Servo power supply sizing?

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11 Feb 2024 01:19 #293048 by TimpanogosSlim
I'm re-controlling a circa 2012 techno-isel lc-3024 wood router. I've never laid eyes on the original controller -- I just have the machine itself, the touchoff pad, and the VFD for the spindle. Bought at a school district auction - the guys at the surplus warehouse had no information. 

It has three ElectroCraft E243 brushed DC servos. The sum total of all of the information i have ever seen regarding these is attached. 

For initial testing i have some transformer iron pulled from old AV receivers and the like that should suffice, but obviously if i am going to use the thing reliably i have to have a properly sized power supply. 

Probably buying like a 35v toroid from Antek and attaching it to a really big bridge rectifier and some large can electrolytic caps with screw terminals. This will result in nominally 48-ish volts (same as the original power supply, based on pictures of LC-series controllers) but the Antek toroids do seem to float a bit high when not under heavy load, and i don't want to get too close to the 60v maximum for the servos. 

I've settled on (and purchased) Geckodrive G320x closed-loop drivers. Max 20A 70v. 

If i have done my math correctly, continuous stall current would be like 3.9 amps for one servo? 

A 600vA transformer would give me 17A of 35vac. 

Do i really need to spend another $40-50 on a 1kva toroid which seems to be what DIYers do? 

 
 
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11 Feb 2024 03:17 #293052 by spumco
Replied by spumco on topic Servo power supply sizing?
It looks like the 320x goes to 80v accoding to the manual:
[b]TERMINAL 2[/b] Power (+)
Connect the positive (red) lead of your power supply to this terminal. It must be between +18VDC to +[b]80VDC[/b].

I think the 80v drive voltage would be your do-not-exceed limit rather than the servos.

My "100v" Antek is at about 104vdc out at ~244vac input with no load.  Slightly high, but I'm also using their turnkey PS rather than a toroid and self-sourced caps & rectifier.

If you've got the room in your cabinet and your supply voltage isn't wildly out of spec, I'd get the 63v or 68v 1kva turnkey power supply and not fool around building the rectifier (unless you've got the parts on-hand).

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11 Feb 2024 11:21 #293077 by tommylight
Gecos say 80V, but i would really, really not exeed 50V as the output MosFets are rated at 100V max.
Also, adding the braking resistors is a good idea, schematics are on GeckoDrives website.

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11 Feb 2024 23:41 #293115 by TimpanogosSlim

Gecos say 80V, but i would really, really not exeed 50V as the output MosFets are rated at 100V max.
Also, adding the braking resistors is a good idea, schematics are on GeckoDrives website.
 

I don't see anything about adding braking resistors. google tells me the word "braking" does not appear within the geckodrive.com domain.
More generally across the internet, no schematics, and a review that appears on amazon and elsewhere saying there's not a way to do it. 

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13 Feb 2024 04:46 #293193 by TimpanogosSlim
That's a way to wire an emergency stop switch that has a braking resistor for the emergency stop with power to the drivers cut.

I was under the impression that braking resistors are also useful when the drivers are powered?

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15 Feb 2024 12:52 - 15 Feb 2024 13:12 #293374 by smc.collins
4Q reversing DC brushed Tacho feedback KB motor drive is what ya want. no need to fuss with a external DC power supply when DC drives with those features already exist. $149-240 USD each, kind of a bargain, and one of these should handle your needs or check the catalog offering they should have a drive to suit your need reasonably priced. Send your tach feedback to the drive, send the encoder feedback to the Linuxcnc control card. a 7i77 in velocity mode is ideal for this type of servo. These are very easy device to tune and those a very high quality servos. I wouldn't put a set of geko drives on them, use the KB drives. 

kb-controls.com/kbmg-21d-8830-scr-regen-...1-5-hp-open-chassis/
kb-controls.com/kbmg-212d-8831-scr-regen...1-2-hp-open-chassis/
kb-controls.com/kbrg-212d-8819-scr-regen...1-2-hp-open-chassis/
 
Last edit: 15 Feb 2024 13:12 by smc.collins.

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18 Feb 2024 03:35 #293665 by TimpanogosSlim
Those look really interesting. 
But it looks like they would save me less than $150 on the power supply while greatly increasing the complexity of the build. 

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18 Feb 2024 13:49 #293683 by tommylight
There is another circuit on geckodrive pages for regen energy dump, but uses a diode to pas the entire supply voltage and current to drives, hence not very efficient, see my link above and click on previous or next page at the bottom.

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19 Feb 2024 02:35 #293738 by TimpanogosSlim

There is another circuit on geckodrive pages for regen energy dump, but uses a diode to pas the entire supply voltage and current to drives, hence not very efficient, see my link above and click on previous or next page at the bottom.


That looks useful. I may lay out a board. 

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