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Anonymous Poster #1

# How To Make Control Diagram For A Double Speed Motor

10/24/2017 4:47 AM

Dear all,

below details of Demag crane hoist motor name plate,

actually the problem is in my workshop it is installed, then i came to know this is only working on single speed with forward and reverse direction ,

but the hoist motor is 2 speed with forward and reverse direction so i would to make it in this way .

so i need suggestion to make the correct control diagram for the above hoist motor.

my region is Saudi Arabia.

if some one has knowledge on the over head cranes please advice/suggest me.

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Guru

Join Date: Dec 2010
Posts: 1268
#1

### Re: how to make control diagram for a double speed motor

10/24/2017 6:02 AM

I am not a crane man, but looking at the motor power (shaft kW, same line as 50 Hz on data plate) & speeds you may have a problem -

- if the motor is currently used at 400 rpm, speed may be too high for gearbox and crane mechanism at 2800 rpm.

If the motor is being used now at 2800 rpm, there will be sufficient torque at 400 rpm - a constant torque design is common for two speed motors. Note data plate speed ratio 2800/400 = 7 : power ratio 2.9/0.43 = 6.74.

However, note that fan cooling air flow at 1/7 of speed will be negligible and the motor may overheat with more than occasional, short duration, use at 400 rpm [cooling capacity proportional to speed squared 1/72 = 1/49 or worse comes to mind]. I would suggest monitoring of winding temperature with a temperature pickup, backed up by evidence from winding resistance measurement when motor is stopped after a test cycle - start with short easy duty & work-up to more severe. Even with this, you may be missing a critical "hot-spot" temperature normally kept down by air blast. Important also to find cooling time when motor is stationary after a work cycle - an engine starter motor I dealt with [obviously no fan and small for its power] needed 20 minutes cooling de-energised after 1 minute at rated power before further use.

Is there an electric or mechanical speed control at present? Of what type if present?

67model

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#2
In reply to #1

### Re: how to make control diagram for a double speed motor

10/24/2017 6:53 AM

thank you 67model,

know presently it is an electrical speed control with mechanical brake interlock system,

it is only dual speed one is slow and another is high ,

as per the data plate the amp is shown approximately taking on the slow speed ,

i need to implement control diagram for high speed winding on the same motor ,

this motor is coupled with the rope drum ,

we used this cranes to lift up to 10 ton weigh ,

2
Guru

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Posts: 1268
#4
In reply to #2

### Re: how to make control diagram for a double speed motor

10/24/2017 6:53 PM

Your rated speed data suggests a speed ratio of 7:1 approximately. As you probably know, motors come in 2, 4, 6, 8, 12.... poles, with speeds nearly 3000, 1500, 1000, 750, 500 rpm. So your motor would have to be 12 pole for the low speed.

But 12 poles means there must be 6 windings for each phase for each winding of a two pole. Interconnecting the windings for many poles is, of course, routinely done - switching from many to two pole is complicated and impracticalbeyond 2:1 or 3:1 speed steps.

I suspect the motor is a two pole rated for a speed range and a duty cycle(s) up & down through the range a number of cycles an hour with a VFD drive.

The pulleys may have been modified to give a useable speed with 2 poles, perhaps with voltage variation to give some speed control.

I suggest you ...

1. Check the motor speed with a tachometer.
2. Look inside the motor terminal box to see how many terminals there are.
3. Contact the crane manufacturer for description of speed control.
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#5
In reply to #4

### Re: how to make control diagram for a double speed motor

10/25/2017 12:51 AM

A diagram showing the wires from the motor and how they connect internally (measure resistance between leads to confirm) is needed to develop control wiring.

Motor connection diagram is often on another nameplate.

Most are Y Y windings, one model is Delta Wye, so one set of 3 wires is the 12 pole low speed, the other set is the high speed. With the speed range you show, they are likely two independent windings. You need to confirm this in order to design the starting circuit, however.

Demag KB series motors are now listed as 8/2 pole motors with conical rotors, so not wound rotor as is often the case in crane drives. If you visit here, you may find the wiring you are looking for.

http://www.demag-doku.de/DDS/suche.jsp

There is a 392 page catalog that has reference to KB motors, this link may get you the English version directly. Further investigation should give you typical wiring diagrams.

http://www.demag-doku.de/DDS/servlet/com.demagcranes.dds.getPDF?IdentNr=20315144

One of the crab crane data sheets has this information, your 12 pole motor is similar.

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#8
In reply to #5

### Re: how to make control diagram for a double speed motor

10/25/2017 6:30 AM

I give rwilliams a vote on this - a good answer! Having "slept on it", I was going to suggest two separate windings.

The user needs to look in the starter panel and motor to see if there are 3 unconnected terminals or wires together with the connected three - with a high resistance to the "used" ones and earth.

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#3

### Re: how to make control diagram for a double speed motor

10/24/2017 7:38 AM

If possible, I would investigate the option of a VFD for this application.

If using only contactors, you will need four--one for each direction and one for each speed. Each of these contactors will need an off-delay function that prevents all the other contactors from energizing until the motor stops from whichever active contactor. Nowadays, this collection of contactors and interlocks is probably more expensive than a VFD setup.

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Guru

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#7
In reply to #3

### Re: how to make control diagram for a double speed motor

10/25/2017 1:41 AM

My original reply said a bit too much. Each speed contactor needs to interlock out its companion, and each direction contactor needs to interlock out its companion; but not all the others.

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#6

### Re: How To Make Control Diagram For A Double Speed Motor

10/25/2017 1:39 AM

These are all good suggestions, but not what you asked. The speed / power ratios from low to high indicate this is a "Dahlander" motor that provides a variable torque connection; the low speed torque is a fraction of the high speed torque. In crane travel this is done to provide a "creep" speed for final positioning of the load vs a fast travel speed. So assuming you have checked that the crane / trolley is capable of the higher speed etc., to regain the two speeds you will use the following motor connections. Go to the bottom on this page for the IEC Variable Torque connections.

https://www.joliettech.com/easa-electrical-engineering-handbook/3ph-motors-2-speed-single-winding-easa-electrical-engineering-handbook/

You will also need to buy a Dahlander starter, which will come with a wiring diagram.

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#9
In reply to #6

### Re: How To Make Control Diagram For A Double Speed Motor

10/25/2017 9:44 AM

All the Dahlander motors I've seen reference to have a 2:1 speed/pole ratio only, this is likely a two winding motor. It does look like it will need 3 contactors just to switch speeds, plus another reversing pair to change direction, which already are existing

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### Users who posted comments:

67model (3); JRaef (1); mohammed ismail (1); rwilliams (2); Tornado (2)

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