Just a quick update...
John repaired the AXBB for me by replacing the faulty Fet. It's all back up and running now. Cheers guys and especially John.
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Just a quick update...
John repaired the AXBB for me by replacing the faulty Fet. It's all back up and running now. Cheers guys and especially John.
Sent from my SM-G920F using Tapatalk
Good to hear you got it fixed.Quote:
Originally Posted by CharlieRam
Do you know what broke it?
Grtz Bert
Verstuurd vanaf mijn SM-A320FL met Tapatalk
If the FET blew due to back EMF from the relay coil, then it's a bit naughty as the AXBB-E manual shows a direct connection with no added clamp diode :suspicion: Funny, I was just about to email Balazs to ask whether such diodes were included on the board, I'll let you know what he says.
I have no idea [emoji848] i have checked the wiring and all looks ok although I have removed all the switch light outputs just in case that was the cause...[emoji848] I've protected it now with a 7001n diode across the relay and a 27ohm resistor on the charge pump output so hopefully it will be ok now.
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It is not easy to tell what the problem was
a case of no fault found that could of damaged the FET
As the relay worked when the wire from the AXBB output was connected to the -24V supply
you can only suspect either there was an intermittent short connecting the +24V supply to the AXBB output
or
an intermittent open circuit that generated a sustained back emf that over stressed the diode in side of the NTR5198NL-D FET
or may be it was a faulty FET
John
PS
the diode added across the relay coil and a 27ohm resistor in series with the relay coil
will help to protect the AXBB output
the resistor limiting the current if coil is short circuited
and the diode clamping the back emf when the relay is switched off
Hi Voicecoil
The diagram in post 40 shows the signal path through the circuit after the HCPL-2631 opto isolators
the only diode is within the NTR5198NL-D FET
hence my comment in post 30
“Its a pity they had not used a DIL (dual in line ) octal transistor array like the ULN2803
or a new FET array
like the Toshiba TB D62381A series DMOS transistor array
that would enable the user to plug in a replacement “
the Gecko G540 has the same issue with a FET that's soldered in
John
Well in that case the manual really should show a clamp diode in parallel with the relay coil IMHO. The intrinsic body diode in the FET will be sod-all use for a coil that's connected between the output and +24 as it'll shoot a long way positive when the FET switches off and over-voltage it in the process. The great thing about drivers like the ULN2803 you mentioned is that they have the clamp diodes built into the chip which makes it a lot less likely that they'll blow. I'll be adding some diodes to all my relay outputs tomorrow.Quote:
Originally Posted by john swift
A little late, but just wanted to clarify.Quote:
it seems strange that the software will allow me to choose any output for the charge pump though.
Yes, you can assign the charge pump signal to any output. But the charge pump signal is a PWM signal. Only Port 1 Pin 1 has circuitry to convert the PWM signal to an on/off state. If you assign the charge pump to a different output, you'll just get the PWM signal on that output, which will not switch a relay.
Of course... you may want to use the PWM charge-pump output to control an existing, external charge-pump.
Hi Gerry
Thank you for the missing detail
that makes sense of the test results when Charlie tried using another output
John
Doddy
something like cnc4pc's C4 charge pump I made reference to in post 12
John
Guess what...its gone and done it again [emoji34] I don't understand what is causing it! I had the 27ohm resistor directly on the charge pump output then through two e-stop switches and onto to 24v- on the relay. The relay 24+ goes direct to the 24v output from the PSU . I also have the diode across the coil of the relay[emoji848]
It is behaving slightly different this time though in that the relay doesn't switch on until the charge pump is active. The problem comes when the reset or estop is tripped. The charge pump led switches off but the relay stays active ( the relay led stays lit but dimly when the charge pump output should be inactive?)
I thought It was going too well[emoji53] I had done a couple of trial parts and was working on reducing backlash and and alignment when I noticed the estop didn't cut the power, I am wondering if it's the actual relay causing it [emoji848]
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So the LED on the AXBB is off, but the relay remains energised and another LED on the relay is on/dim?Quote:
Originally Posted by CharlieRam
That suggests the FET is conducting, when it should be off. No disrespect to John but worth a visual around the replacement FET and a wipe down with IPA if there's any flux residue, but I doubt that will resolve anything (the gate is tied to ground via resistor so can't really believe any parasitics will be able to draw the gate high). Worth measuring the voltage on the gate of the FET (report here) and the voltage ACROSS the relay coil when it should be off - my guess is you'll have a few volts there and if the voltage on the gate is essentially zero then, with the circuit as shown, it can only be the FET. Replace again. If it fails again then replace with a bigger bugger. Or haywire the 74HC14 output to the adjacent FET and use that output instead.
Exactly that...the relay has a green status led in its case. It is dim when the charge output is off but brighter whenever the charge output is on. This is different to the last time because that time the output was on constantly.Quote:
Originally Posted by Doddy
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Hi Charlie
I am surprised the the charge pump output has failed again
I would of thought the combination of the diode added across the relay coil to control the back emf
and the 27 ohm resistor to limit the current if the relay was ever short circuited
would of protected the FET
Can you measure the voltage between the CHP O1 and -24V terminal
when the output should be ON and OFF
and if possible the voltage across the 10K resistor on the PCB
knowing the voltage between the 74HC14 GND pin 7 and output from pin 2
will help
I would expect it to be 0V when OFF and +3 to +5V when ON
from the FET data
Gate Threshold Voltage = min 1.5V to max 2.5 V
John
Sorry for the late reply, so I managed to check a couple of voltages before the battery died on my volunteer again...really should remember to turn it off! It reads 9v when off and 24v when on when the relay is connected. but I had a brainwave and it works so unless you say it's a bad idea I'm going to stick with it...Quote:
Originally Posted by john swift
The charge pump only activates the relay when the software is active and reset state is inactive, the problem was that it wouldn't then shutoff on reset or estop so I have used an opto isolated relay on another output which is the true state of reset and settable in uccnc. This means that the relay isn't active unless the software is active and reset is not. It also protects the AXBB against any other issue causing the charge pump failure..
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EDIT: Ignore below the line below for now, I've re-read your answer and am confused.
I understand you're measuring the OP1 output with respect to the negative supply to the 24V PSU?
The OP1 is a low-side switched output. That means that if the relay is ON, the output voltage should be near zero. If the relay is to be OFF, then the OP1 output should rise (through the pull-up by the relay) towards 24V.
Relay....OP1=Expected.....Reported
..ON..........0V..............24V
.OFF.........24V...............9V
Can I ask you to confirm the reported values? My thoughts, below, were with ON/OFF voltages swapped.
----------------------------------------------
--- Bit below here was original reply
-----------------------------------------------
What you're saying is that you're using the charge-pump as the initial "Computer is now on" signal.
It doesn't safeguard against the computer going doo-laa-lee after the event, but it avoids a spurious start-up spin-up. Not that I believe you're likely to get that with the AXBB - it's more a concern for random start-up on PPs.
A couple of things to consider:-
* You don't have the intended watchdog cut-out protection intended by the charge-pump. Safety is compromised *1
* You're running a board with a failure evident. You cannot predict at this time how this failure will behave - it might remain, or fail completely. *2
* The FET is partially conducting. I'm uncertain if the 9V is across the relay coil, or the relay coil plus 27R resistor. I'm going to randomly guess that you include the resistor, and together with a randomly selected relay coil resistance that you have a total of 750R resistance (feels about right and it makes the maths easier). The problem here is that the current flow is voltage-across-relay-when-off (24-9V / 750R) is 20mA holding current on the relay when the output is set to 9V. That means that you're dissipating (P=V*I) 9x0.02 = 180mW in that FET in its failed state. The max power dissipation in a 2n7002 (don't know if that's the device used to replace the original) is 200mW, derated above 25C, so you might find that the FET subsequently fails differently. Or if the assumption about coil resistance (and therefore current, and therefore power) is inaccurate - then adjust the numbers accordingly. You're likely to see the FET fail over.
*1: But then, most home-grown won't have a charge-pump anyway.
*2: This output would, at best fail to drive the charge-pump, and the machine will fail-safe, or at worst intermittently fail to drive the charge-pump - random shutdowns. Somewhere in the middle it never deactivates the charge-pump and you lose the charge-pump function - see (*1)
My thoughts: I don't think that you are getting any benefit above the controlled output that you have from the reset-discrete output. You may end up with the machine intermittently or hard-failing in the case that the watchdog fails. Likely this will never happen mid-cut, but each time you shut the machine/software down you're risking the machine hard-failing. This uncertainty would lead me personally to either :-
1) Repair the board again in one of several ways previously discussed.
- or -
2) Remove the charge-pump from the system.
EDIT:
It's still worth performing the voltage measurement advised earlier - the voltage-across-the-10k (what I meant by the gate voltage, Vgs) is intended to understand if the FET itself is at fault. If the Vgs is near 0 you expect the FET to be "off" - Resistance Drain-to-Source (Rds) is very very high. If the Vgs is above Gate Threshold Voltage it should be in the (near) fully "on" state, Rds = very very low. The problem lies that between Vgs=0 and Vgs = 3V then the FET operates in it's linear(-ish) mode, where the Rds is a function of Vgs. By understanding if Vgs (voltage across 10k) is a definite 0/3V then we know if the device driving the FET (74HC14) is operating correctly and the FET has failed. If the voltage is somewhat lower than 3V then the FET might be behaving as expected.
Morning, I will be nipping out soon and I'll have a look for a battery for my voltmeter...its a tiny A23 size and hopefully i'll be able to report back later.
Just to clarify....
voltage between 24V- and output one with charge pump active on and off. (Relay and resistor connected or disconnected?)
And voltage across resistor circled, again with charge pump on and off.
Attachment 26746
Sorry, been up to my elbow in a Myford since 9am. Anyway, V(OP1) with Relay / Resistor connected. And, yes, across the resistor marked 01C (one side is ground, the other is the output from the 74HC14), the signal that drives the FET On/Off. I expect that to be either <0.5V / > 4.5V - assuming the local logic (HC14) is supplied at 5V.
yes
that's the resistor
Attachment 26747
unless the FET has gone low resistance between the gate & source
the voltage across the 10K resistor should be the same as the voltage across the FET gate & source
as the static FET gate current is virtually zero ( leakage current 100 nA )
the volt drop you measure across the 220 ohm will be zero
you will find the via (plated through hole ) in the copper trace connecting the 10K resistor and FET source is the – 24V supply - making it an easy test point
with a damaged FET
a fault current with the relay connected could leak out of the gate and alter the gate voltage you measure
John
PS
the FET was replaced by the original part
NTR5198NL from FARNELL
https://uk.farnell.com/on-semiconduc...ngdom%2Fsearch
Ok, bear with me as I'm still learning...
The voltage across the resistor was 0v when off and 4.65v when on
With the relay and resistor connected the voltage was about 1v when on and 14.7 when off (between op1 and -24v)
With the relay disconnected it was 0v both on and off[emoji848]
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"The voltage across the resistor was 0v when off and 4.65v when on "
is what I expect between the FET gate & source
when the CHP 01 is switched off and on
"With the relay and resistor connected the voltage was about 1v when on and 14.7 when off (between op1 and -24v)"
implies the FET is leaky and not switching off completely
when working correctly
the FET's ON resistance should be 155 miliohms
as the relay coil resistance is 650 ohms
at 24V DC
the relay coil and 27 ohm resistance should pass around 35.5 mA
the volt drop across the FET when switched on will be
0.155 ohm x 0.0355 A = 0.0055 V = virtually zero on a basic multimeter
either the FET is not switched hard on so the on resistance is higher
or your measurement includes the volt drop across your wiring and contact resistance of the connections
"14.7 when off (between op1 and -24v)"
when the FET is off no current should flow through the 27 ohm resistor and 650 ohm relay coil !
to measure 14.7V at the output
24- 14.7 must be dropped across the total 677 ohms of the relay coil and resistor
the leakage current must be 9.3/677 =0.137 A
so instead of the FET looking like its open circuit when off
its more like a 107 ohm resistor !!
"With the relay disconnected it was 0v both on and off"
is correct
the FET acts as a switch between the -24V/common
and the CHP O1
without the relay being connected
there is nothing between the +24V and CHP O1 to pull the output up to the +24V supply
John
So you reckon the fet is borked again? [emoji53] I have stripped the control box back again but cant see any shorts and I'm remaking the control panel, mainly because the wire was too short but also I don't like the layout and realised it would be handy to have jog buttons for the axis as well as the hand held MPG. It also seems the perfect opportunity to start again and eliminate any issues although I've looked and can see no potential for shorts? I'm also going to add a slave axis to the machine. I am happy with it but I can see improvements and want to do it before the machine is working proper.
So back to the Fet...my mpg is wired up with a db15 connector, I wanted to extend the wire longer so tried a male to female db15(monitor) extension cable, it didn't work and the usb controller wasn't recognised in Windows until I removed it. That is the only thing that I can think went wrong....[emoji848]
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The SVGA extension cable - there's a couple of no-connection lines in there - perhaps if those aren't wired-through it explains the inability to work. A straight-through 15-w D-type M-F should work without too much drama. Not sure what you mean by the USB controller - unless this is a Windows->pendant interface?, in which case, again, the lack of cabling may possibly explain that (not sure).
The FET behaviour, as described, is borked.
Sorry...i should of explained better. The pendant was one of these...
https://rover.ebay.com/rover/0/0/0?m...2F163108997386
The mpg is wired to inputs on the AXBB but the axis and jograte selectors are wired to a usb controller due to the lack of inputs on the AXBB. The svga wire was advertised as fully wired so I assumed that meant each pin was individually wired but I don't think it Is!
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It seems concerning that, regardless of the reason, failure of the charge pump output can result in an estop being ignored. I was planning on replicating OP's design with the charge pump output controlling my contactor. Now I'm not so sure. What are your thoughts on this?
Quote:
Originally Posted by northbynate
1) This is the only instance I've heard of of the Charge Pump output failing.
2) Use a Safety relay to control your contactor, with the charge pump signal as part of an E-Stop circuit controlling the safety relay. Any E-stop drops the safety relay, which drops the contactor.
Eh, he's back, where you been Ger not seen much of you around, hope you are keeping well and safe.:thumsup:Quote:
Originally Posted by Ger21
I sent you an email some time ago about the screen set for UCCNC, did you ever make it work with the current stable version V1.2111..?
Sorry old friend, didn't see the email.
Had a bad back earlier this year that put me out of commission for about 6 weeks. And projects at the new house have kept me incredibly busy.
The screenset is at the top of my todo list, as soon as I can find the time. Trust me, I want it done as much as everyone else.
The charge pump fault is now fully sorted, the only thing I can assume that caused it was a 15pin dsub extension cable which I used on my pendant, it seems not all of the 15 pins were independent, not had an issue since and repaired it with the help of this forum [emoji16]
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Thanks! The e-stop design has given me quite a headache. My main design goals are:
1. Ideally I want any e-stop signal to be able to drop the contactor, even one from a pendant. That means the e-stop circuit has to monitor the reset status of UCCNC. This also means I'm covered in two ways in light of an accident. First the AXBB-E will stop sending pulses, then power will be cut to the motor's PSU. The safety relay connected to the contactor achieves this - although I'm not clear why I need an extra relay in the system if I have a 24v coil on the contactor? Is it just a way of adding the switches in parallel instead of in series? I've seen circuits (such as https://youtu.be/6dKwOsrnkb4) that build a no volt release just using a contactor.
2. I also want any e-stop to put UCCNC into reset mode which means the AXBB-E needs to monitor the status of the e-stop circuit.
3. The contactor should stay off following power outage and require a manual button press to re-energize the coil.
My conclusion was the only way to accomplish this without getting stuck in a feedback loop between 1 and 2 was to connect all e-stops to the AXBB-E then have it control a relay with the charge pump output pin as shown in the example circuit at the end of the manual. Does that seem like the right approach to you all? I really appreciate your help!
You can only incorporate the pendant in the E-stop circuit if it's a wired pendant, a wireless one is software-driven and will only put UCCNC into Reset mode and not do a hardware E-stop which is the correct way.Quote:
Originally Posted by northbynate
Also, the E-stop circuit doesn't and shouldn't be driven by software so you don't monitor UCCNC you inform it an E-stop occurred using inputs.
You don't actually need a safety relay and can indeed just use the contactor wired in a latching circuit, however, using a separate Relay gives more control. It doesn't need to be a safety relay either just an ordinary ICECUBE type relay works just fine.Quote:
Originally Posted by northbynate
This relay is known as the MASTER relay in the circuit because it controls all the safety and won't be allowed to energize unless all the safety on your machine is correct.
Only when all is correct on the machine will the MASTER relay be allowed to latch, When it does it will do several things.!
#1 sends a signal to UCCNC saying it's ok to allow a Reset.
#2 power the contactor for the drives.
#3 power any other contractors in your system or allow voltage to reach contractors or relays ie: For dust extraction
#4 Turn on any LED's ie: light tower etc
#2 As mentioned above, you inform the AXBB-E using inputs rather than it doing the monitoring. If it sees the input HIGH or LOW depending on how you configure the input then it won't allow the software to RESET.Quote:
Originally Posted by northbynate
#3 This is known as a latching Circuit and is easily done using a relay.
The Charge pump Output is not designed for this purpose, it's designed to monitor the connection between PC and controller so if the software crashes or PC dies the AXBB-E sees this and disables the Output. This, in turn, would drop the relay which should be incorporated into the E-stop circuit and before the MASTER relay.Quote:
Originally Posted by northbynate
I use a safety relay because I got them for $10 for NOS on Ebay. If I had to pay the $200 they actually cost, I'd use Jazz's method.
Thanks!! This is fairly similar to my original plan (minus the relay). I just got hung up on the wireless mpg part and the two types of estop (hard and soft). From what I understand the charge pump can be set to stop when UCCNC is on 'Reset' mode. In Jazz's case this would then be passed on to the safety relay which would in turn cut the contactor. In that case an estop from a wireless mpg could act like a hard wired estop - albiet passing through a layer of software first. Getting the contactor back on would then require both clearing 'Reset' mode in UCCNC and using the physical button to latch the coil of the contactor. I guess my question would be is it possible to have that same behavior from a wireless estop as it is from a hard wired one?
Don't think it works as you think, there is no setting in the software other than to keep the charge pump loaded at all times.Quote:
Originally Posted by northbynate
This is from the manual
"If the 'charge pump always on" checkbox is not set then the PWM signal is only active if the software is not in reset and inactive if in reset.
The charge pump signal can be used to enable an external electronics only if the UCCNC software is loaded or if it is not in reset making the operation of the electronics safe."
Sorry to hear that Gerry, I know all about Bad backs I've had one on and off for over 30yrs, one wrong sneeze can make putting my underpants on a massive chore...:hysterical:Quote:
Originally Posted by Ger21
Let me know when you get it done or if need any help testing etc.
"If the 'charge pump always on" checkbox is not set then the PWM signal is only active if the software is not in reset and inactive if in reset."
That's what I was getting at. In this case if UCCNC goes into reset then the charge pump signal stops right? So that can be used as a way to tell if an e-stop on a wireless mpg has been hit. Thanks again for your help!
Kind of but that then defeats the point of a Charge pump, you want the charge pump working all the time.Quote:
Originally Posted by northbynate
Also, not sure it will work, you could end up stuck in a loop, Master relay won't reset because don't see the charge pump signal and you can't activate the Charge pump without resetting the software which won't come out of reset without the master saying it's safe to do so.??? Give it a try.!
I've just had 2 spinal nerve block injections, so you're not alone guys :thumbdown:Quote:
Originally Posted by JAZZCNC
I also need to figure out my estop circuit and wire up all my inputs next. I'll be looking through all the advice that's been given.
No £5 bob's this time, hope to do this one properly.
(Even though my box has turned out to be a little small :rolleyes:) Balls!.