BLDC speed control

Hello all,
I am interested in driving an industrial-type brushless DC motor with a hobby-type electronic speed controller. There are industrial speed
controllers but they are larger, heavier, and much more expensive.
Are there any issues with doing this? What is different between the two? I did see a warning in a manual for an RC ESC which said that it is not designed to be operated with a power supply. It did not say why but I am guessing it is because there is no schottky diode?
Any input would be appreciated.
thanks!
Tony
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Tony wrote:

A switching power supply may give problems. A brushless controller does a lot of PWM switching/chopping too (not at full throttle though). You could also anwer in the DIY Electronics subforum at RGGroups: http://www.rcgroups.com/diy-electronics-199 /
Workings of a brushless controller: http://www.torcman.de/peterslrk/SPEEDY-BL_eng.html
Several diy designs: <http://www.rcgroups.com/forums/showthread.php?t 0454>
Excellent active development thread: <http://www.rcgroups.com/forums/showthread.php?t 0567>
Development discussion group: http://www.yahoogroups.com/group/osmc
Vriendelijke groeten ;) Ron van Sommeren near Nijmegen, Netherlands int. electric fly-in http://home.hetnet.nl/~ronvans /
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message

Probably right on, as to why it says not to use a power supply.
For the OP, one work around is to use the power supply to charge a battery, and hook the speed controller to the battery. The battery conditions the power to make it truely DC, and the power supply keeps the battery charged.
--
Jim in NC



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"Tony"

** There are many differences.
Hobby speed controllers are designed for the remote control of battery powered vehicles without need for precise rpm regulation or interfacing with anything other than a standard R/C receiver.
They must be lightweight and cheap to make too = no need to be repairable.
The direct opposite applies, in each case, to an industrial BLDC speed control.
..... Phil
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Thanks all for the comments. I guess I am still unclear on why the RC controller manufacturer would say that it cannot be driven from a power supply. Most of the industrial controllers are switchers as well, as that is the only way to obtain reasonable efficiency, and they have no such restriction.
The only things I can think of is that without any diodes on the output, and with the relatively high source impedance of a power supply (compared to a battery) the RC controller will be introducing large voltage spikes across the power supply terminals. The supply would have to be designed to drive an inductive load. A battery however will not be damaged by (brief) spikes across its terminals.
Also, the RC controllers all appear to be sensorless, meaning that they use back-emf to sense motor speed. This works ok for lightly loaded motors, but there are issues for startup/low speed operation and with high torques.
-Tony
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Tony wrote:

From what I've seen in these RC speed controllers, is they have limited input bulk capacitance, just a minimum number of large ceramics to handle the high frequency input ripple current needed with all half bridge drivers. The cost conscious designers would take advantage of battery's low impedance ranging from DC to many 10's of kHz. This is why battery leads are short and close together to minimise inductance.
So to run your controller off a power supply you need to provide a very low impedance voltage source for the ripple current demand. This is easily achieved by connecting a few large low ESR electrolytic capacitors in parallel. Solder an array of capacitors in a row with +ve and -ve wires running in parallel geometry. To minimise lead inductance, minimise wire distances between the capacitors and the controller (comparable to battery lead length and separation). Now your power supply only has to be capable of the DC current drain, and you can use wires as long as you like.
I think worst case input ripple current for a 3 phase half bridge is 1/6 the average input (battery) current. Your capacitor bank must be rated for this amount of ripple. If they start getting warm then the ESR is too high or my calculations are wrong.
regards,
Adam Seychell
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"Tony"

** Likely because, unlike a battery, PSUs cannot absorb current supplied from the load.
The output voltage will rise up and BAD things happen !!

** Drivel.
...... Phil
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