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  #1  
Old Mon 19 July 2010, 07:43
tangocharlie123
Just call me: Pete
 
Gatton Brisbane
Australia
Can someone define about switching PSU

Hi All

Hope some one can help define between unregulated and regulated switching power supplies.

After reading both Geko 203v's manual and Leadshines DM856.

The Geko recomends a unregulated power suypply whereas the Leadshine can use both.

Gerald with all his good work also using a unregulated power supply.

The chinese motor manufacturer recomends one switching PSU per motor/Stepper combo.

personaly I would prefer one PSU per stepper/motor combo (redundancy swap one out if broken).

Please help as I wish to start ordering parts this week.

Cheers Peter
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  #2  
Old Mon 19 July 2010, 08:28
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
There are two variables here: switching vs. linear and regulated vs unregulated. As it turns out, almost all switching power suppliers are regulated.

As a crude analogy, a switching power supply is like a race-tuned, high reving motorcycle engine. A linear power supply is like a tractor engine. The motorcycle produces power in a large quantity of small pulses; the tractor in a small quantity of large pulses. The motorcycle is prone to stalling when overloaded; the tractor tends to just lug on through.

The regulated power supply maintains a constant speed, generally by running the motor a bit too fast and applying the brakes to get the desired speed. This generates heat, and stresses as the brakes are slammed on and off in response to a varying load.

Our application is like trying to tow a wagon across a bumpy field. Either engine can do the job; both will do it better if you have a large, heavy flywheel attached to smooth things out. The capacitors provide this flywheel effect.

So, regulated isn't particular useful to our application; it doesn't hurt, but it introduces one more set of complex electronics to fail - and a set of electronics that don't really like highly variable load.

An unregulated linear power supply is the best match for our application. This is a big transformer, usually toroidal these days, with a large rectifier, and large capacitor(s). However, with sufficient capacitance, any of the power supply types will work if they furnish the correct voltage and amperage.

I don't agree with the recommendation of one PSU per motor. It strikes me that this is recommendation is based on purely economics (small switching PSUs are cheap, in every sense) and not on performance or durability. A single large PSU can have a much better flywheel effect. Linear power supplies have very long lifetimes (decades), switching power supplies tend to die after a few years.
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  #3  
Old Tue 27 July 2010, 17:49
tangocharlie123
Just call me: Pete
 
Gatton Brisbane
Australia
Thanks

Thanks Brad

I do like your crude annology it helped a lot

Cheers
Peter
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