Automation tech brushed servo wiring questions.

I just purchased 2 350oz/inch peak 50oz/inch continuous servos. I will be using them to replace some 25 year old electrocraft motors I got surplus. They are roughly equivalent to each other for specs.

The motors I have now are only 2 wire. One going to a terminal on each brush. The new motors also have a third ground wire. Do I have to use this ground wire or can it be capped in some way. The cables I'm using now are very nice 12awg shielded and I do not want to remove or replace them if I don't have to.

A few more questions. Does anyone know if I will get any better performance out of these new motors over the 25 year old ones I have now? They have pretty much identical ratings.

Last is if anyone can tell me how to know if I'm pushing my motors to hard. I can observe the current draw in my system in real time. The motors do not even get warm after 2-3 hours of continuous cutting. During rapids they draw 1 to 3 amps per motor. There continuous rating is 3.5 amps so this doesn't concern me. During cutting they can draw 7 amps or so of current on reversal with the acceleration limits I have now during complex 3d tool paths and tight cornering. This can happen quite frequently on one or all axis at any time. The higher current is only for a fraction of a second at a time.
I would like to increase the acceleration until worst case is up to twelve amps instead of 7. Is this a problem under my conditions? How will I know if I'm pushing to hard?

Any advice is appreciated and if I've left out any info needed let me know.

Thanks
Ben

What machine are you running them on, and what drives ?

I've used quite a few of those motors, but if you run above 5 amps for 20 seconds or so, they can be toast, with that lovely burnt epoxy smell.

It is definitely advisable to ground the frame of the motor by taking a ground wire back to the common ground point in the enclosure.
You can run a green TEW/MTW (single conductor stranded) by itself.
Al.

Thanks for the reply. The machine is homemade. It uses k-flop and snapamp. I can push up to 80v and 15amps per motor. I have not hooked these motors up yet but they are rated the same as the e543s I'm using now. The machine never draw over 2-3 amps during rapids or cutting. If it peaks above 3amps it is only during instant reversals in 3d tool paths for the most part. They never draw above 3 amps for more then a fraction of a second at a time. The only reason I worry is it can happen very frequently during some programs. I have acceleration turned down low enough that it never peaks above 7 amps. I would like to increase acceleration until it can peak up as high as 12amps if it's safe. Also do I have to use the ground wire seeing as I don't with the motors I have now?

Thanks
Ben

The overcurrent burnouts were usually when the machine is pushing slowly and gets jammed, maybe by a bad limit switch or a very dull cutter. Does the kflop have a max time setting for high currents ?

Yes it does. I can set the max current aloud per axis. It is set to 13amps even though it never gets anywhere near that. If it hit that current it cuts power to the axis within a fraction of a second. Also this system has been running for several years without any problems. I would like to know how far I can push things though.

Thanks
Ben

Here is a link to the snapamp page. Dynomotion Motion Control Boards for CNC Manufacturing and Robotics Applications

It is the motor amplifier. Since you make drives it will tell you far more then I even understand.

Thanks
Ben

Thanks for the reply al. I missed it earlier. Can I run another 12-2 cable and attach 1 wire to each ground or do they need to be separated from each other.

Thanks
Ben

There may be a dutycycle setting that you may want to set to a max of 6-7 amps for 10 seconds max. The continous current rating is about 4 amps.
The 13 amp peak isn't going to save the motor if you are pushing steady at 7 amps because of heavy load. I know small dc servos like these can only take that for less than 30 seconds ,before the windings melt.

Ok thank you. I will check with Tom k and see what he suggests.

Ben