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Author Topic: Question on using DC chokes on SCR drives  (Read 5307 times)

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Offline simpson36

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Question on using DC chokes on SCR drives
« on: August 28, 2010, 06:25:06 AM »
In anticipation of using a larger spindle motor, have switched from a PWM drive with separate relay reversing to a big 4 quadrant regen SCR drive that has reversing built in.

Being spoiled by the smooth PWM power, I am not satisfied with the much coarser SCR performance and have been doing some research on adding a driver or choke to the output and perhaps also a filter on the AC input. I have been able to find only references to using two legs of a very expensive 3 phase reactor filter as a choke between the drive and the motor, but I can get a plain 10A choke for 1/10 the price of the reactor.

Question: with a reversing drive, do I need a choke on each DC wire to the motor or will one choke suffice?

Question: is there any tangible benefit to adding a line filter on the A/C input to the drive relative to motor low speed smoothness?

Offline simpson36

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Re: Question on using DC chokes on SCR drives
« Reply #1 on: August 30, 2010, 09:44:40 AM »
Cancell question. I have found the info I needed.

Considering the filters cost more than the low end controllers, it is not surprising that there is no experience to be found in this forum.
Re: Question on using DC chokes on SCR drives
« Reply #2 on: August 30, 2010, 05:13:17 PM »
I suspect the low frequency of rectified 1 phase SCR control, the choke would have to be quite sizable at that frequency.
The 3 phase chokes as used in VFD's between VFD and motor are mainly to inhibit the higher frequency harmonics that occur due to the much higher switching frequencies than straight SCR 120hz.
If you want smooth switching with full wave SCR, then 3 phase in would  give it to you.
Nosmo.

Offline simpson36

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Re: Question on using DC chokes on SCR drives
« Reply #3 on: September 06, 2010, 06:20:45 AM »
3 phase is not an option for me. The motor controller operates on 220V single phase.

I was able to acquire the motor I wanted, so I will be using the big SRC drive. What I decided to do in this instance is use the exact filters recommended and/or supplied by the manuf of the motor controller.

The in filter is a commercial device and the out filter is supplied by Minarik specifically for their RG series controllers. Together, these filters cost $120, about one third the cost of the controller itself.

The motor is actually a 140V DC servo motor and ultimately I plan to add an encoder and run it as a servo using my Granite Devices VSD drive, powered by a pair of 70V power supplies in series, but for now the SRC will get the job done.

Thanks for your comments.