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Author Topic: Changing from Bipolar Parallel to Bipolar Series  (Read 6423 times)

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Offline gjp

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Changing from Bipolar Parallel to Bipolar Series
« on: January 13, 2010, 01:01:55 PM »
Hello,

My CNC arrived here from the factory with the motors wired bipolar parallel.  After about two and a half happy months, the system decided it didn't want to work anymore.  After consulting with the maker of the driver board, I discovered that the motors in bipolar parallel setup draw too many amps compared to bipolar series, and this likely damaged the driver board.  He recommended that I rewire things to run in bipolar series.

That is all fine and good, but what I am wondering is, once I get this new board and drop it in, do I need to change any settings in Mach3 because I have now switched from a bipolar parallel to a bipolar series setup?
Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #1 on: January 13, 2010, 01:12:40 PM »
Hello,

for the software, the wireing of the steppers is not relevant. So, nothing to change.

But on the other hand: changing the wiring from parallel to serial will cause a loss in torque, and even more remarkable, in maximum speed. This is due to the increased inductivity when wiring the two parts of the coils in serial.

Next question: Doesn't the driver board have a current regulation, which should have been protecting the driver from being damaged?


:-)

Konrad

Offline gjp

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Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #2 on: January 13, 2010, 01:48:47 PM »
Yes it does, but the advice to change from bipolar parallel to bipolar series came from the board manufacturer.  Apparently bipolar parallel draws more amps than the board can handle.

I personally don't mind switching to it, because I don't run the motors very fast anyway.  I like to stay down in the 45 inches per minute area.  My main concern is precise and accurate cuts, not fast cuts.  Slow and steady wins the day.

Offline gjp

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Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #3 on: January 13, 2010, 03:51:51 PM »
To answer your question, the board does have a regulator.  The manufacturer in his infinite wisdom set them to the maximum setting.

Motors that draw 4.2A + regulator set to max + board rated for 2.5A according to manufacturer = fun!

Putting them in bipolar series will bring the draw down to 2.1A.
Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #4 on: January 13, 2010, 03:55:30 PM »
Congratulations  ;-)

 ::)

Offline Jeff_Birt

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Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #5 on: January 13, 2010, 04:23:35 PM »
One correction: Bipolar series wiring will produce more torque but lower acceleration and max velocity with all other things being equal. If you need to make any changes in Mach it will be in motor tuning. You may need to lower your acceleration and max velocity but you'll have to test it out and see.
Happy machining , Jeff Birt
 

Offline stirling

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Re: Changing from Bipolar Parallel to Bipolar Series
« Reply #6 on: January 14, 2010, 06:07:26 AM »
I'd urge a little caution. A stepper drive is by nature a current limiting device. A motor can NOT "draw" more current than the drive is set to source. If the driver has "blown" I would suggest it's not for the reason you give here. If it's max current is 2.5A then that is what it will have been delivering. If the motors are 4.2A then they would have been current starved in parallel. In serial you will presumably set the drive to limit current at 2.1A but that is not hugely less than the 2.5A of before (maybe enough less - but maybe not). I'm guessing that heat sinking may be an issue worth investigating.