[skullworks]

Just stick a Molex connector on there and have users scrounge there own Micro ATX pws unit...

These can be had for under $10 at times NIB.

Creative use of standoffs could also utilize the ATX pws fan to help keep things cool.

[ger21]

How much current do you need for the 5V and 12V?
http://www.mpja.com/productview.asp?product=15347+PS
http://www.mpja.com/productview.asp?product=16693+PS

[kreutz]

Thanks guys,

Any simple wall-pluggable 12 Volt 2 Amp power supply will work fine. I included a 5 Volt regulator on board. The 12 volt power supply will supply the power for the heatsink fans too. There is a screw terminal for the 12 Volt input with inverted polarity protection.

[ger21]

In that case:
http://www.mpja.com/productview.asp?product=16741+PS

[kreutz]

In that case:
http://www.mpja.com/productview.asp?product=16741+PS

Sounds like a good choice!!, and cheap too.

[Kipper]

Thanks guys,

Any simple wall-pluggable 12 Volt 2 Amp power supply will work fine. I included a 5 Volt regulator on board. The 12 volt power supply will supply the power for the heatsink fans too. There is a screw terminal for the 12 Volt input with inverted polarity protection.

Would it be possible to just install this into a PC case and hook up a Molex to it? Interesting thread btw :cheers:

[kreutz]

Would it be possible to just install this into a PC case and hook up a Molex to it? Interesting thread btw :cheers:

Yes, it is possible, but I don't recommend it if it is the same PC you are running your CNC program from. You don't want to share the same ground and power with your CNC equipment (operator's electrical safety), that is why we use opto-isolation stages in the circuit.

[kreutz]

In Rev2.0 boards I am trying to provide basic safety functionality into the board since some space was made available for it when two new components replaced ....

This requires a little deeper explanation.

As it was in Rev01, the board had over temperature and motor over-current protection already incorporated by locally disabling the affected axis. What was missing was the Emergency switch activation when errors were detected, so the other axes stop and the PC program gets halted. That part of the functionality was transferred to the optional safety board. Since the people with less money probably did not want to invest in the optional board, I decided it wasn't fair, and decided to provide this, as well as under-voltage/over-voltage basic protection, for them.

[kreutz]

Yes, it is possible, but I don't recommend it if it is the same PC you are running your CNC program from. You don't want to share the same ground and power with your CNC equipment (operator's electrical safety), that is why we use opto-isolation stages in the circuit.

Clarification on the statement above:


Each equipment protective ground connection is supposed to be connected to a common point in the building's wiring closet in a Star fashion so to avoid ground loops and to avoid faulty isolation on one equipment to develop a ground potential in other equipment due to the potential drop on the wiring.

If you connect the protective ground of your PC to the Ground on your CNC equipment and you have a power insulation failure (easy with a wet motor winding) and/or a broken Neutral, potentially high currents will be flowing on your PC protective Ground circuit, this could damage the thinner ground wire on your PC power cable and unsafe voltages will be present on your PC exposed metal parts.

In order to avoid that we isolate both grounds and power circuits so a failure in your CNC equipment ground will be contained in the CNC equipment and does not produce unsafe voltages on your PC.

Opto-isolators like the HCPL2631 specify High voltage electrical insulation of 3000 VDC minimum and common mode transient immunity of 1000 V/uSec.

"They (opto-isolators) are used to isolate low-current control or signal circuitry from transients generated or transmitted by power supply and high-current control circuits. The latter are used within motor and machine control function blocks" (Wikipedia)

[pminmo]

Kreutz,
Excellent post, many people confuse safety ground, 0v, supply returns, and neutral. The NEC requires all conductive surfaces of electrical equipment to be tied to safety ground. Many people wind up tieing circuit points to that safety ground not knowing any better and create circuit ground currents that can be an issue.

Interesting how we designed equipment and computer peripherials for 3 decades prior to isolators without issues.

One thing we all should do is utilize GFI's on our PC/machine setup for safety's sake as there is no such thing as absolute safety when failures occur.

[cephjedi]

AMEN!

As part of my CNC growing pains, I ordered a 4 ch. Hobby CNC board. Built it just fine (don't know how all those little things work, but I can solder `em together reeel good) and powered it with a ATX PS. Dissatisfied with performance*, I tried daisychaining 2 and three PSes according to the numerous diagrams and references on the intertubes (and CNCzone) and I couldn't get them to work. 36V out of the terminals, but when connected to the board, it was still just 12.

I quit monkeying with them and ordered a 24v/8A PS from MPJA. Wired it up, powered it up, smoked up my workshop and blew my board. Later on HobbyCNC's support forum, I learned that I should have connected the V- terminals to the earth ground- apparantly for such reasons as mentioned above. Ah, it's so much fun to be uninitiated.

Cheers, Jim

* Am I the only one who's obsessed with hotrodding my CNC machine more than actually cutting parts with it?

[pminmo]

AMEN!


I quit monkeying with them and ordered a 24v/8A PS from MPJA. Wired it up, powered it up, smoked up my workshop and blew my board. Later on HobbyCNC's support forum, I learned that I should have connected the V- terminals to the earth ground- apparantly for such reasons as mentioned above. Ah, it's so much fun to be uninitiated.

Cheers, Jim

Having your v- terminal floating by itself wasn't the problem. You had a wiring issue of some sorts but that wasn't it, maybe you didn't have the lpt port pins 18-25 connected via wiring to you hcnc board? If that were true, then a floating v- could have been a problem.

[cephjedi]

Thanks Pminmo!

You know, hearing that really makes me feel better: I thought I'd read up on this stuff pretty well, and I do fancy myself a reasonably smart person. I've played with electrical stuff in the past (used to be really into Tesla Coils and such things) so I felt reasonably confident. I mean, how hard is it to wire up a power supply? Hot, neutral, earth ground. V+ and V-. Big deal! Right?

Well, when my board smoked -took about ten seconds- I was, shall we say, somewhat put out. When I polled the "support forum" for help, this grounding problem was what everybody settled on. I found that hard to believe, but again, I'm no EE. Everywhere you look you hear of people powering their boards with PSes from MPJA, including people that are asking questions like "What parallel port pins do I hook my motor leads to?" I can't believe novice grounding issues weren't popping up all over the place, but what can you do?
Anyway, after that experience and a couple others like it I decided to abandon Hobby CNC forever.

Now I've got a Mechatronics board from eBay and it's working well enough, but I'm still only cutting around 20 ipm (with brand new Keling 425 oz motors.) Needless to say, I'm pretty excited about Kreutz's project.

Cheers! Jim

[pminmo]

Your experience is the primary reason to do what Kuertz is doing with the isolators. Reduce the impact of a ground situation that has a problem.

I designed a piece of equipment in the 80's that sensed both immediate AC loss for a safety shutdown, and improper phase for the plant I worked in for 30 years. We started getting "equipment failures" periodically, wouldn't turn on. As a coworker researched he started finding extenion cords that were miswired. When he had the electricians correct it, they told him it they paid no attention to neutral and hot wiring on these 30A extension cords, didn't think it made any difference!

[kreutz]

many people confuse safety ground, 0v, supply returns, and neutral. The NEC requires all conductive surfaces of electrical equipment to be tied to safety ground. Many people wind up tieing circuit points to that safety ground not knowing any better and create circuit ground currents that can be an issue.

Phil;

I think it sounds like a good idea to post an article about this subject and good and bad wiring diagrams examples on your site. I am sure it will help a lot of people.

Thanks again and Regards,

Kreutz.

[pminmo]

Not a bad idea, one of these days..........

[mugabe]

This patent could also help to make drive more sophisticated :
http://www.freepatentsonline.com/4540928.html

note:edited

[atlab]

Hi.
I think, there is a mistake in figure 2 of this patent. It is necessary to change places of number 18 and 30.

[kiwichris]

Ummmmm,

Unless I've missed something, Kreutz can't used the information in that Patent for his product, because he's selling it. That's the whole point of the patent process..

[mugabe]

2 atlab
the mistake is imho about wrong figure pointing at column 4 lines 20 where it should say :
"As described in greater detail below with respect to the schematic diagram of FIG 1" instead of FIG 2.

2 kiwichris
said does not mean to repeat this patent as it is . It changes duty cycle, why not change something else in new design.