[spank]

I recently picked up a router table that has Reliance Electric Micro 100 DC brush motors (1/2 HP) on the X and Y. The control didn't come with the machine, so I am putting one together now. I'm a Kflop user, so I will be using Kflop/Kanalog to control the machine, and I have been looking around at suitable amplifiers. I found some Aerotech BA20-160 amplifiers that seem like they would be great for this application, and the price is right. They put out 160VDC:

http://www.aerotechmotioncontrol.com...BA10_20_30.pdf

and the motors have a labeled rating of 120vdc. I have read that I can supply up to 50%+ the rated voltage... does that apply in this case? In the Aerotech manual they talk about using one of their transformers to reduce the DC bus voltage, and I did some tracking back, and it seems like I would need an 85 VDC transformer at 1700va to get what I need. 1700VA is hard to find!


Any ideas?

[keebler303]

They will be fine at 160V, common practice on DC servos everywhere. Current is what can fry a motor. The winding insulation will not care if it is 120V or 160V.

If you wanted to reduce the voltage (waste of time and money) you would need an AC transformer (not DC). A "Buck" transformer is made for the job and easily available in 1700VA.

416-1271-000 | 2kVA Buck-Boost Transformer: single-phase, 240x120 VAC to 32x16 VAC

Matt

[spank]

Thanks Matt. I mistyped RE: AC transformer. Ok, so 160V would be fine for a motor rated at 120V. Theoretically what would happen if I supplied 400V?

[keebler303]

Honestly, probably nothing.

As long as the wire used in the windings is capable of withstanding the applied voltage, nothing will happen. The drive constantly measures motor winding current and will alter its output to maintain the proper amount of torque to keep the motor in position.

It is not a good idea to use a high voltage drive with a low voltage motor as the drive will not be operating over its full range so its performance will be reduced. For example it may only ever output 25% of rated voltage (PWM equivalent) so you would have 1/4 of the resolution you would have on a drive operating over the full range of output. It would be a bit like measuring the diameter of a needle with a yardstick (poor resolution).

[Al_The_Man]

The suggested DC supply for a PWM drive etc, is at least 10% above the motor rated voltage, the current decides the torque and the applied voltage decides RPM.
The level of both current and voltage is supplied at a mean level therefore the drive has control on the maximum of each.
Also when looking for drives such as those for DC motors, most makes of BLDC drives will run a DC brushed equally as well when set to 60° commutation.
Al.

[spank]

Al, Thanks for your reply. If I understand you correctly, the drive will limit the voltage based on the speed needed at any given moment?

[keebler303]

Al, Thanks for your reply. If I understand you correctly, the drive will limit the voltage based on the speed needed at any given moment?

Yes, speed is proportional to voltage (you probably know this if you ever messed around with small dc motors for RC cars or similar) and torque is proportional to current.

At no load and max speed, you have very high voltage and little current.
At full load and zero speed, you have very low voltage and very high current.
In between, the drive keeps everything happy.

[Al_The_Man]

Al, Thanks for your reply. If I understand you correctly, the drive will limit the voltage based on the speed needed at any given moment?

Yes, with the torque curve for a typical DC brushed servo is maximum at zero rpm and is fairly flat up to the rated max rpm.
Al.

[spank]

Ok very good. I think my motion needs are sorted for the moment. Thanks for your help guys.