Might have finally killed a DuetWifi
-
If there is a short between the hot end heater cartridge and its casing, the short may only be present when the cartridge is hot.
There are of course other ways to get a short between +3.3V or +5V and VIN, such as mounting the Duet too close to a conductive plate behind it.
In principle, a faulty 5V regulator chip could cause a short between VIN and +5V. However, on the returned boards showing this type of symptom that we tested, I found that the 5V regulator was working correctly in all cases.
-
So I finally found the time to do a full diagnostic of the machine and found the issue. A short between the hotend fan + and E0 heater cartridge, which occurred in the network cable (stranded not solid core) that I have been using to connect my smart effector to the duet.
This explains why even on USB power only (PSU off) with the original board (v1.00) the heater cartridge was warm in the morning, it had been heating up under 5V power from the fan + to the heater cartridge all night. Probably damaging the 5v reg in the process but since its a buck converter IC, not a simple reg I'm not sure how to test it.
The second board (v1.02 clone) instead blew the U11 74HCT02 chip immediately when Vin power was connected.
So its possible the second board might be repairable if anyone can swap the 74HCT02 chip for me cheaply?
Still doesn't quite explain how the paneldue died or the 4gb sd card from the original board. Edit - the second board also killed an 8gb sd card.
But at least I now feel confident to put a third board in the machine once I have replaced all the wiring from Duet to Smart Effector.
It might be just the quality of network cable I chose or how I have implemented/routed it, but I would consider going for something better quality than network cable for this purpose, they are designed to be static, not moving around on the end of a delta effector at high acceleration for hundreds of hours. Cheap cable has cost me 2 duetwifi and one (maybe two) paneldue! I will look into multicore highly flexible quality cable.
Simon. Precision Piezo Z-Probe Technology
www.precisionpiezo.co.uk
PT1000 cartridge sensors NOW IN, just attach to your Duet board directly! -
@djdemond thanks for the detailed investigation and cautionary note about the cables.
The PanelDue has 5V from the Duet so that would have received 24V as David said above, how much damage that has done to the rest of the PanelDue/screen is unknown. As the SD card has failed I guess that the 3.3V regulator also failed, putting 24V onto the 3.3V supply which would have blown all the 3.3V ICs if applied for long enough. You may find the processor, stepper drivers and other assorted ICs are also damaged. I guess the 3.3V LED comes on becasue it was protected from overcurrent by the current limiting resistor.
On the second board you will need to do more investigation to see if it is just that IC that is blown. with 5V only applied to the second board does the 3.3V LED light up and can you connect to the Duet?
-
I am going to try as an alternative to network cable 13 core towing-electrics cable. It has the following wire sizes within it
7 x 0.65mm2 1 x 1.5mm2 and 4 x 2.5mm2
Which should provide 7x 2 amps, 1x 10amps and 4x 20 amps of current handling, with I am sure much tougher insulation. £5/meter.
The only drawback is I suspect it will be rather heavy compared to 2x cat 5 network cables.
Simon. Precision Piezo Z-Probe Technology
www.precisionpiezo.co.uk
PT1000 cartridge sensors NOW IN, just attach to your Duet board directly! -
@djdemond said in Might have finally killed a DuetWifi:
I am going to try as an alternative to network cable 13 core towing-electrics cable. It has the following wire sizes within it
7 x 0.65mm2 1 x 1.5mm2 and 4 x 2.5mm2
Which should provide 7x 2 amps, 1x 10amps and 4x 20 amps of current handling, with I am sure much tougher insulation. £5/meter.
The only drawback is I suspect it will be rather heavy compared to 2x cat 5 network cables.
Simon
Why not look to using silicon covered wire and make your own bundle and then just encase it all in braid 13 core trailer wire is heavy Thick and very Stiff.
Got all mine from Hobbyking
I would suggest 20awg for hot end power (at 24 Volts or 18 at 12) and 26 for all signal cables
HTH Doug
-
Hi Doug,
That sounds like a good solution. I will have a look at both options. My effector has a fair amount of inertia these days as I run water cooling so I am running much lower XY acceleration (1500) than I used to eliminate artefacts. But the silicone cabling look nice.
At this point I am inclined to over-engineer it, this incident has been quite an expensive one, for the sake of a bit of wire.
I also wonder whether to remove the possibility of this happening again whether it might be worthwhile to have a fuse box between the hot end and controller, where every connection is suitably fused. Sounds like overkill but an automotive fusebox and fuses are a lot cheaper than blown controllers and displays.
-
Yep know what you mean and I am soon to fir a water cooled hotend to mine and will re-wire my effector at the same time have been meaning to do it for some time, (doing so I will be able to eliminate 4 cores of the wiring as well as won't need any Fan wires at all).
-
I once looked into using these https://www.igus.co.uk/chainflex/unharnessed-cable?tab=1
Bit expensive though...............
-
@deckingman said in Might have finally killed a DuetWifi:
I once looked into using these https://www.igus.co.uk/chainflex/unharnessed-cable?tab=1
Bit expensive though...............
I looked at them as well until I checked the prices lol
-
@djdemond said in Might have finally killed a DuetWifi:
So I finally found the time to do a full diagnostic of the machine and found the issue. A short between the hotend fan + and E0 heater cartridge, which occurred in the network cable (stranded not solid core) that I have been using to connect my smart effector to the duet.
You were using a 5V hot end fan - confirm?
On the Smart Effector we put the fan/heaters wires on one connector and the low voltage wires on another to try to minimise the risk of this type of short - but of course that doesn't allow for using a 5V fan. Perhaps we shouldn't support 5V fans?
The reason the SD card died is that if the 5V rail is raised to 12V or 24V, that is above the voltage rating of both the 3.3V regulator and the 74HCT02. This results in the voltage on the 3.3v rail also becoming much too high - which blows most of the chips on the board, the WiFi module, and the SD card. There was one user who posted on this forum about replacing all the blown chips in this situation, but he had to replace almost all the chips on the board, including the stepper drivers AFAIR.
-
@dc42 said in Might have finally killed a DuetWifi:
There was one user who posted on this forum about replacing all the blown chips in this situation, but he had to replace almost all the chips on the board, including the stepper drivers AFAIR.
I might enjoy that rework job, if you want to donate such a dead board for "science"
-
@dc42 - yes 5V fan running from the 5v/Vin fan jumper block. - When I rebuild the machine I think I'll go for a Vin/24v fan through a buck converter down to 5v, this seems to be safer in the event of a short. Thank you for the explanation, it does all make sense now. What is your opinion of making a fuse block and fusing everything (fans/sensors/heaters rather than motors etc..) it's not expensive and could save a lot of head scratching and expensive dead PCBs? If you think it isn't a stupid idea what sort of current level would make sense for things like thermistors Pt100's etc...
@raykholo - you are quite welcome to one/both of the boards if you would like to experiment, I am not going to attempt to repair them. PM me.
-
Fuses wouldn't protect against this kind of short unless you also had crowbar protection on the 5V rail.
Why not use 12V or 24V fans?
-
I'm happy to use 12v/24v fans, I'm also happy even to PWM my 5v fans down from 12v to avoid using the 5v rail on the duet (or use buck converters running off the PSU) etc.. it's not such a risky move as it is with heaters at the wrong voltage. I had 5v fans and it was convenient to attach them to the 5v rail (these are the 30mm blowers we sell, which offer a lot of bang for very little mass) however it does seem to be somewhat of a risk. Having said that if the wiring had been either better quality, or possibly better protected by me against fatigue - it's hard to conclude that having a 5V fan option is too risky, but I think it might be worth stating that there is a risk when using 5v fans that a short to the heater cartridge can kill your board and all its attached peripherals.
Is it possible in some future product perhaps with bus architecture that the fan controller module is a separate unit, powered direct from the PSU with no possibility of a failure damaging anything except the fan module itself? Fans do seem to be a common cause of problems.
Simon. Precision Piezo Z-Probe Technology
www.precisionpiezo.co.uk
PT1000 cartridge sensors NOW IN, just attach to your Duet board directly! -
@djdemond regarding having the fan controller as a separate unit. hats definitely achievable however it adds significantly to the overall cost. ove all a completely modular board with everything on different CBs would be the easiest to swap stuff out but he most expensive.
-
Okay so finally got around to starting to get this fixed.
I bought some towing electrics 13 core wire, very thick and heavy as Doug pointed out, but quite flexible and quite cheap too £5/meter.
However I also bought some 7 core signal wire hoping it would be a little less massive, it was but less flexible £4/meter.So I stripped the insulation off both, quite a lot of the mass resides in the insulation, especially on the 13 core cable, and set about working out what I would need in order to cover all bases, current and, as best as I can determine, projected requirements.
In the end I have made a 17 core wiring loom.
I have used the larger 2.5mm sq wire for the hotend heater, 7 amps is more than I will need at 24v (2A suffices) but then if in future heater cartridges get much more powerful, or for some unfathomable reason I go back to 12v, or I possibly consider the positive wire common, and run two negatives for dual hotends then I'm covered).
I have used larger than necessary (0.65, 0.75 mm sq wire) for some of the connections as, firstly I have it in hand, but mainly as it is well insulated, strong and flexible.
I am not currently using a filament monitor, but I have done in the past, and still have one so I have that covered. The hotend fan is not currently used, as this machine has water cooling, but I might go back to an air-cooled system later, so I have that covered too. Also I have a second thermistor which is attached to the water block, so I can directly see how effective the watercooling is. But it is a lot of cable. Here's what it looks like:
I might not need all 2 meters, but it weighs around 400g, which is not as much as I expected, and it will have keychain retractors to hold much of the weight off the effector, but it is going to contribute to lateral inertia on XY moves.
Now to get it installed. All I will say is that I can see why Canbus is quite popular these days, the idea of replacing all of this with 2 decent sized power wires, and two data cables potentially, is very appealing.
-
So all back up and running.
Just to mention that despite the widespread damage the PT100 daughterboard survived.
