Light Machine Corp. Benchman XTr (retrofit)

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05 Nov 2015 18:27 #64805 by andypugh

steve_a wrote: saw appox .8 ohm on both the input coils. I hadn't noticed before but there is only 1 output coil. ( I can only assume that is because this is a custom built toroid specifically for Light Machines and they designed it specifically for this machine.) The output showed about .2 ohms. Since the two .8 input coils are tied in series that makes an equivalent 1.6ohm coil making the input to output ratio 1.6/2 or 8:1. That gives 230V/8 = 28.75 V out


Unless the primary and secondary are wound with exactly the same size of wire a resistance check won't tell you the transformer ratio.

Have you tried turning on the power and measuring the output voltage?

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05 Nov 2015 23:32 #64833 by steve_a
Good point andypugh. I could be totally off base on this. I have powered the unit up but there is no voltage coming out of the servo supply Without a functioning Nextmove card the main control pca in the Benchman will not enable the servo power by energizing the relay. I will have to jump the primary windings and bypass the relay. I think I can safely do that if I disconnect the output from the servo supply connection point since it is just a connector. However, the rectifier needs to be loaded to regulate. I might try it to see if the choke and VOhm meter will be enough of a load. Otherwise I might have to throw a resistor across the output.
My observations were based on my probing and since the toroid is not marked with any information regarding in and out voltages I went ahead and did the ratio calculation to try to verify the voltage I might see. Still, if the motors are rated for 24V, the 28.75V seems a reasonable number. The motor data sheet has two specs; the Rated Terminal Voltage 12-60V and the Terminal Voltage 24V. I took this to mean Tolerance and Operating Voltage, however, I am not shy to admit my ignorance and say that is just an ewag. It may actually be saying that the motors will operate in the range of 12 - 60V and is optimal at 24V. Even so I would think a company would design for optimal. I'll work on doing the test. You are correct in pointing out the wire size issue. Thanks for your input.

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06 Nov 2015 01:29 #64846 by andypugh

steve_a wrote: Still, if the motors are rated for 24V, the 28.75V seems a reasonable number. The motor data sheet has two specs; the Rated Terminal Voltage 12-60V and the Terminal Voltage 24V.


It isn't at all unusual to run motors at a lot more than their DC voltage through a current-limiting drive.
This is especially true for steppers which have a typical DC voltage rating of <5 V but often run at 50V or more.
The voltage rating is the DC voltage that will drive the rated current, but if you limit the current then you can maintain that current (and torque) to much higher motor speeds with higher voltage.

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07 Nov 2015 11:41 #64946 by steve_a
Did a quick test today on the servo power circuit. I didn't have what I needed to run 230VAC to the toroid so I settled for 120VAC from the wall since I had a cord handy. I got a strange jumping reading of 72-75V on the DC output from the toroid transformer and choke circuit, but that was unloaded so I decided to take a chance and plug it in to the main board and see if the controllers made a difference. Yep. Andypugh, looks like you were right. The wire in the toroid might just be a different gauge. I got a nice steady 32.8VDC. Assuming the 230 is roughly twice the voltage as the 120, that means I will probably get something in the range of 65.6VDC... essentially 60V. Which IS the upper limit of my Servo motors. SO having already been totally wrong once I think I will find a cord for 230VAC and verify the actual output of the circuit. Distribution to the controllers happens on the main PCB and I did not have time to do yet another isolation and verify that there is no further regulation happening there, so I will add that to the list of things to try.

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18 Nov 2015 13:50 #65426 by wrightsh
I'm also working on a ProLight 5000 (non Benchman) and if you trace out the circuit on the board that the servo amps & power supply connect to there's two large caps and a power resistor in parallel going from the output of the choke to ground.

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18 Nov 2015 15:02 #65434 by LearningLinuxCNC
Those are smoothing capacitors to take the ripple out of the rectified DC waveform. The resistor is a bleed resistor to slowly discharge the capacitors once the system is powered down, as they are storing a lot of energy. If they were to remain charged it could possibly hurt someone working on the dc power system.

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19 Nov 2015 03:21 #65477 by steve_a
I've been busy with other projects but getting very antsy about this one. I looked at the controller boards today and saw a couple of good sized capacitors. There are two 3300uf and a couple of 4700uf. I'm going to assume that some of those are smoother caps for the servo motor drive and there was mention of bleeder resistors. They seem a little smallish but maybe, with a choke that size, that's all it needs. I suppose that makes sense.
Out of caution, I have not removed anything or disconnected the controller board that is underneath the board that looks like an interface for the encoders, air, etc. I was waiting until I received the replacement controller boards from Mesa. I must not have understood their availability or processes. I ordered the boards on October 21st so I'm still waiting 3 days shy of a month.
I've found a replacement controller board on line and bit the bullet. I know I will receive that on Monday so I can test my educated guess that the machine will come back to life using the old software and system. I still plan to do the upgrade but I need to try to have this thing up by January so I've kind of got my back to the wall. I am itching to get to this thing moving but without the new Mesa cards I'm stuck. On the plus side, if I CAN get it running I can test it and see what it SHOULD look like with the upgrade installed. I think I'll probably have to come up with some kind of PCB for things like the above mentioned caps and just interface in general.
The saga continues.

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09 Dec 2015 03:04 - 09 Dec 2015 05:26 #66663 by steve_a
Well this is unfortunate... I have been waiting for the Mesa Cards for 6 weeks and while I accept the circumstances I don't have the time to waste if I just can't get the boards. Couple with that the possibility of a board crashing at some future date and a replacement taking another 6 weeks... I can't afford that. SO, unfortunately, I have canceled the order and decided to go to my fall back plan and use the Kflop and Kanalog boards. Yes I know that means an open loop system, but an open loop that works is better than a potential closed loop system that is dead in the water while I am waiting for a board.
I will chime in on the modifications since those will still be relevant to the Mesa/Linux systems. Truth be told, there is little difference in the two when it comes to the rewiring and if at some future date Mesa becomes more readily available it would just be a matter of swapping cards and I can have a closed loop system. I just have to set up the Linux CNC and I already have a computer loaded and ready to go. I had set it up in anticipation of the Mesa cards.
Anyway, I have some pretty good ideas for the rewire and I will share those as long as they are possibly relevant to the Linux system.
Last edit: 09 Dec 2015 05:26 by steve_a. Reason: misspelling

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10 Dec 2015 07:13 #66719 by steve_a
Holy cow!!!! Kflop/Kannalog have already replied shipping! I mean Seriously... compared to Mesa... who didn't even grant me the courteous of telling me it might be awhile before shipping.... I have to say, it is inexcusable. Fine... I am a peon user... I only want one board... so I am treated as an ugly stepchild... the OEMs are given priority... Look... there is NO excuse for not delivering an email explaining the delay. I'm sorry... I am P.O.'d... and I think reasonably so. This is not the outcome I wanted... but I am not ready to excuse the unprofessional manner in which this was handled... I feel mislead by the posts on this forum that touted the virtues of the Mesa... The bottom line is that an unavailable board is as good as non existent and as far as the closed loop... it is also non existent... I'm sorry, but I needed this in a timely manner and I feel the site that showed these boards as available completely misrepresented the truth. When a website shows an "availability" I would hope I could depend on that. I feel foolish. I should have remembered that anything that can go wrong will.... So... I will proceed with a less than ideal solution, but I prefer that than relying on a non available solution. Forgive me but I AM PO'd!

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10 Dec 2015 10:38 #66725 by andypugh

steve_a wrote: I feel mislead by the posts on this forum that touted the virtues of the Mesa


I am starting to feel bad for recommending them too.

The Mesa boards are excellent, but if they are not shipping them then, as you say, they might as well not exist.

Eusurplus (in Portugal) do have stock and do ship promptly.

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