How to upgrade from contactors to a drive ...

[mmmert]

Hello everyone,
I've got a very broad question but looking for some maintenance or engineering advice. How to upgrade from contactors to a drive on an old motor system?

I have an ancient straightener with a single speed DC motor, start stop, and reverse buttons, but I would like to get into this century with a variable speed drive so i can slow it down and make it safer. i would like the operator to be able to change the speed with a potentiometer on the operator panel. It is a 15HP DC motor with brushes and a 240VDC field voltage.

Is there some methodology to this? or a procedure that I should follow to upgrade from contactors to a drive?

Thank you!

[3rdshiftguy]

Re: How to upgrade from contactors to a drive ...

Also looking forward to a response to this. I'm also curious how a pro would go about upgrading logically. Anyone?

[Cheller]

As for me being a pro, that depends who you ask...

Anyway, if I had an old DC motor that was being controlled by DC contactors, I would start by taking a step back and looking at the application first.

Do you want the motor to go both directions and have control over the speed? If you answer yes than an electronic drive is the answer.

Congratulations, that's the first step...

[Cheller]

Step 2.

Next you'll need the specs on the DC so you can buy the appropriate drive. The motor nameplate is the key here. You'll need Armature Voltage, Armatures Current, Field Voltage, Field Currents, Horsepower, and the RPM at the bare minimum.

if the motor nameplate is not there, which seems to happen from time to time, you're most likely in trouble. you can determine both field and armature volts and current using a voltmeter, (carefully while the motor is energized). RPM would need to be determined with a handheld tachometer. Horsepower would have to be calculated based on the armature current, you could at least get a ballpark figure on the HP.




Now you're ready to buy a suitable drive....

[Cheller]

Step 3.

If you are new to the electronic drive world, you will need to choose a couple brands that you are comfortable with. Let's say three industrial drive manufacturers. (For example Allen Bradley, Baldor, Toshiba) Now take your specs to each one of their websites and look for an appropriate drive to meet your needs.

All the manufactures will have some type of drive configurator on their site. If you don't like that idea, just contact your local sales rep with your motor specs, and tell him (or her) your application. They can do the leg work if you want them to. Typically they end up contacting their "drives guy" (or "drives lady") who specializes in this type of work.

[3rdshiftguy]

Re: How to upgrade from contactors to a drive ...

If you really analyze the upgrade process, I guess it comes down to research and cautious decision making. i think if you involve more than one drive specialist, you'll get some good ideas. You can use their quotes as guidance if you're making you own decisions on contactor upgrading.