Servo power supply sizing?

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24 Feb 2024 00:35 #294149 by smc.collins
My advice is, return the Geko drives and buy the proper type of drive for the application.

80VDC , 20A maximum for the gecko.

I can tell you from personal experience, stall TQ and accelerations can pull quiet a bit more in practice with brushed DC motors. the data sheet you provided says 34amps and not the voltage. Many of the DC brushed servos of that era from Electrocraft were upto 180vdc. You may not reach the 5000rpm speed maximum with 80v " I didn't see a speed voltage chart" and to keep something in mind, Brushed DC motors vary speed with armature voltage and current with load., and the servo drives may not tolerate the loads on fast accelerations and decelerations and the braking back EMF is likely to kill the geckos with so much overload. That was why I linked the KB drives which are cheaper " albeit dumber" but remove the external power supply requirement as they use SCR type drive topology and input 120vac or 240vac. Spend the money on a good control card pair from mesa and get servo feedback for closed loop. It's your machine you can build it however you like. But I have a affinity for DC motor system " personal preference" and all my machines are DC servo and I have had to replace drives in 2 of them. I've been through through the blood soaked wall of drive issues. if you want a fast accurate machine for not much money, get the mesa cards, get the KB drives, return the geckos, simplify your cabinet. It's probably a wash cost wise at that point. If you need tach feedback attachments for those Servos and encoders, I have 4 dead electrocraft DP600 servos that iirc should be able to donate those parts, they're yours for the price of shipping. 2500ppr encoders and tacho generators. DC driver are not like AC drives, and they can be very difficult to manage with high gain.

It's not the Tim Taylor school of engineering, often it's the school of hard knocks, it's your face to pound on the concrete wall though.

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24 Feb 2024 03:52 #294170 by TimpanogosSlim

I will try to simplify it a bit more, if i can:
go buy a simple plain old switching power supply for LED strips, find one for 24V 400W and start making chips. Set motor current a bit lower, use a bit lower acceleration and speed, and watch the machine work.
Maybe you end up not needing more ... although getting two of those for 48V would give you way more speed! :)
This might also help you decide:
forum.linuxcnc.org/show-your-stuff/47357...hines?start=0#257421

You can clearly see the 400W power supply powering everything, on a huge machine.
What you can not see is another same power supply behind the console waiting to be wired in.


This aint my first rodeo. 

Just the first one with servo motors. 

I know that most SMPS see a motor coil winding that has not yet been energized as close enough to a dead short to go into protection. Indeed, I have some really big (12v 50A) supplies here that decline to power one of these motors at all. 

I also know what transients are, and what transient means. 

If one of these servos gets into a situation where it *needs 20A continuous to keep spinning, it's probably in a situation where it's about to start a fire or break the cutter. 

The math suggests that under normal use these servos may draw up to 4.mumble amps each for up to seconds. 

There will be occasional, even frequent current spikes way above that. But they are crazy brief and the capacitors in a linear power supply from antek should be able to service them without meaningful drama. 

And if they can't, I can spend $20 on a large can capacitor that will. 
The following user(s) said Thank You: tommylight

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01 Mar 2024 23:57 #294874 by TimpanogosSlim

My advice is, return the Geko drives and buy the proper type of drive for the application.

80VDC , 20A maximum for the gecko.

I can tell you from personal experience, stall TQ and accelerations can pull quiet a bit more in practice with brushed DC motors. the data sheet you provided says 34amps and not the voltage. Many of the DC brushed servos of that era from Electrocraft were upto 180vdc. You may not reach the 5000rpm speed maximum with 80v 


Are you saying that the given maximum terminal voltage of 60v means something other than that 60v is the maximum voltage it should see? 

I am reasonably certain these were powered by a 48v supply in their original configuration. 

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