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  #1  
Old Thu 04 December 2008, 07:07
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
General wiring, supply voltages, relays, E-stop considerations

Continued from:
http://www.mechmate.com/forums/showthread.php?t=1178

Okay, Gerald. Thanks for the patience with us newbies.

However, I am going to think a little more about using an SSR for the circuit to the E-Stops on the Gantry and Y-Car. That way there would be no need to run 120 volts AC out to the E-Stops on the Gantry and Y-Car. This circuit could be, say 5 volts.

Regards,
John
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  #2  
Old Thu 04 December 2008, 08:10
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I don't know about SSR's in an e-stop circuit. What are the chances of it getting "stuck" in the "switched" state? Probably nil, but you need to research it thoroughly before using it in a safety circuit. I havn't heard of an SSR as a safety device, but I don't get out too much.
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  #3  
Old Thu 04 December 2008, 14:12
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The purpose of an E-Stop switch is to kill ALL power to the machine.

I see nothing wrong with running 120VAC through an E-Stop switch as long as you use a switch that is designed to handle 120VAC and as long as you use cable that is rated for 120VAC.

By running the circuit to your main contactor's coil through the E-Stop switch as well as through a self-latching momentary push-button switch, you would be well protected. You would have to turn on the main disconnect switch, then assuming that the E-Stop switch was 'closed', you would have to press the momentary push-button switch. That would activate the contactor, which would self-latch using the circuit that Gerald has published.

Then, if you had a true emergency where someone or something was in danger, opening the E-Stop switch would kill the power to the contactor's coil, and all power to the machine would be shut off.
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  #4  
Old Thu 04 December 2008, 21:03
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
Thanks again Gerald and Mike,

Gerald, you have a very good point about an SSR getting "stuck" in the closed state. A quick Google search indicated at least one "rotisserie" supplier indicating a failure mode of a digital control SSR being "stuck" in the closed state.

So, would you have any concern about a "low voltage" Contactor or properly rated Relay in the E-Stop circuit?

I haven't given up since I think there are advantages of not running 120 volts or 240 volts or higher out to the Gantry and Y-Car unnecessarily. There is always the danger of electrocution from high voltage. As well the higher voltage requires higher rated contacts and cables. And, there's also some chance of cross-inductance between the E-Stop circuit, which is always active, and the Stepper Motor signal lines. And, if we made the E-Stop circuit DC we would even further reduce the chance for cross-inductance.

Just some thoughts.

Regards,
John
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  #5  
Old Thu 04 December 2008, 22:32
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
John, you are thinking very clearly - those are exactly the issues that come into play.

"So, would you have any concern about a "low voltage" Contactor or properly rated Relay in the E-Stop circuit?"

Using standard contactors in E-stop circuits is the very standard/conventional way of doing it (as far as my personal experience goes). I do have a tiny concern that even contactors can get "stuck", but everyone else seems to think a contactor is fairly bullet proof. (I have never seen a stuck contactor, only dirty and burnt ones that refused to "make"). I have not been that concerned about a stuck e-stop contactor that I would start looking for alternatives. Besides, we do have the door switch/isolator before the contactor.

"I haven't given up since I think there are advantages of not running 120 volts or 240 volts or higher out to the Gantry and Y-Car unnecessarily."

Very valid concern. A typical thing that is done, is to run 24VAC as a control circuit. That is why you can get contactors with 24VAC coils. DC control circuits are not popular because they make big sparks in the push-button switches.

"There is always the danger of electrocution from high voltage."

We minimise that danger on the MM by emphasising:

- ground the frames/cars/gantries/table

- have shields on the cables and ground those shields

- have GFI protection on the supply breaker

"As well the higher voltage requires higher rated contacts and cables."

All the industrial pushbutton switches and cables (those built tough for a dirty abusive environment) are rated for hundreds of volts. You won't save money by going to lower voltages. You will have additional cost to create the lower voltage.

"And, there's also some chance of cross-inductance between the E-Stop circuit, which is always active, and the Stepper Motor signal lines. And, if we made the E-Stop circuit DC we would even further reduce the chance for cross-inductance."

Quite correct. Hence the shielding of the cables. I am happy that we can make the mains voltage to the cars behave in a harmless way. Remember, we cannot remove the mains voltage that goes all the way to the router/spindle. We have to live with it.

However, cross interference is a valid concern. Remember this is a two sided thing - the mains voltage radiates, but the signal lines receive. If we are worried that voltages can cause interference, we can think of raising the signal receiver voltages. Our signal receivers work on a puny 5V - they would be more reliable if we could bump them up to over 12V. But that is a whole new can of worms.
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  #6  
Old Thu 04 December 2008, 23:31
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Hmmm. Just posted my concerns on this same issue in my thread.

Guess I should have read the other posts first.

Curious to see how this all works out.
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  #7  
Old Fri 05 December 2008, 05:42
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
Gerald,

Thanks for the thoughtful response. I'll proceed with those points in mind.

Greg,

I noted your issues in your thread.

I'm wresling with those same issues. I think I'm going to develop a low voltage E-Stop circuit for the Mains Power Contactor, probably AC based on Gerald's concern for DC wear on contacts. As I work through that, I'll post a schematic.

I don't yet understand the function of the PMDX-122 E-Stop circuit. I can easily understand the Mains Power contactor E-Stop circuit. If you trip one of those E-Stops, EVERYTHING comes to a dead STOP, just what you want!

But the PMDX-122 E-Stop circuit must work somehow with Mach3, probably to do a "soft stop." I don't know Mach3 very well at all, so I need to work through this. Obviously, if you use the same E-Stop switch as the Mains Power Contactor E-Stop, there would be no time to "soft stop" the MechMate table...it would be dead. However, the PMDX-122 E-Stop circuit could send a signal to Mach3 and it could "soft stop" the software. I just don't know, yet.

Regards,
John
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  #8  
Old Fri 05 December 2008, 06:12
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
Send a message via Skype™ to J.R. Hatcher
My limit and e-stop (2 separate circuits) has a simple 12v dc closed loop w\ cheap auto type relays. My debounce is set very low, 1 or 2 hundred I think. Everything is working perfect, no problems at all.
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  #9  
Old Fri 05 December 2008, 07:11
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by jhiggins7 View Post
If you trip one of those E-Stops, EVERYTHING comes to a dead STOP, just what you want!

But the PMDX-122 E-Stop circuit must work somehow with Mach3, probably to do a "soft stop." I don't know Mach3 very well at all, so I need to work through this. Obviously, if you use the same E-Stop switch as the Mains Power Contactor E-Stop, there would be no time to "soft stop" the MechMate table...it would be dead. However, the PMDX-122 E-Stop circuit could send a signal to Mach3 and it could "soft stop" the software. I just don't know, yet.
The capacitor/s of the power supply drain down after the mains contactor opens. ie. the stepper motors can move a bit further . . . .

. . . . but they will only move if they get step pulses from the PMDX. E-stopping the PMDX will stop the pulses instantly. . . .

. . . . .even if your PC has decided to keep on sending them


. . . . . or if interference is sending pulses to the PMDX
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  #10  
Old Fri 05 December 2008, 07:14
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Has anyone installed bleeder resistors with a contact so that when the E-stop fires the bleeder resistors go in shunt with the capacitors and quickly bleed off the capacitors charge once the supply is off? We do that all the time in our systems at work. We use some large capacitor banks that can be pretty deadly if left charged. (sometimes 1 or 2 F of capacitance, yes Farads at upwards of a couple of hundred volts)
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  #11  
Old Fri 05 December 2008, 07:30
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
4x Gecko's attached to the capacitor do a pretty good job of bleeding off.
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  #12  
Old Fri 05 December 2008, 07:30
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
John,

Figure 4 on page nine of the PMDX manual shows how the PMDX's E-Stop connection controls the output of a buffer chip that controls the step/direction circuits. As Gerald said, when the E-stop switch is active (switch opened), the pulses will stop immediately.

In that sense, the PMDX's E-Stop is not a true emergency stop, since power is still present, but the motors will not receive any pulses, so all movement will stop.

I would prefer to use a DPST (double pole, single throw) E-Stop switch with a PMDX. One pole would control the E-Stop circuit on the PMDX and the other pole would be connected in series to the main contactor's coil. Then, if the E-Stop switch were pushed, all power would be cut and all pulses to the motors would stop. What you would gain with a DPST switch is that the motors would stop before the power supply finally drained. For practical purposes, there would be very little difference between killing all power and having the motors stop - but if you could do both for the cost of a second pole on a switch it would be a viable option.
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  #13  
Old Fri 05 December 2008, 08:07
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
I like Mike's approach of a DPST E-Stop with both a high and low voltage loop, as adding an extra pole to the E-Stop buttons is simple and economical.

However, I have a different design consideration: My mechmate has effectively four different wiring domains:

1) Router / Spindle power. High Voltage(120VAC), High Power, High Noise, Direct connection from the control SSR to the outlet on the car that my router plugs into. If/when I move to a spindle, it will run direct from the inverter to the plug for the spindle.

2) Motor power. Mid Voltage(30Vcomplex), Mid Power, High Noise, Direct connection from the Gecko to the connectors at each motor.

3) Signalling. Low Voltage (12VDC), Low Power, Low Noise. Junction boxes in multiple locations to split out the various Proxy sensors and (future) LED crosshair source power, and (future) thermal sensors, and ???

4) E-Stop. High Voltage (120VAC), Low Power, Low Noise. Junction and switch boxes in multiple locations.

As my machine is currently configured, I have #3 and #4 sharing junction boxes, placing two incompatible systems in the same physical space. If I move my E-Stop to a 12V loop using a relay, I eliminate this, and I'll be happier. I'll have only three wiring domains to deal with.

Note that since the Gecko 540 I'm using also provides the "BOB" interface to my PC, a wiring error or malfunction in those shared boxes has to potential to wipe out my proxy system, gecko drivers, bob, and even potentially the PC, since the density of the G540 is such that a 120V arc could jump.

This makes a pretty convincing argument for adding that $10 relay the next time I'm messing around with my wiring.
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  #14  
Old Fri 05 December 2008, 08:34
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Some old threads worth reading:

E-Stops - Emergency Stops and then what? ( 1 2) post #26 onwards

question on the estop wiring
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  #15  
Old Fri 05 December 2008, 21:17
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
Thanks Gerald and Mike, I think I've got it now.

You might not believe it, but I've read those posts before. I've been lurking over a year. But, until I was trying to put the logic together, it just didn't sink in.

J.R...what fun it's been watching your progress...I like your idea of using the auto type relays for the the E-Stop circuit.

Quote:
Originally Posted by J.R. Hatcher View Post
My limit and e-stop (2 separate circuits) has a simple 12v dc closed loop w\ cheap auto type relays. My debounce is set very low, 1 or 2 hundred I think. Everything is working perfect, no problems at all.
I assume you power on the DC with the Mains Power On Button in parallel with the Mains Power Contactor. And then latch it with the Mains Power Contactor? Is that correct?

Mike Richards, I'm not ignoring your views of running the E-Stop circuit at Mains Power levels (120,240,etc.). I've developed the deepest respect for your views, especially concerning driving the Stepper Motors. But, I just can't see a need to run extra high voltage onto the table. The only high voltage I plan to run onto the table is for the router. Some folks, I think, have even avoided running the router cable through the table by hanging it from the ceiling with the dust collector duct.

Regards,
John
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  #16  
Old Fri 05 December 2008, 22:00
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
John,

Running low voltage through the E-stop switch is perfectly acceptable. There's no "right" way to wire a controller. As long as you follow standard practices the controller will work.

Just today I had to tear into my Shopbot PRT-Alpha's controller. One of the proximity sensors started to have problems. When I checked the part number, the data sheet said it was a 12V unit, but Shopbot runs it with 5V. When I did a little more checking, they feed the outputs of both proximity switches to the same TTL logic input. So, they found that they could violate two principles without causing problems with the machine. (I didn't like the way things were wired, so I built an opto-isolated interface board so that I can run a much beefier proximity sensor from a 24VDC line. The interface board also gates the two sensors so that only one logic signal goes to the controller card.)

When it comes to one-of-a-kind controllers, almost everyone does things just a little different. The pragmatic approach works well. In other words, if it works properly, then the design is satisfactory.
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  #17  
Old Sat 06 December 2008, 06:44
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
Thanks again Mike.

Yeah, I'm kinda surprised that those proximity sensors worked at all. And even when they do, given the variance in parts and day-to-day voltage level swings, I can imagine unreliable performance. Might work sometimes and for some parts and not work at other times with other parts.

We appreciate your depth of knowledge and your willingness to share and keep the rest of us honest.

Regards,
John
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  #18  
Old Mon 15 December 2008, 15:34
jhiggins7
Just call me: John #26
 
Hebron, Ohio
United States of America
As promised, here:
Quote:
Originally Posted by jhiggins7 View Post
Gerald,
... As I work through that, I'll post a schematic...
Here is a schematic showing a "low voltage, DC" circuit for the Mains Power E-Stops Circuit. With this approach, there is no need for high voltage, AC on the table for the Mains Power E-Stop Circuit.

Operation:
1. When the ON Button is depressed, power is made available to the 12 or 24 VDC power supply.
2. Then if the E-Stops are "normal", the ES(E-Stop) Relay is energized.
3. Once the ES Relay contact is Closed, the Mains Contactor is energized.
4. Both the Mains Contactor and the 12 or 24 VDC power are "latched" by a Mains Contactor contact.
5. If an "E-Stop" or the "OFF Button" is depressed, all power, including to the 12 or 24 VDC Supply is removed.

I put the 12 or 24 VDC notations on the schematic for those planning to use either of these voltages elsewhere. One could use 5 VDC (including the +5 volts from the PMDX-122) or 9 VDC. I'm planning to use 24 VDC Contactors to control the Router, Hold-Down Vacuum and Dust Collector via MACH3. More on that later.

Regards,
John
Attached Files
File Type: pdf Control Box Schematic-Model.pdf (16.8 KB, 658 views)
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  #19  
Old Wed 11 November 2009, 14:25
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
A little confused....

Maybe I'm missing something in the schematic, but it looks like the only time the 12/24 vdc is cut is when the on/off switch is off. The estop (epo) kills the contactor coil but the feed for the 12/24 vdc stills look hot to me.

Also the use of Estops to kill the pmdx outputs is a good idea but the distance makes grounding them out a bit problematic as the wire size and distance could drop the voltage to the point the pmdx thinks the estop (not the epo) circuit is open and the pmdx won't output pulses.

I'm going to run the estop (partnered with the epo) mushrooms at 24vdc through a relay/interface board to keep those problems at bay.

Stan
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  #20  
Old Wed 11 November 2009, 14:41
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
less confused....

after studying Gerald's schematic (115V US) and the low voltage schematic from john (jhiggins7), I think I have narrowed my confusion a bit....

My confusion arises from the top contacts in the contactor (aux contacts, I believe). What is the purpose of that part of the EPO (I use this to keep separate from Mach3, which is not EPO)?

This has probably been covered somewhere else so please feel free to point me there and I'll dig....

Stan
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  #21  
Old Wed 11 November 2009, 18:38
salewis
Just call me: Stan #67
 
Littleton, NC
United States of America
confusion lifts.....

after reading the thread on "mains wiring" the answer arises.....

The aux contacts are the latching circuit....

Stan
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  #22  
Old Fri 12 March 2010, 19:04
timberlinemd
Just call me: Steve #66
 
Arizona
United States of America
Gotta go with John on this one

Being a licensed HVAC (Heating,Ventilating and Air Conditioning) contractor I will have to lean towards a 120/240v step down transformer to 24v (AC) 40VA with proper contactor for the E-stops. Question-if the cable to the E-stops is carrying this low voltage does it have to be 'screened'?
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  #23  
Old Fri 12 March 2010, 22:34
KenC
Just call me: Ken
 
Klang
Malaysia
No, the current in the E-stop circuit is tiny, won't affect other signals. & since it is only a on/off signal it is most unlikely that they will be affected by external noises.
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  #24  
Old Sat 13 March 2010, 01:49
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The E-stop circuit is permanently energised, and the AC will cause a permanent "hum" in that line. But, I can't predict if it will cause interference.
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  #25  
Old Sat 13 March 2010, 02:01
KenC
Just call me: Ken
 
Klang
Malaysia
IMHO, as long as a PMDX BOB or similar are used this beef up the signal enough to withstand significant noise; screen stepper motor cables to keep the noise of the stepper system in check & no contact problems in the other cables, I wouldn't get to worried over this 50/60hz hum.
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