controller is being replaced with an SCR Controller. The DC Motor will remain.

The issue we are facing is that the new SCR Controller requires a higher current draw than the old M-G Set and controller. Is this normal?

Could this problem have been avoided with a Variable Frequency drive and AC Motor?

Appreciate your reply

-- Mohan Sabapathy (msabapathy@doshiassociates.com), July 11, 2001


These are complex issues and an accurate answer would require examination of a lot of factors by a qualified expert. Even then, it's somewhat a matter of opinion.

That SCR drives require a "stiffer" power supply than MG drives is a given.

AC drives have unique problems, or perhaps I should say side effects, of their own.

If you are still deciding, get a qualified consultant to evaluate the application.

If it's a done deal, don't second guess your vendor. Let the proof of the pudding be in the eating.

Good Luck!

-- John Brannon (akaelevman@AOL.com), July 11, 2001.

Re: Response to Elevator Modernization Project

When you write "That SCR drives require a "stiffer" power supply than MG drives is a given" do you mean that SCR drives will draw more current than a M-G Set for the same horsepower DC Motor?

-- Mohan Sabapathy (msabapathy@doshiassociates.com), July 11, 2001.

"Stiffer" refers to the ability of the power supply to continue to provide rated voltage under load.

Ward-Leonard (MG)systems are very tolerant of voltage variances, but SCR systems are not. So, while the SCR system may not actually draw more power, it must remain more stable under load, which may require a higher rated supply.

In terms of energy consumption, SCR systems typically use less, because they are only "on" when actual car motion is needed, whereas MG sets run continuosly when a demand for service exists, even with the car(s) at rest.

Again, this is a simplified answer to a question involving some sophisticated engineering concepts.

-- John Brannon (akaelevman@AOL.com), July 11, 2001.

well most elevator companies already deal with that sort of thing most use a isolation transformer they take into consideration motor current fla and armature currents breake coil all of it scr drives are nice we have several but another question you might answer is how old are the machines ive seen several mods and a few years later the machine breaks down to get that bearing you need will take 9 to 11 weeks to make at a cost that you could have replaced it

-- jag (gipper066@yahoo.com), July 12, 2001.

The answers are - Yes, and perhaps, But... These are not crystal clear, and are certainly subject to debate and incorrect application.

MagneTek has a publication on their web-site www.elevatordrives.com that helps to explain the issues.

Motion Control Engineering (MCE) has a technical publication titled Motor Generators vs Static Drives dated 1996.

There is also a good article on the subject - Elevator World, January 1997 by Alan Shiner, Kone.

Dig out these articles. All are worth reading.


-- Don Vollrath (dvollrath@magnetek.com), July 15, 2001.

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