Control.com - Nerds in Control

People,

We have a permannet magnet, DC motor (rated voltage 36 V, torque 15 Ncm and speed 5 - 40 krpm), with two field coils. The drive uses a control circuit, ac-dc rectifier and a power H bridge type circuit to generate two quasi sine waves at 180 degrees phase shift. It seems feedback is by back E.m.f.

We need a similar drive which accepts a 0-10 Vdc speed signal and possibly able to drive five such motors concurrently (only one motor loaded).

Can someone suggest possible suppliers?

Thanks

Martin

An AC drive now has the same zero speed torque that is avalible in the DC drives, so there is no reason not to use an AC drive.AC drives also have more applications and better speed control(0-10V or 4-20ma) than DC drives.
I know of a company that sells a new drive called the "PDL" it can operate a number of drives at one time. if you would like to switch to an AC drive E-Mail me and I will gladly give you the name and the number of the company.

HOWEVER, typically DC motors are considerably more robust then AC motors, as are the drives. Try pumping 150% current into an AC motor for 30 seconds or so and see what happens. A DC motor/drive combination will often survive this while an AC motor/drive combination will just trip.

There is also the regen problem. 4 quadrant DC drives are generally less expensive then full regen AC drives. This is a major advantage in some applications.

As for the better speed control idea, I think that is sheer nonsense. Digital DC drives with digital feedback have very similar speed control features as AC vector drive motors with digital feedback. Its true that older analog DC drives or using voltage feedback resulted in lower speed regulation that some AC drives, but this is not a problem associated with using a DC drive in and of itself, but not using the appropriate drive. besides, most digital feedback digital drives can easily maintain 1/2% speed accuracy (in some cases even better). Its not many applications that require anything a lot better than that.

One thing I have observed is that vector drive performance at very low turndowns (maybe < 1/4% of full speed) seem to perform better then a digital drive where you can sometimes see a bit of cogging. But very few applications require this kind of turndown.

Try comparing an AC vector drive/motor combination to a digital DC drive/motor combination where occasional current demand exceeds the motor spec for say 20 seconds twice a day, and regen capability is required. I bet you will be surprised at the cost comparison.

Bob Peterson

Concise and informative, would you say the advantages of dc over ac, and costs also apply to large drives and motors? my application requires traction control of a 40 kW motor from a DC source. regeneration/braking is a must.

thanks Bob

Alex

People will use AC Motor to replace DC Motor most of the reason is on motor side, the AC motor are more maintanese free.

AC or bldc motors can also rotate at higher speeds since there is no mecanical commutation limitations.

We should be able to help you.
http://www.carotron.com

Thanks,
Randall