Newbie- Help with glentek ga4555p-1 amplifier

[salvicrashdrive]

Hello everyone, I'm new to the forums and new to the amplifier world as well. I am trying to figure out if my ga4555p-1 amp is working properly. Here's the deal, the amp only outputs 42 and -42 vdc without any smooth transition in between, and regardless of the amplitude of the input voltage. I am trying to drive a maxon 118743 dc motor with it, but I'm not sure if I'll do some damage to it by applying 42 and -42 vdc to it. (it's rated for +-12vdc). My intuition tells me that I would want to see a nice transition between 12 and -12 coming out of the amp. The system was setup by someone else and now after a year I'm supposed to put it back to work. Any help will be very much appreciated.

[Al_The_Man]

It sounds like the motor is not matched to the amp, or at least what you have for a power supply.
You don't say what system it is on or if it is set up with a tach for velocity mode or current mode of operation.
You will over speed the motor by applying more than its rated voltage.
If the drive is able to work this low, you can tailor you power supply to match the motor.
Al.

[salvicrashdrive]

Thanks for the reply and sorry for the lack of info, I'll try to be more specific. The original application was on a haptic device called the phantom, basically a little robotic arm with three axis of movement and a maxon 118743 dc motor for each one of them. There's an array of three ga4555p-1 glentek amps one for each axis. The power input that the amps are receiving is indeed 42 vdc from the power supply. The system receives its input voltage from a d/a card in the computer and is supposed to translate it to motion. I can input a sine wave as low as 0.1 vpp to the amp and the output will still jump straight from 42 to -42 without any smooth transition. As far as the tach or current mode, I'm not sure. Is there any way I could find this out? The hard part about the whole situation is the people who set it up are now gone, so I'm having to reverse engineer the system and make the arm move nice and smooth. Any tips will help.

[Al_The_Man]

Did it ever work?
A D/A card usually outputs the standard ±10vdc not sinewave unless it is a sinusoidal controlled drive, but the fact that it is a DC motor rules this out.
Which begs another question, Is the command and the drive compatible?
Do you have specs on the drive that will confirm the command requirements?
Al.

[salvicrashdrive]

Hey Al, thanks again. Well the D/A card I'm using is the PCI-DDA08/12. The sine wave is being generated by simulink. The card also comes with a program calles instacal which allows you to test the digital and analog ouputs of the card. Using that you can output specific analog voltages anywhere from -10 to +10 by turning a knob in their GUI. When turning it I can measure the input of the amps and see the voltage change to match what the computer screen says. Regardless of how small the voltage gets the output of the amp remains at 42 until the input crosses 0 at which time the output becomes -42. As far as the drive, sorry to sound dumb, but what do you mean by drive? is the amps or what drives the amps? Thanks again.

P.S. Apparently it did work at some point.

[Al_The_Man]

Although I am not familiar with that drive, it is most likely a PWM drive, which means the output voltage will always switch between 0 and PS + at the modulation rate, to both + & -42v in your case.
The pulse WIDTH of this signal will decide the mean current level through the motor.
If you can input a very low DC analogue signal in and the motor runs at top speed it can be because of tach loss or tach reversal, IF the motor is fitted with a tach.
If the amp is a torque mode amplifier, (no tach on the motor), then you require a very low input signal, to reduce speed.
Also try turning the motor shaft manually with no signal input and see if the motor runs away, if not then the symptom may be that there is no feedback via encoder back to the controller, as this completes the servo loop for precise control.
Al.

I just found some info that indicates these amps require a tach feedback from the motor, if so this loop has to be satisfied first, i.e. no runaway with zero input and the shaft should resist manual turning.

[salvicrashdrive]

Thank you very much for the info Al. It seems like you might be on to something. I'm going to the lab later today and I'll check all that you mentioned. Thanks again and I'll keep you posted.