DC Servo and Power supply problem.

[Ark1]

As I lurk through the forms of CNC builds and Conversions I now see why it takes so long from start to finish as I am in the middle of my own project that I started a year ago.

First off I purchased 3 DC servos, problem 1 was one of the motors was 72 volts and the other 2 are 90 Volts all Nema 34. I clicked on the wrong voltage on the motor when I purchased them a year ago and never unpacked them until now.

Next problem I found today. I have mounted all my componets to the enclosure back board and have started drawings and today began wiring the componets. At age 54 my eyes aren't what they use to be. So reading glasses are needed to read the pages and see the numbers on PC Boards. As I looked at my power supply I realized that what I ordered, a 72 volt supply was now only a 58 volt supply. I have sent an email to the manufactor today asking if a swap is possible I have had the power supply since May? They all look the same in the picture and only when I was looking for the connections did I realize with my glasses on that the number isn't 77 volt but 58 volt. I did order the 77 volt supply.

Anyway, as Al Suggested I rang out my motors for ground and armature I also with the motors connected to the machine with 3 to 1 reduction timing belts ran them from an old car battery sitting on the shop floor. I doubt it had even 12 volts of charge. All axis ran smoothly in both directions. Without any experiance with servo's and voltage. As an opinion, does anyone think that based on the above test with the car battery will 58 volts do or should I turf this power supply and spend another $350 after shipping and taxes to get the 77 volt one. Maybe I can sell this one on ebay.

I know I should have read the label when I got it, but I am long past this now.
I am hoping the manufactor will do a swap, I will pay for shipping one way with the wrong power supply and he can pay the return.

Opinions?

Thanks for all your help.

Ark1 ( TonyK)

[Al_The_Man]

Typically the DC power supply for servo's should be at least 10% higher than the motor voltage.
You should be able to get away with a 100vdc supply for all three motors for optimum performance.
I use Antek Toroidal transformers for supplies, they also build the whole supply if you don't wish to build.
He lists on ebay under Jonango.
Al.

[Ark1]

I wanted to Use a Higher Voltage but the Gecko 320X clearly states 80 volts max or it will blow up. I got this from the Manufactor.

As you can see the power supply is a Torroid type but I was sent the wrong voltage for the application.

I sized the motors on the large side which now with this power supply would be only running them at 60% of their capacity. Is there a down side. With 12 volts from a car battery transit time is about 2 inches per minute. At about 60 volts I suspect the transit times will increase dramaticly.


Ark 1 ( TonyK )

[mike_Kilroy]

I see no reason to rush out and buy a replacement power supply until you try the one you have. Volts makes speed and for quick figuring you can assume it is a direct linear relation. 58V will make your motor go 58/12=4.8x faster than the 12v car batt did - even more if indeed the batt was lower than 12v... So until you build it and try it wait to see if it is indeed to slow for your rapids....

a max voltage on Dc motors has a reason: the commutator the brushes ride over is rated for a max voltage bar-to-bar (next to each other). If you put more than the max voltage on the motor the sparking gets horrendous and can even ionize the air around the comm and be a ball of flame. So not exceeding that 80v is probably a good plan.

Current makes torque so the motors will produce their full torque rating at your 58v so no issue there; you still get 100% of their torque rating.

[Al_The_Man]

Ark1, Here is an excellent article from Electronic Design on sizing a P.S.
Power-Supply Considerations For Servo Amplifiers
Advanced Motion recommend plus between 10% & 50% remember there is not a direct link between motor and P.S., there is drive in between.
Al.

[Ark1]

John from Antek emailed me and told me that this is the correct transformer for my requirements and to do an open circuit voltage test on all of the out puts.

Results are,

80.5 VDC
80.5 VDC
12.1 VDC
4.9 VDC

He stated that the transformer name plate is before the current flows through the rectifer moduals.

One less problem to deal with.

Great service from Antek.

Ark1 ( TonyK)

[Ark1]

Thanks Al,

Although this explaination repeats it's self here and there it brings forward losses that we as reverse builders don't really consider. Also how many of us test the machine for what actual power it will require and then do a selection for servo or stepper motors based on aquired data. Seeing that the motors are now from the 12 volt test big enough to drive any axis, I think I have some wiggle room with a 77 volt power supply. My Z axis has the 72 volt nema 34 motor on it with a 3 : 1 belt reduction. The X and Y are not fighting gravity so although they are 90 volt motors even with 70 volts after losses will produce good rapids.

Ark1 ( TonyK)