AXBB charge pump fault

[CharlieRam]

I wired my machine to use the charge pump output so that the relay would only activate the motor psu if the software was active and not in a reset/error state. This has worked perfectly while testing until I tried it a couple of days ago. When I apply power the relay and therefore the motor Psu all spring to life. I checked all wiring and even stripped it all back to the bare minimum and tested again with the same issue. I have checked the charge pump isolated output and it appears to always be active even if the indicator LED is off? I have checked that the option to always enable charge pump isn't active and am now wondering whether it's faulty...does anyone have any other ideas?

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[john swift]

Does the other outputs work as expected ?

Assuming the output transtor is open drain and grounds the relay coil terminal to switch the relay on

With the power off you can use a multimeter to check the resistance between the negative supply terminal and each isolated output

in the manual
http://www.cncdrive.com/downloads/AXBB_E_manual.pdf
see diagram 9.1.2 .Connecting a solid state relay (SSR)

test between 24V0 and Ox

You should find they are all open circuit unless the transistor controlling the relay is short circuited

John

[CharlieRam]

Cheers John, I'll check the resistance tomorrow but one more thing I remembered. I also tried output 2 of the isolated outputs and that one does read the voltage change if I set that as the charge pump output however that one doesn't activate the relay? The manual states that the isolated outputs can drive upto 500mA so I'm assuming it's not enough power to drive the relay and the output 1 is different. [emoji848]

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[john swift]

what relay are you using ?
any idea what the coil resistance is ?

This one from RS Components has a coil resistance of 650 ohms
https://docs-emea.rs-online.com/webdocs/1585/0900766b815856e9.pdf

If the RS StockNo:450-0425 relay was used with the AXBB and its 24V DC supply only 37 mA would flow via the AXBB output

John

[CharlieRam]

It's like the one below

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F 283248324744

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[john swift]

going by this data sheet
26191

your relay also has a resistance of 650 ohms

page 4
Non-latching – DC
rated voltage = 24V
rated current = 36.90 mA
coil resistance = 650 ohms

John

[CharlieRam]

Forgive my ignorance but does that mean the other isolated outputs are all capable of driving the relay? I did check that and thought so but its been a while since I DoD electronics!

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[CharlieRam]

With the power off you can use a multimeter to check the resistance between the negative supply terminal and each isolated output

in the manual
http://www.cncdrive.com/downloads/AXBB_E_manual.pdf
see diagram 9.1.2 .Connecting a solid state relay (SSR)

test between 24V0 and Ox

You should find they are all open circuit unless the transistor controlling the relay is short circuited

John

It looks like I'm getting approximately 100 ohms on output 1 to ground, all other outputs are open.

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[john swift]

The reference to " other isolated outputs are all capable of driving the relay "

differentiates the outputs from the 5V logic level outputs that you connect to other logic gates or the stepper driver step & direction inputs

from the open drain outputs designed to switch inductive loads like the relays

As an example
Going back to equipment I used and maintained in the eighties
all the logic was built from 7400 series TTL logic

Typical gate inputs passed 1.6 mA when an input a input was grounded
and the outputs could sink 16 mA
so you could only connect 10 inputs to the output of an IC
unless you used a buffer that could pass more current

To connect to other devices like tally lights for the control panel switches

A lamp “driver” / BCD decoder like the 7445 switched 28v bulbs ( run off a 24V supply ) by grounding the other end of the bulbs filament

The 74141 being another version with high voltage outputs for driving Nixie tubes
(which is basically a neon with an anode connected to 180V DC via a resistor and 10 cathodes shaped in the form of the digits 0 to 9 that glows when grounded )

These days you would use a 7447 BCD to 7 segment decoder driver connected to a 7 segment LED display or LCD

John

[john swift]

It looks like the FET for output 1 has short circuited

I would check you don't have a wiring problem that could connect the 24V DC to the AXBB output

Did you check the relays coil resistance is 650 ohms as expected
less than 48 ohms would pass more than the 500mA limit for the output

John

[CharlieRam]

The coil is reporting around 600ohms with my voltmeter but the battery is about dead so I'm not sure how accurate it is atm. No other isolated outputs are being used on the AXBB at the minute. I have proximity switches on the isolated inputs and a cheap 5 axis Bob for the control panel wiring. I'm wondering if I could use the 5 axis bobs relay as a charge pump to control the safety relay...i can assign it in uccnc but I think I read it can only be used by powering the 5v off usb rather than the boards 5v input.

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[john swift]

I having read the manual again I see the charge pump controls the damaged output 1

Not all outputs as I thought last night !

which breakout board are you thinking of using ?

To add another charge pump you need to use a breakout board with a built in charge pump circuit or
something like cnc4pc's C4
https://www.cnc4pc.com/c4-safety-charge-pump.html
the detector circuit is hidden under the board !

You need the circuit that controls the relay to ignore static logic levels
and only detect the 10Khz charge pump signal

older version
https://www.cnc4pc.com/pub/media/productattachment/c/4/c4r6_2_user_manual.pdf
26196


John

[CharlieRam]

In the ucnc software I can configure which outputs to use for the charge pump so I was planning on setting it to the output 17 in the bob which is for the relay or forward reverse control but it isn't switching the relay which is why I think I need to power it from the ish rather than the on-board 5v connectors. I've included the pdf for the bob

I appreciate the help John [emoji4]
Edit.
I should probably add that the bob is connected to port 3 of the AXBB and not to the pc parallel port.
https://uploads.tapatalk-cdn.com/20190812/e2516d0d33bd7dcaf1eadced549cf2be.jpghttp://cloud.tapatalk.com/s/5d514e974d1a7/ST-V2%20%281%29.pdf

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[john swift]

The BOB you have linked to does not have the charge pump / watchdog circuit needed

26197

pin 17 just switches the relay on when the pin is taken high ( +5V )

one DIY circuit from Geckodrive.com

26198

John

[CharlieRam]

The BOB you have linked to does not have the charge pump / watchdog circuit needed

26197

pin 17 just switches the relay on when the pin is taken high ( +5V )

one DIY circuit from Geckodrive.com

26198

JohnOh...my understanding was that the AXBB watched for the signal from the pc and then activates a chosen output for the charge pump. In my case it would be pin 17 controlled through the AXBB's 26pin idc to the bob which would then switch the onboard relay on to complete the circuit to power my safety relay for the drives.

Am I understanding it wrong? There should be no random outputs on the AXBBs port 3 lile would be on a pc's parallel port on start up or at least that's what I assumed.

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[john swift]

last night I expected the AXBB to work as you described but after downloading the manual

at the bottom of page 19
8.1.1 .Digital isolated ports.

Port#1 pins 2. to 8. are isolated outputs. These outputs contain high speed 10Mbit/sec
optocouplers and an N-channel Mosfet transistors.
The outputs can drive upto 500mAmps of current upto 24Volts voltage levels.
The high current capability of the output transistors makes these outputs ideal to drive
relays, solid state relays and other signals which require isolation.
19/29

on page 21
8.3 .Charge pump safety circuit port

There is one charge pump safety circuit integrated on the board in port#1 O1 CHP output.
The charge pump circuit senses the charge pump pulse stream signal from the controller and
if the signal exists then the output is switched on and if it cuts then the output switches off.
The charge pump can be used to control a safety relay to cut power when the software is not running on the computer.

Unless I have missed it
I have not seen an explicit ref to all output being switched off as I would of expected

My be another AXBB user can confirm

John

PS
have you contacted the manufactures ?

[CharlieRam]

last night I expected the AXBB to work as you described but after downloading the manual

at the bottom of page 19
8.1.1 .Digital isolated ports.

Port#1 pins 2. to 8. are isolated outputs. These outputs contain high speed 10Mbit/sec
optocouplers and an N-channel Mosfet transistors.
The outputs can drive upto 500mAmps of current upto 24Volts voltage levels.
The high current capability of the output transistors makes these outputs ideal to drive
relays, solid state relays and other signals which require isolation.
19/29

on page 21
8.3 .Charge pump safety circuit port

There is one charge pump safety circuit integrated on the board in port#1 O1 CHP output.
The charge pump circuit senses the charge pump pulse stream signal from the controller and
if the signal exists then the output is switched on and if it cuts then the output switches off.
The charge pump can be used to control a safety relay to cut power when the software is not running on the computer.

Unless I have missed it
I have not seen an explicit ref to all output being switched off as I would of expected

My be another AXBB user can confirm

John

PS
have you contacted the manufactures ?I think I will have to, I just wanted to check I hadn't missed anything. It was working fine and I'm not sure when it turned faulty but noticed a few days ago that it started straight away[emoji848] it seems strange that the software will allow me to choose any output for the charge pump though.
Cheers for the help[emoji16]

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[CharlieRam]

So I got a response that it could be the input transistor. I have asked whether it is covered under warranty but haven't had a response yet however I decided to check the values myself and the resistors seen in the pic below should be....
30B=2k
221=220ohm
01C=10k
All the values are correct other than the one circled which gives more like 1k value so in your opinion is it blown or do you think there is a path from elsewhere?

Edit
How easy is it to replace a faulty smd and what would be an acceptable cost at an electronica shop? I'm just wondering if the cost will be cheaper than shipping back to CNCDrive.[emoji848]

https://uploads.tapatalk-cdn.com/20190813/b032546c8e8fc95763dac4cc1e064a54.jpg

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[AndyUK]

I've seen people replace them with a thin tip soldering iron, a pair of tweezers, a steady hand and a magnifying glass. Read a tip in the UB1 manual today that said disconnect your iron from the mains and then ground it once it's at temperature. I'm sure you'll find examples on the old YouTube.

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[john swift]

The smt resistor coding used is this -
https://www.hobby-hour.com/electronics/eia96-smd-resistors.php

So far I have not found the transistor marked A66
I thought it would be something like a high current version of a 2N7002

https://uk.farnell.com/search?st=2n7002
http://www.farnell.com/datasheets/2299562.pdf?_ga=2.71303184.242409243.1565638630-273663413.1539186146&_gac=1.25039176.1563533904.Cj0KCQjw1MXpBRDjARIsAHt dN-2a6T70y_WBG29MPq9YRl5CS5iF_Sq3WSMTcSZVEm-jmdPECk1TgQ4aAiVAEALw_wcB


may be a
FDN337N - MOSFET Transistor, N Channel, 2.2 A, 30 V, 0.065 ohm, 4.5 V, 700 mV
is closer to what we are looking for

https://uk.farnell.com/on-semiconductor/fdn337n/mosfet-n-30v-2-2a-sot-23/dp/9845356

could you post some wider pictures to see more of the circuit connections
to see what its connected to

usually I expect resistors to go high resistance when overloaded and semiconductors to go short circuit

John

[CharlieRam]

Here's a pic of the full board, there looked like a lot of dust on it so I've brushed it all off but it's still reading the same resistance. So are you thinking its the transistor and no the resistor? I had a look at the back of the board and it looked like a short from the pin of the led but it brushed off so maybe it just looked worse[emoji848]https://uploads.tapatalk-cdn.com/20190813/03668c108b47b09d5253a79dfec1ec3e.jpghttps://uploads.tapatalk-cdn.com/20190813/1642ad2e2a59caef9dd7e0d23aa5e2b5.jpg

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[john swift]

the board is very much what I expected
basically an all in one UC300 and opto isolated breakout board from what I can see

looking at your photo
the 10K resistor is in parallel with
the 200 ohm resistor that's in series with the FETs gate & drain connections

your probably seeing the 220 ohms in series with the short circuited FET gate & source

26205 26206

I expect the 2K resistor is probably limiting the indicator LED current

whats the 14 pin IC number that you can just see 7 of its pins ?

John

[CharlieRam]

This one says HC14
It's hard to take decent photos!https://uploads.tapatalk-cdn.com/20190813/9858bdbd830207856b3e539da885f704.jpg

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[john swift]

that makes sence

it will be a 74HC14 which is a hex inverter very often used on breakout boards

26207




I think this shows output 1 is fixed for use as the charge pump output
26208

John

[CharlieRam]

Whatever file you posted I can't see it on my phone? So in your opinion do you think it's the transistor with the AA6 that's faulty? And what physically makes that port different? I mean how is that port able to provide enough current to power the solenoid when the others can't? Sorry for all the questions!

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[john swift]

yes , I think the AA6 is faulty

the first file is just a PDF copy of the 74HC14 data sheet

As the same AA6 transistor is used for all 8 opto-isolated outputs
the only obvious differance I can see is the charge pump has control of output 1
and you via mach 3/4 control of the other 7 outputs

any output should be able to control a relay

John

PS
looking back at an earlier post

26209

I would of thought you should be able to change port 1's charge pump to another pin
for example to pin 2

26210

John

[CharlieRam]

That's what I thought too but when I tried it didn't work[emoji848]....
I will have another go tomorrow and report back my findings.
We have a localish electronics shop so I might give them a ring about replacing the smd.. my hands are way too shaky and my eyes are not much better[emoji23]
Thanks again for the help

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[john swift]

its the sort of thing you need to have some practice before you try to repair a valuable board
I found scrap PC boards are good to practice on

the last board I worked on was this XMT-2360 speed control board
the 14 pin IC , a transistor and a few diodes had been damaged by a short circuit to the speed control potentiometer

26211

I guess the main issue is finding the new AA6 transistors

John

PS

have you checked the relay is OK

does it work when its connected directly to the 24V DC supply ?

[Doddy]

I've been following this thread with some interest. Personally I'd RMA the board for replacement/repair, however, if that's not an option...

From the photo of the board it's feasible that some of the analogues to the left of the transistors are involved with the charge-pump - it's not clear but if I squint hard enough I can believe it. At this time I'd give-up looking for a "AA6-j" marked device - it isn't present in the top-hits of SMD-marking google hits. but the purpose of the device is clear - a logic-level N-channel MOSFET with a working voltage in excess of 24V with a commutating diode to avoid problems with back-EMF from the relay (this was one area that concerned me originally when considering this device could be a BJT). This would support the traces to OP1 being the only charge-pump output. That, in itself, is somewhat peculiar as I understand that the micro controller on the AXBB generates the charge-pump output to itself - so I'm not entirely sure of the logic behind this decision - the integrity of this safety feature is then at the lowest integrity of the board - likely the program running on the micro controller... but I digress.

In a bind, I'd look to sweat-off the MOSFET for OP1, and the three resistors for OP2, then haywire the gate signal from the landing pad from OP1 to OP2. This would transfer the charge-pump output to OP2. Or, you could carefully (without overheating) sweat off the MOSFETs for both OP1/2 and swap them - assuming that you don't require the OP2 output. It looks as though any/all of the OP1-8 have the same circuitry/options, with just OP1/2 shifted on the board to avoid the stand-off pillar.

Or replace the MOSFET with a generic with the same SOT-23 packaging and pinout - there's nothing special about it's function that requires it to be matched to the original. John's mention of the 2n7002 is a suitable device in SMD packaging.

John's analysis of the failed MOSFET is, I believe, the most likely scenario here. There is a question as to why this failed, but sometimes s**t happens. It would be worth, if possible, diagnosing this more completely before attempting a repair. OP has a meter, it would be sensible to measure the voltage at the "IC" side of the 220R resistor with the output OFF/ON (0V, 5V respectively) and at the transistor side of the 220R resistor (similarly, 0V, 5V respectively). That he mentions the LED turns on/off, however, it a pretty good indicator that this should be working.

OP asks about a sensible price for a repair shop to perform this - a blind replacement (they won't be able to easily test without a licensed UCCNC installation) would be 5 minutes work and 10 pence of component, but they run a business and have to cover their operating overheads. On a good day - price of a pint, however, if the boss is around I'd expect £30 upwards.

If the OP was closer I'd offer to help - but it's not really viable (100 miles). But if he wants to play with a hot-air rework setup with stereo microscope then the offer is there.

[john swift]

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

26218

26219

If the AXBB controller was mine I would remove the AA6 FET
To prove the 74HC14 and resistors that drive the FET are OK

then either replace the AA6 FET with a
Vishay Si2306DS if it has the same footprint

26220

John

plan B could be link the Gate & Drain PCB pads

that would enable the use of a relay and an external relay driver

for example
26221
after checking the boards details



https://www.ebay.co.uk/itm/24V-TOP-Arduino-Board-1-Channel-Relay-Module-High-Low-Level-Triger-Optocoupler/333194947682?hash=item4d93f76c62&_trkparms=ispr%3D1&enc=AQAEAAADAKvsXIZtBqdkfsZsMtzFbFsbX3WcW5fmB%2Fx7 ZbaZTyexqhfDUIOrOfQIsN5dFaCqZFUuGFNT%2B7JPUJveSfeP 7iOTJhgqsPhq36YBy8O8z%2BrAMc0o4i%2F2BVmd1pQE5fHiR7 PnvteYaF%2BYQe4AhdfQl7lQNmyq%2F2kNo4iHVEAvMfI7XuSt 1d7qOrRyq4pvTr0k5HIsNLrxF8k4SQdGmQU3HMaXqIjr65UXYb vMrAklP6l5VZD9xBWUgNP%2B%2FlCWugmj7cQVnjbgt4%2FlEC o7IxNKDdhGT9d5oyMG3Z6oaSYk65wHLzeNUVR3kQGF%2BoS1NW GZLUJUxRpyYIoKpzjrpVfQKeS%2FxsgtYWmvU5C2xkmXzV%2BC O36i7HERXVoMjzDCJJZkx2RIuD2bCemAVp062o5aYXVuRnwI7N OpkdTdPPZSJ6%2FfWmR4%2BDM5IrDOPJEqDdezDVd1aC57kDiW rRJsLBxjsFnNQRfjFCPWC6Xt4Q6SYg7cH%2BnQlg6WXaRwiMZQ 4S0kkZHmauIXZwmCW4zJW8ziAcYGqEBtzVtiIzJBf44C2wkygh EEccJCQ2NZHuzcxdtkGPef6%2Br6%2BnwzE9F1GLdlSBadbG6T hf7lkfzVQZt9pQguKTDt629iX277Bg7y1DF7t3HTFaY%2BOOjn 7VAcV5YlYB2KxvbaBwto4nzXyfTJXvJYx6rouKsT7x5BooCmfC 4tw2BiPPAqMIsN9c1DqDP3N1TzVfFDzv55WyheJYxGCcUoQh3X wch3j2yk%2BcFfWDiJ9ls07p7rBrdDRPVaP2zdYeuXdroO99zv IGk5AWbUsaa1VSxv%2BCUEfxstl%2BzTqz%2FOp3A1xo7Zje0V BqZjnrEkfOJxossLbgm%2BBv5UyGCOgLli0u4BTfMFd5v9vZ%2 FIWvPdA44wegfgMXwhP9eNm%2FOkUjhVWmSz7nXgxlzs%2FLkz qICIfQGp4f1QK9CCxTcK30%2F6%2BybJTODcxsnc4q4lJekI%2 Fy68H6PmRLXsWNk8inWSOESRQ8lVZKBfTuvY1oCtzC16qA%3D% 3D&checksum=3331949476822d9903e4bbcb4541be592caec3ec0 e9d

[john swift]

Charlie
have you had a quote from CNCdrive what they charge for the repair of the AXBB controller ?
John

[CharlieRam]

I have been in contact with Balazs from CNCDrive and unfortunately it seems it won't be covered...

No, this kind of problem is not covered by warranty, because the transistor can be damaged only with overstressing the output e.g. with misconnecting the output, e.g. connecting a low resistance like a direct connection to the +24Volts.
Or if the issue is something else like a soldering error then we repair in warranty for 12months from purchase (shipping) date.

I haven't asked for a cost of repair but I did ask for the data sheet for the mosfet....

The transistor this one: https://www.digikey.com/products/en?keywords=NTR5198NL
It is not hard to remove and replace this kind of component, I mean it looks harder than it actually is.
You just need a tweezers and a soldering iron.

I haven't had chance to try another output as the charge pump yet but I'll try later. The Relay switches on and off fine when I connect it up to 24v.

I will also check the voltages as suggested but my local electronics shop may still be cheaper than shipping to Hungary and back. I am wondering though what could of caused it and will it happen again[emoji848]

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[john swift]

knowing the part number is a great help

( the Vishay Si2306DS from post 30 looks similar )



if you melt the solder on all 3 legs by adding fresh solder

a Desoldering Pump may well pick it up as well as the solder !

https://uk.farnell.com/duratool/908-366a-f/desoldering-gun-antistatic/dp/3125646

26222

once repaired I would be inclined to use a relay with its own driver !

John

PS
Farnell have the NTR5198NLT1G FET

https://uk.farnell.com/on-semiconductor/ntr5198nlt1g/mosfet-n-channel-60v-2-2a-sot/dp/2399121?ost=NTR5198NLT1G&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fsearch

[Doddy]

<deleted - just really agreeing with John>

[john swift]

Hi Doddy

I see you changed your mind
dont worry
your original reply just pointed out we use the technique that we are happy with

I have to admit unless I am under instructions to maintain a lead free status
I use 60/40 solder and add some rework flux

If lead tin solder is good enough for use in pacemakers and other mission-critical equipment
its good enough for me :welcoming:

John

[Doddy]

If lead tin solder is good enough for use in pacemakers and other mission-critical equipment
its good enough for me :welcoming:

John

Similarly, gifted with an industry that embraces the old 60/40.

Right, just tried a quick experiment - I have some 2N7002's in the shed so hooked one up to a signal generator set to 1Hz (though I ramped up to 35Hz out of boredom).


Basic circuit...

26226

...using a practice board for SMDs as a breadboard...

26227

So, this ran for 5 minutes without fail.

I then cut the diode (observed in image) to see if the back EMF would pop the transistor. I ran that for 5 minutes at upto 35Hz, with no failure.

Out of interest, I wet my fingers and placed across the relay coil - this calibrated method of measuring EMF confirmed that there was OUCH! volts of back-emf. Recovering the diode did quench the back emf, as expected.

I had expected the 2n7002 to fail due to the excessive VDS, but for the duration that I ran this it did not. The OUCH! test did confirm the expected high EMF present on the drain of the transistor.

So, CharlieRAM - you asked what could cause this to happen again... although inconclusive I'd recommend placing a diode, e.g. 1n4004 across the relay coil, cathode to +24V, anode to the AXBB board output. If you want a couple of diodes and a couple of 2n7002s thrown into the post let me know.

I'd recommend this for any output driving a relay or other inductive load.

[CharlieRam]

I think I have some of those diodes lying around from a previous project, I'm all for belt and braces approach [emoji16] I've contacted my local shop regarding the repair so I'll wait for a response.

Just a thought....my machine is in a log cabin at the bottom of the garden connected by an RCD in the house so if I leave anything on in there and then decide not to go back down I just trip the RCD. Would that likely cause an issue? It's just easier than going back down to turn it all off![emoji87]

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[Doddy]

if I leave anything on in there and then decide not to go back down I just trip the RCD. Would that likely cause an issue? It's just easier than going back down to turn it all off!


I don't see anything wrong with that approach.

[john swift]

The belt and braces approach of adding a diode across the relay coil works for me
( As long as you have it the correct way round )

26228

I would look for a wiring problem that could of shorted the +24V to the AXBB output

As semiconductors fuse faster than expensive fuses thats supposed to protect them
you could try adding a 22 ohm 1/4W resistor in series with the relay coil
( the resistor should only fail if the relay coil is shorted )

The only issue I would expect with tripping the RCD will be corrupting the PC hard drive
If you have not shut the PC down

John

[john swift]

Another diagram to expand on the one in post 39

26320

John

[CharlieRam]

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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[driftspin]

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 TapatalkGood to hear you got it fixed.

Do you know what broke it?

Grtz Bert



Verstuurd vanaf mijn SM-A320FL met Tapatalk

[Voicecoil]

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.

[CharlieRam]

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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[john swift]

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

[john swift]

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

[Voicecoil]

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.

[Ger21]

it seems strange that the software will allow me to choose any output for the charge pump though.

A little late, but just wanted to clarify.

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.

[Doddy]

Of course... you may want to use the PWM charge-pump output to control an existing, external charge-pump.

[john swift]

Hi Gerry

Thank you for the missing detail

that makes sense of the test results when Charlie tried using another output

John

[john swift]

Doddy

something like cnc4pc's C4 charge pump I made reference to in post 12

John

[CharlieRam]

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]

Sent from my SM-G920F using Tapatalk

[Doddy]

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?)


So the LED on the AXBB is off, but the relay remains energised and another LED on the relay is on/dim?

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.

[CharlieRam]

So the LED on the AXBB is off, but the relay remains energised and another LED on the relay is on/dim?


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.



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[john swift]

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

[CharlieRam]

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

JohnSorry 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...
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..

Sent from my SM-G920F using Tapatalk

[Doddy]

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.

[CharlieRam]

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.
26746

[Doddy]

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.

[john swift]

yes
that's the resistor

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-semiconductor/ntr5198nlt1g/mosfet-n-channel-60v-2-2a-sot/dp/2399121?ost=NTR5198NL&ddkey=https%3Aen-GB%2FElement14_United_Kingdom%2Fsearch

[CharlieRam]

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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[john swift]

"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

[CharlieRam]

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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[Doddy]

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.

[CharlieRam]

Sorry...i should of explained better. The pendant was one of these...
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F 163108997386

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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[northbynate]

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?

[Ger21]

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?


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.

[JAZZCNC]

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:

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..?

[Ger21]

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.

[CharlieRam]

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]

Sent from my M2003J15SC using Tapatalk

[northbynate]

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!

[JAZZCNC]

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.

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.
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.


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.

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.

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. 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.

#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.

#3 This is known as a latching Circuit and is easily done using a relay.



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!

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.

[Ger21]

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.

[northbynate]

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?

[JAZZCNC]

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.

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."

[JAZZCNC]

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.

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:

Let me know when you get it done or if need any help testing etc.

[northbynate]

"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!

[JAZZCNC]

"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.

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.!

[dazp1976]

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:

Let me know when you get it done or if need any help testing etc.

I've just had 2 spinal nerve block injections, so you're not alone guys :thumbdown:

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!.