Irregular Surface Finish with Heated Bed?
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@gestalt73:
Hey dc42 & bot,
Thank you so much for your help with this. I think there are three things going on here:
- The Rostock Max Onyx heated bed is a power hog
- The Budget pc psu has a pretty extreme voltage drop while powering the onyx
- The DuetWifi is sensitive to voltage drop in this configuration
It's not the Duet WiFi that's sensitive to the voltage drop, it's the hot end heater. The power produced by a heater is proportional to the square of the voltage applied to it. When the bed heater turns on and as a result the VIN voltage drops from 12V to 10.6V, the hot end heater power drops by 22%. This is a large drop and will cause a significant drop in the nozzle temperature, which the PID will take a few seconds to correct for (the dead time of a hot end is typically around 5 seconds, so the PID can't react much faster than that). This temperature fluctuation will affect the viscosity of the filament, which in turns affects extrusion width and back pressure.
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Alright, I think we can put this one to bed.
tldr; Wrong gauge wire used for hotend heater. Getting perfect prints after using 18gauge stranded instead of what was originally used.
Truth be told, I have a client build that I'm troubleshooting, and as part of the process I upgraded him to the DuetWifi. I love this board!
dc42, your comment prodded me to examine the hot end setup, and I noticed earlier that the gauge of wire used for the hotend seemed a bit smallish. I just rigged up an alternative wiring harness using a heavier gauge wire, and the irregular surface finish all but disappeared.
I'm still concerned about the vdrop though, so I'm going to try out a dedicated 12v power supply before I hand the machine back over to its owner.
Thanks everyone for your help!
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I was using a PC PSU on one of my printers for a while and I also had a problem with voltage drop. Switching to a Corsair CX430M PSU mostly solved it. However, the bed heater on that printer only draws about 10A; your client's may be drawing more.
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One of the common issues with PC PSUs is voltage drop on the 12V rail when loaded, adding sufficient load onto the 3.3V and 5Vs often significantly reduces this drop on the 12V rail.
For more details see:
http://reprap.org/wiki/PC_Power_Supply#Minimum_Load
http://hydraraptor.blogspot.co.uk/2012/12/mendel90-updates.html (10R on 5V and 4R7 on 3.3V rails) -
Also to keep in mind, some ATX PSUs now come with "Zero load" rating – meaning they are designed to work as we use them, without having to add load to the 5v or 3v rails. see, for example: http://www.coolermaster.com/powersupply/modular-gm-series/g750m/
- Haswell C6/C7 support & zero load operation
I don't know how the zero load operation relates to haswell c6/c7 state support, but there ya go. Also notice the single 12v rail – helpful when hacking the psu.
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Ahh that's good to know. I imagine the cheaper PSUs don't have this feature or did not a couple of years ago when I was still using PC power supplies.
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My guess is that PSUs with zero load rating have independent regulation on the 5V and 12V rails - and therefore better regulation of both - because I think it would be difficult to achieve a zero load capability with a single regulation feedback signal for both rails.
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Thanks guys for all your help.
I think I'm sold on these dedicated 12v power supplies. They're only $35-$40.
Found a 12v power supply locally, wanted a meanwell but couldn't find one on short notice.
http://www.microcenter.com/product/446051/12V_360W_Dedicated_Power_Supply_for_3D_Printer_HEAVY_DUTYThis power supply only sees a vdrop of 0.5 volts under full load. Tuned to 12.1 idle, drops to 11.6 volts.
There's only two challenges with this type of power supply. No power switch and a really really loud fan.
I hacked on a 100mm silenx case fan and I found these to install to get a proper power switch.
http://www.ebay.com/itm/like/142086311320?lpid=82&chn=ps&ul_noapp=trueI've got his printer for another week for burn in and testing. If it all checks out I think I see some power supply upgrades in the near future for my printers.
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I use a fanless 12V 300W PSU to power one of my printers, and I printed a cover for it to safeguard the wiring and fit a switch. See http://www.thingiverse.com/thing:441081.
I think the Meanwell PSUs have thermostatically-controlled fans.
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We use similar power supplies but 24V on the Kossels and I have another in the BigBox. David's Cover is a good idea.
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After two months of troubleshooting the same issue I tried your fix and increased the wire gauge to the hot end and it WORKED! THANK YOU!!!
