Gecko G320 and 12V servo motor

Anybody using a G320 drive with a 12V servo motor? How risky is this? G320
specs state 18V as minimum voltage and voltage should not exceed motor rated
voltage by more than 5V. Would forward/reversed biased diodes in parallel
connected in series with each armature lead be wise or not necessary? I'm
about to call Gecko but the more help the better.
Reply to
oparr
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I wouldn't worrry about it - set a current limit to not exceed the motor's max current and you'll be OK. voltage doesn't really matter to a DC motor unless you exceed the insulation breakdown voltage, it's the current that matters. When run from a battery or a uncontrolled source, voltage and current and RPM are all related, but with a servo drive, you can set the current limit which will control the voltage appropriately. I wouldn't want to put much over 100VDC on a 12V motor, but I woldn't worry about 20 or 30VDC bill
Reply to
william_b_noble
No help from me but, I would like to know more about what you are doing. I am also working on a CNC project and am trying to absorb as much as possible. I haven't bought drives yet but am leaning heavily to Rutex. I did find a good source for motors and got three and a Compumotor 6K4 controller.
Reply to
Tom Gardner
Post your question on the Yahoo Groups geckodrive group and Mariss will answer it himself, typically immediately. Great guy. (Happy customer.)
Reply to
Fred R
Thanks Bill.
Reply to
oparr
Wasting money according to my wife. Working on a CNC x-y positioner. Prefer servos to steppers.
Reply to
oparr
Thanks, I posted there but looks like he's sick today.
Reply to
oparr
It's likely the motor can handle > 18 VDC.
Note that DC motor voltage is related to speed. You can also limit the DC voltage to the motor by limiting the RPMs in software.
Reply to
Richard J Kinch
I have two 27V 5.6A power supplies from a previous project so 24V servos would have been ideal but unfortunately not possible, have to use 12V servos. The current at 12V, rated RPM and maximum torque is 2.3A. I'm going to test the performance of the motors with the 27V PS under real mechanical load using a 6 ohm 40W series resistor.
Reply to
oparr
Dunno what you application is, but that is a puny motor.
Reply to
Richard J Kinch
More than sufficient for the application. With the PS adjusted to 23V and with a 8 ohm series resistor the voltage fluctuates between 13 and 16V at the motor indicating a maximum current draw of just over 1A. And this included loading the table with a 25lb weight (about 25 times what I'll be using), stopping and starting etc..
Reply to
oparr
Oparr - I'd strongly suggest making a test without the resistor - take the same measurments - if you are comfortable that the motor is not overstressed, use it without the resitor (you can add a fuse if you like) - in a servo circuit, the series resistor degrades performance and accuracy, you will be better off without it.
as an aside to those using low voltage motors, the big pile of Minarik controllers I picked up has a bunch of low voltage DC motor controllers - in the 12 to 48 V range - I haven't tested any yet, It will be a few days before I have access to them again, but if you have interest in the Minarik controllers, drop me a note. The DC controllers I have tested are all for 90 to 180VDC motors (with 110 to 220VAC input).
Reply to
william_b_noble
The resistor isn't doing anything useful and may actually degrade the performance of the system. As suggested earlier, you'd do better to limit the motor's speed in software.
Ned Simmons
Reply to
Ned Simmons
Motor spins way to fast. Bearings and brushes will go in no time. Still looking for a lower voltage drive. The popular MC33886 H-bridge controller operates from 5 - 30V and all other support chips (quadrature to count, counters etc.) can be found in 5V versions so don't see why such a drive doesn't exist. May have to make my own.
Called Gecko on Friday for their take on my scenario but their Tech Support was out sick. Also, left e-mail in the Gecko Yahoo group but it hasn't appeared yet.
Reply to
oparr
The resistor is reducing the voltage and hence the speed of the motor, preventing a 5000 RPM motor from spinning at over 10000 RPM leading to bearing, commutation, brush and possible winding (excess centrifugal force) problems. Yes, I can run the motor at 24V and 50% duty cycle and do the same thing but there may be other issues.
Using 10 rectifier diodes in series I see only a .8V variation at the motor (13.6V - 14.4V) with the PS at 23V and under the same load conditions mentioned earlier. Yes, I'll need 20 for both directions but they're cheap. Bottom line....G320 and 12V motor should be feasible one way or another at 24V. Just waiting on Gecko's take on it and still looking for a 12V compatible drive.
Reply to
oparr
If they are like stepper motors, your supposed to run the motor at 5 to 20 times the rated voltage. I've not messed with servos, I'm considering it because I've got a machine I want to retro fit controls on and I'd have to replace all the servos, but I'm just not into "Tuning" the servos.
Reply to
Russ Wizinsky
The resistor is a bad idea, but the diodes are a *really bad* idea. At least the resistor is a linear circuit element. The diodes are going to introduce a stepped voltage drop between the amp and motor. This is guaranteed to play havoc with the servo tuning.
I still don't understand why you can't simply limit the motor velocity in your software. The amp is isn't going to deliver any more voltage than what is required to drive the motor at a given speed.
Re low voltage amps, AMC makes some that will operate as low as 16V, but I don't recall if they're for brush or brushless motors, and I'm sure they'll be much more expensive than the Gecko drives.
Ned Simmons
Reply to
Ned Simmons
I'll discover this for myself first hand then.
Me neither, it's just not going to be the first option tried. Prefer a hardware solution.
Thanks!
Reply to
oparr
i always look for faster and faster
Reply to
HaroldA102
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These drives operate at 12-30volts. $65/ea in quantities of 3 or more.
Fred Smith - IMService
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Reply to
Fred Smith

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