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DC motor torque by amps

DC motor torque by amps

DC motor torque by amps

(OP)
I have some partial information about two old DC drives that a customer would like to replace with AC.  These drives are on a coil slitting line.  They are slitting aluminum, 14ga max, 4 blades max.  The slitter runs for a few hours each week.  They would like to go to AC because of the maintenance cost of old drives and motors.  I suspect that getting the old drives repaired is the main problem.
 
The layout has the de-coiler which does not have a drive.  Then a 15hp slitter which feeds into a slack/take up pit.  Then through a pneumatic tensioner before going into a 50hp winder.

The customer thinks the slitter is over powered and would like to save some money by reducing the motor size.  The only information I have is partial name plate and amp draw on their thickest sheet.  I would prefer to leave the motor sized to the slitter and not the current material being run through it myself but I am not signing the checks.

Slitter Motor
15hp  1750/2300 rpm
Frame AD258AJ
Arm Volts 500 Arm Amps 25.2
Field Volts 150/800  Field Amps 2.8-1.58/1.4-.79
Encl DPF   Power Code D

Amp Reading while running
3-9 amps, spike 12-15 amps

Winder Motor Emerson (very old)
50hp  1750/2100
Frame  328AT
No other name plate info

Amp Reading while running
26-44 amps, spike 55-60 amps

I don’t have a torque constant, voltage or any speed information.  A new (Baldor)15hp motor has a FLA of 25 amps and a new 50hp motor is 84 amps.

Can I just go by proportion?  Actual Amps/FLA * Torque(at rated speed)
For 15hp, 9/25.2 * 45 ft-lb = 16 ft-lb?

What would be the minimum data to determine required torque?  I am going to try to get some rpm data so if they go to an AC motor it won’t be running at low rpm.

Barry1961



RE: DC motor torque by amps

I get confused with all your ft-lbs and stuff. I think someone on your side of the big water can say something about that.

Winders can be tricky. Is this one a constant power winder (centre driven with field weakening) or is it some other kind of winder? AC drives sometimes cannot do exactly what a DC motor with field weakening can do when it comes to winders.

About the slitter drive sizing. Yes, agree. Size motor according to slitter. Makes things a lot easier (mechanical fit) and better reliability too. I think that you should mention that to your customer.

Gunnar Englund
www.gke.org

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