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#1 bob

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Posted 21 February 2006 - 06:37 AM

Hi,

I am stuck with an automatic arcing machine. The cross travel and feeding movements are carried out with two dc motors 90 V dc as written on the nameplate. The electronic card for the control of the machine is dead and back up is no longer available. I am looking for another alternative to control the machine. The motors have got only two terminals and rotation of the motors are changed by reversing the polarities. I am looking for a way to control the speed of the motors. Any help appreciated.

Bob

#2 marke

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Posted 21 February 2006 - 10:14 AM

Hi Bob,

We need more data.
I am assuming that these are permanent magnet machines if you can reverse by reversing the polarity. If they were series wound, you would not be able to reverse by reversing the polarity on the two terminals.

That being the case, they are probably relatively small motors.
Does the "card include the power elements, or is this the driver for external power control elements (SCRs).

How is the control achieved, i.e. 4 - 20 mA, 0 - 10V etc.
Is there any external feedback, i.e. shaft encoder or tachogenerator.
What is the input voltage and current.

Small DC controllers are available, but we need more data to ensure that you get a good apple!

Best regards,

#3 bob

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Posted 22 February 2006 - 04:10 AM

Thanks Marke, The motor in question is a small motor 1 A 90 V brushless DC motor. The DC controller has failed beyond repairs. The control is achieved through a pot and an encoder is mounted on the shaft of the motor. The operator achieved the required parameters through a keypad wired to the card. I am looking for a sort of dc controller, a rather cheap one, and I will use a micro PLC to do the control.

Thanks for your always useful input.

Bob

#4 marke

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Posted 22 February 2006 - 04:59 AM

Hi Bob.
If this is a brushless DC motor, then you may have some difficulty finding a standard controller as the controller and motor need to be matched. In effect, the controller is a form of inverter, usually with several phases and position sensing circuits to ensure that the excitation is in synch with the rotor.
If it was a standard DC motor with brushes, then it would be pretty easy to find a replacement controller.
Because the brushless controller is essentially and inverter system, you will not save money by trying to do the control with a PLC.

Do you have any specific data on the motor? If I have enough information, I may be able to come up with a solution for you.

Best regards,

#5 bob

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Posted 24 February 2006 - 07:06 AM

Hi Marke,

Sorry to come bck to you late. The motor is 1/20 HP, 0.58 AMPS 90 V and torque 100 in lbs. Its a dc gearmotor and make Minarik. In addition an encoder with 60 ppr is mounted on its shaft. The motor is manufactured by BISON Gear & Engineering Corp.

Bob

#6 marke

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Posted 24 February 2006 - 09:27 PM

Hi Bob

Are you sure that this is a brushless DC motor? The website data only lists brushed motors with replacable brushes.
How many connections are there between the motor and the controller (ignoring the encoder)?

Best regards,

#7 bob

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Posted 27 February 2006 - 04:22 AM

Hi Marke,

Only two wires come out of the motor, a black and a white one. Reversing is achieved by interchanging the connection.

Rgds.

Bob

#8 marke

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Posted 27 February 2006 - 05:21 AM

Hi Bob,
I should have picked that up from your first post, however you did regfer to these as brushless DC in a later post.
These are permanent magnet motors and do have replaceable brushes. This makes the controller pretty simple and should not be a problem to replace.

I can look into it from here if you wish.

Best regards,

#9 bob

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Posted 27 February 2006 - 05:30 AM

Thanks Marke,

I have got some options from Eurotherm but I am rather looking one with encoder input . If it does not bother you much. grateful you advise me on some options.

Thanks and best regards.

Bob




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