DC motor torque by amps

[Barry1961]

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

 

[Skogsgurra]

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

http://www.gke.org